Plaintext
Vulkan Tutorial
Alexander Overvoorde
April 2023
Contents
Introduction 6
About . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
E-book . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Tutorial structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Overview 9
Origin of Vulkan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
What it takes to draw a triangle . . . . . . . . . . . . . . . . . . . . . 10
Step 1 - Instance and physical device selection . . . . . . . . . . . 10
Step 2 - Logical device and queue families . . . . . . . . . . . . . 10
Step 3 - Window surface and swap chain . . . . . . . . . . . . . . 10
Step 4 - Image views and framebuffers . . . . . . . . . . . . . . . 11
Step 5 - Render passes . . . . . . . . . . . . . . . . . . . . . . . . 11
Step 6 - Graphics pipeline . . . . . . . . . . . . . . . . . . . . . . 12
Step 7 - Command pools and command buffers . . . . . . . . . . 12
Step 8 - Main loop . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
API concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Coding conventions . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Validation layers . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Development environment 16
Windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Vulkan SDK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
GLFW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
GLM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Setting up Visual Studio . . . . . . . . . . . . . . . . . . . . . . . 19
Linux . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Vulkan Packages . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
GLFW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
GLM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Shader Compiler . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Setting up a makefile project . . . . . . . . . . . . . . . . . . . . 28
1
MacOS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Vulkan SDK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
GLFW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
GLM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Setting up Xcode . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Drawing a triangle 39
Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Base code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Instance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Validation layers . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Physical devices and queue families . . . . . . . . . . . . . . . . . 58
Logical device and queues . . . . . . . . . . . . . . . . . . . . . . 65
Presentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
Window surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
Swap chain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
Image views . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
Graphics pipeline basics . . . . . . . . . . . . . . . . . . . . . . . . . . 87
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
Shader modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
Fixed functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
Render passes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
Drawing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
Framebuffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
Command buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
Rendering and presentation . . . . . . . . . . . . . . . . . . . . . 124
Frames in flight . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
Swap chain recreation . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
Recreating the swap chain . . . . . . . . . . . . . . . . . . . . . . 139
Suboptimal or out-of-date swap chain . . . . . . . . . . . . . . . 142
Fixing a deadlock . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
Handling resizes explicitly . . . . . . . . . . . . . . . . . . . . . . 143
Handling minimization . . . . . . . . . . . . . . . . . . . . . . . . 145
Vertex buffers 146
Vertex input description . . . . . . . . . . . . . . . . . . . . . . . . . . 146
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
Vertex shader . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
Vertex data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
Binding descriptions . . . . . . . . . . . . . . . . . . . . . . . . . 147
Attribute descriptions . . . . . . . . . . . . . . . . . . . . . . . . 148
Pipeline vertex input . . . . . . . . . . . . . . . . . . . . . . . . . 150
Vertex buffer creation . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
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Buffer creation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
Memory requirements . . . . . . . . . . . . . . . . . . . . . . . . 152
Memory allocation . . . . . . . . . . . . . . . . . . . . . . . . . . 154
Filling the vertex buffer . . . . . . . . . . . . . . . . . . . . . . . 155
Binding the vertex buffer . . . . . . . . . . . . . . . . . . . . . . 156
Staging buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
Transfer queue . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
Abstracting buffer creation . . . . . . . . . . . . . . . . . . . . . 159
Using a staging buffer . . . . . . . . . . . . . . . . . . . . . . . . 160
Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
Index buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164
Index buffer creation . . . . . . . . . . . . . . . . . . . . . . . . . 165
Using an index buffer . . . . . . . . . . . . . . . . . . . . . . . . . 167
Uniform buffers 169
Descriptor layout and buffer . . . . . . . . . . . . . . . . . . . . . . . . 169
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169
Vertex shader . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
Descriptor set layout . . . . . . . . . . . . . . . . . . . . . . . . . 171
Uniform buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173
Updating uniform data . . . . . . . . . . . . . . . . . . . . . . . . 175
Descriptor pool and sets . . . . . . . . . . . . . . . . . . . . . . . . . . 177
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
Descriptor pool . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
Descriptor set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178
Using descriptor sets . . . . . . . . . . . . . . . . . . . . . . . . . 181
Alignment requirements . . . . . . . . . . . . . . . . . . . . . . . 182
Multiple descriptor sets . . . . . . . . . . . . . . . . . . . . . . . 185
Texture mapping 186
Images . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
Image library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
Loading an image . . . . . . . . . . . . . . . . . . . . . . . . . . . 188
Staging buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
Texture Image . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
Layout transitions . . . . . . . . . . . . . . . . . . . . . . . . . . 195
Copying buffer to image . . . . . . . . . . . . . . . . . . . . . . . 198
Preparing the texture image . . . . . . . . . . . . . . . . . . . . . 199
Transition barrier masks . . . . . . . . . . . . . . . . . . . . . . . 200
Cleanup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202
Image view and sampler . . . . . . . . . . . . . . . . . . . . . . . . . . 202
Texture image view . . . . . . . . . . . . . . . . . . . . . . . . . . 202
Samplers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205
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Anisotropy device feature . . . . . . . . . . . . . . . . . . . . . . 209
Combined image sampler . . . . . . . . . . . . . . . . . . . . . . . . . 210
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210
Updating the descriptors . . . . . . . . . . . . . . . . . . . . . . . 210
Texture coordinates . . . . . . . . . . . . . . . . . . . . . . . . . 213
Shaders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
Depth buffering 219
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219
3D geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219
Depth image and view . . . . . . . . . . . . . . . . . . . . . . . . . . . 222
Explicitly transitioning the depth image . . . . . . . . . . . . . . 226
Render pass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227
Framebuffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229
Clear values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229
Depth and stencil state . . . . . . . . . . . . . . . . . . . . . . . . . . 230
Handling window resize . . . . . . . . . . . . . . . . . . . . . . . . . . 231
Loading models 233
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233
Library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233
Sample mesh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234
Loading vertices and indices . . . . . . . . . . . . . . . . . . . . . . . . 235
Vertex deduplication . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
Generating Mipmaps 242
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242
Image creation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243
Generating Mipmaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244
Linear filtering support . . . . . . . . . . . . . . . . . . . . . . . . . . 249
Sampler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250
Multisampling 254
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254
Getting available sample count . . . . . . . . . . . . . . . . . . . . . . 256
Setting up a render target . . . . . . . . . . . . . . . . . . . . . . . . . 257
Adding new attachments . . . . . . . . . . . . . . . . . . . . . . . . . . 259
Quality improvements . . . . . . . . . . . . . . . . . . . . . . . . . . . 262
Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263
Compute Shader 265
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265
Advantages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265
The Vulkan pipeline . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266
An example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266
Data manipulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268
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Shader storage buffer objects (SSBO) . . . . . . . . . . . . . . . . 268
Storage images . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269
Compute queue families . . . . . . . . . . . . . . . . . . . . . . . . . . 270
The compute shader stage . . . . . . . . . . . . . . . . . . . . . . . . . 271
Loading compute shaders . . . . . . . . . . . . . . . . . . . . . . . . . 271
Preparing the shader storage buffers . . . . . . . . . . . . . . . . . . . 272
Descriptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273
Compute pipelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
Compute space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277
Compute shaders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278
Running compute commands . . . . . . . . . . . . . . . . . . . . . . . 280
Dispatch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280
Submitting work . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
Synchronizing graphics and compute . . . . . . . . . . . . . . . . 281
Drawing the particle system . . . . . . . . . . . . . . . . . . . . . . . . 284
Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285
FAQ 286
I get an access violation error in the core validation layer . . . . . . . 286
I don’t see any messages from the validation layers / Validation layers
are not available . . . . . . . . . . . . . . . . . . . . . . . . . . . 286
vkCreateSwapchainKHR triggers an error in SteamOverlayVulkan-
Layer64.dll . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286
vkCreateInstance fails with VK_ERROR_INCOMPATIBLE_DRIVER287
5
Introduction
About
This tutorial will teach you the basics of using the Vulkan graphics and compute
API. Vulkan is a new API by the Khronos group (known for OpenGL) that
provides a much better abstraction of modern graphics cards. This new interface
allows you to better describe what your application intends to do, which can lead
to better performance and less surprising driver behavior compared to existing
APIs like OpenGL and Direct3D. The ideas behind Vulkan are similar to those
of Direct3D 12 and Metal, but Vulkan has the advantage of being fully cross-
platform and allows you to develop for Windows, Linux and Android at the
same time.
However, the price you pay for these benefits is that you have to work with a
significantly more verbose API. Every detail related to the graphics API needs
to be set up from scratch by your application, including initial frame buffer
creation and memory management for objects like buffers and texture images.
The graphics driver will do a lot less hand holding, which means that you will
have to do more work in your application to ensure correct behavior.
The takeaway message here is that Vulkan is not for everyone. It is targeted at
programmers who are enthusiastic about high performance computer graphics,
and are willing to put some work in. If you are more interested in game devel-
opment, rather than computer graphics, then you may wish to stick to OpenGL
or Direct3D, which will not be deprecated in favor of Vulkan anytime soon. An-
other alternative is to use an engine like Unreal Engine or Unity, which will be
able to use Vulkan while exposing a much higher level API to you.
With that out of the way, let’s cover some prerequisites for following this tutorial:
• A graphics card and driver compatible with Vulkan (NVIDIA, AMD, Intel,
Apple Silicon (Or the Apple M1))
• Experience with C++ (familiarity with RAII, initializer lists)
• A compiler with decent support of C++17 features (Visual Studio 2017+,
GCC 7+, Or Clang 5+)
• Some existing experience with 3D computer graphics
6
This tutorial will not assume knowledge of OpenGL or Direct3D concepts, but
it does require you to know the basics of 3D computer graphics. It will not
explain the math behind perspective projection, for example. See this online
book for a great introduction of computer graphics concepts. Some other great
computer graphics resources are:
• Ray tracing in one weekend
• Physically Based Rendering book
• Vulkan being used in a real engine in the open-source Quake and DOOM
3
You can use C instead of C++ if you want, but you will have to use a different
linear algebra library and you will be on your own in terms of code structuring.
We will use C++ features like classes and RAII to organize logic and resource
lifetimes. There is also an alternative version of this tutorial available for Rust
developers.
To make it easier to follow along for developers using other programming lan-
guages, and to get some experience with the base API we’ll be using the original
C API to work with Vulkan. If you are using C++, however, you may prefer
using the newer Vulkan-Hpp bindings that abstract some of the dirty work and
help prevent certain classes of errors.
E-book
If you prefer to read this tutorial as an e-book, then you can download an EPUB
or PDF version here:
• EPUB
• PDF
Tutorial structure
We’ll start with an overview of how Vulkan works and the work we’ll have
to do to get the first triangle on the screen. The purpose of all the smaller
steps will make more sense after you’ve understood their basic role in the whole
picture. Next, we’ll set up the development environment with the Vulkan SDK,
the GLM library for linear algebra operations and GLFW for window creation.
The tutorial will cover how to set these up on Windows with Visual Studio, and
on Ubuntu Linux with GCC.
After that we’ll implement all of the basic components of a Vulkan program that
are necessary to render your first triangle. Each chapter will follow roughly the
following structure:
• Introduce a new concept and its purpose
• Use all of the relevant API calls to integrate it into your program
7
• Abstract parts of it into helper functions
Although each chapter is written as a follow-up on the previous one, it is also
possible to read the chapters as standalone articles introducing a certain Vulkan
feature. That means that the site is also useful as a reference. All of the Vulkan
functions and types are linked to the specification, so you can click them to
learn more. Vulkan is a very new API, so there may be some shortcomings in
the specification itself. You are encouraged to submit feedback to this Khronos
repository.
As mentioned before, the Vulkan API has a rather verbose API with many
parameters to give you maximum control over the graphics hardware. This
causes basic operations like creating a texture to take a lot of steps that have to
be repeated every time. Therefore we’ll be creating our own collection of helper
functions throughout the tutorial.
Every chapter will also conclude with a link to the full code listing up to that
point. You can refer to it if you have any doubts about the structure of the code,
or if you’re dealing with a bug and want to compare. All of the code files have
been tested on graphics cards from multiple vendors to verify correctness. Each
chapter also has a comment section at the end where you can ask any questions
that are relevant to the specific subject matter. Please specify your platform,
driver version, source code, expected behavior and actual behavior to help us
help you.
This tutorial is intended to be a community effort. Vulkan is still a very new
API and best practices have not really been established yet. If you have any
type of feedback on the tutorial and site itself, then please don’t hesitate to
submit an issue or pull request to the GitHub repository. You can watch the
repository to be notified of updates to the tutorial.
After you’ve gone through the ritual of drawing your very first Vulkan powered
triangle onscreen, we’ll start expanding the program to include linear transfor-
mations, textures and 3D models.
If you’ve played with graphics APIs before, then you’ll know that there can be
a lot of steps until the first geometry shows up on the screen. There are many
of these initial steps in Vulkan, but you’ll see that each of the individual steps
is easy to understand and does not feel redundant. It’s also important to keep
in mind that once you have that boring looking triangle, drawing fully textured
3D models does not take that much extra work, and each step beyond that point
is much more rewarding.
If you encounter any problems while following the tutorial, then first check the
FAQ to see if your problem and its solution is already listed there. If you are
still stuck after that, then feel free to ask for help in the comment section of the
closest related chapter.
Ready to dive into the future of high performance graphics APIs? Let’s go!
8
Overview
This chapter will start off with an introduction of Vulkan and the problems it
addresses. After that we’re going to look at the ingredients that are required for
the first triangle. This will give you a big picture to place each of the subsequent
chapters in. We will conclude by covering the structure of the Vulkan API and
the general usage patterns.
Origin of Vulkan
Just like the previous graphics APIs, Vulkan is designed as a cross-platform
abstraction over GPUs. The problem with most of these APIs is that the era in
which they were designed featured graphics hardware that was mostly limited
to configurable fixed functionality. Programmers had to provide the vertex data
in a standard format and were at the mercy of the GPU manufacturers with
regards to lighting and shading options.
As graphics card architectures matured, they started offering more and more
programmable functionality. All this new functionality had to be integrated
with the existing APIs somehow. This resulted in less than ideal abstractions
and a lot of guesswork on the graphics driver side to map the programmer’s in-
tent to the modern graphics architectures. That’s why there are so many driver
updates for improving the performance in games, sometimes by significant mar-
gins. Because of the complexity of these drivers, application developers also need
to deal with inconsistencies between vendors, like the syntax that is accepted
for shaders. Aside from these new features, the past decade also saw an influx
of mobile devices with powerful graphics hardware. These mobile GPUs have
different architectures based on their energy and space requirements. One such
example is tiled rendering, which would benefit from improved performance by
offering the programmer more control over this functionality. Another limita-
tion originating from the age of these APIs is limited multi-threading support,
which can result in a bottleneck on the CPU side.
Vulkan solves these problems by being designed from scratch for modern graph-
ics architectures. It reduces driver overhead by allowing programmers to clearly
specify their intent using a more verbose API, and allows multiple threads to
9
create and submit commands in parallel. It reduces inconsistencies in shader
compilation by switching to a standardized byte code format with a single com-
piler. Lastly, it acknowledges the general purpose processing capabilities of
modern graphics cards by unifying the graphics and compute functionality into
a single API.
What it takes to draw a triangle
We’ll now look at an overview of all the steps it takes to render a triangle in
a well-behaved Vulkan program. All of the concepts introduced here will be
elaborated on in the next chapters. This is just to give you a big picture to
relate all of the individual components to.
Step 1 - Instance and physical device selection
A Vulkan application starts by setting up the Vulkan API through a VkInstance.
An instance is created by describing your application and any API extensions
you will be using. After creating the instance, you can query for Vulkan sup-
ported hardware and select one or more VkPhysicalDevices to use for opera-
tions. You can query for properties like VRAM size and device capabilities to
select desired devices, for example to prefer using dedicated graphics cards.
Step 2 - Logical device and queue families
After selecting the right hardware device to use, you need to create a VkDevice
(logical device), where you describe more specifically which VkPhysicalDevice-
Features you will be using, like multi viewport rendering and 64 bit floats. You
also need to specify which queue families you would like to use. Most opera-
tions performed with Vulkan, like draw commands and memory operations, are
asynchronously executed by submitting them to a VkQueue. Queues are allo-
cated from queue families, where each queue family supports a specific set of
operations in its queues. For example, there could be separate queue families for
graphics, compute and memory transfer operations. The availability of queue
families could also be used as a distinguishing factor in physical device selection.
It is possible for a device with Vulkan support to not offer any graphics func-
tionality, however all graphics cards with Vulkan support today will generally
support all queue operations that we’re interested in.
Step 3 - Window surface and swap chain
Unless you’re only interested in offscreen rendering, you will need to create a
window to present rendered images to. Windows can be created with the native
platform APIs or libraries like GLFW and SDL. We will be using GLFW in this
tutorial, but more about that in the next chapter.
10
We need two more components to actually render to a window: a window surface
(VkSurfaceKHR) and a swap chain (VkSwapchainKHR). Note the KHR postfix,
which means that these objects are part of a Vulkan extension. The Vulkan
API itself is completely platform agnostic, which is why we need to use the
standardized WSI (Window System Interface) extension to interact with the
window manager. The surface is a cross-platform abstraction over windows to
render to and is generally instantiated by providing a reference to the native
window handle, for example HWND on Windows. Luckily, the GLFW library has
a built-in function to deal with the platform specific details of this.
The swap chain is a collection of render targets. Its basic purpose is to ensure
that the image that we’re currently rendering to is different from the one that
is currently on the screen. This is important to make sure that only complete
images are shown. Every time we want to draw a frame we have to ask the
swap chain to provide us with an image to render to. When we’ve finished
drawing a frame, the image is returned to the swap chain for it to be presented
to the screen at some point. The number of render targets and conditions for
presenting finished images to the screen depends on the present mode. Common
present modes are double buffering (vsync) and triple buffering. We’ll look into
these in the swap chain creation chapter.
Some platforms allow you to render directly to a display without in-
teracting with any window manager through the VK_KHR_display and
VK_KHR_display_swapchain extensions. These allow you to create a surface
that represents the entire screen and could be used to implement your own
window manager, for example.
Step 4 - Image views and framebuffers
To draw to an image acquired from the swap chain, we have to wrap it into
a VkImageView and VkFramebuffer. An image view references a specific part
of an image to be used, and a framebuffer references image views that are to
be used for color, depth and stencil targets. Because there could be many
different images in the swap chain, we’ll preemptively create an image view and
framebuffer for each of them and select the right one at draw time.
Step 5 - Render passes
Render passes in Vulkan describe the type of images that are used during render-
ing operations, how they will be used, and how their contents should be treated.
In our initial triangle rendering application, we’ll tell Vulkan that we will use a
single image as color target and that we want it to be cleared to a solid color
right before the drawing operation. Whereas a render pass only describes the
type of images, a VkFramebuffer actually binds specific images to these slots.
11
Step 6 - Graphics pipeline
The graphics pipeline in Vulkan is set up by creating a VkPipeline object. It
describes the configurable state of the graphics card, like the viewport size
and depth buffer operation and the programmable state using VkShaderModule
objects. The VkShaderModule objects are created from shader byte code. The
driver also needs to know which render targets will be used in the pipeline,
which we specify by referencing the render pass.
One of the most distinctive features of Vulkan compared to existing APIs, is
that almost all configuration of the graphics pipeline needs to be set in advance.
That means that if you want to switch to a different shader or slightly change
your vertex layout, then you need to entirely recreate the graphics pipeline.
That means that you will have to create many VkPipeline objects in advance
for all the different combinations you need for your rendering operations. Only
some basic configuration, like viewport size and clear color, can be changed
dynamically. All of the state also needs to be described explicitly, there is no
default color blend state, for example.
The good news is that because you’re doing the equivalent of ahead-of-time
compilation versus just-in-time compilation, there are more optimization oppor-
tunities for the driver and runtime performance is more predictable, because
large state changes like switching to a different graphics pipeline are made very
explicit.
Step 7 - Command pools and command buffers
As mentioned earlier, many of the operations in Vulkan that we want to execute,
like drawing operations, need to be submitted to a queue. These operations first
need to be recorded into a VkCommandBuffer before they can be submitted.
These command buffers are allocated from a VkCommandPool that is associated
with a specific queue family. To draw a simple triangle, we need to record a
command buffer with the following operations:
• Begin the render pass
• Bind the graphics pipeline
• Draw 3 vertices
• End the render pass
Because the image in the framebuffer depends on which specific image the swap
chain will give us, we need to record a command buffer for each possible image
and select the right one at draw time. The alternative would be to record the
command buffer again every frame, which is not as efficient.
Step 8 - Main loop
Now that the drawing commands have been wrapped into a command buffer,
the main loop is quite straightforward. We first acquire an image from the
12
swap chain with vkAcquireNextImageKHR. We can then select the appropri-
ate command buffer for that image and execute it with vkQueueSubmit. Fi-
nally, we return the image to the swap chain for presentation to the screen with
vkQueuePresentKHR.
Operations that are submitted to queues are executed asynchronously. There-
fore we have to use synchronization objects like semaphores to ensure a correct
order of execution. Execution of the draw command buffer must be set up to
wait on image acquisition to finish, otherwise it may occur that we start ren-
dering to an image that is still being read for presentation on the screen. The
vkQueuePresentKHR call in turn needs to wait for rendering to be finished, for
which we’ll use a second semaphore that is signaled after rendering completes.
Summary
This whirlwind tour should give you a basic understanding of the work ahead
for drawing the first triangle. A real-world program contains more steps, like
allocating vertex buffers, creating uniform buffers and uploading texture im-
ages that will be covered in subsequent chapters, but we’ll start simple because
Vulkan has enough of a steep learning curve as it is. Note that we’ll cheat a
bit by initially embedding the vertex coordinates in the vertex shader instead
of using a vertex buffer. That’s because managing vertex buffers requires some
familiarity with command buffers first.
So in short, to draw the first triangle we need to:
• Create a VkInstance
• Select a supported graphics card (VkPhysicalDevice)
• Create a VkDevice and VkQueue for drawing and presentation
• Create a window, window surface and swap chain
• Wrap the swap chain images into VkImageView
• Create a render pass that specifies the render targets and usage
• Create framebuffers for the render pass
• Set up the graphics pipeline
• Allocate and record a command buffer with the draw commands for every
possible swap chain image
• Draw frames by acquiring images, submitting the right draw command
buffer and returning the images back to the swap chain
It’s a lot of steps, but the purpose of each individual step will be made very
simple and clear in the upcoming chapters. If you’re confused about the relation
of a single step compared to the whole program, you should refer back to this
chapter.
13
API concepts
This chapter will conclude with a short overview of how the Vulkan API is
structured at a lower level.
Coding conventions
All of the Vulkan functions, enumerations and structs are defined in the
vulkan.h header, which is included in the Vulkan SDK developed by LunarG.
We’ll look into installing this SDK in the next chapter.
Functions have a lower case vk prefix, types like enumerations and structs have
a Vk prefix and enumeration values have a VK_ prefix. The API heavily uses
structs to provide parameters to functions. For example, object creation gener-
ally follows this pattern:
1 VkXXXCreateInfo createInfo{};
2 createInfo.sType = VK_STRUCTURE_TYPE_XXX_CREATE_INFO;
3 createInfo.pNext = nullptr;
4 createInfo.foo = ...;
5 createInfo.bar = ...;
6
7 VkXXX object;
8 if (vkCreateXXX(&createInfo, nullptr, &object) != VK_SUCCESS) {
9 std::cerr << "failed to create object" << std::endl;
10 return false;
11 }
Many structures in Vulkan require you to explicitly specify the type of structure
in the sType member. The pNext member can point to an extension structure
and will always be nullptr in this tutorial. Functions that create or destroy
an object will have a VkAllocationCallbacks parameter that allows you to use
a custom allocator for driver memory, which will also be left nullptr in this
tutorial.
Almost all functions return a VkResult that is either VK_SUCCESS or an error
code. The specification describes which error codes each function can return
and what they mean.
Validation layers
As mentioned earlier, Vulkan is designed for high performance and low driver
overhead. Therefore it will include very limited error checking and debugging
capabilities by default. The driver will often crash instead of returning an error
code if you do something wrong, or worse, it will appear to work on your graphics
card and completely fail on others.
14
Vulkan allows you to enable extensive checks through a feature known as vali-
dation layers. Validation layers are pieces of code that can be inserted between
the API and the graphics driver to do things like running extra checks on func-
tion parameters and tracking memory management problems. The nice thing
is that you can enable them during development and then completely disable
them when releasing your application for zero overhead. Anyone can write their
own validation layers, but the Vulkan SDK by LunarG provides a standard set
of validation layers that we’ll be using in this tutorial. You also need to register
a callback function to receive debug messages from the layers.
Because Vulkan is so explicit about every operation and the validation layers
are so extensive, it can actually be a lot easier to find out why your screen is
black compared to OpenGL and Direct3D!
There’s only one more step before we’ll start writing code and that’s setting up
the development environment.
15
Development environment
In this chapter we’ll set up your environment for developing Vulkan applications
and install some useful libraries. All of the tools we’ll use, with the exception of
the compiler, are compatible with Windows, Linux and MacOS, but the steps
for installing them differ a bit, which is why they’re described separately here.
Windows
If you’re developing for Windows, then I will assume that you are using Visual
Studio to compile your code. For complete C++17 support, you need to use
either Visual Studio 2017 or 2019. The steps outlined below were written for
VS 2017.
Vulkan SDK
The most important component you’ll need for developing Vulkan applications
is the SDK. It includes the headers, standard validation layers, debugging tools
and a loader for the Vulkan functions. The loader looks up the functions in the
driver at runtime, similarly to GLEW for OpenGL - if you’re familiar with that.
The SDK can be downloaded from the LunarG website using the buttons at the
bottom of the page. You don’t have to create an account, but it will give you
access to some additional documentation that may be useful to you.
Proceed through the installation and pay attention to the install location of
the SDK. The first thing we’ll do is verify that your graphics card and driver
properly support Vulkan. Go to the directory where you installed the SDK,
16
open the Bin directory and run the vkcube.exe demo. You should see the
following:
If you receive an error message then ensure that your drivers are up-to-date,
include the Vulkan runtime and that your graphics card is supported. See the
introduction chapter for links to drivers from the major vendors.
There is another program in this directory that will be useful for development.
The glslangValidator.exe and glslc.exe programs will be used to compile
shaders from the human-readable GLSL to bytecode. We’ll cover this in depth
in the shader modules chapter. The Bin directory also contains the binaries of
the Vulkan loader and the validation layers, while the Lib directory contains
the libraries.
Lastly, there’s the Include directory that contains the Vulkan headers. Feel
free to explore the other files, but we won’t need them for this tutorial.
17
GLFW
As mentioned before, Vulkan by itself is a platform agnostic API and does not
include tools for creating a window to display the rendered results. To benefit
from the cross-platform advantages of Vulkan and to avoid the horrors of Win32,
we’ll use the GLFW library to create a window, which supports Windows, Linux
and MacOS. There are other libraries available for this purpose, like SDL, but
the advantage of GLFW is that it also abstracts away some of the other platform-
specific things in Vulkan besides just window creation.
You can find the latest release of GLFW on the official website. In this tutorial
we’ll be using the 64-bit binaries, but you can of course also choose to build in
32 bit mode. In that case make sure to link with the Vulkan SDK binaries in
the Lib32 directory instead of Lib. After downloading it, extract the archive to
a convenient location. I’ve chosen to create a Libraries directory in the Visual
Studio directory under documents.
GLM
Unlike DirectX 12, Vulkan does not include a library for linear algebra opera-
tions, so we’ll have to download one. GLM is a nice library that is designed for
use with graphics APIs and is also commonly used with OpenGL.
GLM is a header-only library, so just download the latest version and store it
in a convenient location. You should have a directory structure similar to the
following now:
18
Setting up Visual Studio
Now that you’ve installed all of the dependencies we can set up a basic Vi-
sual Studio project for Vulkan and write a little bit of code to make sure that
everything works.
Start Visual Studio and create a new Windows Desktop Wizard project by en-
tering a name and pressing OK.
19
Make sure that Console Application (.exe) is selected as application type
so that we have a place to print debug messages to, and check Empty Project
to prevent Visual Studio from adding boilerplate code.
20
Press OK to create the project and add a C++ source file. You should already
know how to do that, but the steps are included here for completeness.
Now add the following code to the file. Don’t worry about trying to understand
it right now; we’re just making sure that you can compile and run Vulkan
applications. We’ll start from scratch in the next chapter.
1 #define GLFW_INCLUDE_VULKAN
2 #include <GLFW/glfw3.h>
3
4 #define GLM_FORCE_RADIANS
5 #define GLM_FORCE_DEPTH_ZERO_TO_ONE
6 #include <glm/vec4.hpp>
7 #include <glm/mat4x4.hpp>
8
9 #include <iostream>
10
21
11 int main() {
12 glfwInit();
13
14 glfwWindowHint(GLFW_CLIENT_API, GLFW_NO_API);
15 GLFWwindow* window = glfwCreateWindow(800, 600, "Vulkan window",
nullptr, nullptr);
16
17 uint32_t extensionCount = 0;
18 vkEnumerateInstanceExtensionProperties(nullptr, &extensionCount,
nullptr);
19
20 std::cout << extensionCount << " extensions supported\n";
21
22 glm::mat4 matrix;
23 glm::vec4 vec;
24 auto test = matrix * vec;
25
26 while(!glfwWindowShouldClose(window)) {
27 glfwPollEvents();
28 }
29
30 glfwDestroyWindow(window);
31
32 glfwTerminate();
33
34 return 0;
35 }
Let’s now configure the project to get rid of the errors. Open the project prop-
erties dialog and ensure that All Configurations is selected, because most of
the settings apply to both Debug and Release mode.
22
Go to C++ -> General -> Additional Include Directories and press
<Edit...> in the dropdown box.
Add the header directories for Vulkan, GLFW and GLM:
23
Next, open the editor for library directories under Linker -> General:
And add the locations of the object files for Vulkan and GLFW:
Go to Linker -> Input and press <Edit...> in the Additional
Dependencies dropdown box.
24
Enter the names of the Vulkan and GLFW object files:
And finally change the compiler to support C++17 features:
You can now close the project properties dialog. If you did everything right
then you should no longer see any more errors being highlighted in the code.
Finally, ensure that you are actually compiling in 64 bit mode:
Press F5 to compile and run the project and you should see a command prompt
and a window pop up like this:
25
The number of extensions should be non-zero. Congratulations, you’re all set
for playing with Vulkan!
Linux
These instructions will be aimed at Ubuntu, Fedora and Arch Linux users, but
you may be able to follow along by changing the package manager-specific com-
mands to the ones that are appropriate for you. You should have a compiler
that supports C++17 (GCC 7+ or Clang 5+). You’ll also need make.
Vulkan Packages
The most important components you’ll need for developing Vulkan applications
on Linux are the Vulkan loader, validation layers, and a couple of command-line
utilities to test whether your machine is Vulkan-capable:
• sudo apt install vulkan-tools or sudo dnf install vulkan-tools:
Command-line utilities, most importantly vulkaninfo and vkcube. Run
these to confirm your machine supports Vulkan.
• sudo apt install libvulkan-dev or sudo dnf install vulkan-loader-devel
: Installs Vulkan loader. The loader looks up the functions in the driver
at runtime, similarly to GLEW for OpenGL - if you’re familiar with that.
• sudo apt install vulkan-validationlayers-dev spirv-tools or
sudo dnf install mesa-vulkan-devel vulkan-validation-layers-devel:
Installs the standard validation layers and required SPIR-V tools. These
are crucial when debugging Vulkan applications, and we’ll discuss them
in the upcoming chapter.
On Arch Linux, you can run sudo pacman -S vulkan-devel to install all the
required tools above.
If installation was successful, you should be all set with the Vulkan portion.
Remember to run vkcube and ensure you see the following pop up in a window:
26
If you receive an error message then ensure that your drivers are up-to-date,
include the Vulkan runtime and that your graphics card is supported. See the
introduction chapter for links to drivers from the major vendors.
GLFW
As mentioned before, Vulkan by itself is a platform agnostic API and does not
include tools for creation a window to display the rendered results. To benefit
from the cross-platform advantages of Vulkan and to avoid the horrors of X11,
we’ll use the GLFW library to create a window, which supports Windows, Linux
and MacOS. There are other libraries available for this purpose, like SDL, but
the advantage of GLFW is that it also abstracts away some of the other platform-
specific things in Vulkan besides just window creation.
We’ll be installing GLFW from the following command:
1 sudo apt install libglfw3-dev
27
or
1 sudo dnf install glfw-devel
or
1 sudo pacman -S glfw-wayland # glfw-x11 for X11 users
GLM
Unlike DirectX 12, Vulkan does not include a library for linear algebra opera-
tions, so we’ll have to download one. GLM is a nice library that is designed for
use with graphics APIs and is also commonly used with OpenGL.
It is a header-only library that can be installed from the libglm-dev or
glm-devel package:
1 sudo apt install libglm-dev
or
1 sudo dnf install glm-devel
or
1 sudo pacman -S glm
Shader Compiler
We have just about all we need, except we’ll want a program to compile shaders
from the human-readable GLSL to bytecode.
Two popular shader compilers are Khronos Group’s glslangValidator and
Google’s glslc. The latter has a familiar GCC- and Clang-like usage, so we’ll
go with that: on Ubuntu, download Google’s unofficial binaries and copy glslc
to your /usr/local/bin. Note you may need to sudo depending on your per-
missions. On Fedora use sudo dnf install glslc, while on Arch Linux run
sudo pacman -S shaderc. To test, run glslc and it should rightfully complain
we didn’t pass any shaders to compile:
glslc: error: no input files
We’ll cover glslc in depth in the shader modules chapter.
Setting up a makefile project
Now that you have installed all of the dependencies, we can set up a basic
makefile project for Vulkan and write a little bit of code to make sure that
everything works.
28
Create a new directory at a convenient location with a name like VulkanTest.
Create a source file called main.cpp and insert the following code. Don’t worry
about trying to understand it right now; we’re just making sure that you can
compile and run Vulkan applications. We’ll start from scratch in the next
chapter.
1 #define GLFW_INCLUDE_VULKAN
2 #include <GLFW/glfw3.h>
3
4 #define GLM_FORCE_RADIANS
5 #define GLM_FORCE_DEPTH_ZERO_TO_ONE
6 #include <glm/vec4.hpp>
7 #include <glm/mat4x4.hpp>
8
9 #include <iostream>
10
11 int main() {
12 glfwInit();
13
14 glfwWindowHint(GLFW_CLIENT_API, GLFW_NO_API);
15 GLFWwindow* window = glfwCreateWindow(800, 600, "Vulkan window",
nullptr, nullptr);
16
17 uint32_t extensionCount = 0;
18 vkEnumerateInstanceExtensionProperties(nullptr, &extensionCount,
nullptr);
19
20 std::cout << extensionCount << " extensions supported\n";
21
22 glm::mat4 matrix;
23 glm::vec4 vec;
24 auto test = matrix * vec;
25
26 while(!glfwWindowShouldClose(window)) {
27 glfwPollEvents();
28 }
29
30 glfwDestroyWindow(window);
31
32 glfwTerminate();
33
34 return 0;
35 }
Next, we’ll write a makefile to compile and run this basic Vulkan code. Create
a new empty file called Makefile. I will assume that you already have some
29
basic experience with makefiles, like how variables and rules work. If not, you
can get up to speed very quickly with this tutorial.
We’ll first define a couple of variables to simplify the remainder of the file. Define
a CFLAGS variable that will specify the basic compiler flags:
1 CFLAGS = -std=c++17 -O2
We’re going to use modern C++ (-std=c++17), and we’ll set optimization level
to O2. We can remove -O2 to compile programs faster, but we should remember
to place it back for release builds.
Similarly, define the linker flags in a LDFLAGS variable:
1 LDFLAGS = -lglfw -lvulkan -ldl -lpthread -lX11 -lXxf86vm -lXrandr
-lXi
The flag -lglfw is for GLFW, -lvulkan links with the Vulkan function loader
and the remaining flags are low-level system libraries that GLFW needs. The
remaining flags are dependencies of GLFW itself: the threading and window
management.
It is possible that the Xxf68vm and Xi libraries are not yet installed on your
system. You can find them in the following packages:
1 sudo apt install libxxf86vm-dev libxi-dev
or
1 sudo dnf install libXi-devel libXxf86vm-devel
or
1 sudo pacman -S libxi libxxf86vm
Specifying the rule to compile VulkanTest is straightforward now. Make sure
to use tabs for indentation instead of spaces.
1 VulkanTest: main.cpp
2 g++ $(CFLAGS) -o VulkanTest main.cpp $(LDFLAGS)
Verify that this rule works by saving the makefile and running make in the
directory with main.cpp and Makefile. This should result in a VulkanTest
executable.
We’ll now define two more rules, test and clean, where the former will run the
executable and the latter will remove a built executable:
1 .PHONY: test clean
2
3 test: VulkanTest
30
4 ./VulkanTest
5
6 clean:
7 rm -f VulkanTest
Running make test should show the program running successfully, and dis-
playing the number of Vulkan extensions. The application should exit with the
success return code (0) when you close the empty window. You should now
have a complete makefile that resembles the following:
1 CFLAGS = -std=c++17 -O2
2 LDFLAGS = -lglfw -lvulkan -ldl -lpthread -lX11 -lXxf86vm -lXrandr
-lXi
3
4 VulkanTest: main.cpp
5 g++ $(CFLAGS) -o VulkanTest main.cpp $(LDFLAGS)
6
7 .PHONY: test clean
8
9 test: VulkanTest
10 ./VulkanTest
11
12 clean:
13 rm -f VulkanTest
You can now use this directory as a template for your Vulkan projects. Make a
copy, rename it to something like HelloTriangle and remove all of the code in
main.cpp.
You are now all set for the real adventure.
MacOS
These instructions will assume you are using Xcode and the Homebrew package
manager. Also, keep in mind that you will need at least MacOS version 10.11,
and your device needs to support the Metal API.
Vulkan SDK
The most important component you’ll need for developing Vulkan applications
is the SDK. It includes the headers, standard validation layers, debugging tools
and a loader for the Vulkan functions. The loader looks up the functions in the
driver at runtime, similarly to GLEW for OpenGL - if you’re familiar with that.
The SDK can be downloaded from the LunarG website using the buttons at the
bottom of the page. You don’t have to create an account, but it will give you
access to some additional documentation that may be useful to you.
31
The SDK version for MacOS internally uses MoltenVK. There is no native sup-
port for Vulkan on MacOS, so what MoltenVK does is actually act as a layer
that translates Vulkan API calls to Apple’s Metal graphics framework. With
this you can take advantage of debugging and performance benefits of Apple’s
Metal framework.
After downloading it, simply extract the contents to a folder of your choice
(keep in mind you will need to reference it when creating your projects on
Xcode). Inside the extracted folder, in the Applications folder you should
have some executable files that will run a few demos using the SDK. Run the
vkcube executable and you will see the following:
32
GLFW
As mentioned before, Vulkan by itself is a platform agnostic API and does not
include tools for creation a window to display the rendered results. We’ll use the
GLFW library to create a window, which supports Windows, Linux and MacOS.
There are other libraries available for this purpose, like SDL, but the advantage
of GLFW is that it also abstracts away some of the other platform-specific things
in Vulkan besides just window creation.
To install GLFW on MacOS we will use the Homebrew package manager to get
the glfw package:
1 brew install glfw
GLM
Vulkan does not include a library for linear algebra operations, so we’ll have
to download one. GLM is a nice library that is designed for use with graphics
APIs and is also commonly used with OpenGL.
It is a header-only library that can be installed from the glm package:
1 brew install glm
Setting up Xcode
Now that all the dependencies are installed we can set up a basic Xcode project
for Vulkan. Most of the instructions here are essentially a lot of “plumbing” so
we can get all the dependencies linked to the project. Also, keep in mind that
during the following instructions whenever we mention the folder vulkansdk we
are refering to the folder where you extracted the Vulkan SDK.
Start Xcode and create a new Xcode project. On the window that will open
select Application > Command Line Tool.
33
Select Next, write a name for the project and for Language select C++.
Press Next and the project should have been created. Now, let’s change the
code in the generated main.cpp file to the following code:
1 #define GLFW_INCLUDE_VULKAN
2 #include <GLFW/glfw3.h>
3
4 #define GLM_FORCE_RADIANS
34
5 #define GLM_FORCE_DEPTH_ZERO_TO_ONE
6 #include <glm/vec4.hpp>
7 #include <glm/mat4x4.hpp>
8
9 #include <iostream>
10
11 int main() {
12 glfwInit();
13
14 glfwWindowHint(GLFW_CLIENT_API, GLFW_NO_API);
15 GLFWwindow* window = glfwCreateWindow(800, 600, "Vulkan window",
nullptr, nullptr);
16
17 uint32_t extensionCount = 0;
18 vkEnumerateInstanceExtensionProperties(nullptr, &extensionCount,
nullptr);
19
20 std::cout << extensionCount << " extensions supported\n";
21
22 glm::mat4 matrix;
23 glm::vec4 vec;
24 auto test = matrix * vec;
25
26 while(!glfwWindowShouldClose(window)) {
27 glfwPollEvents();
28 }
29
30 glfwDestroyWindow(window);
31
32 glfwTerminate();
33
34 return 0;
35 }
Keep in mind you are not required to understand all this code is doing yet, we
are just setting up some API calls to make sure everything is working.
Xcode should already be showing some errors such as libraries it cannot find.
We will now start configuring the project to get rid of those errors. On the
Project Navigator panel select your project. Open the Build Settings tab and
then:
• Find the Header Search Paths field and add a link to /usr/local/include
(this is where Homebrew installs headers, so the glm and glfw3 header
files should be there) and a link to vulkansdk/macOS/include for the
Vulkan headers.
• Find the Library Search Paths field and add a link to /usr/local/lib
35
(again, this is where Homebrew installs libraries, so the glm and glfw3 lib
files should be there) and a link to vulkansdk/macOS/lib.
It should look like so (obviously, paths will be different depending on where you
placed on your files):
Now, in the Build Phases tab, on Link Binary With Libraries we will add
both the glfw3 and the vulkan frameworks. To make things easier we will be
adding the dynamic libraries in the project (you can check the documentation
of these libraries if you want to use the static frameworks).
• For glfw open the folder /usr/local/lib and there you will find a file
name like libglfw.3.x.dylib (“x” is the library’s version number, it
might be different depending on when you downloaded the package from
Homebrew). Simply drag that file to the Linked Frameworks and Libraries
tab on Xcode.
• For vulkan, go to vulkansdk/macOS/lib. Do the same for the both files
libvulkan.1.dylib and libvulkan.1.x.xx.dylib (where “x” will be
the version number of the the SDK you downloaded).
After adding those libraries, in the same tab on Copy Files change
Destination to “Frameworks”, clear the subpath and deselect “Copy only
when installing”. Click on the “+” sign and add all those three frameworks
here aswell.
Your Xcode configuration should look like:
36
The last thing you need to setup are a couple of environment variables. On
Xcode toolbar go to Product > Scheme > Edit Scheme..., and in the
Arguments tab add the two following environment variables:
• VK_ICD_FILENAMES = vulkansdk/macOS/share/vulkan/icd.d/MoltenVK_icd.json
• VK_LAYER_PATH = vulkansdk/macOS/share/vulkan/explicit_layer.d
It should look like so:
Finally, you should be all set! Now if you run the project (remembering to set-
ting the build configuration to Debug or Release depending on the configuration
37
you chose) you should see the following:
The number of extensions should be non-zero. The other logs are from the
libraries, you might get different messages from those depending on your con-
figuration.
You are now all set for the real thing.
38
Drawing a triangle
Setup
Base code
General structure
In the previous chapter you’ve created a Vulkan project with all of the proper
configuration and tested it with the sample code. In this chapter we’re starting
from scratch with the following code:
1 #include <vulkan/vulkan.h>
2
3 #include <iostream>
4 #include <stdexcept>
5 #include <cstdlib>
6
7 class HelloTriangleApplication {
8 public:
9 void run() {
10 initVulkan();
11 mainLoop();
12 cleanup();
13 }
14
15 private:
16 void initVulkan() {
17
18 }
19
20 void mainLoop() {
21
22 }
23
24 void cleanup() {
25
39
26 }
27 };
28
29 int main() {
30 HelloTriangleApplication app;
31
32 try {
33 app.run();
34 } catch (const std::exception& e) {
35 std::cerr << e.what() << std::endl;
36 return EXIT_FAILURE;
37 }
38
39 return EXIT_SUCCESS;
40 }
We first include the Vulkan header from the LunarG SDK, which provides the
functions, structures and enumerations. The stdexcept and iostream headers
are included for reporting and propagating errors. The cstdlib header provides
the EXIT_SUCCESS and EXIT_FAILURE macros.
The program itself is wrapped into a class where we’ll store the Vulkan objects
as private class members and add functions to initiate each of them, which will
be called from the initVulkan function. Once everything has been prepared,
we enter the main loop to start rendering frames. We’ll fill in the mainLoop
function to include a loop that iterates until the window is closed in a moment.
Once the window is closed and mainLoop returns, we’ll make sure to deallocate
the resources we’ve used in the cleanup function.
If any kind of fatal error occurs during execution then we’ll throw a
std::runtime_error exception with a descriptive message, which will propa-
gate back to the main function and be printed to the command prompt. To
handle a variety of standard exception types as well, we catch the more general
std::exception. One example of an error that we will deal with soon is
finding out that a certain required extension is not supported.
Roughly every chapter that follows after this one will add one new function
that will be called from initVulkan and one or more new Vulkan objects to the
private class members that need to be freed at the end in cleanup.
Resource management
Just like each chunk of memory allocated with malloc requires a call to free,
every Vulkan object that we create needs to be explicitly destroyed when we no
longer need it. In C++ it is possible to perform automatic resource management
using RAII or smart pointers provided in the <memory> header. However, I’ve
chosen to be explicit about allocation and deallocation of Vulkan objects in this
40
tutorial. After all, Vulkan’s niche is to be explicit about every operation to
avoid mistakes, so it’s good to be explicit about the lifetime of objects to learn
how the API works.
After following this tutorial, you could implement automatic resource manage-
ment by writing C++ classes that acquire Vulkan objects in their constructor
and release them in their destructor, or by providing a custom deleter to either
std::unique_ptr or std::shared_ptr, depending on your ownership require-
ments. RAII is the recommended model for larger Vulkan programs, but for
learning purposes it’s always good to know what’s going on behind the scenes.
Vulkan objects are either created directly with functions like vkCreateXXX, or
allocated through another object with functions like vkAllocateXXX. After
making sure that an object is no longer used anywhere, you need to destroy
it with the counterparts vkDestroyXXX and vkFreeXXX. The parameters for
these functions generally vary for different types of objects, but there is one
parameter that they all share: pAllocator. This is an optional parameter that
allows you to specify callbacks for a custom memory allocator. We will ignore
this parameter in the tutorial and always pass nullptr as argument.
Integrating GLFW
Vulkan works perfectly fine without creating a window if you want to use it for
off-screen rendering, but it’s a lot more exciting to actually show something!
First replace the #include <vulkan/vulkan.h> line with
1 #define GLFW_INCLUDE_VULKAN
2 #include <GLFW/glfw3.h>
That way GLFW will include its own definitions and automatically load the
Vulkan header with it. Add a initWindow function and add a call to it from
the run function before the other calls. We’ll use that function to initialize
GLFW and create a window.
1 void run() {
2 initWindow();
3 initVulkan();
4 mainLoop();
5 cleanup();
6 }
7
8 private:
9 void initWindow() {
10
11 }
The very first call in initWindow should be glfwInit(), which initializes the
GLFW library. Because GLFW was originally designed to create an OpenGL
41
context, we need to tell it to not create an OpenGL context with a subsequent
call:
1 glfwWindowHint(GLFW_CLIENT_API, GLFW_NO_API);
Because handling resized windows takes special care that we’ll look into later,
disable it for now with another window hint call:
1 glfwWindowHint(GLFW_RESIZABLE, GLFW_FALSE);
All that’s left now is creating the actual window. Add a GLFWwindow* window;
private class member to store a reference to it and initialize the window with:
1 window = glfwCreateWindow(800, 600, "Vulkan", nullptr, nullptr);
The first three parameters specify the width, height and title of the window.
The fourth parameter allows you to optionally specify a monitor to open the
window on and the last parameter is only relevant to OpenGL.
It’s a good idea to use constants instead of hardcoded width and height num-
bers because we’ll be referring to these values a couple of times in the future.
I’ve added the following lines above the HelloTriangleApplication class defi-
nition:
1 const uint32_t WIDTH = 800;
2 const uint32_t HEIGHT = 600;
and replaced the window creation call with
1 window = glfwCreateWindow(WIDTH, HEIGHT, "Vulkan", nullptr, nullptr);
You should now have a initWindow function that looks like this:
1 void initWindow() {
2 glfwInit();
3
4 glfwWindowHint(GLFW_CLIENT_API, GLFW_NO_API);
5 glfwWindowHint(GLFW_RESIZABLE, GLFW_FALSE);
6
7 window = glfwCreateWindow(WIDTH, HEIGHT, "Vulkan", nullptr,
nullptr);
8 }
To keep the application running until either an error occurs or the window is
closed, we need to add an event loop to the mainLoop function as follows:
1 void mainLoop() {
2 while (!glfwWindowShouldClose(window)) {
3 glfwPollEvents();
4 }
5 }
42
This code should be fairly self-explanatory. It loops and checks for events like
pressing the X button until the window has been closed by the user. This is
also the loop where we’ll later call a function to render a single frame.
Once the window is closed, we need to clean up resources by destroying it and
terminating GLFW itself. This will be our first cleanup code:
1 void cleanup() {
2 glfwDestroyWindow(window);
3
4 glfwTerminate();
5 }
When you run the program now you should see a window titled Vulkan show
up until the application is terminated by closing the window. Now that we have
the skeleton for the Vulkan application, let’s create the first Vulkan object!
C++ code
Instance
Creating an instance
The very first thing you need to do is initialize the Vulkan library by creat-
ing an instance. The instance is the connection between your application and
the Vulkan library and creating it involves specifying some details about your
application to the driver.
Start by adding a createInstance function and invoking it in the initVulkan
function.
1 void initVulkan() {
2 createInstance();
3 }
Additionally add a data member to hold the handle to the instance:
1 private:
2 VkInstance instance;
Now, to create an instance we’ll first have to fill in a struct with some information
about our application. This data is technically optional, but it may provide some
useful information to the driver in order to optimize our specific application
(e.g. because it uses a well-known graphics engine with certain special behavior).
This struct is called VkApplicationInfo:
1 void createInstance() {
2 VkApplicationInfo appInfo{};
3 appInfo.sType = VK_STRUCTURE_TYPE_APPLICATION_INFO;
4 appInfo.pApplicationName = "Hello Triangle";
43
5 appInfo.applicationVersion = VK_MAKE_VERSION(1, 0, 0);
6 appInfo.pEngineName = "No Engine";
7 appInfo.engineVersion = VK_MAKE_VERSION(1, 0, 0);
8 appInfo.apiVersion = VK_API_VERSION_1_0;
9 }
As mentioned before, many structs in Vulkan require you to explicitly specify
the type in the sType member. This is also one of the many structs with a
pNext member that can point to extension information in the future. We’re
using value initialization here to leave it as nullptr.
A lot of information in Vulkan is passed through structs instead of function
parameters and we’ll have to fill in one more struct to provide sufficient in-
formation for creating an instance. This next struct is not optional and tells
the Vulkan driver which global extensions and validation layers we want to use.
Global here means that they apply to the entire program and not a specific
device, which will become clear in the next few chapters.
1 VkInstanceCreateInfo createInfo{};
2 createInfo.sType = VK_STRUCTURE_TYPE_INSTANCE_CREATE_INFO;
3 createInfo.pApplicationInfo = &appInfo;
The first two parameters are straightforward. The next two layers specify the
desired global extensions. As mentioned in the overview chapter, Vulkan is a
platform agnostic API, which means that you need an extension to interface
with the window system. GLFW has a handy built-in function that returns the
extension(s) it needs to do that which we can pass to the struct:
1 uint32_t glfwExtensionCount = 0;
2 const char** glfwExtensions;
3
4 glfwExtensions =
glfwGetRequiredInstanceExtensions(&glfwExtensionCount);
5
6 createInfo.enabledExtensionCount = glfwExtensionCount;
7 createInfo.ppEnabledExtensionNames = glfwExtensions;
The last two members of the struct determine the global validation layers to
enable. We’ll talk about these more in-depth in the next chapter, so just leave
these empty for now.
1 createInfo.enabledLayerCount = 0;
We’ve now specified everything Vulkan needs to create an instance and we can
finally issue the vkCreateInstance call:
1 VkResult result = vkCreateInstance(&createInfo, nullptr, &instance);
44
As you’ll see, the general pattern that object creation function parameters in
Vulkan follow is:
• Pointer to struct with creation info
• Pointer to custom allocator callbacks, always nullptr in this tutorial
• Pointer to the variable that stores the handle to the new object
If everything went well then the handle to the instance was stored in the
VkInstance class member. Nearly all Vulkan functions return a value of type
VkResult that is either VK_SUCCESS or an error code. To check if the instance
was created successfully, we don’t need to store the result and can just use a
check for the success value instead:
1 if (vkCreateInstance(&createInfo, nullptr, &instance) != VK_SUCCESS)
{
2 throw std::runtime_error("failed to create instance!");
3 }
Now run the program to make sure that the instance is created successfully.
Encountered VK_ERROR_INCOMPATIBLE_DRIVER:
If using MacOS with the latest MoltenVK sdk, you may get VK_ERROR_INCOMPATIBLE_DRIVER
returned from vkCreateInstance. According to the Getting Start Notes. Be-
ginning with the 1.3.216 Vulkan SDK, the VK_KHR_PORTABILITY_subset
extension is mandatory.
To get over this error, first add the VK_INSTANCE_CREATE_ENUMERATE_PORTABILITY_BIT_KHR
bit to VkInstanceCreateInfo struct’s flags, then add VK_KHR_PORTABILITY_ENUMERATION_EXTENSION_NAME
to instance enabled extension list.
Typically the code could be like this:
1 ...
2
3 std::vector<const char*> requiredExtensions;
4
5 for(uint32_t i = 0; i < glfwExtensionCount; i++) {
6 requiredExtensions.emplace_back(glfwExtensions[i]);
7 }
8
9 requiredExtensions.emplace_back(VK_KHR_PORTABILITY_ENUMERATION_EXTENSION_NAME);
10
11 createInfo.flags |= VK_INSTANCE_CREATE_ENUMERATE_PORTABILITY_BIT_KHR;
12
13 createInfo.enabledExtensionCount = (uint32_t)
requiredExtensions.size();
14 createInfo.ppEnabledExtensionNames = requiredExtensions.data();
15
45
16 if (vkCreateInstance(&createInfo, nullptr, &instance) != VK_SUCCESS)
{
17 throw std::runtime_error("failed to create instance!");
18 }
Checking for extension support
If you look at the vkCreateInstance documentation then you’ll see that one
of the possible error codes is VK_ERROR_EXTENSION_NOT_PRESENT. We could
simply specify the extensions we require and terminate if that error code comes
back. That makes sense for essential extensions like the window system interface,
but what if we want to check for optional functionality?
To retrieve a list of supported extensions before creating an instance,
there’s the vkEnumerateInstanceExtensionProperties function. It takes
a pointer to a variable that stores the number of extensions and an array
of VkExtensionProperties to store details of the extensions. It also takes
an optional first parameter that allows us to filter extensions by a specific
validation layer, which we’ll ignore for now.
To allocate an array to hold the extension details we first need to know how
many there are. You can request just the number of extensions by leaving the
latter parameter empty:
1 uint32_t extensionCount = 0;
2 vkEnumerateInstanceExtensionProperties(nullptr, &extensionCount,
nullptr);
Now allocate an array to hold the extension details (include <vector>):
1 std::vector<VkExtensionProperties> extensions(extensionCount);
Finally we can query the extension details:
1 vkEnumerateInstanceExtensionProperties(nullptr, &extensionCount,
extensions.data());
Each VkExtensionProperties struct contains the name and version of an ex-
tension. We can list them with a simple for loop (\t is a tab for indentation):
1 std::cout << "available extensions:\n";
2
3 for (const auto& extension : extensions) {
4 std::cout << '\t' << extension.extensionName << '\n';
5 }
You can add this code to the createInstance function if you’d like
to provide some details about the Vulkan support. As a challenge, try
to create a function that checks if all of the extensions returned by
46
glfwGetRequiredInstanceExtensions are included in the supported ex-
tensions list.
Cleaning up
The VkInstance should be only destroyed right before the program exits. It
can be destroyed in cleanup with the vkDestroyInstance function:
1 void cleanup() {
2 vkDestroyInstance(instance, nullptr);
3
4 glfwDestroyWindow(window);
5
6 glfwTerminate();
7 }
The parameters for the vkDestroyInstance function are straightforward. As
mentioned in the previous chapter, the allocation and deallocation functions in
Vulkan have an optional allocator callback that we’ll ignore by passing nullptr
to it. All of the other Vulkan resources that we’ll create in the following chapters
should be cleaned up before the instance is destroyed.
Before continuing with the more complex steps after instance creation, it’s time
to evaluate our debugging options by checking out validation layers.
C++ code
Validation layers
What are validation layers?
The Vulkan API is designed around the idea of minimal driver overhead and one
of the manifestations of that goal is that there is very limited error checking in
the API by default. Even mistakes as simple as setting enumerations to incorrect
values or passing null pointers to required parameters are generally not explicitly
handled and will simply result in crashes or undefined behavior. Because Vulkan
requires you to be very explicit about everything you’re doing, it’s easy to make
many small mistakes like using a new GPU feature and forgetting to request it
at logical device creation time.
However, that doesn’t mean that these checks can’t be added to the API. Vulkan
introduces an elegant system for this known as validation layers. Validation
layers are optional components that hook into Vulkan function calls to apply
additional operations. Common operations in validation layers are:
• Checking the values of parameters against the specification to detect mis-
use
• Tracking creation and destruction of objects to find resource leaks
• Checking thread safety by tracking the threads that calls originate from
47
• Logging every call and its parameters to the standard output
• Tracing Vulkan calls for profiling and replaying
Here’s an example of what the implementation of a function in a diagnostics
validation layer could look like:
1 VkResult vkCreateInstance(
2 const VkInstanceCreateInfo* pCreateInfo,
3 const VkAllocationCallbacks* pAllocator,
4 VkInstance* instance) {
5
6 if (pCreateInfo == nullptr || instance == nullptr) {
7 log("Null pointer passed to required parameter!");
8 return VK_ERROR_INITIALIZATION_FAILED;
9 }
10
11 return real_vkCreateInstance(pCreateInfo, pAllocator, instance);
12 }
These validation layers can be freely stacked to include all the debugging func-
tionality that you’re interested in. You can simply enable validation layers for
debug builds and completely disable them for release builds, which gives you
the best of both worlds!
Vulkan does not come with any validation layers built-in, but the LunarG
Vulkan SDK provides a nice set of layers that check for common errors. They’re
also completely open source, so you can check which kind of mistakes they check
for and contribute. Using the validation layers is the best way to avoid your
application breaking on different drivers by accidentally relying on undefined
behavior.
Validation layers can only be used if they have been installed onto the system.
For example, the LunarG validation layers are only available on PCs with the
Vulkan SDK installed.
There were formerly two different types of validation layers in Vulkan: instance
and device specific. The idea was that instance layers would only check calls
related to global Vulkan objects like instances, and device specific layers would
only check calls related to a specific GPU. Device specific layers have now been
deprecated, which means that instance validation layers apply to all Vulkan calls.
The specification document still recommends that you enable validation layers at
device level as well for compatibility, which is required by some implementations.
We’ll simply specify the same layers as the instance at logical device level, which
we’ll see later on.
Using validation layers
In this section we’ll see how to enable the standard diagnostics layers provided
by the Vulkan SDK. Just like extensions, validation layers need to be enabled
48
by specifying their name. All of the useful standard validation is bundled into
a layer included in the SDK that is known as VK_LAYER_KHRONOS_validation.
Let’s first add two configuration variables to the program to specify the layers
to enable and whether to enable them or not. I’ve chosen to base that value
on whether the program is being compiled in debug mode or not. The NDEBUG
macro is part of the C++ standard and means “not debug”.
1 const uint32_t WIDTH = 800;
2 const uint32_t HEIGHT = 600;
3
4 const std::vector<const char*> validationLayers = {
5 "VK_LAYER_KHRONOS_validation"
6 };
7
8 #ifdef NDEBUG
9 const bool enableValidationLayers = false;
10 #else
11 const bool enableValidationLayers = true;
12 #endif
We’ll add a new function checkValidationLayerSupport that checks if all of
the requested layers are available. First list all of the available layers using
the vkEnumerateInstanceLayerProperties function. Its usage is identical to
that of vkEnumerateInstanceExtensionProperties which was discussed in
the instance creation chapter.
1 bool checkValidationLayerSupport() {
2 uint32_t layerCount;
3 vkEnumerateInstanceLayerProperties(&layerCount, nullptr);
4
5 std::vector<VkLayerProperties> availableLayers(layerCount);
6 vkEnumerateInstanceLayerProperties(&layerCount,
availableLayers.data());
7
8 return false;
9 }
Next, check if all of the layers in validationLayers exist in the availableLayers
list. You may need to include <cstring> for strcmp.
1 for (const char* layerName : validationLayers) {
2 bool layerFound = false;
3
4 for (const auto& layerProperties : availableLayers) {
5 if (strcmp(layerName, layerProperties.layerName) == 0) {
6 layerFound = true;
7 break;
49
8 }
9 }
10
11 if (!layerFound) {
12 return false;
13 }
14 }
15
16 return true;
We can now use this function in createInstance:
1 void createInstance() {
2 if (enableValidationLayers && !checkValidationLayerSupport()) {
3 throw std::runtime_error("validation layers requested, but
not available!");
4 }
5
6 ...
7 }
Now run the program in debug mode and ensure that the error does not occur.
If it does, then have a look at the FAQ.
Finally, modify the VkInstanceCreateInfo struct instantiation to include the
validation layer names if they are enabled:
1 if (enableValidationLayers) {
2 createInfo.enabledLayerCount =
static_cast<uint32_t>(validationLayers.size());
3 createInfo.ppEnabledLayerNames = validationLayers.data();
4 } else {
5 createInfo.enabledLayerCount = 0;
6 }
If the check was successful then vkCreateInstance should not ever return a
VK_ERROR_LAYER_NOT_PRESENT error, but you should run the program to make
sure.
Message callback
The validation layers will print debug messages to the standard output by de-
fault, but we can also handle them ourselves by providing an explicit callback
in our program. This will also allow you to decide which kind of messages you
would like to see, because not all are necessarily (fatal) errors. If you don’t want
to do that right now then you may skip to the last section in this chapter.
50
To set up a callback in the program to handle messages and the associated
details, we have to set up a debug messenger with a callback using the
VK_EXT_debug_utils extension.
We’ll first create a getRequiredExtensions function that will return the re-
quired list of extensions based on whether validation layers are enabled or not:
1 std::vector<const char*> getRequiredExtensions() {
2 uint32_t glfwExtensionCount = 0;
3 const char** glfwExtensions;
4 glfwExtensions =
glfwGetRequiredInstanceExtensions(&glfwExtensionCount);
5
6 std::vector<const char*> extensions(glfwExtensions,
glfwExtensions + glfwExtensionCount);
7
8 if (enableValidationLayers) {
9 extensions.push_back(VK_EXT_DEBUG_UTILS_EXTENSION_NAME);
10 }
11
12 return extensions;
13 }
The extensions specified by GLFW are always required, but the debug
messenger extension is conditionally added. Note that I’ve used the
VK_EXT_DEBUG_UTILS_EXTENSION_NAME macro here which is equal to the
literal string “VK_EXT_debug_utils”. Using this macro lets you avoid typos.
We can now use this function in createInstance:
1 auto extensions = getRequiredExtensions();
2 createInfo.enabledExtensionCount =
static_cast<uint32_t>(extensions.size());
3 createInfo.ppEnabledExtensionNames = extensions.data();
Run the program to make sure you don’t receive a VK_ERROR_EXTENSION_NOT_PRESENT
error. We don’t really need to check for the existence of this extension, because
it should be implied by the availability of the validation layers.
Now let’s see what a debug callback function looks like. Add a new static mem-
ber function called debugCallback with the PFN_vkDebugUtilsMessengerCallbackEXT
prototype. The VKAPI_ATTR and VKAPI_CALL ensure that the function has the
right signature for Vulkan to call it.
1 static VKAPI_ATTR VkBool32 VKAPI_CALL debugCallback(
2 VkDebugUtilsMessageSeverityFlagBitsEXT messageSeverity,
3 VkDebugUtilsMessageTypeFlagsEXT messageType,
4 const VkDebugUtilsMessengerCallbackDataEXT* pCallbackData,
5 void* pUserData) {
51
6
7 std::cerr << "validation layer: " << pCallbackData->pMessage <<
std::endl;
8
9 return VK_FALSE;
10 }
The first parameter specifies the severity of the message, which is one of the
following flags:
• VK_DEBUG_UTILS_MESSAGE_SEVERITY_VERBOSE_BIT_EXT: Diagnostic
message
• VK_DEBUG_UTILS_MESSAGE_SEVERITY_INFO_BIT_EXT: Informational mes-
sage like the creation of a resource
• VK_DEBUG_UTILS_MESSAGE_SEVERITY_WARNING_BIT_EXT: Message about
behavior that is not necessarily an error, but very likely a bug in your
application
• VK_DEBUG_UTILS_MESSAGE_SEVERITY_ERROR_BIT_EXT: Message about
behavior that is invalid and may cause crashes
The values of this enumeration are set up in such a way that you can use a
comparison operation to check if a message is equal or worse compared to some
level of severity, for example:
1 if (messageSeverity >=
VK_DEBUG_UTILS_MESSAGE_SEVERITY_WARNING_BIT_EXT) {
2 // Message is important enough to show
3 }
The messageType parameter can have the following values:
• VK_DEBUG_UTILS_MESSAGE_TYPE_GENERAL_BIT_EXT: Some event has hap-
pened that is unrelated to the specification or performance
• VK_DEBUG_UTILS_MESSAGE_TYPE_VALIDATION_BIT_EXT: Something has
happened that violates the specification or indicates a possible mistake
• VK_DEBUG_UTILS_MESSAGE_TYPE_PERFORMANCE_BIT_EXT: Potential non-
optimal use of Vulkan
The pCallbackData parameter refers to a VkDebugUtilsMessengerCallbackDataEXT
struct containing the details of the message itself, with the most important
members being:
• pMessage: The debug message as a null-terminated string
• pObjects: Array of Vulkan object handles related to the message
• objectCount: Number of objects in array
Finally, the pUserData parameter contains a pointer that was specified during
the setup of the callback and allows you to pass your own data to it.
52
The callback returns a boolean that indicates if the Vulkan call that triggered
the validation layer message should be aborted. If the callback returns true, then
the call is aborted with the VK_ERROR_VALIDATION_FAILED_EXT error. This is
normally only used to test the validation layers themselves, so you should always
return VK_FALSE.
All that remains now is telling Vulkan about the callback function. Perhaps
somewhat surprisingly, even the debug callback in Vulkan is managed with a
handle that needs to be explicitly created and destroyed. Such a callback is part
of a debug messenger and you can have as many of them as you want. Add a
class member for this handle right under instance:
1 VkDebugUtilsMessengerEXT debugMessenger;
Now add a function setupDebugMessenger to be called from initVulkan right
after createInstance:
1 void initVulkan() {
2 createInstance();
3 setupDebugMessenger();
4 }
5
6 void setupDebugMessenger() {
7 if (!enableValidationLayers) return;
8
9 }
We’ll need to fill in a structure with details about the messenger and its callback:
1 VkDebugUtilsMessengerCreateInfoEXT createInfo{};
2 createInfo.sType =
VK_STRUCTURE_TYPE_DEBUG_UTILS_MESSENGER_CREATE_INFO_EXT;
3 createInfo.messageSeverity =
VK_DEBUG_UTILS_MESSAGE_SEVERITY_VERBOSE_BIT_EXT |
VK_DEBUG_UTILS_MESSAGE_SEVERITY_WARNING_BIT_EXT |
VK_DEBUG_UTILS_MESSAGE_SEVERITY_ERROR_BIT_EXT;
4 createInfo.messageType = VK_DEBUG_UTILS_MESSAGE_TYPE_GENERAL_BIT_EXT
| VK_DEBUG_UTILS_MESSAGE_TYPE_VALIDATION_BIT_EXT |
VK_DEBUG_UTILS_MESSAGE_TYPE_PERFORMANCE_BIT_EXT;
5 createInfo.pfnUserCallback = debugCallback;
6 createInfo.pUserData = nullptr; // Optional
The messageSeverity field allows you to specify all the types of severities
you would like your callback to be called for. I’ve specified all types except
for VK_DEBUG_UTILS_MESSAGE_SEVERITY_INFO_BIT_EXT here to receive notifi-
cations about possible problems while leaving out verbose general debug info.
Similarly the messageType field lets you filter which types of messages your
53
callback is notified about. I’ve simply enabled all types here. You can always
disable some if they’re not useful to you.
Finally, the pfnUserCallback field specifies the pointer to the callback function.
You can optionally pass a pointer to the pUserData field which will be passed
along to the callback function via the pUserData parameter. You could use this
to pass a pointer to the HelloTriangleApplication class, for example.
Note that there are many more ways to configure validation layer messages and
debug callbacks, but this is a good setup to get started with for this tutorial.
See the extension specification for more info about the possibilities.
This struct should be passed to the vkCreateDebugUtilsMessengerEXT func-
tion to create the VkDebugUtilsMessengerEXT object. Unfortunately, because
this function is an extension function, it is not automatically loaded. We have
to look up its address ourselves using vkGetInstanceProcAddr. We’re going to
create our own proxy function that handles this in the background. I’ve added
it right above the HelloTriangleApplication class definition.
1 VkResult CreateDebugUtilsMessengerEXT(VkInstance instance, const
VkDebugUtilsMessengerCreateInfoEXT* pCreateInfo, const
VkAllocationCallbacks* pAllocator, VkDebugUtilsMessengerEXT*
pDebugMessenger) {
2 auto func = (PFN_vkCreateDebugUtilsMessengerEXT)
vkGetInstanceProcAddr(instance,
"vkCreateDebugUtilsMessengerEXT");
3 if (func != nullptr) {
4 return func(instance, pCreateInfo, pAllocator,
pDebugMessenger);
5 } else {
6 return VK_ERROR_EXTENSION_NOT_PRESENT;
7 }
8 }
The vkGetInstanceProcAddr function will return nullptr if the function
couldn’t be loaded. We can now call this function to create the extension object
if it’s available:
1 if (CreateDebugUtilsMessengerEXT(instance, &createInfo, nullptr,
&debugMessenger) != VK_SUCCESS) {
2 throw std::runtime_error("failed to set up debug messenger!");
3 }
The second to last parameter is again the optional allocator callback that we
set to nullptr, other than that the parameters are fairly straightforward. Since
the debug messenger is specific to our Vulkan instance and its layers, it needs
to be explicitly specified as first argument. You will also see this pattern with
other child objects later on.
54
The VkDebugUtilsMessengerEXT object also needs to be cleaned up with a call
to vkDestroyDebugUtilsMessengerEXT. Similarly to vkCreateDebugUtilsMessengerEXT
the function needs to be explicitly loaded.
Create another proxy function right below CreateDebugUtilsMessengerEXT:
1 void DestroyDebugUtilsMessengerEXT(VkInstance instance,
VkDebugUtilsMessengerEXT debugMessenger, const
VkAllocationCallbacks* pAllocator) {
2 auto func = (PFN_vkDestroyDebugUtilsMessengerEXT)
vkGetInstanceProcAddr(instance,
"vkDestroyDebugUtilsMessengerEXT");
3 if (func != nullptr) {
4 func(instance, debugMessenger, pAllocator);
5 }
6 }
Make sure that this function is either a static class function or a function outside
the class. We can then call it in the cleanup function:
1 void cleanup() {
2 if (enableValidationLayers) {
3 DestroyDebugUtilsMessengerEXT(instance, debugMessenger,
nullptr);
4 }
5
6 vkDestroyInstance(instance, nullptr);
7
8 glfwDestroyWindow(window);
9
10 glfwTerminate();
11 }
Debugging instance creation and destruction
Although we’ve now added debugging with validation layers to the program
we’re not covering everything quite yet. The vkCreateDebugUtilsMessengerEXT
call requires a valid instance to have been created and vkDestroyDebugUtilsMessengerEXT
must be called before the instance is destroyed. This currently leaves us unable
to debug any issues in the vkCreateInstance and vkDestroyInstance calls.
However, if you closely read the extension documentation, you’ll see that
there is a way to create a separate debug utils messenger specifically for
those two function calls. It requires you to simply pass a pointer to a
VkDebugUtilsMessengerCreateInfoEXT struct in the pNext extension field of
VkInstanceCreateInfo. First extract population of the messenger create info
into a separate function:
55
1 void
populateDebugMessengerCreateInfo(VkDebugUtilsMessengerCreateInfoEXT&
createInfo) {
2 createInfo = {};
3 createInfo.sType =
VK_STRUCTURE_TYPE_DEBUG_UTILS_MESSENGER_CREATE_INFO_EXT;
4 createInfo.messageSeverity =
VK_DEBUG_UTILS_MESSAGE_SEVERITY_VERBOSE_BIT_EXT |
VK_DEBUG_UTILS_MESSAGE_SEVERITY_WARNING_BIT_EXT |
VK_DEBUG_UTILS_MESSAGE_SEVERITY_ERROR_BIT_EXT;
5 createInfo.messageType =
VK_DEBUG_UTILS_MESSAGE_TYPE_GENERAL_BIT_EXT |
VK_DEBUG_UTILS_MESSAGE_TYPE_VALIDATION_BIT_EXT |
VK_DEBUG_UTILS_MESSAGE_TYPE_PERFORMANCE_BIT_EXT;
6 createInfo.pfnUserCallback = debugCallback;
7 }
8
9 ...
10
11 void setupDebugMessenger() {
12 if (!enableValidationLayers) return;
13
14 VkDebugUtilsMessengerCreateInfoEXT createInfo;
15 populateDebugMessengerCreateInfo(createInfo);
16
17 if (CreateDebugUtilsMessengerEXT(instance, &createInfo, nullptr,
&debugMessenger) != VK_SUCCESS) {
18 throw std::runtime_error("failed to set up debug
messenger!");
19 }
20 }
We can now re-use this in the createInstance function:
1 void createInstance() {
2 ...
3
4 VkInstanceCreateInfo createInfo{};
5 createInfo.sType = VK_STRUCTURE_TYPE_INSTANCE_CREATE_INFO;
6 createInfo.pApplicationInfo = &appInfo;
7
8 ...
9
10 VkDebugUtilsMessengerCreateInfoEXT debugCreateInfo{};
11 if (enableValidationLayers) {
12 createInfo.enabledLayerCount =
56
static_cast<uint32_t>(validationLayers.size());
13 createInfo.ppEnabledLayerNames = validationLayers.data();
14
15 populateDebugMessengerCreateInfo(debugCreateInfo);
16 createInfo.pNext = (VkDebugUtilsMessengerCreateInfoEXT*)
&debugCreateInfo;
17 } else {
18 createInfo.enabledLayerCount = 0;
19
20 createInfo.pNext = nullptr;
21 }
22
23 if (vkCreateInstance(&createInfo, nullptr, &instance) !=
VK_SUCCESS) {
24 throw std::runtime_error("failed to create instance!");
25 }
26 }
The debugCreateInfo variable is placed outside the if statement to ensure
that it is not destroyed before the vkCreateInstance call. By creating an
additional debug messenger this way it will automatically be used during
vkCreateInstance and vkDestroyInstance and cleaned up after that.
Testing
Now let’s intentionally make a mistake to see the validation layers in action.
Temporarily remove the call to DestroyDebugUtilsMessengerEXT in the
cleanup function and run your program. Once it exits you should see
something like this:
If you don’t see any messages then check your installation.
If you want to see which call triggered a message, you can add a breakpoint to
the message callback and look at the stack trace.
Configuration
There are a lot more settings for the behavior of validation layers than just the
flags specified in the VkDebugUtilsMessengerCreateInfoEXT struct. Browse
57
to the Vulkan SDK and go to the Config directory. There you will find a
vk_layer_settings.txt file that explains how to configure the layers.
To configure the layer settings for your own application, copy the file to the
Debug and Release directories of your project and follow the instructions to
set the desired behavior. However, for the remainder of this tutorial I’ll assume
that you’re using the default settings.
Throughout this tutorial I’ll be making a couple of intentional mistakes to show
you how helpful the validation layers are with catching them and to teach you
how important it is to know exactly what you’re doing with Vulkan. Now it’s
time to look at Vulkan devices in the system.
C++ code
Physical devices and queue families
Selecting a physical device
After initializing the Vulkan library through a VkInstance we need to look for
and select a graphics card in the system that supports the features we need. In
fact we can select any number of graphics cards and use them simultaneously,
but in this tutorial we’ll stick to the first graphics card that suits our needs.
We’ll add a function pickPhysicalDevice and add a call to it in the initVulkan
function.
1 void initVulkan() {
2 createInstance();
3 setupDebugMessenger();
4 pickPhysicalDevice();
5 }
6
7 void pickPhysicalDevice() {
8
9 }
The graphics card that we’ll end up selecting will be stored in a VkPhysicalDe-
vice handle that is added as a new class member. This object will be implicitly
destroyed when the VkInstance is destroyed, so we won’t need to do anything
new in the cleanup function.
1 VkPhysicalDevice physicalDevice = VK_NULL_HANDLE;
Listing the graphics cards is very similar to listing extensions and starts with
querying just the number.
1 uint32_t deviceCount = 0;
2 vkEnumeratePhysicalDevices(instance, &deviceCount, nullptr);
58
If there are 0 devices with Vulkan support then there is no point going further.
1 if (deviceCount == 0) {
2 throw std::runtime_error("failed to find GPUs with Vulkan
support!");
3 }
Otherwise we can now allocate an array to hold all of the VkPhysicalDevice
handles.
1 std::vector<VkPhysicalDevice> devices(deviceCount);
2 vkEnumeratePhysicalDevices(instance, &deviceCount, devices.data());
Now we need to evaluate each of them and check if they are suitable for the
operations we want to perform, because not all graphics cards are created equal.
For that we’ll introduce a new function:
1 bool isDeviceSuitable(VkPhysicalDevice device) {
2 return true;
3 }
And we’ll check if any of the physical devices meet the requirements that we’ll
add to that function.
1 for (const auto& device : devices) {
2 if (isDeviceSuitable(device)) {
3 physicalDevice = device;
4 break;
5 }
6 }
7
8 if (physicalDevice == VK_NULL_HANDLE) {
9 throw std::runtime_error("failed to find a suitable GPU!");
10 }
The next section will introduce the first requirements that we’ll check for in the
isDeviceSuitable function. As we’ll start using more Vulkan features in the
later chapters we will also extend this function to include more checks.
Base device suitability checks
To evaluate the suitability of a device we can start by querying for some details.
Basic device properties like the name, type and supported Vulkan version can
be queried using vkGetPhysicalDeviceProperties.
1 VkPhysicalDeviceProperties deviceProperties;
2 vkGetPhysicalDeviceProperties(device, &deviceProperties);
59
The support for optional features like texture compression, 64 bit floats and
multi viewport rendering (useful for VR) can be queried using vkGetPhysi-
calDeviceFeatures:
1 VkPhysicalDeviceFeatures deviceFeatures;
2 vkGetPhysicalDeviceFeatures(device, &deviceFeatures);
There are more details that can be queried from devices that we’ll discuss later
concerning device memory and queue families (see the next section).
As an example, let’s say we consider our application only usable for dedicated
graphics cards that support geometry shaders. Then the isDeviceSuitable
function would look like this:
1 bool isDeviceSuitable(VkPhysicalDevice device) {
2 VkPhysicalDeviceProperties deviceProperties;
3 VkPhysicalDeviceFeatures deviceFeatures;
4 vkGetPhysicalDeviceProperties(device, &deviceProperties);
5 vkGetPhysicalDeviceFeatures(device, &deviceFeatures);
6
7 return deviceProperties.deviceType ==
VK_PHYSICAL_DEVICE_TYPE_DISCRETE_GPU &&
8 deviceFeatures.geometryShader;
9 }
Instead of just checking if a device is suitable or not and going with the first one,
you could also give each device a score and pick the highest one. That way you
could favor a dedicated graphics card by giving it a higher score, but fall back
to an integrated GPU if that’s the only available one. You could implement
something like that as follows:
1 #include <map>
2
3 ...
4
5 void pickPhysicalDevice() {
6 ...
7
8 // Use an ordered map to automatically sort candidates by
increasing score
9 std::multimap<int, VkPhysicalDevice> candidates;
10
11 for (const auto& device : devices) {
12 int score = rateDeviceSuitability(device);
13 candidates.insert(std::make_pair(score, device));
14 }
15
16 // Check if the best candidate is suitable at all
60
17 if (candidates.rbegin()->first > 0) {
18 physicalDevice = candidates.rbegin()->second;
19 } else {
20 throw std::runtime_error("failed to find a suitable GPU!");
21 }
22 }
23
24 int rateDeviceSuitability(VkPhysicalDevice device) {
25 ...
26
27 int score = 0;
28
29 // Discrete GPUs have a significant performance advantage
30 if (deviceProperties.deviceType ==
VK_PHYSICAL_DEVICE_TYPE_DISCRETE_GPU) {
31 score += 1000;
32 }
33
34 // Maximum possible size of textures affects graphics quality
35 score += deviceProperties.limits.maxImageDimension2D;
36
37 // Application can't function without geometry shaders
38 if (!deviceFeatures.geometryShader) {
39 return 0;
40 }
41
42 return score;
43 }
You don’t need to implement all that for this tutorial, but it’s to give you an
idea of how you could design your device selection process. Of course you can
also just display the names of the choices and allow the user to select.
Because we’re just starting out, Vulkan support is the only thing we need and
therefore we’ll settle for just any GPU:
1 bool isDeviceSuitable(VkPhysicalDevice device) {
2 return true;
3 }
In the next section we’ll discuss the first real required feature to check for.
Queue families
It has been briefly touched upon before that almost every operation in Vulkan,
anything from drawing to uploading textures, requires commands to be submit-
ted to a queue. There are different types of queues that originate from different
61
queue families and each family of queues allows only a subset of commands. For
example, there could be a queue family that only allows processing of compute
commands or one that only allows memory transfer related commands.
We need to check which queue families are supported by the device and which
one of these supports the commands that we want to use. For that purpose we’ll
add a new function findQueueFamilies that looks for all the queue families we
need.
Right now we are only going to look for a queue that supports graphics com-
mands, so the function could look like this:
1 uint32_t findQueueFamilies(VkPhysicalDevice device) {
2 // Logic to find graphics queue family
3 }
However, in one of the next chapters we’re already going to look for yet another
queue, so it’s better to prepare for that and bundle the indices into a struct:
1 struct QueueFamilyIndices {
2 uint32_t graphicsFamily;
3 };
4
5 QueueFamilyIndices findQueueFamilies(VkPhysicalDevice device) {
6 QueueFamilyIndices indices;
7 // Logic to find queue family indices to populate struct with
8 return indices;
9 }
But what if a queue family is not available? We could throw an exception in
findQueueFamilies, but this function is not really the right place to make
decisions about device suitability. For example, we may prefer devices with a
dedicated transfer queue family, but not require it. Therefore we need some way
of indicating whether a particular queue family was found.
It’s not really possible to use a magic value to indicate the nonexistence of a
queue family, since any value of uint32_t could in theory be a valid queue family
index including 0. Luckily C++17 introduced a data structure to distinguish
between the case of a value existing or not:
1 #include <optional>
2
3 ...
4
5 std::optional<uint32_t> graphicsFamily;
6
7 std::cout << std::boolalpha << graphicsFamily.has_value() <<
std::endl; // false
8
62
9 graphicsFamily = 0;
10
11 std::cout << std::boolalpha << graphicsFamily.has_value() <<
std::endl; // true
std::optional is a wrapper that contains no value until you assign something
to it. At any point you can query if it contains a value or not by calling its
has_value() member function. That means that we can change the logic to:
1 #include <optional>
2
3 ...
4
5 struct QueueFamilyIndices {
6 std::optional<uint32_t> graphicsFamily;
7 };
8
9 QueueFamilyIndices findQueueFamilies(VkPhysicalDevice device) {
10 QueueFamilyIndices indices;
11 // Assign index to queue families that could be found
12 return indices;
13 }
We can now begin to actually implement findQueueFamilies:
1 QueueFamilyIndices findQueueFamilies(VkPhysicalDevice device) {
2 QueueFamilyIndices indices;
3
4 ...
5
6 return indices;
7 }
The process of retrieving the list of queue families is exactly what you expect
and uses vkGetPhysicalDeviceQueueFamilyProperties:
1 uint32_t queueFamilyCount = 0;
2 vkGetPhysicalDeviceQueueFamilyProperties(device, &queueFamilyCount,
nullptr);
3
4 std::vector<VkQueueFamilyProperties> queueFamilies(queueFamilyCount);
5 vkGetPhysicalDeviceQueueFamilyProperties(device, &queueFamilyCount,
queueFamilies.data());
The VkQueueFamilyProperties struct contains some details about the queue
family, including the type of operations that are supported and the number of
queues that can be created based on that family. We need to find at least one
queue family that supports VK_QUEUE_GRAPHICS_BIT.
63
1 int i = 0;
2 for (const auto& queueFamily : queueFamilies) {
3 if (queueFamily.queueFlags & VK_QUEUE_GRAPHICS_BIT) {
4 indices.graphicsFamily = i;
5 }
6
7 i++;
8 }
Now that we have this fancy queue family lookup function, we can use it as a
check in the isDeviceSuitable function to ensure that the device can process
the commands we want to use:
1 bool isDeviceSuitable(VkPhysicalDevice device) {
2 QueueFamilyIndices indices = findQueueFamilies(device);
3
4 return indices.graphicsFamily.has_value();
5 }
To make this a little bit more convenient, we’ll also add a generic check to the
struct itself:
1 struct QueueFamilyIndices {
2 std::optional<uint32_t> graphicsFamily;
3
4 bool isComplete() {
5 return graphicsFamily.has_value();
6 }
7 };
8
9 ...
10
11 bool isDeviceSuitable(VkPhysicalDevice device) {
12 QueueFamilyIndices indices = findQueueFamilies(device);
13
14 return indices.isComplete();
15 }
We can now also use this for an early exit from findQueueFamilies:
1 for (const auto& queueFamily : queueFamilies) {
2 ...
3
4 if (indices.isComplete()) {
5 break;
6 }
7
64
8 i++;
9 }
Great, that’s all we need for now to find the right physical device! The next
step is to create a logical device to interface with it.
C++ code
Logical device and queues
Introduction
After selecting a physical device to use we need to set up a logical device to
interface with it. The logical device creation process is similar to the instance
creation process and describes the features we want to use. We also need to
specify which queues to create now that we’ve queried which queue families are
available. You can even create multiple logical devices from the same physical
device if you have varying requirements.
Start by adding a new class member to store the logical device handle in.
1 VkDevice device;
Next, add a createLogicalDevice function that is called from initVulkan.
1 void initVulkan() {
2 createInstance();
3 setupDebugMessenger();
4 pickPhysicalDevice();
5 createLogicalDevice();
6 }
7
8 void createLogicalDevice() {
9
10 }
Specifying the queues to be created
The creation of a logical device involves specifying a bunch of details in structs
again, of which the first one will be VkDeviceQueueCreateInfo. This structure
describes the number of queues we want for a single queue family. Right now
we’re only interested in a queue with graphics capabilities.
1 QueueFamilyIndices indices = findQueueFamilies(physicalDevice);
2
3 VkDeviceQueueCreateInfo queueCreateInfo{};
4 queueCreateInfo.sType = VK_STRUCTURE_TYPE_DEVICE_QUEUE_CREATE_INFO;
5 queueCreateInfo.queueFamilyIndex = indices.graphicsFamily.value();
6 queueCreateInfo.queueCount = 1;
65
The currently available drivers will only allow you to create a small number of
queues for each queue family and you don’t really need more than one. That’s
because you can create all of the command buffers on multiple threads and then
submit them all at once on the main thread with a single low-overhead call.
Vulkan lets you assign priorities to queues to influence the scheduling of com-
mand buffer execution using floating point numbers between 0.0 and 1.0. This
is required even if there is only a single queue:
1 float queuePriority = 1.0f;
2 queueCreateInfo.pQueuePriorities = &queuePriority;
Specifying used device features
The next information to specify is the set of device features that we’ll
be using. These are the features that we queried support for with
vkGetPhysicalDeviceFeatures in the previous chapter, like geometry
shaders. Right now we don’t need anything special, so we can simply define
it and leave everything to VK_FALSE. We’ll come back to this structure once
we’re about to start doing more interesting things with Vulkan.
1 VkPhysicalDeviceFeatures deviceFeatures{};
Creating the logical device
With the previous two structures in place, we can start filling in the main
VkDeviceCreateInfo structure.
1 VkDeviceCreateInfo createInfo{};
2 createInfo.sType = VK_STRUCTURE_TYPE_DEVICE_CREATE_INFO;
First add pointers to the queue creation info and device features structs:
1 createInfo.pQueueCreateInfos = &queueCreateInfo;
2 createInfo.queueCreateInfoCount = 1;
3
4 createInfo.pEnabledFeatures = &deviceFeatures;
The remainder of the information bears a resemblance to the VkInstanceCreateInfo
struct and requires you to specify extensions and validation layers. The differ-
ence is that these are device specific this time.
An example of a device specific extension is VK_KHR_swapchain, which allows
you to present rendered images from that device to windows. It is possible that
there are Vulkan devices in the system that lack this ability, for example because
they only support compute operations. We will come back to this extension in
the swap chain chapter.
66
Previous implementations of Vulkan made a distinction between instance and de-
vice specific validation layers, but this is no longer the case. That means that the
enabledLayerCount and ppEnabledLayerNames fields of VkDeviceCreateInfo
are ignored by up-to-date implementations. However, it is still a good idea to
set them anyway to be compatible with older implementations:
1 createInfo.enabledExtensionCount = 0;
2
3 if (enableValidationLayers) {
4 createInfo.enabledLayerCount =
static_cast<uint32_t>(validationLayers.size());
5 createInfo.ppEnabledLayerNames = validationLayers.data();
6 } else {
7 createInfo.enabledLayerCount = 0;
8 }
We won’t need any device specific extensions for now.
That’s it, we’re now ready to instantiate the logical device with a call to the
appropriately named vkCreateDevice function.
1 if (vkCreateDevice(physicalDevice, &createInfo, nullptr, &device) !=
VK_SUCCESS) {
2 throw std::runtime_error("failed to create logical device!");
3 }
The parameters are the physical device to interface with, the queue and usage
info we just specified, the optional allocation callbacks pointer and a pointer to
a variable to store the logical device handle in. Similarly to the instance creation
function, this call can return errors based on enabling non-existent extensions
or specifying the desired usage of unsupported features.
The device should be destroyed in cleanup with the vkDestroyDevice function:
1 void cleanup() {
2 vkDestroyDevice(device, nullptr);
3 ...
4 }
Logical devices don’t interact directly with instances, which is why it’s not
included as a parameter.
Retrieving queue handles
The queues are automatically created along with the logical device, but we don’t
have a handle to interface with them yet. First add a class member to store a
handle to the graphics queue:
1 VkQueue graphicsQueue;
67
Device queues are implicitly cleaned up when the device is destroyed, so we
don’t need to do anything in cleanup.
We can use the vkGetDeviceQueue function to retrieve queue handles for each
queue family. The parameters are the logical device, queue family, queue index
and a pointer to the variable to store the queue handle in. Because we’re only
creating a single queue from this family, we’ll simply use index 0.
1 vkGetDeviceQueue(device, indices.graphicsFamily.value(), 0,
&graphicsQueue);
With the logical device and queue handles we can now actually start using the
graphics card to do things! In the next few chapters we’ll set up the resources
to present results to the window system.
C++ code
Presentation
Window surface
Since Vulkan is a platform agnostic API, it can not interface directly with
the window system on its own. To establish the connection between Vulkan
and the window system to present results to the screen, we need to use the
WSI (Window System Integration) extensions. In this chapter we’ll discuss
the first one, which is VK_KHR_surface. It exposes a VkSurfaceKHR object that
represents an abstract type of surface to present rendered images to. The surface
in our program will be backed by the window that we’ve already opened with
GLFW.
The VK_KHR_surface extension is an instance level extension and we’ve
actually already enabled it, because it’s included in the list returned by
glfwGetRequiredInstanceExtensions. The list also includes some other WSI
extensions that we’ll use in the next couple of chapters.
The window surface needs to be created right after the instance creation, because
it can actually influence the physical device selection. The reason we postponed
this is because window surfaces are part of the larger topic of render targets and
presentation for which the explanation would have cluttered the basic setup. It
should also be noted that window surfaces are an entirely optional component
in Vulkan, if you just need off-screen rendering. Vulkan allows you to do that
without hacks like creating an invisible window (necessary for OpenGL).
Window surface creation
Start by adding a surface class member right below the debug callback.
1 VkSurfaceKHR surface;
68
Although the VkSurfaceKHR object and its usage is platform agnostic, its
creation isn’t because it depends on window system details. For example,
it needs the HWND and HMODULE handles on Windows. Therefore there is
a platform-specific addition to the extension, which on Windows is called
VK_KHR_win32_surface and is also automatically included in the list from
glfwGetRequiredInstanceExtensions.
I will demonstrate how this platform specific extension can be used to create a
surface on Windows, but we won’t actually use it in this tutorial. It doesn’t make
any sense to use a library like GLFW and then proceed to use platform-specific
code anyway. GLFW actually has glfwCreateWindowSurface that handles the
platform differences for us. Still, it’s good to see what it does behind the scenes
before we start relying on it.
To access native platform functions, you need to update the includes at the top:
1 #define VK_USE_PLATFORM_WIN32_KHR
2 #define GLFW_INCLUDE_VULKAN
3 #include <GLFW/glfw3.h>
4 #define GLFW_EXPOSE_NATIVE_WIN32
5 #include <GLFW/glfw3native.h>
Because a window surface is a Vulkan object, it comes with a VkWin32SurfaceCreateInfoKHR
struct that needs to be filled in. It has two important parameters: hwnd and
hinstance. These are the handles to the window and the process.
1 VkWin32SurfaceCreateInfoKHR createInfo{};
2 createInfo.sType = VK_STRUCTURE_TYPE_WIN32_SURFACE_CREATE_INFO_KHR;
3 createInfo.hwnd = glfwGetWin32Window(window);
4 createInfo.hinstance = GetModuleHandle(nullptr);
The glfwGetWin32Window function is used to get the raw HWND from the GLFW
window object. The GetModuleHandle call returns the HINSTANCE handle of the
current process.
After that the surface can be created with vkCreateWin32SurfaceKHR, which
includes a parameter for the instance, surface creation details, custom allocators
and the variable for the surface handle to be stored in. Technically this is a WSI
extension function, but it is so commonly used that the standard Vulkan loader
includes it, so unlike other extensions you don’t need to explicitly load it.
1 if (vkCreateWin32SurfaceKHR(instance, &createInfo, nullptr,
&surface) != VK_SUCCESS) {
2 throw std::runtime_error("failed to create window surface!");
3 }
The process is similar for other platforms like Linux, where vkCreateXcbSurfaceKHR
takes an XCB connection and window as creation details with X11.
69
The glfwCreateWindowSurface function performs exactly this operation with
a different implementation for each platform. We’ll now integrate it into our
program. Add a function createSurface to be called from initVulkan right
after instance creation and setupDebugMessenger.
1 void initVulkan() {
2 createInstance();
3 setupDebugMessenger();
4 createSurface();
5 pickPhysicalDevice();
6 createLogicalDevice();
7 }
8
9 void createSurface() {
10
11 }
The GLFW call takes simple parameters instead of a struct which makes the
implementation of the function very straightforward:
1 void createSurface() {
2 if (glfwCreateWindowSurface(instance, window, nullptr, &surface)
!= VK_SUCCESS) {
3 throw std::runtime_error("failed to create window surface!");
4 }
5 }
The parameters are the VkInstance, GLFW window pointer, custom allocators
and pointer to VkSurfaceKHR variable. It simply passes through the VkResult
from the relevant platform call. GLFW doesn’t offer a special function for
destroying a surface, but that can easily be done through the original API:
1 void cleanup() {
2 ...
3 vkDestroySurfaceKHR(instance, surface, nullptr);
4 vkDestroyInstance(instance, nullptr);
5 ...
6 }
Make sure that the surface is destroyed before the instance.
Querying for presentation support
Although the Vulkan implementation may support window system integration,
that does not mean that every device in the system supports it. Therefore we
need to extend isDeviceSuitable to ensure that a device can present images
to the surface we created. Since the presentation is a queue-specific feature, the
70
problem is actually about finding a queue family that supports presenting to
the surface we created.
It’s actually possible that the queue families supporting drawing commands and
the ones supporting presentation do not overlap. Therefore we have to take into
account that there could be a distinct presentation queue by modifying the
QueueFamilyIndices structure:
1 struct QueueFamilyIndices {
2 std::optional<uint32_t> graphicsFamily;
3 std::optional<uint32_t> presentFamily;
4
5 bool isComplete() {
6 return graphicsFamily.has_value() &&
presentFamily.has_value();
7 }
8 };
Next, we’ll modify the findQueueFamilies function to look for a queue family
that has the capability of presenting to our window surface. The function to
check for that is vkGetPhysicalDeviceSurfaceSupportKHR, which takes the
physical device, queue family index and surface as parameters. Add a call to it
in the same loop as the VK_QUEUE_GRAPHICS_BIT:
1 VkBool32 presentSupport = false;
2 vkGetPhysicalDeviceSurfaceSupportKHR(device, i, surface,
&presentSupport);
Then simply check the value of the boolean and store the presentation family
queue index:
1 if (presentSupport) {
2 indices.presentFamily = i;
3 }
Note that it’s very likely that these end up being the same queue family after all,
but throughout the program we will treat them as if they were separate queues
for a uniform approach. Nevertheless, you could add logic to explicitly prefer a
physical device that supports drawing and presentation in the same queue for
improved performance.
Creating the presentation queue
The one thing that remains is modifying the logical device creation procedure to
create the presentation queue and retrieve the VkQueue handle. Add a member
variable for the handle:
1 VkQueue presentQueue;
71
Next, we need to have multiple VkDeviceQueueCreateInfo structs to create a
queue from both families. An elegant way to do that is to create a set of all
unique queue families that are necessary for the required queues:
1 #include <set>
2
3 ...
4
5 QueueFamilyIndices indices = findQueueFamilies(physicalDevice);
6
7 std::vector<VkDeviceQueueCreateInfo> queueCreateInfos;
8 std::set<uint32_t> uniqueQueueFamilies =
{indices.graphicsFamily.value(), indices.presentFamily.value()};
9
10 float queuePriority = 1.0f;
11 for (uint32_t queueFamily : uniqueQueueFamilies) {
12 VkDeviceQueueCreateInfo queueCreateInfo{};
13 queueCreateInfo.sType =
VK_STRUCTURE_TYPE_DEVICE_QUEUE_CREATE_INFO;
14 queueCreateInfo.queueFamilyIndex = queueFamily;
15 queueCreateInfo.queueCount = 1;
16 queueCreateInfo.pQueuePriorities = &queuePriority;
17 queueCreateInfos.push_back(queueCreateInfo);
18 }
And modify VkDeviceCreateInfo to point to the vector:
1 createInfo.queueCreateInfoCount =
static_cast<uint32_t>(queueCreateInfos.size());
2 createInfo.pQueueCreateInfos = queueCreateInfos.data();
If the queue families are the same, then we only need to pass its index once.
Finally, add a call to retrieve the queue handle:
1 vkGetDeviceQueue(device, indices.presentFamily.value(), 0,
&presentQueue);
In case the queue families are the same, the two handles will most likely have
the same value now. In the next chapter we’re going to look at swap chains and
how they give us the ability to present images to the surface.
C++ code
Swap chain
Vulkan does not have the concept of a “default framebuffer”, hence it requires
an infrastructure that will own the buffers we will render to before we visualize
them on the screen. This infrastructure is known as the swap chain and must
72
be created explicitly in Vulkan. The swap chain is essentially a queue of images
that are waiting to be presented to the screen. Our application will acquire
such an image to draw to it, and then return it to the queue. How exactly the
queue works and the conditions for presenting an image from the queue depend
on how the swap chain is set up, but the general purpose of the swap chain is
to synchronize the presentation of images with the refresh rate of the screen.
Checking for swap chain support
Not all graphics cards are capable of presenting images directly to a screen for
various reasons, for example because they are designed for servers and don’t
have any display outputs. Secondly, since image presentation is heavily tied
into the window system and the surfaces associated with windows, it is not
actually part of the Vulkan core. You have to enable the VK_KHR_swapchain
device extension after querying for its support.
For that purpose we’ll first extend the isDeviceSuitable function to check if
this extension is supported. We’ve previously seen how to list the extensions
that are supported by a VkPhysicalDevice, so doing that should be fairly
straightforward. Note that the Vulkan header file provides a nice macro
VK_KHR_SWAPCHAIN_EXTENSION_NAME that is defined as VK_KHR_swapchain.
The advantage of using this macro is that the compiler will catch misspellings.
First declare a list of required device extensions, similar to the list of validation
layers to enable.
1 const std::vector<const char*> deviceExtensions = {
2 VK_KHR_SWAPCHAIN_EXTENSION_NAME
3 };
Next, create a new function checkDeviceExtensionSupport that is called from
isDeviceSuitable as an additional check:
1 bool isDeviceSuitable(VkPhysicalDevice device) {
2 QueueFamilyIndices indices = findQueueFamilies(device);
3
4 bool extensionsSupported = checkDeviceExtensionSupport(device);
5
6 return indices.isComplete() && extensionsSupported;
7 }
8
9 bool checkDeviceExtensionSupport(VkPhysicalDevice device) {
10 return true;
11 }
Modify the body of the function to enumerate the extensions and check if all of
the required extensions are amongst them.
73
1 bool checkDeviceExtensionSupport(VkPhysicalDevice device) {
2 uint32_t extensionCount;
3 vkEnumerateDeviceExtensionProperties(device, nullptr,
&extensionCount, nullptr);
4
5 std::vector<VkExtensionProperties>
availableExtensions(extensionCount);
6 vkEnumerateDeviceExtensionProperties(device, nullptr,
&extensionCount, availableExtensions.data());
7
8 std::set<std::string>
requiredExtensions(deviceExtensions.begin(),
deviceExtensions.end());
9
10 for (const auto& extension : availableExtensions) {
11 requiredExtensions.erase(extension.extensionName);
12 }
13
14 return requiredExtensions.empty();
15 }
I’ve chosen to use a set of strings here to represent the unconfirmed required
extensions. That way we can easily tick them off while enumerating the se-
quence of available extensions. Of course you can also use a nested loop like in
checkValidationLayerSupport. The performance difference is irrelevant. Now
run the code and verify that your graphics card is indeed capable of creating
a swap chain. It should be noted that the availability of a presentation queue,
as we checked in the previous chapter, implies that the swap chain extension
must be supported. However, it’s still good to be explicit about things, and the
extension does have to be explicitly enabled.
Enabling device extensions
Using a swapchain requires enabling the VK_KHR_swapchain extension first. En-
abling the extension just requires a small change to the logical device creation
structure:
1 createInfo.enabledExtensionCount =
static_cast<uint32_t>(deviceExtensions.size());
2 createInfo.ppEnabledExtensionNames = deviceExtensions.data();
Make sure to replace the existing line createInfo.enabledExtensionCount
= 0; when you do so.
74
Querying details of swap chain support
Just checking if a swap chain is available is not sufficient, because it may not
actually be compatible with our window surface. Creating a swap chain also
involves a lot more settings than instance and device creation, so we need to
query for some more details before we’re able to proceed.
There are basically three kinds of properties we need to check:
• Basic surface capabilities (min/max number of images in swap chain, min/-
max width and height of images)
• Surface formats (pixel format, color space)
• Available presentation modes
Similar to findQueueFamilies, we’ll use a struct to pass these details around
once they’ve been queried. The three aforementioned types of properties come
in the form of the following structs and lists of structs:
1 struct SwapChainSupportDetails {
2 VkSurfaceCapabilitiesKHR capabilities;
3 std::vector<VkSurfaceFormatKHR> formats;
4 std::vector<VkPresentModeKHR> presentModes;
5 };
We’ll now create a new function querySwapChainSupport that will populate
this struct.
1 SwapChainSupportDetails querySwapChainSupport(VkPhysicalDevice
device) {
2 SwapChainSupportDetails details;
3
4 return details;
5 }
This section covers how to query the structs that include this information. The
meaning of these structs and exactly which data they contain is discussed in the
next section.
Let’s start with the basic surface capabilities. These properties are simple to
query and are returned into a single VkSurfaceCapabilitiesKHR struct.
1 vkGetPhysicalDeviceSurfaceCapabilitiesKHR(device, surface,
&details.capabilities);
This function takes the specified VkPhysicalDevice and VkSurfaceKHR window
surface into account when determining the supported capabilities. All of the
support querying functions have these two as first parameters because they are
the core components of the swap chain.
The next step is about querying the supported surface formats. Because this is
a list of structs, it follows the familiar ritual of 2 function calls:
75
1 uint32_t formatCount;
2 vkGetPhysicalDeviceSurfaceFormatsKHR(device, surface, &formatCount,
nullptr);
3
4 if (formatCount != 0) {
5 details.formats.resize(formatCount);
6 vkGetPhysicalDeviceSurfaceFormatsKHR(device, surface,
&formatCount, details.formats.data());
7 }
Make sure that the vector is resized to hold all the available formats. And
finally, querying the supported presentation modes works exactly the same way
with vkGetPhysicalDeviceSurfacePresentModesKHR:
1 uint32_t presentModeCount;
2 vkGetPhysicalDeviceSurfacePresentModesKHR(device, surface,
&presentModeCount, nullptr);
3
4 if (presentModeCount != 0) {
5 details.presentModes.resize(presentModeCount);
6 vkGetPhysicalDeviceSurfacePresentModesKHR(device, surface,
&presentModeCount, details.presentModes.data());
7 }
All of the details are in the struct now, so let’s extend isDeviceSuitable once
more to utilize this function to verify that swap chain support is adequate. Swap
chain support is sufficient for this tutorial if there is at least one supported image
format and one supported presentation mode given the window surface we have.
1 bool swapChainAdequate = false;
2 if (extensionsSupported) {
3 SwapChainSupportDetails swapChainSupport =
querySwapChainSupport(device);
4 swapChainAdequate = !swapChainSupport.formats.empty() &&
!swapChainSupport.presentModes.empty();
5 }
It is important that we only try to query for swap chain support after verifying
that the extension is available. The last line of the function changes to:
1 return indices.isComplete() && extensionsSupported &&
swapChainAdequate;
Choosing the right settings for the swap chain
If the swapChainAdequate conditions were met then the support is definitely
sufficient, but there may still be many different modes of varying optimality.
76
We’ll now write a couple of functions to find the right settings for the best
possible swap chain. There are three types of settings to determine:
• Surface format (color depth)
• Presentation mode (conditions for “swapping” images to the screen)
• Swap extent (resolution of images in swap chain)
For each of these settings we’ll have an ideal value in mind that we’ll go with if
it’s available and otherwise we’ll create some logic to find the next best thing.
Surface format The function for this setting starts out like this. We’ll later
pass the formats member of the SwapChainSupportDetails struct as argu-
ment.
1 VkSurfaceFormatKHR chooseSwapSurfaceFormat(const
std::vector<VkSurfaceFormatKHR>& availableFormats) {
2
3 }
Each VkSurfaceFormatKHR entry contains a format and a colorSpace mem-
ber. The format member specifies the color channels and types. For example,
VK_FORMAT_B8G8R8A8_SRGB means that we store the B, G, R and alpha chan-
nels in that order with an 8 bit unsigned integer for a total of 32 bits per pixel.
The colorSpace member indicates if the SRGB color space is supported or
not using the VK_COLOR_SPACE_SRGB_NONLINEAR_KHR flag. Note that this flag
used to be called VK_COLORSPACE_SRGB_NONLINEAR_KHR in old versions of the
specification.
For the color space we’ll use SRGB if it is available, because it results in more
accurate perceived colors. It is also pretty much the standard color space
for images, like the textures we’ll use later on. Because of that we should
also use an SRGB color format, of which one of the most common ones is
VK_FORMAT_B8G8R8A8_SRGB.
Let’s go through the list and see if the preferred combination is available:
1 for (const auto& availableFormat : availableFormats) {
2 if (availableFormat.format == VK_FORMAT_B8G8R8A8_SRGB &&
availableFormat.colorSpace ==
VK_COLOR_SPACE_SRGB_NONLINEAR_KHR) {
3 return availableFormat;
4 }
5 }
If that also fails then we could start ranking the available formats based on how
“good” they are, but in most cases it’s okay to just settle with the first format
that is specified.
77
1 VkSurfaceFormatKHR chooseSwapSurfaceFormat(const
std::vector<VkSurfaceFormatKHR>& availableFormats) {
2 for (const auto& availableFormat : availableFormats) {
3 if (availableFormat.format == VK_FORMAT_B8G8R8A8_SRGB &&
availableFormat.colorSpace ==
VK_COLOR_SPACE_SRGB_NONLINEAR_KHR) {
4 return availableFormat;
5 }
6 }
7
8 return availableFormats[0];
9 }
Presentation mode The presentation mode is arguably the most important
setting for the swap chain, because it represents the actual conditions for show-
ing images to the screen. There are four possible modes available in Vulkan:
• VK_PRESENT_MODE_IMMEDIATE_KHR: Images submitted by your applica-
tion are transferred to the screen right away, which may result in tearing.
• VK_PRESENT_MODE_FIFO_KHR: The swap chain is a queue where the display
takes an image from the front of the queue when the display is refreshed
and the program inserts rendered images at the back of the queue. If the
queue is full then the program has to wait. This is most similar to vertical
sync as found in modern games. The moment that the display is refreshed
is known as “vertical blank”.
• VK_PRESENT_MODE_FIFO_RELAXED_KHR: This mode only differs from the
previous one if the application is late and the queue was empty at the last
vertical blank. Instead of waiting for the next vertical blank, the image is
transferred right away when it finally arrives. This may result in visible
tearing.
• VK_PRESENT_MODE_MAILBOX_KHR: This is another variation of the second
mode. Instead of blocking the application when the queue is full, the
images that are already queued are simply replaced with the newer ones.
This mode can be used to render frames as fast as possible while still
avoiding tearing, resulting in fewer latency issues than standard vertical
sync. This is commonly known as “triple buffering”, although the exis-
tence of three buffers alone does not necessarily mean that the framerate
is unlocked.
Only the VK_PRESENT_MODE_FIFO_KHR mode is guaranteed to be available, so
we’ll again have to write a function that looks for the best mode that is available:
1 VkPresentModeKHR chooseSwapPresentMode(const
std::vector<VkPresentModeKHR>& availablePresentModes) {
2 return VK_PRESENT_MODE_FIFO_KHR;
3 }
78
I personally think that VK_PRESENT_MODE_MAILBOX_KHR is a very nice trade-off if
energy usage is not a concern. It allows us to avoid tearing while still maintaining
a fairly low latency by rendering new images that are as up-to-date as possible
right until the vertical blank. On mobile devices, where energy usage is more
important, you will probably want to use VK_PRESENT_MODE_FIFO_KHR instead.
Now, let’s look through the list to see if VK_PRESENT_MODE_MAILBOX_KHR is
available:
1 VkPresentModeKHR chooseSwapPresentMode(const
std::vector<VkPresentModeKHR>& availablePresentModes) {
2 for (const auto& availablePresentMode : availablePresentModes) {
3 if (availablePresentMode == VK_PRESENT_MODE_MAILBOX_KHR) {
4 return availablePresentMode;
5 }
6 }
7
8 return VK_PRESENT_MODE_FIFO_KHR;
9 }
Swap extent That leaves only one major property, for which we’ll add one
last function:
1 VkExtent2D chooseSwapExtent(const VkSurfaceCapabilitiesKHR&
capabilities) {
2
3 }
The swap extent is the resolution of the swap chain images and it’s almost always
exactly equal to the resolution of the window that we’re drawing to in pixels
(more on that in a moment). The range of the possible resolutions is defined
in the VkSurfaceCapabilitiesKHR structure. Vulkan tells us to match the
resolution of the window by setting the width and height in the currentExtent
member. However, some window managers do allow us to differ here and this is
indicated by setting the width and height in currentExtent to a special value:
the maximum value of uint32_t. In that case we’ll pick the resolution that best
matches the window within the minImageExtent and maxImageExtent bounds.
But we must specify the resolution in the correct unit.
GLFW uses two units when measuring sizes: pixels and screen coordinates. For
example, the resolution {WIDTH, HEIGHT} that we specified earlier when cre-
ating the window is measured in screen coordinates. But Vulkan works with
pixels, so the swap chain extent must be specified in pixels as well. Unfortu-
nately, if you are using a high DPI display (like Apple’s Retina display), screen
coordinates don’t correspond to pixels. Instead, due to the higher pixel density,
the resolution of the window in pixel will be larger than the resolution in screen
coordinates. So if Vulkan doesn’t fix the swap extent for us, we can’t just use
the original {WIDTH, HEIGHT}. Instead, we must use glfwGetFramebufferSize
79
to query the resolution of the window in pixel before matching it against the
minimum and maximum image extent.
1 #include <cstdint> // Necessary for uint32_t
2 #include <limits> // Necessary for std::numeric_limits
3 #include <algorithm> // Necessary for std::clamp
4
5 ...
6
7 VkExtent2D chooseSwapExtent(const VkSurfaceCapabilitiesKHR&
capabilities) {
8 if (capabilities.currentExtent.width !=
std::numeric_limits<uint32_t>::max()) {
9 return capabilities.currentExtent;
10 } else {
11 int width, height;
12 glfwGetFramebufferSize(window, &width, &height);
13
14 VkExtent2D actualExtent = {
15 static_cast<uint32_t>(width),
16 static_cast<uint32_t>(height)
17 };
18
19 actualExtent.width = std::clamp(actualExtent.width,
capabilities.minImageExtent.width,
capabilities.maxImageExtent.width);
20 actualExtent.height = std::clamp(actualExtent.height,
capabilities.minImageExtent.height,
capabilities.maxImageExtent.height);
21
22 return actualExtent;
23 }
24 }
The clamp function is used here to bound the values of width and height
between the allowed minimum and maximum extents that are supported by the
implementation.
Creating the swap chain
Now that we have all of these helper functions assisting us with the choices we
have to make at runtime, we finally have all the information that is needed to
create a working swap chain.
Create a createSwapChain function that starts out with the results of these
calls and make sure to call it from initVulkan after logical device creation.
1 void initVulkan() {
80
2 createInstance();
3 setupDebugMessenger();
4 createSurface();
5 pickPhysicalDevice();
6 createLogicalDevice();
7 createSwapChain();
8 }
9
10 void createSwapChain() {
11 SwapChainSupportDetails swapChainSupport =
querySwapChainSupport(physicalDevice);
12
13 VkSurfaceFormatKHR surfaceFormat =
chooseSwapSurfaceFormat(swapChainSupport.formats);
14 VkPresentModeKHR presentMode =
chooseSwapPresentMode(swapChainSupport.presentModes);
15 VkExtent2D extent =
chooseSwapExtent(swapChainSupport.capabilities);
16 }
Aside from these properties we also have to decide how many images we would
like to have in the swap chain. The implementation specifies the minimum
number that it requires to function:
1 uint32_t imageCount = swapChainSupport.capabilities.minImageCount;
However, simply sticking to this minimum means that we may sometimes have
to wait on the driver to complete internal operations before we can acquire
another image to render to. Therefore it is recommended to request at least one
more image than the minimum:
1 uint32_t imageCount = swapChainSupport.capabilities.minImageCount +
1;
We should also make sure to not exceed the maximum number of images while
doing this, where 0 is a special value that means that there is no maximum:
1 if (swapChainSupport.capabilities.maxImageCount > 0 && imageCount >
swapChainSupport.capabilities.maxImageCount) {
2 imageCount = swapChainSupport.capabilities.maxImageCount;
3 }
As is tradition with Vulkan objects, creating the swap chain object requires
filling in a large structure. It starts out very familiarly:
1 VkSwapchainCreateInfoKHR createInfo{};
2 createInfo.sType = VK_STRUCTURE_TYPE_SWAPCHAIN_CREATE_INFO_KHR;
3 createInfo.surface = surface;
81
After specifying which surface the swap chain should be tied to, the details of
the swap chain images are specified:
1 createInfo.minImageCount = imageCount;
2 createInfo.imageFormat = surfaceFormat.format;
3 createInfo.imageColorSpace = surfaceFormat.colorSpace;
4 createInfo.imageExtent = extent;
5 createInfo.imageArrayLayers = 1;
6 createInfo.imageUsage = VK_IMAGE_USAGE_COLOR_ATTACHMENT_BIT;
The imageArrayLayers specifies the amount of layers each image consists of.
This is always 1 unless you are developing a stereoscopic 3D application. The
imageUsage bit field specifies what kind of operations we’ll use the images in
the swap chain for. In this tutorial we’re going to render directly to them, which
means that they’re used as color attachment. It is also possible that you’ll render
images to a separate image first to perform operations like post-processing. In
that case you may use a value like VK_IMAGE_USAGE_TRANSFER_DST_BIT instead
and use a memory operation to transfer the rendered image to a swap chain
image.
1 QueueFamilyIndices indices = findQueueFamilies(physicalDevice);
2 uint32_t queueFamilyIndices[] = {indices.graphicsFamily.value(),
indices.presentFamily.value()};
3
4 if (indices.graphicsFamily != indices.presentFamily) {
5 createInfo.imageSharingMode = VK_SHARING_MODE_CONCURRENT;
6 createInfo.queueFamilyIndexCount = 2;
7 createInfo.pQueueFamilyIndices = queueFamilyIndices;
8 } else {
9 createInfo.imageSharingMode = VK_SHARING_MODE_EXCLUSIVE;
10 createInfo.queueFamilyIndexCount = 0; // Optional
11 createInfo.pQueueFamilyIndices = nullptr; // Optional
12 }
Next, we need to specify how to handle swap chain images that will be used
across multiple queue families. That will be the case in our application if the
graphics queue family is different from the presentation queue. We’ll be drawing
on the images in the swap chain from the graphics queue and then submitting
them on the presentation queue. There are two ways to handle images that are
accessed from multiple queues:
• VK_SHARING_MODE_EXCLUSIVE: An image is owned by one queue family
at a time and ownership must be explicitly transferred before using it in
another queue family. This option offers the best performance.
• VK_SHARING_MODE_CONCURRENT: Images can be used across multiple queue
families without explicit ownership transfers.
If the queue families differ, then we’ll be using the concurrent mode in this
82
tutorial to avoid having to do the ownership chapters, because these involve some
concepts that are better explained at a later time. Concurrent mode requires
you to specify in advance between which queue families ownership will be shared
using the queueFamilyIndexCount and pQueueFamilyIndices parameters. If
the graphics queue family and presentation queue family are the same, which
will be the case on most hardware, then we should stick to exclusive mode,
because concurrent mode requires you to specify at least two distinct queue
families.
1 createInfo.preTransform =
swapChainSupport.capabilities.currentTransform;
We can specify that a certain transform should be applied to images in the
swap chain if it is supported (supportedTransforms in capabilities), like a
90 degree clockwise rotation or horizontal flip. To specify that you do not want
any transformation, simply specify the current transformation.
1 createInfo.compositeAlpha = VK_COMPOSITE_ALPHA_OPAQUE_BIT_KHR;
The compositeAlpha field specifies if the alpha channel should be used for blend-
ing with other windows in the window system. You’ll almost always want to
simply ignore the alpha channel, hence VK_COMPOSITE_ALPHA_OPAQUE_BIT_KHR.
1 createInfo.presentMode = presentMode;
2 createInfo.clipped = VK_TRUE;
The presentMode member speaks for itself. If the clipped member is set to
VK_TRUE then that means that we don’t care about the color of pixels that are
obscured, for example because another window is in front of them. Unless you
really need to be able to read these pixels back and get predictable results, you’ll
get the best performance by enabling clipping.
1 createInfo.oldSwapchain = VK_NULL_HANDLE;
That leaves one last field, oldSwapChain. With Vulkan it’s possible that your
swap chain becomes invalid or unoptimized while your application is running, for
example because the window was resized. In that case the swap chain actually
needs to be recreated from scratch and a reference to the old one must be
specified in this field. This is a complex topic that we’ll learn more about in a
future chapter. For now we’ll assume that we’ll only ever create one swap chain.
Now add a class member to store the VkSwapchainKHR object:
1 VkSwapchainKHR swapChain;
Creating the swap chain is now as simple as calling vkCreateSwapchainKHR:
1 if (vkCreateSwapchainKHR(device, &createInfo, nullptr, &swapChain)
!= VK_SUCCESS) {
83
2 throw std::runtime_error("failed to create swap chain!");
3 }
The parameters are the logical device, swap chain creation info, optional custom
allocators and a pointer to the variable to store the handle in. No surprises there.
It should be cleaned up using vkDestroySwapchainKHR before the device:
1 void cleanup() {
2 vkDestroySwapchainKHR(device, swapChain, nullptr);
3 ...
4 }
Now run the application to ensure that the swap chain is created successfully!
If at this point you get an access violation error in vkCreateSwapchainKHR or
see a message like Failed to find 'vkGetInstanceProcAddress' in layer
SteamOverlayVulkanLayer.dll, then see the FAQ entry about the Steam over-
lay layer.
Try removing the createInfo.imageExtent = extent; line with validation
layers enabled. You’ll see that one of the validation layers immediately catches
the mistake and a helpful message is printed:
Retrieving the swap chain images
The swap chain has been created now, so all that remains is retrieving the
handles of the VkImages in it. We’ll reference these during rendering operations
in later chapters. Add a class member to store the handles:
1 std::vector<VkImage> swapChainImages;
The images were created by the implementation for the swap chain and they will
be automatically cleaned up once the swap chain has been destroyed, therefore
we don’t need to add any cleanup code.
I’m adding the code to retrieve the handles to the end of the createSwapChain
function, right after the vkCreateSwapchainKHR call. Retrieving them is
very similar to the other times where we retrieved an array of objects from
Vulkan. Remember that we only specified a minimum number of images
in the swap chain, so the implementation is allowed to create a swap chain
with more. That’s why we’ll first query the final number of images with
vkGetSwapchainImagesKHR, then resize the container and finally call it again
to retrieve the handles.
1 vkGetSwapchainImagesKHR(device, swapChain, &imageCount, nullptr);
2 swapChainImages.resize(imageCount);
84
3 vkGetSwapchainImagesKHR(device, swapChain, &imageCount,
swapChainImages.data());
One last thing, store the format and extent we’ve chosen for the swap chain
images in member variables. We’ll need them in future chapters.
1 VkSwapchainKHR swapChain;
2 std::vector<VkImage> swapChainImages;
3 VkFormat swapChainImageFormat;
4 VkExtent2D swapChainExtent;
5
6 ...
7
8 swapChainImageFormat = surfaceFormat.format;
9 swapChainExtent = extent;
We now have a set of images that can be drawn onto and can be presented to
the window. The next chapter will begin to cover how we can set up the images
as render targets and then we start looking into the actual graphics pipeline
and drawing commands!
C++ code
Image views
To use any VkImage, including those in the swap chain, in the render pipeline
we have to create a VkImageView object. An image view is quite literally a
view into an image. It describes how to access the image and which part of
the image to access, for example if it should be treated as a 2D texture depth
texture without any mipmapping levels.
In this chapter we’ll write a createImageViews function that creates a basic
image view for every image in the swap chain so that we can use them as color
targets later on.
First add a class member to store the image views in:
1 std::vector<VkImageView> swapChainImageViews;
Create the createImageViews function and call it right after swap chain cre-
ation.
1 void initVulkan() {
2 createInstance();
3 setupDebugMessenger();
4 createSurface();
5 pickPhysicalDevice();
6 createLogicalDevice();
7 createSwapChain();
85
8 createImageViews();
9 }
10
11 void createImageViews() {
12
13 }
The first thing we need to do is resize the list to fit all of the image views we’ll
be creating:
1 void createImageViews() {
2 swapChainImageViews.resize(swapChainImages.size());
3
4 }
Next, set up the loop that iterates over all of the swap chain images.
1 for (size_t i = 0; i < swapChainImages.size(); i++) {
2
3 }
The parameters for image view creation are specified in a VkImageViewCreateInfo
structure. The first few parameters are straightforward.
1 VkImageViewCreateInfo createInfo{};
2 createInfo.sType = VK_STRUCTURE_TYPE_IMAGE_VIEW_CREATE_INFO;
3 createInfo.image = swapChainImages[i];
The viewType and format fields specify how the image data should be inter-
preted. The viewType parameter allows you to treat images as 1D textures, 2D
textures, 3D textures and cube maps.
1 createInfo.viewType = VK_IMAGE_VIEW_TYPE_2D;
2 createInfo.format = swapChainImageFormat;
The components field allows you to swizzle the color channels around. For
example, you can map all of the channels to the red channel for a monochrome
texture. You can also map constant values of 0 and 1 to a channel. In our case
we’ll stick to the default mapping.
1 createInfo.components.r = VK_COMPONENT_SWIZZLE_IDENTITY;
2 createInfo.components.g = VK_COMPONENT_SWIZZLE_IDENTITY;
3 createInfo.components.b = VK_COMPONENT_SWIZZLE_IDENTITY;
4 createInfo.components.a = VK_COMPONENT_SWIZZLE_IDENTITY;
The subresourceRange field describes what the image’s purpose is and which
part of the image should be accessed. Our images will be used as color targets
without any mipmapping levels or multiple layers.
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1 createInfo.subresourceRange.aspectMask = VK_IMAGE_ASPECT_COLOR_BIT;
2 createInfo.subresourceRange.baseMipLevel = 0;
3 createInfo.subresourceRange.levelCount = 1;
4 createInfo.subresourceRange.baseArrayLayer = 0;
5 createInfo.subresourceRange.layerCount = 1;
If you were working on a stereographic 3D application, then you would create
a swap chain with multiple layers. You could then create multiple image views
for each image representing the views for the left and right eyes by accessing
different layers.
Creating the image view is now a matter of calling vkCreateImageView:
1 if (vkCreateImageView(device, &createInfo, nullptr,
&swapChainImageViews[i]) != VK_SUCCESS) {
2 throw std::runtime_error("failed to create image views!");
3 }
Unlike images, the image views were explicitly created by us, so we need to add
a similar loop to destroy them again at the end of the program:
1 void cleanup() {
2 for (auto imageView : swapChainImageViews) {
3 vkDestroyImageView(device, imageView, nullptr);
4 }
5
6 ...
7 }
An image view is sufficient to start using an image as a texture, but it’s not
quite ready to be used as a render target just yet. That requires one more
step of indirection, known as a framebuffer. But first we’ll have to set up the
graphics pipeline.
C++ code
Graphics pipeline basics
Introduction
Over the course of the next few chapters we’ll be setting up a graphics pipeline
that is configured to draw our first triangle. The graphics pipeline is the se-
quence of operations that take the vertices and textures of your meshes all the
way to the pixels in the render targets. A simplified overview is displayed below:
87
The input assembler collects the raw vertex data from the buffers you specify
and may also use an index buffer to repeat certain elements without having to
duplicate the vertex data itself.
The vertex shader is run for every vertex and generally applies transformations
88
to turn vertex positions from model space to screen space. It also passes per-
vertex data down the pipeline.
The tessellation shaders allow you to subdivide geometry based on certain rules
to increase the mesh quality. This is often used to make surfaces like brick walls
and staircases look less flat when they are nearby.
The geometry shader is run on every primitive (triangle, line, point) and can
discard it or output more primitives than came in. This is similar to the tessel-
lation shader, but much more flexible. However, it is not used much in today’s
applications because the performance is not that good on most graphics cards
except for Intel’s integrated GPUs.
The rasterization stage discretizes the primitives into fragments. These are the
pixel elements that they fill on the framebuffer. Any fragments that fall outside
the screen are discarded and the attributes outputted by the vertex shader are
interpolated across the fragments, as shown in the figure. Usually the fragments
that are behind other primitive fragments are also discarded here because of
depth testing.
The fragment shader is invoked for every fragment that survives and determines
which framebuffer(s) the fragments are written to and with which color and
depth values. It can do this using the interpolated data from the vertex shader,
which can include things like texture coordinates and normals for lighting.
The color blending stage applies operations to mix different fragments that map
to the same pixel in the framebuffer. Fragments can simply overwrite each other,
add up or be mixed based upon transparency.
Stages with a green color are known as fixed-function stages. These stages
allow you to tweak their operations using parameters, but the way they work is
predefined.
Stages with an orange color on the other hand are programmable, which means
that you can upload your own code to the graphics card to apply exactly the
operations you want. This allows you to use fragment shaders, for example, to
implement anything from texturing and lighting to ray tracers. These programs
run on many GPU cores simultaneously to process many objects, like vertices
and fragments in parallel.
If you’ve used older APIs like OpenGL and Direct3D before, then you’ll be used
to being able to change any pipeline settings at will with calls like glBlendFunc
and OMSetBlendState. The graphics pipeline in Vulkan is almost completely
immutable, so you must recreate the pipeline from scratch if you want to change
shaders, bind different framebuffers or change the blend function. The disadvan-
tage is that you’ll have to create a number of pipelines that represent all of the
different combinations of states you want to use in your rendering operations.
However, because all of the operations you’ll be doing in the pipeline are known
in advance, the driver can optimize for it much better.
89
Some of the programmable stages are optional based on what you intend to
do. For example, the tessellation and geometry stages can be disabled if you
are just drawing simple geometry. If you are only interested in depth values
then you can disable the fragment shader stage, which is useful for shadow map
generation.
In the next chapter we’ll first create the two programmable stages required to
put a triangle onto the screen: the vertex shader and fragment shader. The
fixed-function configuration like blending mode, viewport, rasterization will be
set up in the chapter after that. The final part of setting up the graphics pipeline
in Vulkan involves the specification of input and output framebuffers.
Create a createGraphicsPipeline function that is called right after
createImageViews in initVulkan. We’ll work on this function throughout the
following chapters.
1 void initVulkan() {
2 createInstance();
3 setupDebugMessenger();
4 createSurface();
5 pickPhysicalDevice();
6 createLogicalDevice();
7 createSwapChain();
8 createImageViews();
9 createGraphicsPipeline();
10 }
11
12 ...
13
14 void createGraphicsPipeline() {
15
16 }
C++ code
Shader modules
Unlike earlier APIs, shader code in Vulkan has to be specified in a bytecode
format as opposed to human-readable syntax like GLSL and HLSL. This byte-
code format is called SPIR-V and is designed to be used with both Vulkan and
OpenCL (both Khronos APIs). It is a format that can be used to write graphics
and compute shaders, but we will focus on shaders used in Vulkan’s graphics
pipelines in this tutorial.
The advantage of using a bytecode format is that the compilers written by GPU
vendors to turn shader code into native code are significantly less complex. The
past has shown that with human-readable syntax like GLSL, some GPU vendors
were rather flexible with their interpretation of the standard. If you happen to
90
write non-trivial shaders with a GPU from one of these vendors, then you’d risk
other vendor’s drivers rejecting your code due to syntax errors, or worse, your
shader running differently because of compiler bugs. With a straightforward
bytecode format like SPIR-V that will hopefully be avoided.
However, that does not mean that we need to write this bytecode by hand.
Khronos has released their own vendor-independent compiler that compiles
GLSL to SPIR-V. This compiler is designed to verify that your shader code
is fully standards compliant and produces one SPIR-V binary that you can ship
with your program. You can also include this compiler as a library to produce
SPIR-V at runtime, but we won’t be doing that in this tutorial. Although
we can use this compiler directly via glslangValidator.exe, we will be using
glslc.exe by Google instead. The advantage of glslc is that it uses the same
parameter format as well-known compilers like GCC and Clang and includes
some extra functionality like includes. Both of them are already included in the
Vulkan SDK, so you don’t need to download anything extra.
GLSL is a shading language with a C-style syntax. Programs written in it have
a main function that is invoked for every object. Instead of using parameters
for input and a return value as output, GLSL uses global variables to handle
input and output. The language includes many features to aid in graphics pro-
gramming, like built-in vector and matrix primitives. Functions for operations
like cross products, matrix-vector products and reflections around a vector are
included. The vector type is called vec with a number indicating the amount of
elements. For example, a 3D position would be stored in a vec3. It is possible
to access single components through members like .x, but it’s also possible to
create a new vector from multiple components at the same time. For example,
the expression vec3(1.0, 2.0, 3.0).xy would result in vec2. The construc-
tors of vectors can also take combinations of vector objects and scalar values.
For example, a vec3 can be constructed with vec3(vec2(1.0, 2.0), 3.0).
As the previous chapter mentioned, we need to write a vertex shader and a
fragment shader to get a triangle on the screen. The next two sections will cover
the GLSL code of each of those and after that I’ll show you how to produce two
SPIR-V binaries and load them into the program.
Vertex shader
The vertex shader processes each incoming vertex. It takes its attributes, like
world position, color, normal and texture coordinates as input. The output is
the final position in clip coordinates and the attributes that need to be passed
on to the fragment shader, like color and texture coordinates. These values will
then be interpolated over the fragments by the rasterizer to produce a smooth
gradient.
A clip coordinate is a four dimensional vector from the vertex shader that is
subsequently turned into a normalized device coordinate by dividing the whole
vector by its last component. These normalized device coordinates are homo-
91
geneous coordinates that map the framebuffer to a [-1, 1] by [-1, 1] coordinate
system that looks like the following:
You should already be familiar with these if you have dabbled in computer
graphics before. If you have used OpenGL before, then you’ll notice that the
sign of the Y coordinates is now flipped. The Z coordinate now uses the same
range as it does in Direct3D, from 0 to 1.
For our first triangle we won’t be applying any transformations, we’ll just specify
the positions of the three vertices directly as normalized device coordinates to
create the following shape:
We can directly output normalized device coordinates by outputting them as
clip coordinates from the vertex shader with the last component set to 1. That
way the division to transform clip coordinates to normalized device coordinates
will not change anything.
Normally these coordinates would be stored in a vertex buffer, but creating
a vertex buffer in Vulkan and filling it with data is not trivial. Therefore I’ve
92
decided to postpone that until after we’ve had the satisfaction of seeing a triangle
pop up on the screen. We’re going to do something a little unorthodox in the
meanwhile: include the coordinates directly inside the vertex shader. The code
looks like this:
1 #version 450
2
3 vec2 positions[3] = vec2[](
4 vec2(0.0, -0.5),
5 vec2(0.5, 0.5),
6 vec2(-0.5, 0.5)
7 );
8
9 void main() {
10 gl_Position = vec4(positions[gl_VertexIndex], 0.0, 1.0);
11 }
The main function is invoked for every vertex. The built-in gl_VertexIndex
variable contains the index of the current vertex. This is usually an index into
the vertex buffer, but in our case it will be an index into a hardcoded array of
vertex data. The position of each vertex is accessed from the constant array
in the shader and combined with dummy z and w components to produce a
position in clip coordinates. The built-in variable gl_Position functions as the
output.
Fragment shader
The triangle that is formed by the positions from the vertex shader fills an
area on the screen with fragments. The fragment shader is invoked on these
fragments to produce a color and depth for the framebuffer (or framebuffers).
A simple fragment shader that outputs the color red for the entire triangle looks
like this:
1 #version 450
2
3 layout(location = 0) out vec4 outColor;
4
5 void main() {
6 outColor = vec4(1.0, 0.0, 0.0, 1.0);
7 }
The main function is called for every fragment just like the vertex shader main
function is called for every vertex. Colors in GLSL are 4-component vectors with
the R, G, B and alpha channels within the [0, 1] range. Unlike gl_Position in
the vertex shader, there is no built-in variable to output a color for the current
fragment. You have to specify your own output variable for each framebuffer
93
where the layout(location = 0) modifier specifies the index of the frame-
buffer. The color red is written to this outColor variable that is linked to the
first (and only) framebuffer at index 0.
Per-vertex colors
Making the entire triangle red is not very interesting, wouldn’t something like
the following look a lot nicer?
We have to make a couple of changes to both shaders to accomplish this. First
off, we need to specify a distinct color for each of the three vertices. The vertex
shader should now include an array with colors just like it does for positions:
1 vec3 colors[3] = vec3[](
2 vec3(1.0, 0.0, 0.0),
3 vec3(0.0, 1.0, 0.0),
4 vec3(0.0, 0.0, 1.0)
5 );
Now we just need to pass these per-vertex colors to the fragment shader so it
can output their interpolated values to the framebuffer. Add an output for color
to the vertex shader and write to it in the main function:
1 layout(location = 0) out vec3 fragColor;
2
3 void main() {
4 gl_Position = vec4(positions[gl_VertexIndex], 0.0, 1.0);
5 fragColor = colors[gl_VertexIndex];
6 }
Next, we need to add a matching input in the fragment shader:
1 layout(location = 0) in vec3 fragColor;
2
94
3 void main() {
4 outColor = vec4(fragColor, 1.0);
5 }
The input variable does not necessarily have to use the same name, they will
be linked together using the indexes specified by the location directives. The
main function has been modified to output the color along with an alpha value.
As shown in the image above, the values for fragColor will be automatically
interpolated for the fragments between the three vertices, resulting in a smooth
gradient.
Compiling the shaders
Create a directory called shaders in the root directory of your project and
store the vertex shader in a file called shader.vert and the fragment shader in
a file called shader.frag in that directory. GLSL shaders don’t have an official
extension, but these two are commonly used to distinguish them.
The contents of shader.vert should be:
1 #version 450
2
3 layout(location = 0) out vec3 fragColor;
4
5 vec2 positions[3] = vec2[](
6 vec2(0.0, -0.5),
7 vec2(0.5, 0.5),
8 vec2(-0.5, 0.5)
9 );
10
11 vec3 colors[3] = vec3[](
12 vec3(1.0, 0.0, 0.0),
13 vec3(0.0, 1.0, 0.0),
14 vec3(0.0, 0.0, 1.0)
15 );
16
17 void main() {
18 gl_Position = vec4(positions[gl_VertexIndex], 0.0, 1.0);
19 fragColor = colors[gl_VertexIndex];
20 }
And the contents of shader.frag should be:
1 #version 450
2
3 layout(location = 0) in vec3 fragColor;
4
5 layout(location = 0) out vec4 outColor;
95
6
7 void main() {
8 outColor = vec4(fragColor, 1.0);
9 }
We’re now going to compile these into SPIR-V bytecode using the glslc pro-
gram.
Windows
Create a compile.bat file with the following contents:
1 C:/VulkanSDK/x.x.x.x/Bin32/glslc.exe shader.vert -o vert.spv
2 C:/VulkanSDK/x.x.x.x/Bin32/glslc.exe shader.frag -o frag.spv
3 pause
Replace the path to glslc.exe with the path to where you installed the Vulkan
SDK. Double click the file to run it.
Linux
Create a compile.sh file with the following contents:
1 /home/user/VulkanSDK/x.x.x.x/x86_64/bin/glslc shader.vert -o vert.spv
2 /home/user/VulkanSDK/x.x.x.x/x86_64/bin/glslc shader.frag -o frag.spv
Replace the path to glslc with the path to where you installed the Vulkan
SDK. Make the script executable with chmod +x compile.sh and run it.
End of platform-specific instructions
These two commands tell the compiler to read the GLSL source file and output
a SPIR-V bytecode file using the -o (output) flag.
If your shader contains a syntax error then the compiler will tell you the line
number and problem, as you would expect. Try leaving out a semicolon for
example and run the compile script again. Also try running the compiler without
any arguments to see what kinds of flags it supports. It can, for example, also
output the bytecode into a human-readable format so you can see exactly what
your shader is doing and any optimizations that have been applied at this stage.
Compiling shaders on the commandline is one of the most straightforward op-
tions and it’s the one that we’ll use in this tutorial, but it’s also possible to
compile shaders directly from your own code. The Vulkan SDK includes lib-
shaderc, which is a library to compile GLSL code to SPIR-V from within your
program.
Loading a shader
Now that we have a way of producing SPIR-V shaders, it’s time to load them
into our program to plug them into the graphics pipeline at some point. We’ll
first write a simple helper function to load the binary data from the files.
96
1 #include <fstream>
2
3 ...
4
5 static std::vector<char> readFile(const std::string& filename) {
6 std::ifstream file(filename, std::ios::ate | std::ios::binary);
7
8 if (!file.is_open()) {
9 throw std::runtime_error("failed to open file!");
10 }
11 }
The readFile function will read all of the bytes from the specified file and
return them in a byte array managed by std::vector. We start by opening
the file with two flags:
• ate: Start reading at the end of the file
• binary: Read the file as binary file (avoid text transformations)
The advantage of starting to read at the end of the file is that we can use the
read position to determine the size of the file and allocate a buffer:
1 size_t fileSize = (size_t) file.tellg();
2 std::vector<char> buffer(fileSize);
After that, we can seek back to the beginning of the file and read all of the bytes
at once:
1 file.seekg(0);
2 file.read(buffer.data(), fileSize);
And finally close the file and return the bytes:
1 file.close();
2
3 return buffer;
We’ll now call this function from createGraphicsPipeline to load the bytecode
of the two shaders:
1 void createGraphicsPipeline() {
2 auto vertShaderCode = readFile("shaders/vert.spv");
3 auto fragShaderCode = readFile("shaders/frag.spv");
4 }
Make sure that the shaders are loaded correctly by printing the size of the
buffers and checking if they match the actual file size in bytes. Note that the
code doesn’t need to be null terminated since it’s binary code and we will later
be explicit about its size.
97
Creating shader modules
Before we can pass the code to the pipeline, we have to wrap it in a
VkShaderModule object. Let’s create a helper function createShaderModule
to do that.
1 VkShaderModule createShaderModule(const std::vector<char>& code) {
2
3 }
The function will take a buffer with the bytecode as parameter and create a
VkShaderModule from it.
Creating a shader module is simple, we only need to specify a pointer to the
buffer with the bytecode and the length of it. This information is specified in
a VkShaderModuleCreateInfo structure. The one catch is that the size of the
bytecode is specified in bytes, but the bytecode pointer is a uint32_t pointer
rather than a char pointer. Therefore we will need to cast the pointer with
reinterpret_cast as shown below. When you perform a cast like this, you also
need to ensure that the data satisfies the alignment requirements of uint32_t.
Lucky for us, the data is stored in an std::vector where the default allocator
already ensures that the data satisfies the worst case alignment requirements.
1 VkShaderModuleCreateInfo createInfo{};
2 createInfo.sType = VK_STRUCTURE_TYPE_SHADER_MODULE_CREATE_INFO;
3 createInfo.codeSize = code.size();
4 createInfo.pCode = reinterpret_cast<const uint32_t*>(code.data());
The VkShaderModule can then be created with a call to vkCreateShaderModule:
1 VkShaderModule shaderModule;
2 if (vkCreateShaderModule(device, &createInfo, nullptr,
&shaderModule) != VK_SUCCESS) {
3 throw std::runtime_error("failed to create shader module!");
4 }
The parameters are the same as those in previous object creation functions:
the logical device, pointer to create info structure, optional pointer to custom
allocators and handle output variable. The buffer with the code can be freed
immediately after creating the shader module. Don’t forget to return the created
shader module:
1 return shaderModule;
Shader modules are just a thin wrapper around the shader bytecode that we’ve
previously loaded from a file and the functions defined in it. The compilation
and linking of the SPIR-V bytecode to machine code for execution by the GPU
doesn’t happen until the graphics pipeline is created. That means that we’re al-
lowed to destroy the shader modules again as soon as pipeline creation is finished,
98
which is why we’ll make them local variables in the createGraphicsPipeline
function instead of class members:
1 void createGraphicsPipeline() {
2 auto vertShaderCode = readFile("shaders/vert.spv");
3 auto fragShaderCode = readFile("shaders/frag.spv");
4
5 VkShaderModule vertShaderModule =
createShaderModule(vertShaderCode);
6 VkShaderModule fragShaderModule =
createShaderModule(fragShaderCode);
The cleanup should then happen at the end of the function by adding two calls
to vkDestroyShaderModule. All of the remaining code in this chapter will be
inserted before these lines.
1 ...
2 vkDestroyShaderModule(device, fragShaderModule, nullptr);
3 vkDestroyShaderModule(device, vertShaderModule, nullptr);
4 }
Shader stage creation
To actually use the shaders we’ll need to assign them to a specific pipeline stage
through VkPipelineShaderStageCreateInfo structures as part of the actual
pipeline creation process.
We’ll start by filling in the structure for the vertex shader, again in the
createGraphicsPipeline function.
1 VkPipelineShaderStageCreateInfo vertShaderStageInfo{};
2 vertShaderStageInfo.sType =
VK_STRUCTURE_TYPE_PIPELINE_SHADER_STAGE_CREATE_INFO;
3 vertShaderStageInfo.stage = VK_SHADER_STAGE_VERTEX_BIT;
The first step, besides the obligatory sType member, is telling Vulkan in which
pipeline stage the shader is going to be used. There is an enum value for each
of the programmable stages described in the previous chapter.
1 vertShaderStageInfo.module = vertShaderModule;
2 vertShaderStageInfo.pName = "main";
The next two members specify the shader module containing the code, and the
function to invoke, known as the entrypoint. That means that it’s possible to
combine multiple fragment shaders into a single shader module and use different
entry points to differentiate between their behaviors. In this case we’ll stick to
the standard main, however.
99
There is one more (optional) member, pSpecializationInfo, which we won’t
be using here, but is worth discussing. It allows you to specify values for shader
constants. You can use a single shader module where its behavior can be config-
ured at pipeline creation by specifying different values for the constants used in
it. This is more efficient than configuring the shader using variables at render
time, because the compiler can do optimizations like eliminating if statements
that depend on these values. If you don’t have any constants like that, then you
can set the member to nullptr, which our struct initialization does automati-
cally.
Modifying the structure to suit the fragment shader is easy:
1 VkPipelineShaderStageCreateInfo fragShaderStageInfo{};
2 fragShaderStageInfo.sType =
VK_STRUCTURE_TYPE_PIPELINE_SHADER_STAGE_CREATE_INFO;
3 fragShaderStageInfo.stage = VK_SHADER_STAGE_FRAGMENT_BIT;
4 fragShaderStageInfo.module = fragShaderModule;
5 fragShaderStageInfo.pName = "main";
Finish by defining an array that contains these two structs, which we’ll later
use to reference them in the actual pipeline creation step.
1 VkPipelineShaderStageCreateInfo shaderStages[] =
{vertShaderStageInfo, fragShaderStageInfo};
That’s all there is to describing the programmable stages of the pipeline. In the
next chapter we’ll look at the fixed-function stages.
C++ code / Vertex shader / Fragment shader
Fixed functions
The older graphics APIs provided default state for most of the stages of the
graphics pipeline. In Vulkan you have to be explicit about most pipeline states
as it’ll be baked into an immutable pipeline state object. In this chapter we’ll
fill in all of the structures to configure these fixed-function operations.
Dynamic state
While most of the pipeline state needs to be baked into the pipeline state, a
limited amount of the state can actually be changed without recreating the
pipeline at draw time. Examples are the size of the viewport, line width and
blend constants. If you want to use dynamic state and keep these properties out,
then you’ll have to fill in a VkPipelineDynamicStateCreateInfo structure like
this:
1 std::vector<VkDynamicState> dynamicStates = {
2 VK_DYNAMIC_STATE_VIEWPORT,
3 VK_DYNAMIC_STATE_SCISSOR
100
4 };
5
6 VkPipelineDynamicStateCreateInfo dynamicState{};
7 dynamicState.sType =
VK_STRUCTURE_TYPE_PIPELINE_DYNAMIC_STATE_CREATE_INFO;
8 dynamicState.dynamicStateCount =
static_cast<uint32_t>(dynamicStates.size());
9 dynamicState.pDynamicStates = dynamicStates.data();
This will cause the configuration of these values to be ignored and you will be
able (and required) to specify the data at drawing time. This results in a more
flexible setup and is very common for things like viewport and scissor state,
which would result in a more complex setup when being baked into the pipeline
state.
Vertex input
The VkPipelineVertexInputStateCreateInfo structure describes the format
of the vertex data that will be passed to the vertex shader. It describes this in
roughly two ways:
• Bindings: spacing between data and whether the data is per-vertex or
per-instance (see instancing)
• Attribute descriptions: type of the attributes passed to the vertex shader,
which binding to load them from and at which offset
Because we’re hard coding the vertex data directly in the vertex shader, we’ll
fill in this structure to specify that there is no vertex data to load for now. We’ll
get back to it in the vertex buffer chapter.
1 VkPipelineVertexInputStateCreateInfo vertexInputInfo{};
2 vertexInputInfo.sType =
VK_STRUCTURE_TYPE_PIPELINE_VERTEX_INPUT_STATE_CREATE_INFO;
3 vertexInputInfo.vertexBindingDescriptionCount = 0;
4 vertexInputInfo.pVertexBindingDescriptions = nullptr; // Optional
5 vertexInputInfo.vertexAttributeDescriptionCount = 0;
6 vertexInputInfo.pVertexAttributeDescriptions = nullptr; // Optional
The pVertexBindingDescriptions and pVertexAttributeDescriptions
members point to an array of structs that describe the aforementioned details
for loading vertex data. Add this structure to the createGraphicsPipeline
function right after the shaderStages array.
Input assembly
The VkPipelineInputAssemblyStateCreateInfo struct describes two things:
what kind of geometry will be drawn from the vertices and if primitive restart
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should be enabled. The former is specified in the topology member and can
have values like:
• VK_PRIMITIVE_TOPOLOGY_POINT_LIST: points from vertices
• VK_PRIMITIVE_TOPOLOGY_LINE_LIST: line from every 2 vertices without
reuse
• VK_PRIMITIVE_TOPOLOGY_LINE_STRIP: the end vertex of every line is used
as start vertex for the next line
• VK_PRIMITIVE_TOPOLOGY_TRIANGLE_LIST: triangle from every 3 vertices
without reuse
• VK_PRIMITIVE_TOPOLOGY_TRIANGLE_STRIP: the second and third vertex
of every triangle are used as first two vertices of the next triangle
Normally, the vertices are loaded from the vertex buffer by index in sequential
order, but with an element buffer you can specify the indices to use yourself.
This allows you to perform optimizations like reusing vertices. If you set the
primitiveRestartEnable member to VK_TRUE, then it’s possible to break up
lines and triangles in the _STRIP topology modes by using a special index of
0xFFFF or 0xFFFFFFFF.
We intend to draw triangles throughout this tutorial, so we’ll stick to the fol-
lowing data for the structure:
1 VkPipelineInputAssemblyStateCreateInfo inputAssembly{};
2 inputAssembly.sType =
VK_STRUCTURE_TYPE_PIPELINE_INPUT_ASSEMBLY_STATE_CREATE_INFO;
3 inputAssembly.topology = VK_PRIMITIVE_TOPOLOGY_TRIANGLE_LIST;
4 inputAssembly.primitiveRestartEnable = VK_FALSE;
Viewports and scissors
A viewport basically describes the region of the framebuffer that the output will
be rendered to. This will almost always be (0, 0) to (width, height) and in
this tutorial that will also be the case.
1 VkViewport viewport{};
2 viewport.x = 0.0f;
3 viewport.y = 0.0f;
4 viewport.width = (float) swapChainExtent.width;
5 viewport.height = (float) swapChainExtent.height;
6 viewport.minDepth = 0.0f;
7 viewport.maxDepth = 1.0f;
Remember that the size of the swap chain and its images may differ from the
WIDTH and HEIGHT of the window. The swap chain images will be used as
framebuffers later on, so we should stick to their size.
The minDepth and maxDepth values specify the range of depth values to use
for the framebuffer. These values must be within the [0.0f, 1.0f] range, but
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minDepth may be higher than maxDepth. If you aren’t doing anything special,
then you should stick to the standard values of 0.0f and 1.0f.
While viewports define the transformation from the image to the framebuffer,
scissor rectangles define in which regions pixels will actually be stored. Any
pixels outside the scissor rectangles will be discarded by the rasterizer. They
function like a filter rather than a transformation. The difference is illustrated
below. Note that the left scissor rectangle is just one of the many possibilities
that would result in that image, as long as it’s larger than the viewport.
So if we wanted to draw to the entire framebuffer, we would specify a scissor
rectangle that covers it entirely:
1 VkRect2D scissor{};
2 scissor.offset = {0, 0};
3 scissor.extent = swapChainExtent;
Viewport(s) and scissor rectangle(s) can either be specified as a static part of
the pipeline or as a dynamic state set in the command buffer. While the former
is more in line with the other states it’s often convenient to make viewport and
scissor state dynamic as it gives you a lot more flexibility. This is very common
and all implementations can handle this dynamic state without a performance
penalty.
When opting for dynamic viewport(s) and scissor rectangle(s) you need to enable
the respective dynamic states for the pipeline:
1 std::vector<VkDynamicState> dynamicStates = {
2 VK_DYNAMIC_STATE_VIEWPORT,
3 VK_DYNAMIC_STATE_SCISSOR
4 };
5
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6 VkPipelineDynamicStateCreateInfo dynamicState{};
7 dynamicState.sType =
VK_STRUCTURE_TYPE_PIPELINE_DYNAMIC_STATE_CREATE_INFO;
8 dynamicState.dynamicStateCount =
static_cast<uint32_t>(dynamicStates.size());
9 dynamicState.pDynamicStates = dynamicStates.data();
And then you only need to specify their count at pipeline creation time:
1 VkPipelineViewportStateCreateInfo viewportState{};
2 viewportState.sType =
VK_STRUCTURE_TYPE_PIPELINE_VIEWPORT_STATE_CREATE_INFO;
3 viewportState.viewportCount = 1;
4 viewportState.scissorCount = 1;
The actual viewport(s) and scissor rectangle(s) will then later be set up at
drawing time.
With dynamic state it’s even possible to specify different viewports and or scissor
rectangles within a single command buffer.
Without dynamic state, the viewport and scissor rectangle need to be set in the
pipeline using the VkPipelineViewportStateCreateInfo struct. This makes
the viewport and scissor rectangle for this pipeline immutable. Any changes
required to these values would require a new pipeline to be created with the
new values.
1 VkPipelineViewportStateCreateInfo viewportState{};
2 viewportState.sType =
VK_STRUCTURE_TYPE_PIPELINE_VIEWPORT_STATE_CREATE_INFO;
3 viewportState.viewportCount = 1;
4 viewportState.pViewports = &viewport;
5 viewportState.scissorCount = 1;
6 viewportState.pScissors = &scissor;
Independent of how you set them, it’s is possible to use multiple viewports and
scissor rectangles on some graphics cards, so the structure members reference
an array of them. Using multiple requires enabling a GPU feature (see logical
device creation).
Rasterizer
The rasterizer takes the geometry that is shaped by the vertices from the
vertex shader and turns it into fragments to be colored by the fragment
shader. It also performs depth testing, face culling and the scissor test,
and it can be configured to output fragments that fill entire polygons
or just the edges (wireframe rendering). All this is configured using the
VkPipelineRasterizationStateCreateInfo structure.
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1 VkPipelineRasterizationStateCreateInfo rasterizer{};
2 rasterizer.sType =
VK_STRUCTURE_TYPE_PIPELINE_RASTERIZATION_STATE_CREATE_INFO;
3 rasterizer.depthClampEnable = VK_FALSE;
If depthClampEnable is set to VK_TRUE, then fragments that are beyond the
near and far planes are clamped to them as opposed to discarding them. This
is useful in some special cases like shadow maps. Using this requires enabling a
GPU feature.
1 rasterizer.rasterizerDiscardEnable = VK_FALSE;
If rasterizerDiscardEnable is set to VK_TRUE, then geometry never passes
through the rasterizer stage. This basically disables any output to the frame-
buffer.
1 rasterizer.polygonMode = VK_POLYGON_MODE_FILL;
The polygonMode determines how fragments are generated for geometry. The
following modes are available:
• VK_POLYGON_MODE_FILL: fill the area of the polygon with fragments
• VK_POLYGON_MODE_LINE: polygon edges are drawn as lines
• VK_POLYGON_MODE_POINT: polygon vertices are drawn as points
Using any mode other than fill requires enabling a GPU feature.
1 rasterizer.lineWidth = 1.0f;
The lineWidth member is straightforward, it describes the thickness of lines
in terms of number of fragments. The maximum line width that is supported
depends on the hardware and any line thicker than 1.0f requires you to enable
the wideLines GPU feature.
1 rasterizer.cullMode = VK_CULL_MODE_BACK_BIT;
2 rasterizer.frontFace = VK_FRONT_FACE_CLOCKWISE;
The cullMode variable determines the type of face culling to use. You can
disable culling, cull the front faces, cull the back faces or both. The frontFace
variable specifies the vertex order for faces to be considered front-facing and can
be clockwise or counterclockwise.
1 rasterizer.depthBiasEnable = VK_FALSE;
2 rasterizer.depthBiasConstantFactor = 0.0f; // Optional
3 rasterizer.depthBiasClamp = 0.0f; // Optional
4 rasterizer.depthBiasSlopeFactor = 0.0f; // Optional
The rasterizer can alter the depth values by adding a constant value or biasing
them based on a fragment’s slope. This is sometimes used for shadow mapping,
but we won’t be using it. Just set depthBiasEnable to VK_FALSE.
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Multisampling
The VkPipelineMultisampleStateCreateInfo struct configures multisam-
pling, which is one of the ways to perform anti-aliasing. It works by combining
the fragment shader results of multiple polygons that rasterize to the same
pixel. This mainly occurs along edges, which is also where the most noticeable
aliasing artifacts occur. Because it doesn’t need to run the fragment shader
multiple times if only one polygon maps to a pixel, it is significantly less
expensive than simply rendering to a higher resolution and then downscaling.
Enabling it requires enabling a GPU feature.
1 VkPipelineMultisampleStateCreateInfo multisampling{};
2 multisampling.sType =
VK_STRUCTURE_TYPE_PIPELINE_MULTISAMPLE_STATE_CREATE_INFO;
3 multisampling.sampleShadingEnable = VK_FALSE;
4 multisampling.rasterizationSamples = VK_SAMPLE_COUNT_1_BIT;
5 multisampling.minSampleShading = 1.0f; // Optional
6 multisampling.pSampleMask = nullptr; // Optional
7 multisampling.alphaToCoverageEnable = VK_FALSE; // Optional
8 multisampling.alphaToOneEnable = VK_FALSE; // Optional
We’ll revisit multisampling in later chapter, for now let’s keep it disabled.
Depth and stencil testing
If you are using a depth and/or stencil buffer, then you also need to configure
the depth and stencil tests using VkPipelineDepthStencilStateCreateInfo.
We don’t have one right now, so we can simply pass a nullptr instead of a
pointer to such a struct. We’ll get back to it in the depth buffering chapter.
Color blending
After a fragment shader has returned a color, it needs to be combined with the
color that is already in the framebuffer. This transformation is known as color
blending and there are two ways to do it:
• Mix the old and new value to produce a final color
• Combine the old and new value using a bitwise operation
There are two types of structs to configure color blending. The first struct,
VkPipelineColorBlendAttachmentState contains the configuration per at-
tached framebuffer and the second struct, VkPipelineColorBlendStateCreateInfo
contains the global color blending settings. In our case we only have one frame-
buffer:
1 VkPipelineColorBlendAttachmentState colorBlendAttachment{};
2 colorBlendAttachment.colorWriteMask = VK_COLOR_COMPONENT_R_BIT |
VK_COLOR_COMPONENT_G_BIT | VK_COLOR_COMPONENT_B_BIT |
VK_COLOR_COMPONENT_A_BIT;
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3 colorBlendAttachment.blendEnable = VK_FALSE;
4 colorBlendAttachment.srcColorBlendFactor = VK_BLEND_FACTOR_ONE; //
Optional
5 colorBlendAttachment.dstColorBlendFactor = VK_BLEND_FACTOR_ZERO; //
Optional
6 colorBlendAttachment.colorBlendOp = VK_BLEND_OP_ADD; // Optional
7 colorBlendAttachment.srcAlphaBlendFactor = VK_BLEND_FACTOR_ONE; //
Optional
8 colorBlendAttachment.dstAlphaBlendFactor = VK_BLEND_FACTOR_ZERO; //
Optional
9 colorBlendAttachment.alphaBlendOp = VK_BLEND_OP_ADD; // Optional
This per-framebuffer struct allows you to configure the first way of color blending.
The operations that will be performed are best demonstrated using the following
pseudocode:
1 if (blendEnable) {
2 finalColor.rgb = (srcColorBlendFactor * newColor.rgb)
<colorBlendOp> (dstColorBlendFactor * oldColor.rgb);
3 finalColor.a = (srcAlphaBlendFactor * newColor.a) <alphaBlendOp>
(dstAlphaBlendFactor * oldColor.a);
4 } else {
5 finalColor = newColor;
6 }
7
8 finalColor = finalColor & colorWriteMask;
If blendEnable is set to VK_FALSE, then the new color from the fragment
shader is passed through unmodified. Otherwise, the two mixing operations
are performed to compute a new color. The resulting color is AND’d with the
colorWriteMask to determine which channels are actually passed through.
The most common way to use color blending is to implement alpha blending,
where we want the new color to be blended with the old color based on its
opacity. The finalColor should then be computed as follows:
1 finalColor.rgb = newAlpha * newColor + (1 - newAlpha) * oldColor;
2 finalColor.a = newAlpha.a;
This can be accomplished with the following parameters:
1 colorBlendAttachment.blendEnable = VK_TRUE;
2 colorBlendAttachment.srcColorBlendFactor = VK_BLEND_FACTOR_SRC_ALPHA;
3 colorBlendAttachment.dstColorBlendFactor =
VK_BLEND_FACTOR_ONE_MINUS_SRC_ALPHA;
4 colorBlendAttachment.colorBlendOp = VK_BLEND_OP_ADD;
5 colorBlendAttachment.srcAlphaBlendFactor = VK_BLEND_FACTOR_ONE;
6 colorBlendAttachment.dstAlphaBlendFactor = VK_BLEND_FACTOR_ZERO;
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7 colorBlendAttachment.alphaBlendOp = VK_BLEND_OP_ADD;
You can find all of the possible operations in the VkBlendFactor and VkBlendOp
enumerations in the specification.
The second structure references the array of structures for all of the framebuffers
and allows you to set blend constants that you can use as blend factors in the
aforementioned calculations.
1 VkPipelineColorBlendStateCreateInfo colorBlending{};
2 colorBlending.sType =
VK_STRUCTURE_TYPE_PIPELINE_COLOR_BLEND_STATE_CREATE_INFO;
3 colorBlending.logicOpEnable = VK_FALSE;
4 colorBlending.logicOp = VK_LOGIC_OP_COPY; // Optional
5 colorBlending.attachmentCount = 1;
6 colorBlending.pAttachments = &colorBlendAttachment;
7 colorBlending.blendConstants[0] = 0.0f; // Optional
8 colorBlending.blendConstants[1] = 0.0f; // Optional
9 colorBlending.blendConstants[2] = 0.0f; // Optional
10 colorBlending.blendConstants[3] = 0.0f; // Optional
If you want to use the second method of blending (bitwise combination), then
you should set logicOpEnable to VK_TRUE. The bitwise operation can then be
specified in the logicOp field. Note that this will automatically disable the
first method, as if you had set blendEnable to VK_FALSE for every attached
framebuffer! The colorWriteMask will also be used in this mode to determine
which channels in the framebuffer will actually be affected. It is also possible to
disable both modes, as we’ve done here, in which case the fragment colors will
be written to the framebuffer unmodified.
Pipeline layout
You can use uniform values in shaders, which are globals similar to dynamic
state variables that can be changed at drawing time to alter the behavior of
your shaders without having to recreate them. They are commonly used to pass
the transformation matrix to the vertex shader, or to create texture samplers
in the fragment shader.
These uniform values need to be specified during pipeline creation by creating a
VkPipelineLayout object. Even though we won’t be using them until a future
chapter, we are still required to create an empty pipeline layout.
Create a class member to hold this object, because we’ll refer to it from other
functions at a later point in time:
1 VkPipelineLayout pipelineLayout;
And then create the object in the createGraphicsPipeline function:
108
1 VkPipelineLayoutCreateInfo pipelineLayoutInfo{};
2 pipelineLayoutInfo.sType =
VK_STRUCTURE_TYPE_PIPELINE_LAYOUT_CREATE_INFO;
3 pipelineLayoutInfo.setLayoutCount = 0; // Optional
4 pipelineLayoutInfo.pSetLayouts = nullptr; // Optional
5 pipelineLayoutInfo.pushConstantRangeCount = 0; // Optional
6 pipelineLayoutInfo.pPushConstantRanges = nullptr; // Optional
7
8 if (vkCreatePipelineLayout(device, &pipelineLayoutInfo, nullptr,
&pipelineLayout) != VK_SUCCESS) {
9 throw std::runtime_error("failed to create pipeline layout!");
10 }
The structure also specifies push constants, which are another way of passing
dynamic values to shaders that we may get into in a future chapter. The pipeline
layout will be referenced throughout the program’s lifetime, so it should be
destroyed at the end:
1 void cleanup() {
2 vkDestroyPipelineLayout(device, pipelineLayout, nullptr);
3 ...
4 }
Conclusion
That’s it for all of the fixed-function state! It’s a lot of work to set all of this
up from scratch, but the advantage is that we’re now nearly fully aware of ev-
erything that is going on in the graphics pipeline! This reduces the chance of
running into unexpected behavior because the default state of certain compo-
nents is not what you expect.
There is however one more object to create before we can finally create the
graphics pipeline and that is a render pass.
C++ code / Vertex shader / Fragment shader
Render passes
Setup
Before we can finish creating the pipeline, we need to tell Vulkan about the
framebuffer attachments that will be used while rendering. We need to specify
how many color and depth buffers there will be, how many samples to use
for each of them and how their contents should be handled throughout the
rendering operations. All of this information is wrapped in a render pass object,
for which we’ll create a new createRenderPass function. Call this function
from initVulkan before createGraphicsPipeline.
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1 void initVulkan() {
2 createInstance();
3 setupDebugMessenger();
4 createSurface();
5 pickPhysicalDevice();
6 createLogicalDevice();
7 createSwapChain();
8 createImageViews();
9 createRenderPass();
10 createGraphicsPipeline();
11 }
12
13 ...
14
15 void createRenderPass() {
16
17 }
Attachment description
In our case we’ll have just a single color buffer attachment represented by one
of the images from the swap chain.
1 void createRenderPass() {
2 VkAttachmentDescription colorAttachment{};
3 colorAttachment.format = swapChainImageFormat;
4 colorAttachment.samples = VK_SAMPLE_COUNT_1_BIT;
5 }
The format of the color attachment should match the format of the swap chain
images, and we’re not doing anything with multisampling yet, so we’ll stick to
1 sample.
1 colorAttachment.loadOp = VK_ATTACHMENT_LOAD_OP_CLEAR;
2 colorAttachment.storeOp = VK_ATTACHMENT_STORE_OP_STORE;
The loadOp and storeOp determine what to do with the data in the attachment
before rendering and after rendering. We have the following choices for loadOp:
• VK_ATTACHMENT_LOAD_OP_LOAD: Preserve the existing contents of the at-
tachment
• VK_ATTACHMENT_LOAD_OP_CLEAR: Clear the values to a constant at the
start
• VK_ATTACHMENT_LOAD_OP_DONT_CARE: Existing contents are undefined;
we don’t care about them
In our case we’re going to use the clear operation to clear the framebuffer to
black before drawing a new frame. There are only two possibilities for the
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storeOp:
• VK_ATTACHMENT_STORE_OP_STORE: Rendered contents will be stored in
memory and can be read later
• VK_ATTACHMENT_STORE_OP_DONT_CARE: Contents of the framebuffer will
be undefined after the rendering operation
We’re interested in seeing the rendered triangle on the screen, so we’re going
with the store operation here.
1 colorAttachment.stencilLoadOp = VK_ATTACHMENT_LOAD_OP_DONT_CARE;
2 colorAttachment.stencilStoreOp = VK_ATTACHMENT_STORE_OP_DONT_CARE;
The loadOp and storeOp apply to color and depth data, and stencilLoadOp /
stencilStoreOp apply to stencil data. Our application won’t do anything with
the stencil buffer, so the results of loading and storing are irrelevant.
1 colorAttachment.initialLayout = VK_IMAGE_LAYOUT_UNDEFINED;
2 colorAttachment.finalLayout = VK_IMAGE_LAYOUT_PRESENT_SRC_KHR;
Textures and framebuffers in Vulkan are represented by VkImage objects with
a certain pixel format, however the layout of the pixels in memory can change
based on what you’re trying to do with an image.
Some of the most common layouts are:
• VK_IMAGE_LAYOUT_COLOR_ATTACHMENT_OPTIMAL: Images used as color at-
tachment
• VK_IMAGE_LAYOUT_PRESENT_SRC_KHR: Images to be presented in the swap
chain
• VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL: Images to be used as destina-
tion for a memory copy operation
We’ll discuss this topic in more depth in the texturing chapter, but what’s
important to know right now is that images need to be transitioned to specific
layouts that are suitable for the operation that they’re going to be involved in
next.
The initialLayout specifies which layout the image will have before the ren-
der pass begins. The finalLayout specifies the layout to automatically transi-
tion to when the render pass finishes. Using VK_IMAGE_LAYOUT_UNDEFINED for
initialLayout means that we don’t care what previous layout the image was
in. The caveat of this special value is that the contents of the image are not
guaranteed to be preserved, but that doesn’t matter since we’re going to clear it
anyway. We want the image to be ready for presentation using the swap chain
after rendering, which is why we use VK_IMAGE_LAYOUT_PRESENT_SRC_KHR as
finalLayout.
111
Subpasses and attachment references
A single render pass can consist of multiple subpasses. Subpasses are subsequent
rendering operations that depend on the contents of framebuffers in previous
passes, for example a sequence of post-processing effects that are applied one
after another. If you group these rendering operations into one render pass,
then Vulkan is able to reorder the operations and conserve memory bandwidth
for possibly better performance. For our very first triangle, however, we’ll stick
to a single subpass.
Every subpass references one or more of the attachments that we’ve described
using the structure in the previous sections. These references are themselves
VkAttachmentReference structs that look like this:
1 VkAttachmentReference colorAttachmentRef{};
2 colorAttachmentRef.attachment = 0;
3 colorAttachmentRef.layout = VK_IMAGE_LAYOUT_COLOR_ATTACHMENT_OPTIMAL;
The attachment parameter specifies which attachment to reference by its
index in the attachment descriptions array. Our array consists of a single
VkAttachmentDescription, so its index is 0. The layout specifies which
layout we would like the attachment to have during a subpass that uses this
reference. Vulkan will automatically transition the attachment to this layout
when the subpass is started. We intend to use the attachment to function as
a color buffer and the VK_IMAGE_LAYOUT_COLOR_ATTACHMENT_OPTIMAL layout
will give us the best performance, as its name implies.
The subpass is described using a VkSubpassDescription structure:
1 VkSubpassDescription subpass{};
2 subpass.pipelineBindPoint = VK_PIPELINE_BIND_POINT_GRAPHICS;
Vulkan may also support compute subpasses in the future, so we have to be
explicit about this being a graphics subpass. Next, we specify the reference to
the color attachment:
1 subpass.colorAttachmentCount = 1;
2 subpass.pColorAttachments = &colorAttachmentRef;
The index of the attachment in this array is directly referenced from the fragment
shader with the layout(location = 0)out vec4 outColor directive!
The following other types of attachments can be referenced by a subpass:
• pInputAttachments: Attachments that are read from a shader
• pResolveAttachments: Attachments used for multisampling color attach-
ments
• pDepthStencilAttachment: Attachment for depth and stencil data
• pPreserveAttachments: Attachments that are not used by this subpass,
but for which the data must be preserved
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Render pass
Now that the attachment and a basic subpass referencing it have been described,
we can create the render pass itself. Create a new class member variable to hold
the VkRenderPass object right above the pipelineLayout variable:
1 VkRenderPass renderPass;
2 VkPipelineLayout pipelineLayout;
The render pass object can then be created by filling in the VkRenderPassCreateInfo
structure with an array of attachments and subpasses. The VkAttachmentReference
objects reference attachments using the indices of this array.
1 VkRenderPassCreateInfo renderPassInfo{};
2 renderPassInfo.sType = VK_STRUCTURE_TYPE_RENDER_PASS_CREATE_INFO;
3 renderPassInfo.attachmentCount = 1;
4 renderPassInfo.pAttachments = &colorAttachment;
5 renderPassInfo.subpassCount = 1;
6 renderPassInfo.pSubpasses = &subpass;
7
8 if (vkCreateRenderPass(device, &renderPassInfo, nullptr,
&renderPass) != VK_SUCCESS) {
9 throw std::runtime_error("failed to create render pass!");
10 }
Just like the pipeline layout, the render pass will be referenced throughout the
program, so it should only be cleaned up at the end:
1 void cleanup() {
2 vkDestroyPipelineLayout(device, pipelineLayout, nullptr);
3 vkDestroyRenderPass(device, renderPass, nullptr);
4 ...
5 }
That was a lot of work, but in the next chapter it all comes together to finally
create the graphics pipeline object!
C++ code / Vertex shader / Fragment shader
Conclusion
We can now combine all of the structures and objects from the previous chapters
to create the graphics pipeline! Here’s the types of objects we have now, as a
quick recap:
• Shader stages: the shader modules that define the functionality of the
programmable stages of the graphics pipeline
• Fixed-function state: all of the structures that define the fixed-function
stages of the pipeline, like input assembly, rasterizer, viewport and color
blending
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• Pipeline layout: the uniform and push values referenced by the shader
that can be updated at draw time
• Render pass: the attachments referenced by the pipeline stages and their
usage
All of these combined fully define the functionality of the graphics pipeline,
so we can now begin filling in the VkGraphicsPipelineCreateInfo structure
at the end of the createGraphicsPipeline function. But before the calls to
vkDestroyShaderModule because these are still to be used during the creation.
1 VkGraphicsPipelineCreateInfo pipelineInfo{};
2 pipelineInfo.sType = VK_STRUCTURE_TYPE_GRAPHICS_PIPELINE_CREATE_INFO;
3 pipelineInfo.stageCount = 2;
4 pipelineInfo.pStages = shaderStages;
We start by referencing the array of VkPipelineShaderStageCreateInfo
structs.
1 pipelineInfo.pVertexInputState = &vertexInputInfo;
2 pipelineInfo.pInputAssemblyState = &inputAssembly;
3 pipelineInfo.pViewportState = &viewportState;
4 pipelineInfo.pRasterizationState = &rasterizer;
5 pipelineInfo.pMultisampleState = &multisampling;
6 pipelineInfo.pDepthStencilState = nullptr; // Optional
7 pipelineInfo.pColorBlendState = &colorBlending;
8 pipelineInfo.pDynamicState = &dynamicState;
Then we reference all of the structures describing the fixed-function stage.
1 pipelineInfo.layout = pipelineLayout;
After that comes the pipeline layout, which is a Vulkan handle rather than a
struct pointer.
1 pipelineInfo.renderPass = renderPass;
2 pipelineInfo.subpass = 0;
And finally we have the reference to the render pass and the index of the sub pass
where this graphics pipeline will be used. It is also possible to use other render
passes with this pipeline instead of this specific instance, but they have to be
compatible with renderPass. The requirements for compatibility are described
here, but we won’t be using that feature in this tutorial.
1 pipelineInfo.basePipelineHandle = VK_NULL_HANDLE; // Optional
2 pipelineInfo.basePipelineIndex = -1; // Optional
There are actually two more parameters: basePipelineHandle and
basePipelineIndex. Vulkan allows you to create a new graphics pipeline by
deriving from an existing pipeline. The idea of pipeline derivatives is that
114
it is less expensive to set up pipelines when they have much functionality in
common with an existing pipeline and switching between pipelines from the
same parent can also be done quicker. You can either specify the handle of an
existing pipeline with basePipelineHandle or reference another pipeline that
is about to be created by index with basePipelineIndex. Right now there is
only a single pipeline, so we’ll simply specify a null handle and an invalid index.
These values are only used if the VK_PIPELINE_CREATE_DERIVATIVE_BIT flag
is also specified in the flags field of VkGraphicsPipelineCreateInfo.
Now prepare for the final step by creating a class member to hold the
VkPipeline object:
1 VkPipeline graphicsPipeline;
And finally create the graphics pipeline:
1 if (vkCreateGraphicsPipelines(device, VK_NULL_HANDLE, 1,
&pipelineInfo, nullptr, &graphicsPipeline) != VK_SUCCESS) {
2 throw std::runtime_error("failed to create graphics pipeline!");
3 }
The vkCreateGraphicsPipelines function actually has more parameters than
the usual object creation functions in Vulkan. It is designed to take multiple
VkGraphicsPipelineCreateInfo objects and create multiple VkPipeline ob-
jects in a single call.
The second parameter, for which we’ve passed the VK_NULL_HANDLE argument,
references an optional VkPipelineCache object. A pipeline cache can be used
to store and reuse data relevant to pipeline creation across multiple calls to
vkCreateGraphicsPipelines and even across program executions if the cache
is stored to a file. This makes it possible to significantly speed up pipeline
creation at a later time. We’ll get into this in the pipeline cache chapter.
The graphics pipeline is required for all common drawing operations, so it should
also only be destroyed at the end of the program:
1 void cleanup() {
2 vkDestroyPipeline(device, graphicsPipeline, nullptr);
3 vkDestroyPipelineLayout(device, pipelineLayout, nullptr);
4 ...
5 }
Now run your program to confirm that all this hard work has resulted in a suc-
cessful pipeline creation! We are already getting quite close to seeing something
pop up on the screen. In the next couple of chapters we’ll set up the actual
framebuffers from the swap chain images and prepare the drawing commands.
C++ code / Vertex shader / Fragment shader
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Drawing
Framebuffers
We’ve talked a lot about framebuffers in the past few chapters and we’ve set
up the render pass to expect a single framebuffer with the same format as the
swap chain images, but we haven’t actually created any yet.
The attachments specified during render pass creation are bound by wrapping
them into a VkFramebuffer object. A framebuffer object references all of the
VkImageView objects that represent the attachments. In our case that will be
only a single one: the color attachment. However, the image that we have to
use for the attachment depends on which image the swap chain returns when we
retrieve one for presentation. That means that we have to create a framebuffer
for all of the images in the swap chain and use the one that corresponds to the
retrieved image at drawing time.
To that end, create another std::vector class member to hold the framebuffers:
1 std::vector<VkFramebuffer> swapChainFramebuffers;
We’ll create the objects for this array in a new function createFramebuffers
that is called from initVulkan right after creating the graphics pipeline:
1 void initVulkan() {
2 createInstance();
3 setupDebugMessenger();
4 createSurface();
5 pickPhysicalDevice();
6 createLogicalDevice();
7 createSwapChain();
8 createImageViews();
9 createRenderPass();
10 createGraphicsPipeline();
11 createFramebuffers();
12 }
13
14 ...
15
16 void createFramebuffers() {
17
18 }
Start by resizing the container to hold all of the framebuffers:
1 void createFramebuffers() {
2 swapChainFramebuffers.resize(swapChainImageViews.size());
3 }
116
We’ll then iterate through the image views and create framebuffers from them:
1 for (size_t i = 0; i < swapChainImageViews.size(); i++) {
2 VkImageView attachments[] = {
3 swapChainImageViews[i]
4 };
5
6 VkFramebufferCreateInfo framebufferInfo{};
7 framebufferInfo.sType =
VK_STRUCTURE_TYPE_FRAMEBUFFER_CREATE_INFO;
8 framebufferInfo.renderPass = renderPass;
9 framebufferInfo.attachmentCount = 1;
10 framebufferInfo.pAttachments = attachments;
11 framebufferInfo.width = swapChainExtent.width;
12 framebufferInfo.height = swapChainExtent.height;
13 framebufferInfo.layers = 1;
14
15 if (vkCreateFramebuffer(device, &framebufferInfo, nullptr,
&swapChainFramebuffers[i]) != VK_SUCCESS) {
16 throw std::runtime_error("failed to create framebuffer!");
17 }
18 }
As you can see, creation of framebuffers is quite straightforward. We first need
to specify with which renderPass the framebuffer needs to be compatible. You
can only use a framebuffer with the render passes that it is compatible with,
which roughly means that they use the same number and type of attachments.
The attachmentCount and pAttachments parameters specify the VkImageView
objects that should be bound to the respective attachment descriptions in the
render pass pAttachment array.
The width and height parameters are self-explanatory and layers refers to
the number of layers in image arrays. Our swap chain images are single images,
so the number of layers is 1.
We should delete the framebuffers before the image views and render pass that
they are based on, but only after we’ve finished rendering:
1 void cleanup() {
2 for (auto framebuffer : swapChainFramebuffers) {
3 vkDestroyFramebuffer(device, framebuffer, nullptr);
4 }
5
6 ...
7 }
We’ve now reached the milestone where we have all of the objects that are
117
required for rendering. In the next chapter we’re going to write the first actual
drawing commands.
C++ code / Vertex shader / Fragment shader
Command buffers
Commands in Vulkan, like drawing operations and memory transfers, are not
executed directly using function calls. You have to record all of the operations
you want to perform in command buffer objects. The advantage of this is
that when we are ready to tell the Vulkan what we want to do, all of the
commands are submitted together and Vulkan can more efficiently process the
commands since all of them are available together. In addition, this allows
command recording to happen in multiple threads if so desired.
Command pools
We have to create a command pool before we can create command buffers.
Command pools manage the memory that is used to store the buffers and com-
mand buffers are allocated from them. Add a new class member to store a
VkCommandPool:
1 VkCommandPool commandPool;
Then create a new function createCommandPool and call it from initVulkan
after the framebuffers were created.
1 void initVulkan() {
2 createInstance();
3 setupDebugMessenger();
4 createSurface();
5 pickPhysicalDevice();
6 createLogicalDevice();
7 createSwapChain();
8 createImageViews();
9 createRenderPass();
10 createGraphicsPipeline();
11 createFramebuffers();
12 createCommandPool();
13 }
14
15 ...
16
17 void createCommandPool() {
18
19 }
Command pool creation only takes two parameters:
118
1 QueueFamilyIndices queueFamilyIndices =
findQueueFamilies(physicalDevice);
2
3 VkCommandPoolCreateInfo poolInfo{};
4 poolInfo.sType = VK_STRUCTURE_TYPE_COMMAND_POOL_CREATE_INFO;
5 poolInfo.flags = VK_COMMAND_POOL_CREATE_RESET_COMMAND_BUFFER_BIT;
6 poolInfo.queueFamilyIndex =
queueFamilyIndices.graphicsFamily.value();
There are two possible flags for command pools:
• VK_COMMAND_POOL_CREATE_TRANSIENT_BIT: Hint that command buffers
are rerecorded with new commands very often (may change memory allo-
cation behavior)
• VK_COMMAND_POOL_CREATE_RESET_COMMAND_BUFFER_BIT: Allow com-
mand buffers to be rerecorded individually, without this flag they all have
to be reset together
We will be recording a command buffer every frame, so we want to be able to re-
set and rerecord over it. Thus, we need to set the VK_COMMAND_POOL_CREATE_RESET_COMMAND_BUFFER_BIT
flag bit for our command pool.
Command buffers are executed by submitting them on one of the device queues,
like the graphics and presentation queues we retrieved. Each command pool
can only allocate command buffers that are submitted on a single type of queue.
We’re going to record commands for drawing, which is why we’ve chosen the
graphics queue family.
1 if (vkCreateCommandPool(device, &poolInfo, nullptr, &commandPool) !=
VK_SUCCESS) {
2 throw std::runtime_error("failed to create command pool!");
3 }
Finish creating the command pool using the vkCreateCommandPool function. It
doesn’t have any special parameters. Commands will be used throughout the
program to draw things on the screen, so the pool should only be destroyed at
the end:
1 void cleanup() {
2 vkDestroyCommandPool(device, commandPool, nullptr);
3
4 ...
5 }
Command buffer allocation
We can now start allocating command buffers.
119
Create a VkCommandBuffer object as a class member. Command buffers will be
automatically freed when their command pool is destroyed, so we don’t need
explicit cleanup.
1 VkCommandBuffer commandBuffer;
We’ll now start working on a createCommandBuffer function to allocate a single
command buffer from the command pool.
1 void initVulkan() {
2 createInstance();
3 setupDebugMessenger();
4 createSurface();
5 pickPhysicalDevice();
6 createLogicalDevice();
7 createSwapChain();
8 createImageViews();
9 createRenderPass();
10 createGraphicsPipeline();
11 createFramebuffers();
12 createCommandPool();
13 createCommandBuffer();
14 }
15
16 ...
17
18 void createCommandBuffer() {
19
20 }
Command buffers are allocated with the vkAllocateCommandBuffers function,
which takes a VkCommandBufferAllocateInfo struct as parameter that specifies
the command pool and number of buffers to allocate:
1 VkCommandBufferAllocateInfo allocInfo{};
2 allocInfo.sType = VK_STRUCTURE_TYPE_COMMAND_BUFFER_ALLOCATE_INFO;
3 allocInfo.commandPool = commandPool;
4 allocInfo.level = VK_COMMAND_BUFFER_LEVEL_PRIMARY;
5 allocInfo.commandBufferCount = 1;
6
7 if (vkAllocateCommandBuffers(device, &allocInfo, &commandBuffer) !=
VK_SUCCESS) {
8 throw std::runtime_error("failed to allocate command buffers!");
9 }
The level parameter specifies if the allocated command buffers are primary or
secondary command buffers.
120
• VK_COMMAND_BUFFER_LEVEL_PRIMARY: Can be submitted to a queue for
execution, but cannot be called from other command buffers.
• VK_COMMAND_BUFFER_LEVEL_SECONDARY: Cannot be submitted directly,
but can be called from primary command buffers.
We won’t make use of the secondary command buffer functionality here, but
you can imagine that it’s helpful to reuse common operations from primary
command buffers.
Since we are only allocating one command buffer, the commandBufferCount
parameter is just one.
Command buffer recording
We’ll now start working on the recordCommandBuffer function that writes the
commands we want to execute into a command buffer. The VkCommandBuffer
used will be passed in as a parameter, as well as the index of the current
swapchain image we want to write to.
1 void recordCommandBuffer(VkCommandBuffer commandBuffer, uint32_t
imageIndex) {
2
3 }
We always begin recording a command buffer by calling vkBeginCommandBuffer
with a small VkCommandBufferBeginInfo structure as argument that specifies
some details about the usage of this specific command buffer.
1 VkCommandBufferBeginInfo beginInfo{};
2 beginInfo.sType = VK_STRUCTURE_TYPE_COMMAND_BUFFER_BEGIN_INFO;
3 beginInfo.flags = 0; // Optional
4 beginInfo.pInheritanceInfo = nullptr; // Optional
5
6 if (vkBeginCommandBuffer(commandBuffer, &beginInfo) != VK_SUCCESS) {
7 throw std::runtime_error("failed to begin recording command
buffer!");
8 }
The flags parameter specifies how we’re going to use the command buffer. The
following values are available:
• VK_COMMAND_BUFFER_USAGE_ONE_TIME_SUBMIT_BIT: The command
buffer will be rerecorded right after executing it once.
• VK_COMMAND_BUFFER_USAGE_RENDER_PASS_CONTINUE_BIT: This is a sec-
ondary command buffer that will be entirely within a single render pass.
• VK_COMMAND_BUFFER_USAGE_SIMULTANEOUS_USE_BIT: The command
buffer can be resubmitted while it is also already pending execution.
None of these flags are applicable for us right now.
121
The pInheritanceInfo parameter is only relevant for secondary command
buffers. It specifies which state to inherit from the calling primary command
buffers.
If the command buffer was already recorded once, then a call to vkBeginCommandBuffer
will implicitly reset it. It’s not possible to append commands to a buffer at a
later time.
Starting a render pass
Drawing starts by beginning the render pass with vkCmdBeginRenderPass. The
render pass is configured using some parameters in a VkRenderPassBeginInfo
struct.
1 VkRenderPassBeginInfo renderPassInfo{};
2 renderPassInfo.sType = VK_STRUCTURE_TYPE_RENDER_PASS_BEGIN_INFO;
3 renderPassInfo.renderPass = renderPass;
4 renderPassInfo.framebuffer = swapChainFramebuffers[imageIndex];
The first parameters are the render pass itself and the attachments to bind. We
created a framebuffer for each swap chain image where it is specified as a color
attachment. Thus we need to bind the framebuffer for the swapchain image we
want to draw to. Using the imageIndex parameter which was passed in, we can
pick the right framebuffer for the current swapchain image.
1 renderPassInfo.renderArea.offset = {0, 0};
2 renderPassInfo.renderArea.extent = swapChainExtent;
The next two parameters define the size of the render area. The render area
defines where shader loads and stores will take place. The pixels outside this
region will have undefined values. It should match the size of the attachments
for best performance.
1 VkClearValue clearColor = {{{0.0f, 0.0f, 0.0f, 1.0f}}};
2 renderPassInfo.clearValueCount = 1;
3 renderPassInfo.pClearValues = &clearColor;
The last two parameters define the clear values to use for VK_ATTACHMENT_LOAD_OP_CLEAR,
which we used as load operation for the color attachment. I’ve defined the clear
color to simply be black with 100% opacity.
1 vkCmdBeginRenderPass(commandBuffer, &renderPassInfo,
VK_SUBPASS_CONTENTS_INLINE);
The render pass can now begin. All of the functions that record commands can
be recognized by their vkCmd prefix. They all return void, so there will be no
error handling until we’ve finished recording.
The first parameter for every command is always the command buffer to record
the command to. The second parameter specifies the details of the render pass
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we’ve just provided. The final parameter controls how the drawing commands
within the render pass will be provided. It can have one of two values:
• VK_SUBPASS_CONTENTS_INLINE: The render pass commands will be em-
bedded in the primary command buffer itself and no secondary command
buffers will be executed.
• VK_SUBPASS_CONTENTS_SECONDARY_COMMAND_BUFFERS: The render pass
commands will be executed from secondary command buffers.
We will not be using secondary command buffers, so we’ll go with the first
option.
Basic drawing commands
We can now bind the graphics pipeline:
1 vkCmdBindPipeline(commandBuffer, VK_PIPELINE_BIND_POINT_GRAPHICS,
graphicsPipeline);
The second parameter specifies if the pipeline object is a graphics or compute
pipeline. We’ve now told Vulkan which operations to execute in the graphics
pipeline and which attachment to use in the fragment shader.
As noted in the fixed functions chapter, we did specify viewport and scissor
state for this pipeline to be dynamic. So we need to set them in the command
buffer before issuing our draw command:
1 VkViewport viewport{};
2 viewport.x = 0.0f;
3 viewport.y = 0.0f;
4 viewport.width = static_cast<float>(swapChainExtent.width);
5 viewport.height = static_cast<float>(swapChainExtent.height);
6 viewport.minDepth = 0.0f;
7 viewport.maxDepth = 1.0f;
8 vkCmdSetViewport(commandBuffer, 0, 1, &viewport);
9
10 VkRect2D scissor{};
11 scissor.offset = {0, 0};
12 scissor.extent = swapChainExtent;
13 vkCmdSetScissor(commandBuffer, 0, 1, &scissor);
Now we are ready to issue the draw command for the triangle:
1 vkCmdDraw(commandBuffer, 3, 1, 0, 0);
The actual vkCmdDraw function is a bit anticlimactic, but it’s so simple because
of all the information we specified in advance. It has the following parameters,
aside from the command buffer:
123
• vertexCount: Even though we don’t have a vertex buffer, we technically
still have 3 vertices to draw.
• instanceCount: Used for instanced rendering, use 1 if you’re not doing
that.
• firstVertex: Used as an offset into the vertex buffer, defines the lowest
value of gl_VertexIndex.
• firstInstance: Used as an offset for instanced rendering, defines the
lowest value of gl_InstanceIndex.
Finishing up
The render pass can now be ended:
1 vkCmdEndRenderPass(commandBuffer);
And we’ve finished recording the command buffer:
1 if (vkEndCommandBuffer(commandBuffer) != VK_SUCCESS) {
2 throw std::runtime_error("failed to record command buffer!");
3 }
In the next chapter we’ll write the code for the main loop, which will acquire an
image from the swap chain, record and execute a command buffer, then return
the finished image to the swap chain.
C++ code / Vertex shader / Fragment shader
Rendering and presentation
This is the chapter where everything is going to come together. We’re going
to write the drawFrame function that will be called from the main loop to put
the triangle on the screen. Let’s start by creating the function and call it from
mainLoop:
1 void mainLoop() {
2 while (!glfwWindowShouldClose(window)) {
3 glfwPollEvents();
4 drawFrame();
5 }
6 }
7
8 ...
9
10 void drawFrame() {
11
12 }
124
Outline of a frame
At a high level, rendering a frame in Vulkan consists of a common set of steps:
• Wait for the previous frame to finish
• Acquire an image from the swap chain
• Record a command buffer which draws the scene onto that image
• Submit the recorded command buffer
• Present the swap chain image
While we will expand the drawing function in later chapters, for now this is the
core of our render loop.
Synchronization
A core design philosophy in Vulkan is that synchronization of execution on the
GPU is explicit. The order of operations is up to us to define using various
synchronization primitives which tell the driver the order we want things to
run in. This means that many Vulkan API calls which start executing work on
the GPU are asynchronous, the functions will return before the operation has
finished.
In this chapter there are a number of events that we need to order explicitly
because they happen on the GPU, such as:
• Acquire an image from the swap chain
• Execute commands that draw onto the acquired image
• Present that image to the screen for presentation, returning it to the
swapchain
Each of these events is set in motion using a single function call, but are all
executed asynchronously. The function calls will return before the operations
are actually finished and the order of execution is also undefined. That is un-
fortunate, because each of the operations depends on the previous one finishing.
Thus we need to explore which primitives we can use to achieve the desired
ordering.
Semaphores A semaphore is used to add order between queue operations.
Queue operations refer to the work we submit to a queue, either in a command
buffer or from within a function as we will see later. Examples of queues are
the graphics queue and the presentation queue. Semaphores are used both to
order work inside the same queue and between different queues.
There happens to be two kinds of semaphores in Vulkan, binary and timeline.
Because only binary semaphores will be used in this tutorial, we will not discuss
timeline semaphores. Further mention of the term semaphore exclusively refers
to binary semaphores.
A semaphore is either unsignaled or signaled. It begins life as unsignaled.
The way we use a semaphore to order queue operations is by providing the
125
same semaphore as a ‘signal’ semaphore in one queue operation and as a ‘wait’
semaphore in another queue operation. For example, lets say we have semaphore
S and queue operations A and B that we want to execute in order. What we
tell Vulkan is that operation A will ‘signal’ semaphore S when it finishes exe-
cuting, and operation B will ‘wait’ on semaphore S before it begins executing.
When operation A finishes, semaphore S will be signaled, while operation B
wont start until S is signaled. After operation B begins executing, semaphore S
is automatically reset back to being unsignaled, allowing it to be used again.
Pseudo-code of what was just described:
1 VkCommandBuffer A, B = ... // record command buffers
2 VkSemaphore S = ... // create a semaphore
3
4 // enqueue A, signal S when done - starts executing immediately
5 vkQueueSubmit(work: A, signal: S, wait: None)
6
7 // enqueue B, wait on S to start
8 vkQueueSubmit(work: B, signal: None, wait: S)
Note that in this code snippet, both calls to vkQueueSubmit() return imme-
diately - the waiting only happens on the GPU. The CPU continues running
without blocking. To make the CPU wait, we need a different synchronization
primitive, which we will now describe.
Fences A fence has a similar purpose, in that it is used to synchronize exe-
cution, but it is for ordering the execution on the CPU, otherwise known as
the host. Simply put, if the host needs to know when the GPU has finished
something, we use a fence.
Similar to semaphores, fences are either in a signaled or unsignaled state. When-
ever we submit work to execute, we can attach a fence to that work. When the
work is finished, the fence will be signaled. Then we can make the host wait
for the fence to be signaled, guaranteeing that the work has finished before the
host continues.
A concrete example is taking a screenshot. Say we have already done the neces-
sary work on the GPU. Now need to transfer the image from the GPU over to
the host and then save the memory to a file. We have command buffer A which
executes the transfer and fence F. We submit command buffer A with fence F,
then immediately tell the host to wait for F to signal. This causes the host to
block until command buffer A finishes execution. Thus we are safe to let the
host save the file to disk, as the memory transfer has completed.
Pseudo-code for what was described:
1 VkCommandBuffer A = ... // record command buffer with the transfer
2 VkFence F = ... // create the fence
3
126
4 // enqueue A, start work immediately, signal F when done
5 vkQueueSubmit(work: A, fence: F)
6
7 vkWaitForFence(F) // blocks execution until A has finished executing
8
9 save_screenshot_to_disk() // can't run until the transfer has
finished
Unlike the semaphore example, this example does block host execution. This
means the host won’t do anything except wait until execution has finished. For
this case, we had to make sure the transfer was complete before we could save
the screenshot to disk.
In general, it is preferable to not block the host unless necessary. We want
to feed the GPU and the host with useful work to do. Waiting on fences to
signal is not useful work. Thus we prefer semaphores, or other synchronization
primitives not yet covered, to synchronize our work.
Fences must be reset manually to put them back into the unsignaled state. This
is because fences are used to control the execution of the host, and so the host
gets to decide when to reset the fence. Contrast this to semaphores which are
used to order work on the GPU without the host being involved.
In summary, semaphores are used to specify the execution order of operations
on the GPU while fences are used to keep the CPU and GPU in sync with
each-other.
What to choose? We have two synchronization primitives to use and conve-
niently two places to apply synchronization: Swapchain operations and waiting
for the previous frame to finish. We want to use semaphores for swapchain
operations because they happen on the GPU, thus we don’t want to make the
host wait around if we can help it. For waiting on the previous frame to finish,
we want to use fences for the opposite reason, because we need the host to wait.
This is so we don’t draw more than one frame at a time. Because we re-record
the command buffer every frame, we cannot record the next frame’s work to
the command buffer until the current frame has finished executing, as we don’t
want to overwrite the current contents of the command buffer while the GPU
is using it.
Creating the synchronization objects
We’ll need one semaphore to signal that an image has been acquired from the
swapchain and is ready for rendering, another one to signal that rendering has
finished and presentation can happen, and a fence to make sure only one frame
is rendering at a time.
Create three class members to store these semaphore objects and fence object:
127
1 VkSemaphore imageAvailableSemaphore;
2 VkSemaphore renderFinishedSemaphore;
3 VkFence inFlightFence;
To create the semaphores, we’ll add the last create function for this part of the
tutorial: createSyncObjects:
1 void initVulkan() {
2 createInstance();
3 setupDebugMessenger();
4 createSurface();
5 pickPhysicalDevice();
6 createLogicalDevice();
7 createSwapChain();
8 createImageViews();
9 createRenderPass();
10 createGraphicsPipeline();
11 createFramebuffers();
12 createCommandPool();
13 createCommandBuffer();
14 createSyncObjects();
15 }
16
17 ...
18
19 void createSyncObjects() {
20
21 }
Creating semaphores requires filling in the VkSemaphoreCreateInfo, but in the
current version of the API it doesn’t actually have any required fields besides
sType:
1 void createSyncObjects() {
2 VkSemaphoreCreateInfo semaphoreInfo{};
3 semaphoreInfo.sType = VK_STRUCTURE_TYPE_SEMAPHORE_CREATE_INFO;
4 }
Future versions of the Vulkan API or extensions may add functionality for the
flags and pNext parameters like it does for the other structures.
Creating a fence requires filling in the VkFenceCreateInfo:
1 VkFenceCreateInfo fenceInfo{};
2 fenceInfo.sType = VK_STRUCTURE_TYPE_FENCE_CREATE_INFO;
Creating the semaphores and fence follows the familiar pattern with
vkCreateSemaphore & vkCreateFence:
128
1 if (vkCreateSemaphore(device, &semaphoreInfo, nullptr,
&imageAvailableSemaphore) != VK_SUCCESS ||
2 vkCreateSemaphore(device, &semaphoreInfo, nullptr,
&renderFinishedSemaphore) != VK_SUCCESS ||
3 vkCreateFence(device, &fenceInfo, nullptr, &inFlightFence) !=
VK_SUCCESS) {
4 throw std::runtime_error("failed to create semaphores!");
5 }
The semaphores and fence should be cleaned up at the end of the program, when
all commands have finished and no more synchronization is necessary:
1 void cleanup() {
2 vkDestroySemaphore(device, imageAvailableSemaphore, nullptr);
3 vkDestroySemaphore(device, renderFinishedSemaphore, nullptr);
4 vkDestroyFence(device, inFlightFence, nullptr);
Onto the main drawing function!
Waiting for the previous frame
At the start of the frame, we want to wait until the previous frame has finished,
so that the command buffer and semaphores are available to use. To do that,
we call vkWaitForFences:
1 void drawFrame() {
2 vkWaitForFences(device, 1, &inFlightFence, VK_TRUE, UINT64_MAX);
3 }
The vkWaitForFences function takes an array of fences and waits on the host
for either any or all of the fences to be signaled before returning. The VK_TRUE
we pass here indicates that we want to wait for all fences, but in the case of a
single one it doesn’t matter. This function also has a timeout parameter that
we set to the maximum value of a 64 bit unsigned integer, UINT64_MAX, which
effectively disables the timeout.
After waiting, we need to manually reset the fence to the unsignaled state with
the vkResetFences call:
1 vkResetFences(device, 1, &inFlightFence);
Before we can proceed, there is a slight hiccup in our design. On the first
frame we call drawFrame(), which immediately waits on inFlightFence to be
signaled. inFlightFence is only signaled after a frame has finished rendering,
yet since this is the first frame, there are no previous frames in which to signal
the fence! Thus vkWaitForFences() blocks indefinitely, waiting on something
which will never happen.
129
Of the many solutions to this dilemma, there is a clever workaround built
into the API. Create the fence in the signaled state, so that the first call to
vkWaitForFences() returns immediately since the fence is already signaled.
To do this, we add the VK_FENCE_CREATE_SIGNALED_BIT flag to the
VkFenceCreateInfo:
1 void createSyncObjects() {
2 ...
3
4 VkFenceCreateInfo fenceInfo{};
5 fenceInfo.sType = VK_STRUCTURE_TYPE_FENCE_CREATE_INFO;
6 fenceInfo.flags = VK_FENCE_CREATE_SIGNALED_BIT;
7
8 ...
9 }
Acquiring an image from the swap chain
The next thing we need to do in the drawFrame function is acquire an image
from the swap chain. Recall that the swap chain is an extension feature, so we
must use a function with the vk*KHR naming convention:
1 void drawFrame() {
2 uint32_t imageIndex;
3 vkAcquireNextImageKHR(device, swapChain, UINT64_MAX,
imageAvailableSemaphore, VK_NULL_HANDLE, &imageIndex);
4 }
The first two parameters of vkAcquireNextImageKHR are the logical device and
the swap chain from which we wish to acquire an image. The third parameter
specifies a timeout in nanoseconds for an image to become available. Using the
maximum value of a 64 bit unsigned integer means we effectively disable the
timeout.
The next two parameters specify synchronization objects that are to be signaled
when the presentation engine is finished using the image. That’s the point in
time where we can start drawing to it. It is possible to specify a semaphore, fence
or both. We’re going to use our imageAvailableSemaphore for that purpose
here.
The last parameter specifies a variable to output the index of the swap
chain image that has become available. The index refers to the VkImage
in our swapChainImages array. We’re going to use that index to pick the
VkFrameBuffer.
130
Recording the command buffer
With the imageIndex specifying the swap chain image to use in hand, we can
now record the command buffer. First, we call vkResetCommandBuffer on the
command buffer to make sure it is able to be recorded.
1 vkResetCommandBuffer(commandBuffer, 0);
The second parameter of vkResetCommandBuffer is a VkCommandBufferResetFlagBits
flag. Since we don’t want to do anything special, we leave it as 0.
Now call the function recordCommandBuffer to record the commands we want.
1 recordCommandBuffer(commandBuffer, imageIndex);
With a fully recorded command buffer, we can now submit it.
Submitting the command buffer
Queue submission and synchronization is configured through parameters in the
VkSubmitInfo structure.
1 VkSubmitInfo submitInfo{};
2 submitInfo.sType = VK_STRUCTURE_TYPE_SUBMIT_INFO;
3
4 VkSemaphore waitSemaphores[] = {imageAvailableSemaphore};
5 VkPipelineStageFlags waitStages[] =
{VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT};
6 submitInfo.waitSemaphoreCount = 1;
7 submitInfo.pWaitSemaphores = waitSemaphores;
8 submitInfo.pWaitDstStageMask = waitStages;
The first three parameters specify which semaphores to wait on before execution
begins and in which stage(s) of the pipeline to wait. We want to wait with
writing colors to the image until it’s available, so we’re specifying the stage of
the graphics pipeline that writes to the color attachment. That means that
theoretically the implementation can already start executing our vertex shader
and such while the image is not yet available. Each entry in the waitStages
array corresponds to the semaphore with the same index in pWaitSemaphores.
1 submitInfo.commandBufferCount = 1;
2 submitInfo.pCommandBuffers = &commandBuffer;
The next two parameters specify which command buffers to actually submit for
execution. We simply submit the single command buffer we have.
1 VkSemaphore signalSemaphores[] = {renderFinishedSemaphore};
2 submitInfo.signalSemaphoreCount = 1;
3 submitInfo.pSignalSemaphores = signalSemaphores;
131
The signalSemaphoreCount and pSignalSemaphores parameters specify which
semaphores to signal once the command buffer(s) have finished execution. In
our case we’re using the renderFinishedSemaphore for that purpose.
1 if (vkQueueSubmit(graphicsQueue, 1, &submitInfo, inFlightFence) !=
VK_SUCCESS) {
2 throw std::runtime_error("failed to submit draw command
buffer!");
3 }
We can now submit the command buffer to the graphics queue using
vkQueueSubmit. The function takes an array of VkSubmitInfo structures as
argument for efficiency when the workload is much larger. The last parameter
references an optional fence that will be signaled when the command buffers
finish execution. This allows us to know when it is safe for the command buffer
to be reused, thus we want to give it inFlightFence. Now on the next frame,
the CPU will wait for this command buffer to finish executing before it records
new commands into it.
Subpass dependencies
Remember that the subpasses in a render pass automatically take care of image
layout transitions. These transitions are controlled by subpass dependencies,
which specify memory and execution dependencies between subpasses. We have
only a single subpass right now, but the operations right before and right after
this subpass also count as implicit “subpasses”.
There are two built-in dependencies that take care of the transition at
the start of the render pass and at the end of the render pass, but the
former does not occur at the right time. It assumes that the transi-
tion occurs at the start of the pipeline, but we haven’t acquired the
image yet at that point! There are two ways to deal with this problem.
We could change the waitStages for the imageAvailableSemaphore to
VK_PIPELINE_STAGE_TOP_OF_PIPE_BIT to ensure that the render passes don’t
begin until the image is available, or we can make the render pass wait for the
VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT stage. I’ve decided to
go with the second option here, because it’s a good excuse to have a look at
subpass dependencies and how they work.
Subpass dependencies are specified in VkSubpassDependency structs. Go to the
createRenderPass function and add one:
1 VkSubpassDependency dependency{};
2 dependency.srcSubpass = VK_SUBPASS_EXTERNAL;
3 dependency.dstSubpass = 0;
The first two fields specify the indices of the dependency and the dependent sub-
pass. The special value VK_SUBPASS_EXTERNAL refers to the implicit subpass be-
fore or after the render pass depending on whether it is specified in srcSubpass
132
or dstSubpass. The index 0 refers to our subpass, which is the first and only
one. The dstSubpass must always be higher than srcSubpass to prevent cycles
in the dependency graph (unless one of the subpasses is VK_SUBPASS_EXTERNAL).
1 dependency.srcStageMask =
VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT;
2 dependency.srcAccessMask = 0;
The next two fields specify the operations to wait on and the stages in which
these operations occur. We need to wait for the swap chain to finish reading
from the image before we can access it. This can be accomplished by waiting
on the color attachment output stage itself.
1 dependency.dstStageMask =
VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT;
2 dependency.dstAccessMask = VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT;
The operations that should wait on this are in the color attachment stage and
involve the writing of the color attachment. These settings will prevent the
transition from happening until it’s actually necessary (and allowed): when we
want to start writing colors to it.
1 renderPassInfo.dependencyCount = 1;
2 renderPassInfo.pDependencies = &dependency;
The VkRenderPassCreateInfo struct has two fields to specify an array of de-
pendencies.
Presentation
The last step of drawing a frame is submitting the result back to the swap chain
to have it eventually show up on the screen. Presentation is configured through
a VkPresentInfoKHR structure at the end of the drawFrame function.
1 VkPresentInfoKHR presentInfo{};
2 presentInfo.sType = VK_STRUCTURE_TYPE_PRESENT_INFO_KHR;
3
4 presentInfo.waitSemaphoreCount = 1;
5 presentInfo.pWaitSemaphores = signalSemaphores;
The first two parameters specify which semaphores to wait on before presenta-
tion can happen, just like VkSubmitInfo. Since we want to wait on the command
buffer to finish execution, thus our triangle being drawn, we take the semaphores
which will be signalled and wait on them, thus we use signalSemaphores.
1 VkSwapchainKHR swapChains[] = {swapChain};
2 presentInfo.swapchainCount = 1;
3 presentInfo.pSwapchains = swapChains;
4 presentInfo.pImageIndices = &imageIndex;
133
The next two parameters specify the swap chains to present images to and the
index of the image for each swap chain. This will almost always be a single one.
1 presentInfo.pResults = nullptr; // Optional
There is one last optional parameter called pResults. It allows you to specify
an array of VkResult values to check for every individual swap chain if presen-
tation was successful. It’s not necessary if you’re only using a single swap chain,
because you can simply use the return value of the present function.
1 vkQueuePresentKHR(presentQueue, &presentInfo);
The vkQueuePresentKHR function submits the request to present an image to
the swap chain. We’ll add error handling for both vkAcquireNextImageKHR
and vkQueuePresentKHR in the next chapter, because their failure does not
necessarily mean that the program should terminate, unlike the functions we’ve
seen so far.
If you did everything correctly up to this point, then you should now see some-
thing resembling the following when you run your program:
This colored triangle may look a bit different from the one you’re
used to seeing in graphics tutorials. That’s because this tutorial lets
the shader interpolate in linear color space and converts to sRGB
134
color space afterwards. See this blog post for a discussion of the
difference.
Yay! Unfortunately, you’ll see that when validation layers are enabled, the
program crashes as soon as you close it. The messages printed to the terminal
from debugCallback tell us why:
Remember that all of the operations in drawFrame are asynchronous. That
means that when we exit the loop in mainLoop, drawing and presentation oper-
ations may still be going on. Cleaning up resources while that is happening is
a bad idea.
To fix that problem, we should wait for the logical device to finish operations
before exiting mainLoop and destroying the window:
1 void mainLoop() {
2 while (!glfwWindowShouldClose(window)) {
3 glfwPollEvents();
4 drawFrame();
5 }
6
7 vkDeviceWaitIdle(device);
8 }
You can also wait for operations in a specific command queue to be finished
with vkQueueWaitIdle. These functions can be used as a very rudimentary
way to perform synchronization. You’ll see that the program now exits without
problems when closing the window.
Conclusion
A little over 900 lines of code later, we’ve finally gotten to the stage of seeing
something pop up on the screen! Bootstrapping a Vulkan program is definitely
a lot of work, but the take-away message is that Vulkan gives you an immense
amount of control through its explicitness. I recommend you to take some time
now to reread the code and build a mental model of the purpose of all of the
Vulkan objects in the program and how they relate to each other. We’ll be
building on top of that knowledge to extend the functionality of the program
from this point on.
The next chapter will expand the render loop to handle multiple frames in flight.
C++ code / Vertex shader / Fragment shader
135
Frames in flight
Frames in flight
Right now our render loop has one glaring flaw. We are required to wait on the
previous frame to finish before we can start rendering the next which results in
unnecessary idling of the host.
The way to fix this is to allow multiple frames to be in-flight at once, that
is to say, allow the rendering of one frame to not interfere with the recording
of the next. How do we do this? Any resource that is accessed and modified
during rendering must be duplicated. Thus, we need multiple command buffers,
semaphores, and fences. In later chapters we will also add multiple instances of
other resources, so we will see this concept reappear.
Start by adding a constant at the top of the program that defines how many
frames should be processed concurrently:
1 const int MAX_FRAMES_IN_FLIGHT = 2;
We choose the number 2 because we don’t want the CPU to get too far ahead
of the GPU. With 2 frames in flight, the CPU and the GPU can be working
on their own tasks at the same time. If the CPU finishes early, it will wait
till the GPU finishes rendering before submitting more work. With 3 or more
frames in flight, the CPU could get ahead of the GPU, adding frames of latency.
Generally, extra latency isn’t desired. But giving the application control over
the number of frames in flight is another example of Vulkan being explicit.
Each frame should have its own command buffer, set of semaphores, and fence.
Rename and then change them to be std::vectors of the objects:
1 std::vector<VkCommandBuffer> commandBuffers;
2
3 ...
4
5 std::vector<VkSemaphore> imageAvailableSemaphores;
6 std::vector<VkSemaphore> renderFinishedSemaphores;
7 std::vector<VkFence> inFlightFences;
Then we need to create multiple command buffers. Rename createCommandBuffer
to createCommandBuffers. Next we need to resize the command buffers vector
to the size of MAX_FRAMES_IN_FLIGHT, alter the VkCommandBufferAllocateInfo
to contain that many command buffers, and then change the destination to our
vector of command buffers:
1 void createCommandBuffers() {
2 commandBuffers.resize(MAX_FRAMES_IN_FLIGHT);
3 ...
4 allocInfo.commandBufferCount = (uint32_t) commandBuffers.size();
5
136
6 if (vkAllocateCommandBuffers(device, &allocInfo,
commandBuffers.data()) != VK_SUCCESS) {
7 throw std::runtime_error("failed to allocate command
buffers!");
8 }
9 }
The createSyncObjects function should be changed to create all of the objects:
1 void createSyncObjects() {
2 imageAvailableSemaphores.resize(MAX_FRAMES_IN_FLIGHT);
3 renderFinishedSemaphores.resize(MAX_FRAMES_IN_FLIGHT);
4 inFlightFences.resize(MAX_FRAMES_IN_FLIGHT);
5
6 VkSemaphoreCreateInfo semaphoreInfo{};
7 semaphoreInfo.sType = VK_STRUCTURE_TYPE_SEMAPHORE_CREATE_INFO;
8
9 VkFenceCreateInfo fenceInfo{};
10 fenceInfo.sType = VK_STRUCTURE_TYPE_FENCE_CREATE_INFO;
11 fenceInfo.flags = VK_FENCE_CREATE_SIGNALED_BIT;
12
13 for (size_t i = 0; i < MAX_FRAMES_IN_FLIGHT; i++) {
14 if (vkCreateSemaphore(device, &semaphoreInfo, nullptr,
&imageAvailableSemaphores[i]) != VK_SUCCESS ||
15 vkCreateSemaphore(device, &semaphoreInfo, nullptr,
&renderFinishedSemaphores[i]) != VK_SUCCESS ||
16 vkCreateFence(device, &fenceInfo, nullptr,
&inFlightFences[i]) != VK_SUCCESS) {
17
18 throw std::runtime_error("failed to create
synchronization objects for a frame!");
19 }
20 }
21 }
Similarly, they should also all be cleaned up:
1 void cleanup() {
2 for (size_t i = 0; i < MAX_FRAMES_IN_FLIGHT; i++) {
3 vkDestroySemaphore(device, renderFinishedSemaphores[i],
nullptr);
4 vkDestroySemaphore(device, imageAvailableSemaphores[i],
nullptr);
5 vkDestroyFence(device, inFlightFences[i], nullptr);
6 }
7
8 ...
137
9 }
Remember, because command buffers are freed for us when we free the command
pool, there is nothing extra to do for command buffer cleanup.
To use the right objects every frame, we need to keep track of the current frame.
We will use a frame index for that purpose:
1 uint32_t currentFrame = 0;
The drawFrame function can now be modified to use the right objects:
1 void drawFrame() {
2 vkWaitForFences(device, 1, &inFlightFences[currentFrame],
VK_TRUE, UINT64_MAX);
3 vkResetFences(device, 1, &inFlightFences[currentFrame]);
4
5 vkAcquireNextImageKHR(device, swapChain, UINT64_MAX,
imageAvailableSemaphores[currentFrame], VK_NULL_HANDLE,
&imageIndex);
6
7 ...
8
9 vkResetCommandBuffer(commandBuffers[currentFrame], 0);
10 recordCommandBuffer(commandBuffers[currentFrame], imageIndex);
11
12 ...
13
14 submitInfo.pCommandBuffers = &commandBuffers[currentFrame];
15
16 ...
17
18 VkSemaphore waitSemaphores[] =
{imageAvailableSemaphores[currentFrame]};
19
20 ...
21
22 VkSemaphore signalSemaphores[] =
{renderFinishedSemaphores[currentFrame]};
23
24 ...
25
26 if (vkQueueSubmit(graphicsQueue, 1, &submitInfo,
inFlightFences[currentFrame]) != VK_SUCCESS) {
27 }
Of course, we shouldn’t forget to advance to the next frame every time:
138
1 void drawFrame() {
2 ...
3
4 currentFrame = (currentFrame + 1) % MAX_FRAMES_IN_FLIGHT;
5 }
By using the modulo (%) operator, we ensure that the frame index loops around
after every MAX_FRAMES_IN_FLIGHT enqueued frames.
We’ve now implemented all the needed synchronization to ensure that there
are no more than MAX_FRAMES_IN_FLIGHT frames of work enqueued and that
these frames are not stepping over eachother. Note that it is fine for other
parts of the code, like the final cleanup, to rely on more rough synchronization
like vkDeviceWaitIdle. You should decide on which approach to use based on
performance requirements.
To learn more about synchronization through examples, have a look at this
extensive overview by Khronos.
In the next chapter we’ll deal with one more small thing that is required for a
well-behaved Vulkan program.
C++ code / Vertex shader / Fragment shader
Swap chain recreation
Introduction
The application we have now successfully draws a triangle, but there are some
circumstances that it isn’t handling properly yet. It is possible for the window
surface to change such that the swap chain is no longer compatible with it. One
of the reasons that could cause this to happen is the size of the window changing.
We have to catch these events and recreate the swap chain.
Recreating the swap chain
Create a new recreateSwapChain function that calls createSwapChain and all
of the creation functions for the objects that depend on the swap chain or the
window size.
1 void recreateSwapChain() {
2 vkDeviceWaitIdle(device);
3
4 createSwapChain();
5 createImageViews();
6 createFramebuffers();
7 }
139
We first call vkDeviceWaitIdle, because just like in the last chapter, we
shouldn’t touch resources that may still be in use. Obviously, we’ll have to
recreate the swap chain itself. The image views need to be recreated because
they are based directly on the swap chain images. Finally, the framebuffers
directly depend on the swap chain images, and thus must be recreated as well.
To make sure that the old versions of these objects are cleaned up before recre-
ating them, we should move some of the cleanup code to a separate func-
tion that we can call from the recreateSwapChain function. Let’s call it
cleanupSwapChain:
1 void cleanupSwapChain() {
2
3 }
4
5 void recreateSwapChain() {
6 vkDeviceWaitIdle(device);
7
8 cleanupSwapChain();
9
10 createSwapChain();
11 createImageViews();
12 createFramebuffers();
13 }
Note that we don’t recreate the renderpass here for simplicity. In theory it can
be possible for the swap chain image format to change during an applications’
lifetime, e.g. when moving a window from an standard range to an high dynamic
range monitor. This may require the application to recreate the renderpass to
make sure the change between dynamic ranges is properly reflected.
We’ll move the cleanup code of all objects that are recreated as part of a swap
chain refresh from cleanup to cleanupSwapChain:
1 void cleanupSwapChain() {
2 for (size_t i = 0; i < swapChainFramebuffers.size(); i++) {
3 vkDestroyFramebuffer(device, swapChainFramebuffers[i],
nullptr);
4 }
5
6 for (size_t i = 0; i < swapChainImageViews.size(); i++) {
7 vkDestroyImageView(device, swapChainImageViews[i], nullptr);
8 }
9
10 vkDestroySwapchainKHR(device, swapChain, nullptr);
11 }
12
13 void cleanup() {
140
14 cleanupSwapChain();
15
16 vkDestroyPipeline(device, graphicsPipeline, nullptr);
17 vkDestroyPipelineLayout(device, pipelineLayout, nullptr);
18
19 vkDestroyRenderPass(device, renderPass, nullptr);
20
21 for (size_t i = 0; i < MAX_FRAMES_IN_FLIGHT; i++) {
22 vkDestroySemaphore(device, renderFinishedSemaphores[i],
nullptr);
23 vkDestroySemaphore(device, imageAvailableSemaphores[i],
nullptr);
24 vkDestroyFence(device, inFlightFences[i], nullptr);
25 }
26
27 vkDestroyCommandPool(device, commandPool, nullptr);
28
29 vkDestroyDevice(device, nullptr);
30
31 if (enableValidationLayers) {
32 DestroyDebugUtilsMessengerEXT(instance, debugMessenger,
nullptr);
33 }
34
35 vkDestroySurfaceKHR(instance, surface, nullptr);
36 vkDestroyInstance(instance, nullptr);
37
38 glfwDestroyWindow(window);
39
40 glfwTerminate();
41 }
Note that in chooseSwapExtent we already query the new window resolution
to make sure that the swap chain images have the (new) right size, so there’s
no need to modify chooseSwapExtent (remember that we already had to use
glfwGetFramebufferSize get the resolution of the surface in pixels when cre-
ating the swap chain).
That’s all it takes to recreate the swap chain! However, the disadvantage of this
approach is that we need to stop all rendering before creating the new swap
chain. It is possible to create a new swap chain while drawing commands on an
image from the old swap chain are still in-flight. You need to pass the previous
swap chain to the oldSwapChain field in the VkSwapchainCreateInfoKHR struct
and destroy the old swap chain as soon as you’ve finished using it.
141
Suboptimal or out-of-date swap chain
Now we just need to figure out when swap chain recreation is necessary and
call our new recreateSwapChain function. Luckily, Vulkan will usually just
tell us that the swap chain is no longer adequate during presentation. The
vkAcquireNextImageKHR and vkQueuePresentKHR functions can return the fol-
lowing special values to indicate this.
• VK_ERROR_OUT_OF_DATE_KHR: The swap chain has become incompatible
with the surface and can no longer be used for rendering. Usually happens
after a window resize.
• VK_SUBOPTIMAL_KHR: The swap chain can still be used to successfully
present to the surface, but the surface properties are no longer matched
exactly.
1 VkResult result = vkAcquireNextImageKHR(device, swapChain,
UINT64_MAX, imageAvailableSemaphores[currentFrame],
VK_NULL_HANDLE, &imageIndex);
2
3 if (result == VK_ERROR_OUT_OF_DATE_KHR) {
4 recreateSwapChain();
5 return;
6 } else if (result != VK_SUCCESS && result != VK_SUBOPTIMAL_KHR) {
7 throw std::runtime_error("failed to acquire swap chain image!");
8 }
If the swap chain turns out to be out of date when attempting to acquire an
image, then it is no longer possible to present to it. Therefore we should imme-
diately recreate the swap chain and try again in the next drawFrame call.
You could also decide to do that if the swap chain is suboptimal, but I’ve chosen
to proceed anyway in that case because we’ve already acquired an image. Both
VK_SUCCESS and VK_SUBOPTIMAL_KHR are considered “success” return codes.
1 result = vkQueuePresentKHR(presentQueue, &presentInfo);
2
3 if (result == VK_ERROR_OUT_OF_DATE_KHR || result ==
VK_SUBOPTIMAL_KHR) {
4 recreateSwapChain();
5 } else if (result != VK_SUCCESS) {
6 throw std::runtime_error("failed to present swap chain image!");
7 }
8
9 currentFrame = (currentFrame + 1) % MAX_FRAMES_IN_FLIGHT;
The vkQueuePresentKHR function returns the same values with the same mean-
ing. In this case we will also recreate the swap chain if it is suboptimal, because
we want the best possible result.
142
Fixing a deadlock
If we try to run the code now, it is possible to encounter a deadlock. De-
bugging the code, we find that the application reaches vkWaitForFences but
never continues past it. This is because when vkAcquireNextImageKHR returns
VK_ERROR_OUT_OF_DATE_KHR, we recreate the swapchain and then return from
drawFrame. But before that happens, the current frame’s fence was waited upon
and reset. Since we return immediately, no work is submitted for execution and
the fence will never be signaled, causing vkWaitForFences to halt forever.
There is a simple fix thankfully. Delay resetting the fence until after we know
for sure we will be submitting work with it. Thus, if we return early, the fence
is still signaled and vkWaitForFences wont deadlock the next time we use the
same fence object.
The beginning of drawFrame should now look like this:
1 vkWaitForFences(device, 1, &inFlightFences[currentFrame], VK_TRUE,
UINT64_MAX);
2
3 uint32_t imageIndex;
4 VkResult result = vkAcquireNextImageKHR(device, swapChain,
UINT64_MAX, imageAvailableSemaphores[currentFrame],
VK_NULL_HANDLE, &imageIndex);
5
6 if (result == VK_ERROR_OUT_OF_DATE_KHR) {
7 recreateSwapChain();
8 return;
9 } else if (result != VK_SUCCESS && result != VK_SUBOPTIMAL_KHR) {
10 throw std::runtime_error("failed to acquire swap chain image!");
11 }
12
13 // Only reset the fence if we are submitting work
14 vkResetFences(device, 1, &inFlightFences[currentFrame]);
Handling resizes explicitly
Although many drivers and platforms trigger VK_ERROR_OUT_OF_DATE_KHR au-
tomatically after a window resize, it is not guaranteed to happen. That’s why
we’ll add some extra code to also handle resizes explicitly. First add a new
member variable that flags that a resize has happened:
1 std::vector<VkFence> inFlightFences;
2
3 bool framebufferResized = false;
The drawFrame function should then be modified to also check for this flag:
143
1 if (result == VK_ERROR_OUT_OF_DATE_KHR || result ==
VK_SUBOPTIMAL_KHR || framebufferResized) {
2 framebufferResized = false;
3 recreateSwapChain();
4 } else if (result != VK_SUCCESS) {
5 ...
6 }
It is important to do this after vkQueuePresentKHR to ensure that the
semaphores are in a consistent state, otherwise a signaled semaphore may
never be properly waited upon. Now to actually detect resizes we can use the
glfwSetFramebufferSizeCallback function in the GLFW framework to set
up a callback:
1 void initWindow() {
2 glfwInit();
3
4 glfwWindowHint(GLFW_CLIENT_API, GLFW_NO_API);
5
6 window = glfwCreateWindow(WIDTH, HEIGHT, "Vulkan", nullptr,
nullptr);
7 glfwSetFramebufferSizeCallback(window,
framebufferResizeCallback);
8 }
9
10 static void framebufferResizeCallback(GLFWwindow* window, int width,
int height) {
11
12 }
The reason that we’re creating a static function as a callback is because GLFW
does not know how to properly call a member function with the right this
pointer to our HelloTriangleApplication instance.
However, we do get a reference to the GLFWwindow in the callback and there is
another GLFW function that allows you to store an arbitrary pointer inside of
it: glfwSetWindowUserPointer:
1 window = glfwCreateWindow(WIDTH, HEIGHT, "Vulkan", nullptr, nullptr);
2 glfwSetWindowUserPointer(window, this);
3 glfwSetFramebufferSizeCallback(window, framebufferResizeCallback);
This value can now be retrieved from within the callback with glfwGetWindowUserPointer
to properly set the flag:
1 static void framebufferResizeCallback(GLFWwindow* window, int width,
int height) {
144
2 auto app =
reinterpret_cast<HelloTriangleApplication*>(glfwGetWindowUserPointer(window));
3 app->framebufferResized = true;
4 }
Now try to run the program and resize the window to see if the framebuffer is
indeed resized properly with the window.
Handling minimization
There is another case where a swap chain may become out of date and that is
a special kind of window resizing: window minimization. This case is special
because it will result in a frame buffer size of 0. In this tutorial we will handle
that by pausing until the window is in the foreground again by extending the
recreateSwapChain function:
1 void recreateSwapChain() {
2 int width = 0, height = 0;
3 glfwGetFramebufferSize(window, &width, &height);
4 while (width == 0 || height == 0) {
5 glfwGetFramebufferSize(window, &width, &height);
6 glfwWaitEvents();
7 }
8
9 vkDeviceWaitIdle(device);
10
11 ...
12 }
The initial call to glfwGetFramebufferSize handles the case where the size is
already correct and glfwWaitEvents would have nothing to wait on.
Congratulations, you’ve now finished your very first well-behaved Vulkan pro-
gram! In the next chapter we’re going to get rid of the hardcoded vertices in
the vertex shader and actually use a vertex buffer.
C++ code / Vertex shader / Fragment shader
145
Vertex buffers
Vertex input description
Introduction
In the next few chapters, we’re going to replace the hardcoded vertex data in
the vertex shader with a vertex buffer in memory. We’ll start with the easiest
approach of creating a CPU visible buffer and using memcpy to copy the vertex
data into it directly, and after that we’ll see how to use a staging buffer to copy
the vertex data to high performance memory.
Vertex shader
First change the vertex shader to no longer include the vertex data in the shader
code itself. The vertex shader takes input from a vertex buffer using the in
keyword.
1 #version 450
2
3 layout(location = 0) in vec2 inPosition;
4 layout(location = 1) in vec3 inColor;
5
6 layout(location = 0) out vec3 fragColor;
7
8 void main() {
9 gl_Position = vec4(inPosition, 0.0, 1.0);
10 fragColor = inColor;
11 }
The inPosition and inColor variables are vertex attributes. They’re properties
that are specified per-vertex in the vertex buffer, just like we manually specified
a position and color per vertex using the two arrays. Make sure to recompile
the vertex shader!
Just like fragColor, the layout(location = x) annotations assign indices to
the inputs that we can later use to reference them. It is important to know that
146
some types, like dvec3 64 bit vectors, use multiple slots. That means that the
index after it must be at least 2 higher:
1 layout(location = 0) in dvec3 inPosition;
2 layout(location = 2) in vec3 inColor;
You can find more info about the layout qualifier in the OpenGL wiki.
Vertex data
We’re moving the vertex data from the shader code to an array in the code of
our program. Start by including the GLM library, which provides us with linear
algebra related types like vectors and matrices. We’re going to use these types
to specify the position and color vectors.
1 #include <glm/glm.hpp>
Create a new structure called Vertex with the two attributes that we’re going
to use in the vertex shader inside it:
1 struct Vertex {
2 glm::vec2 pos;
3 glm::vec3 color;
4 };
GLM conveniently provides us with C++ types that exactly match the vector
types used in the shader language.
1 const std::vector<Vertex> vertices = {
2 {{0.0f, -0.5f}, {1.0f, 0.0f, 0.0f}},
3 {{0.5f, 0.5f}, {0.0f, 1.0f, 0.0f}},
4 {{-0.5f, 0.5f}, {0.0f, 0.0f, 1.0f}}
5 };
Now use the Vertex structure to specify an array of vertex data. We’re using
exactly the same position and color values as before, but now they’re combined
into one array of vertices. This is known as interleaving vertex attributes.
Binding descriptions
The next step is to tell Vulkan how to pass this data format to the vertex shader
once it’s been uploaded into GPU memory. There are two types of structures
needed to convey this information.
The first structure is VkVertexInputBindingDescription and we’ll add a mem-
ber function to the Vertex struct to populate it with the right data.
1 struct Vertex {
2 glm::vec2 pos;
147
3 glm::vec3 color;
4
5 static VkVertexInputBindingDescription getBindingDescription() {
6 VkVertexInputBindingDescription bindingDescription{};
7
8 return bindingDescription;
9 }
10 };
A vertex binding describes at which rate to load data from memory throughout
the vertices. It specifies the number of bytes between data entries and whether
to move to the next data entry after each vertex or after each instance.
1 VkVertexInputBindingDescription bindingDescription{};
2 bindingDescription.binding = 0;
3 bindingDescription.stride = sizeof(Vertex);
4 bindingDescription.inputRate = VK_VERTEX_INPUT_RATE_VERTEX;
All of our per-vertex data is packed together in one array, so we’re only going
to have one binding. The binding parameter specifies the index of the binding
in the array of bindings. The stride parameter specifies the number of bytes
from one entry to the next, and the inputRate parameter can have one of the
following values:
• VK_VERTEX_INPUT_RATE_VERTEX: Move to the next data entry after each
vertex
• VK_VERTEX_INPUT_RATE_INSTANCE: Move to the next data entry after
each instance
We’re not going to use instanced rendering, so we’ll stick to per-vertex data.
Attribute descriptions
The second structure that describes how to handle vertex input is
VkVertexInputAttributeDescription. We’re going to add another helper
function to Vertex to fill in these structs.
1 #include <array>
2
3 ...
4
5 static std::array<VkVertexInputAttributeDescription, 2>
getAttributeDescriptions() {
6 std::array<VkVertexInputAttributeDescription, 2>
attributeDescriptions{};
7
8 return attributeDescriptions;
9 }
148
As the function prototype indicates, there are going to be two of these structures.
An attribute description struct describes how to extract a vertex attribute from
a chunk of vertex data originating from a binding description. We have two
attributes, position and color, so we need two attribute description structs.
1 attributeDescriptions[0].binding = 0;
2 attributeDescriptions[0].location = 0;
3 attributeDescriptions[0].format = VK_FORMAT_R32G32_SFLOAT;
4 attributeDescriptions[0].offset = offsetof(Vertex, pos);
The binding parameter tells Vulkan from which binding the per-vertex data
comes. The location parameter references the location directive of the input
in the vertex shader. The input in the vertex shader with location 0 is the
position, which has two 32-bit float components.
The format parameter describes the type of data for the attribute. A bit con-
fusingly, the formats are specified using the same enumeration as color formats.
The following shader types and formats are commonly used together:
• float: VK_FORMAT_R32_SFLOAT
• vec2: VK_FORMAT_R32G32_SFLOAT
• vec3: VK_FORMAT_R32G32B32_SFLOAT
• vec4: VK_FORMAT_R32G32B32A32_SFLOAT
As you can see, you should use the format where the amount of color channels
matches the number of components in the shader data type. It is allowed to
use more channels than the number of components in the shader, but they will
be silently discarded. If the number of channels is lower than the number of
components, then the BGA components will use default values of (0, 0, 1).
The color type (SFLOAT, UINT, SINT) and bit width should also match the type
of the shader input. See the following examples:
• ivec2: VK_FORMAT_R32G32_SINT, a 2-component vector of 32-bit signed
integers
• uvec4: VK_FORMAT_R32G32B32A32_UINT, a 4-component vector of 32-bit
unsigned integers
• double: VK_FORMAT_R64_SFLOAT, a double-precision (64-bit) float
The format parameter implicitly defines the byte size of attribute data and the
offset parameter specifies the number of bytes since the start of the per-vertex
data to read from. The binding is loading one Vertex at a time and the position
attribute (pos) is at an offset of 0 bytes from the beginning of this struct. This
is automatically calculated using the offsetof macro.
1 attributeDescriptions[1].binding = 0;
2 attributeDescriptions[1].location = 1;
3 attributeDescriptions[1].format = VK_FORMAT_R32G32B32_SFLOAT;
4 attributeDescriptions[1].offset = offsetof(Vertex, color);
The color attribute is described in much the same way.
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Pipeline vertex input
We now need to set up the graphics pipeline to accept vertex data in this
format by referencing the structures in createGraphicsPipeline. Find the
vertexInputInfo struct and modify it to reference the two descriptions:
1 auto bindingDescription = Vertex::getBindingDescription();
2 auto attributeDescriptions = Vertex::getAttributeDescriptions();
3
4 vertexInputInfo.vertexBindingDescriptionCount = 1;
5 vertexInputInfo.vertexAttributeDescriptionCount =
static_cast<uint32_t>(attributeDescriptions.size());
6 vertexInputInfo.pVertexBindingDescriptions = &bindingDescription;
7 vertexInputInfo.pVertexAttributeDescriptions =
attributeDescriptions.data();
The pipeline is now ready to accept vertex data in the format of the vertices
container and pass it on to our vertex shader. If you run the program now with
validation layers enabled, you’ll see that it complains that there is no vertex
buffer bound to the binding. The next step is to create a vertex buffer and
move the vertex data to it so the GPU is able to access it.
C++ code / Vertex shader / Fragment shader
Vertex buffer creation
Introduction
Buffers in Vulkan are regions of memory used for storing arbitrary data that can
be read by the graphics card. They can be used to store vertex data, which we’ll
do in this chapter, but they can also be used for many other purposes that we’ll
explore in future chapters. Unlike the Vulkan objects we’ve been dealing with
so far, buffers do not automatically allocate memory for themselves. The work
from the previous chapters has shown that the Vulkan API puts the programmer
in control of almost everything and memory management is one of those things.
Buffer creation
Create a new function createVertexBuffer and call it from initVulkan right
before createCommandBuffers.
1 void initVulkan() {
2 createInstance();
3 setupDebugMessenger();
4 createSurface();
5 pickPhysicalDevice();
6 createLogicalDevice();
7 createSwapChain();
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8 createImageViews();
9 createRenderPass();
10 createGraphicsPipeline();
11 createFramebuffers();
12 createCommandPool();
13 createVertexBuffer();
14 createCommandBuffers();
15 createSyncObjects();
16 }
17
18 ...
19
20 void createVertexBuffer() {
21
22 }
Creating a buffer requires us to fill a VkBufferCreateInfo structure.
1 VkBufferCreateInfo bufferInfo{};
2 bufferInfo.sType = VK_STRUCTURE_TYPE_BUFFER_CREATE_INFO;
3 bufferInfo.size = sizeof(vertices[0]) * vertices.size();
The first field of the struct is size, which specifies the size of the buffer in bytes.
Calculating the byte size of the vertex data is straightforward with sizeof.
1 bufferInfo.usage = VK_BUFFER_USAGE_VERTEX_BUFFER_BIT;
The second field is usage, which indicates for which purposes the data in the
buffer is going to be used. It is possible to specify multiple purposes using a
bitwise or. Our use case will be a vertex buffer, we’ll look at other types of
usage in future chapters.
1 bufferInfo.sharingMode = VK_SHARING_MODE_EXCLUSIVE;
Just like the images in the swap chain, buffers can also be owned by a specific
queue family or be shared between multiple at the same time. The buffer will
only be used from the graphics queue, so we can stick to exclusive access.
The flags parameter is used to configure sparse buffer memory, which is not
relevant right now. We’ll leave it at the default value of 0.
We can now create the buffer with vkCreateBuffer. Define a class member to
hold the buffer handle and call it vertexBuffer.
1 VkBuffer vertexBuffer;
2
3 ...
4
5 void createVertexBuffer() {
151
6 VkBufferCreateInfo bufferInfo{};
7 bufferInfo.sType = VK_STRUCTURE_TYPE_BUFFER_CREATE_INFO;
8 bufferInfo.size = sizeof(vertices[0]) * vertices.size();
9 bufferInfo.usage = VK_BUFFER_USAGE_VERTEX_BUFFER_BIT;
10 bufferInfo.sharingMode = VK_SHARING_MODE_EXCLUSIVE;
11
12 if (vkCreateBuffer(device, &bufferInfo, nullptr, &vertexBuffer)
!= VK_SUCCESS) {
13 throw std::runtime_error("failed to create vertex buffer!");
14 }
15 }
The buffer should be available for use in rendering commands until the end of
the program and it does not depend on the swap chain, so we’ll clean it up in
the original cleanup function:
1 void cleanup() {
2 cleanupSwapChain();
3
4 vkDestroyBuffer(device, vertexBuffer, nullptr);
5
6 ...
7 }
Memory requirements
The buffer has been created, but it doesn’t actually have any memory assigned to
it yet. The first step of allocating memory for the buffer is to query its memory
requirements using the aptly named vkGetBufferMemoryRequirements func-
tion.
1 VkMemoryRequirements memRequirements;
2 vkGetBufferMemoryRequirements(device, vertexBuffer,
&memRequirements);
The VkMemoryRequirements struct has three fields:
• size: The size of the required amount of memory in bytes, may differ
from bufferInfo.size.
• alignment: The offset in bytes where the buffer begins in the allocated re-
gion of memory, depends on bufferInfo.usage and bufferInfo.flags.
• memoryTypeBits: Bit field of the memory types that are suitable for the
buffer.
Graphics cards can offer different types of memory to allocate from. Each type of
memory varies in terms of allowed operations and performance characteristics.
We need to combine the requirements of the buffer and our own application
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requirements to find the right type of memory to use. Let’s create a new function
findMemoryType for this purpose.
1 uint32_t findMemoryType(uint32_t typeFilter, VkMemoryPropertyFlags
properties) {
2
3 }
First we need to query info about the available types of memory using
vkGetPhysicalDeviceMemoryProperties.
1 VkPhysicalDeviceMemoryProperties memProperties;
2 vkGetPhysicalDeviceMemoryProperties(physicalDevice, &memProperties);
The VkPhysicalDeviceMemoryProperties structure has two arrays
memoryTypes and memoryHeaps. Memory heaps are distinct memory re-
sources like dedicated VRAM and swap space in RAM for when VRAM runs
out. The different types of memory exist within these heaps. Right now we’ll
only concern ourselves with the type of memory and not the heap it comes
from, but you can imagine that this can affect performance.
Let’s first find a memory type that is suitable for the buffer itself:
1 for (uint32_t i = 0; i < memProperties.memoryTypeCount; i++) {
2 if (typeFilter & (1 << i)) {
3 return i;
4 }
5 }
6
7 throw std::runtime_error("failed to find suitable memory type!");
The typeFilter parameter will be used to specify the bit field of memory types
that are suitable. That means that we can find the index of a suitable memory
type by simply iterating over them and checking if the corresponding bit is set
to 1.
However, we’re not just interested in a memory type that is suitable for the
vertex buffer. We also need to be able to write our vertex data to that memory.
The memoryTypes array consists of VkMemoryType structs that specify the heap
and properties of each type of memory. The properties define special features
of the memory, like being able to map it so we can write to it from the CPU.
This property is indicated with VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT, but
we also need to use the VK_MEMORY_PROPERTY_HOST_COHERENT_BIT property.
We’ll see why when we map the memory.
We can now modify the loop to also check for the support of this property:
1 for (uint32_t i = 0; i < memProperties.memoryTypeCount; i++) {
153
2 if ((typeFilter & (1 << i)) &&
(memProperties.memoryTypes[i].propertyFlags & properties) ==
properties) {
3 return i;
4 }
5 }
We may have more than one desirable property, so we should check if the result
of the bitwise AND is not just non-zero, but equal to the desired properties bit
field. If there is a memory type suitable for the buffer that also has all of the
properties we need, then we return its index, otherwise we throw an exception.
Memory allocation
We now have a way to determine the right memory type, so we can actually
allocate the memory by filling in the VkMemoryAllocateInfo structure.
1 VkMemoryAllocateInfo allocInfo{};
2 allocInfo.sType = VK_STRUCTURE_TYPE_MEMORY_ALLOCATE_INFO;
3 allocInfo.allocationSize = memRequirements.size;
4 allocInfo.memoryTypeIndex =
findMemoryType(memRequirements.memoryTypeBits,
VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT |
VK_MEMORY_PROPERTY_HOST_COHERENT_BIT);
Memory allocation is now as simple as specifying the size and type, both of
which are derived from the memory requirements of the vertex buffer and the
desired property. Create a class member to store the handle to the memory and
allocate it with vkAllocateMemory.
1 VkBuffer vertexBuffer;
2 VkDeviceMemory vertexBufferMemory;
3
4 ...
5
6 if (vkAllocateMemory(device, &allocInfo, nullptr,
&vertexBufferMemory) != VK_SUCCESS) {
7 throw std::runtime_error("failed to allocate vertex buffer
memory!");
8 }
If memory allocation was successful, then we can now associate this memory
with the buffer using vkBindBufferMemory:
1 vkBindBufferMemory(device, vertexBuffer, vertexBufferMemory, 0);
The first three parameters are self-explanatory and the fourth parameter is the
offset within the region of memory. Since this memory is allocated specifically
154
for this the vertex buffer, the offset is simply 0. If the offset is non-zero, then it
is required to be divisible by memRequirements.alignment.
Of course, just like dynamic memory allocation in C++, the memory should be
freed at some point. Memory that is bound to a buffer object may be freed once
the buffer is no longer used, so let’s free it after the buffer has been destroyed:
1 void cleanup() {
2 cleanupSwapChain();
3
4 vkDestroyBuffer(device, vertexBuffer, nullptr);
5 vkFreeMemory(device, vertexBufferMemory, nullptr);
Filling the vertex buffer
It is now time to copy the vertex data to the buffer. This is done by mapping
the buffer memory into CPU accessible memory with vkMapMemory.
1 void* data;
2 vkMapMemory(device, vertexBufferMemory, 0, bufferInfo.size, 0,
&data);
This function allows us to access a region of the specified memory resource de-
fined by an offset and size. The offset and size here are 0 and bufferInfo.size,
respectively. It is also possible to specify the special value VK_WHOLE_SIZE to
map all of the memory. The second to last parameter can be used to specify
flags, but there aren’t any available yet in the current API. It must be set to the
value 0. The last parameter specifies the output for the pointer to the mapped
memory.
1 void* data;
2 vkMapMemory(device, vertexBufferMemory, 0, bufferInfo.size, 0,
&data);
3 memcpy(data, vertices.data(), (size_t) bufferInfo.size);
4 vkUnmapMemory(device, vertexBufferMemory);
You can now simply memcpy the vertex data to the mapped memory and unmap
it again using vkUnmapMemory. Unfortunately the driver may not immediately
copy the data into the buffer memory, for example because of caching. It is also
possible that writes to the buffer are not visible in the mapped memory yet.
There are two ways to deal with that problem:
• Use a memory heap that is host coherent, indicated with VK_MEMORY_PROPERTY_HOST_COHERENT_BIT
• Call vkFlushMappedMemoryRanges after writing to the mapped memory,
and call vkInvalidateMappedMemoryRanges before reading from the
mapped memory
We went for the first approach, which ensures that the mapped memory always
matches the contents of the allocated memory. Do keep in mind that this may
155
lead to slightly worse performance than explicit flushing, but we’ll see why that
doesn’t matter in the next chapter.
Flushing memory ranges or using a coherent memory heap means that the driver
will be aware of our writes to the buffer, but it doesn’t mean that they are
actually visible on the GPU yet. The transfer of data to the GPU is an operation
that happens in the background and the specification simply tells us that it is
guaranteed to be complete as of the next call to vkQueueSubmit.
Binding the vertex buffer
All that remains now is binding the vertex buffer during rendering operations.
We’re going to extend the recordCommandBuffer function to do that.
1 vkCmdBindPipeline(commandBuffer, VK_PIPELINE_BIND_POINT_GRAPHICS,
graphicsPipeline);
2
3 VkBuffer vertexBuffers[] = {vertexBuffer};
4 VkDeviceSize offsets[] = {0};
5 vkCmdBindVertexBuffers(commandBuffer, 0, 1, vertexBuffers, offsets);
6
7 vkCmdDraw(commandBuffer, static_cast<uint32_t>(vertices.size()), 1,
0, 0);
The vkCmdBindVertexBuffers function is used to bind vertex buffers to bind-
ings, like the one we set up in the previous chapter. The first two parameters,
besides the command buffer, specify the offset and number of bindings we’re
going to specify vertex buffers for. The last two parameters specify the array
of vertex buffers to bind and the byte offsets to start reading vertex data from.
You should also change the call to vkCmdDraw to pass the number of vertices in
the buffer as opposed to the hardcoded number 3.
Now run the program and you should see the familiar triangle again:
156
Try changing the color of the top vertex to white by modifying the vertices
array:
1 const std::vector<Vertex> vertices = {
2 {{0.0f, -0.5f}, {1.0f, 1.0f, 1.0f}},
3 {{0.5f, 0.5f}, {0.0f, 1.0f, 0.0f}},
4 {{-0.5f, 0.5f}, {0.0f, 0.0f, 1.0f}}
5 };
Run the program again and you should see the following:
157
In the next chapter we’ll look at a different way to copy vertex data to a vertex
buffer that results in better performance, but takes some more work.
C++ code / Vertex shader / Fragment shader
Staging buffer
Introduction
The vertex buffer we have right now works correctly, but the memory type that
allows us to access it from the CPU may not be the most optimal memory type
for the graphics card itself to read from. The most optimal memory has the
VK_MEMORY_PROPERTY_DEVICE_LOCAL_BIT flag and is usually not accessible by
the CPU on dedicated graphics cards. In this chapter we’re going to create
two vertex buffers. One staging buffer in CPU accessible memory to upload the
data from the vertex array to, and the final vertex buffer in device local memory.
We’ll then use a buffer copy command to move the data from the staging buffer
to the actual vertex buffer.
Transfer queue
The buffer copy command requires a queue family that supports transfer opera-
tions, which is indicated using VK_QUEUE_TRANSFER_BIT. The good news is that
158
any queue family with VK_QUEUE_GRAPHICS_BIT or VK_QUEUE_COMPUTE_BIT ca-
pabilities already implicitly support VK_QUEUE_TRANSFER_BIT operations. The
implementation is not required to explicitly list it in queueFlags in those cases.
If you like a challenge, then you can still try to use a different queue family
specifically for transfer operations. It will require you to make the following
modifications to your program:
• Modify QueueFamilyIndices and findQueueFamilies to explicitly look
for a queue family with the VK_QUEUE_TRANSFER_BIT bit, but not the
VK_QUEUE_GRAPHICS_BIT.
• Modify createLogicalDevice to request a handle to the transfer queue
• Create a second command pool for command buffers that are submitted
on the transfer queue family
• Change the sharingMode of resources to be VK_SHARING_MODE_CONCURRENT
and specify both the graphics and transfer queue families
• Submit any transfer commands like vkCmdCopyBuffer (which we’ll be
using in this chapter) to the transfer queue instead of the graphics queue
It’s a bit of work, but it’ll teach you a lot about how resources are shared
between queue families.
Abstracting buffer creation
Because we’re going to create multiple buffers in this chapter, it’s a good idea to
move buffer creation to a helper function. Create a new function createBuffer
and move the code in createVertexBuffer (except mapping) to it.
1 void createBuffer(VkDeviceSize size, VkBufferUsageFlags usage,
VkMemoryPropertyFlags properties, VkBuffer& buffer,
VkDeviceMemory& bufferMemory) {
2 VkBufferCreateInfo bufferInfo{};
3 bufferInfo.sType = VK_STRUCTURE_TYPE_BUFFER_CREATE_INFO;
4 bufferInfo.size = size;
5 bufferInfo.usage = usage;
6 bufferInfo.sharingMode = VK_SHARING_MODE_EXCLUSIVE;
7
8 if (vkCreateBuffer(device, &bufferInfo, nullptr, &buffer) !=
VK_SUCCESS) {
9 throw std::runtime_error("failed to create buffer!");
10 }
11
12 VkMemoryRequirements memRequirements;
13 vkGetBufferMemoryRequirements(device, buffer, &memRequirements);
14
15 VkMemoryAllocateInfo allocInfo{};
16 allocInfo.sType = VK_STRUCTURE_TYPE_MEMORY_ALLOCATE_INFO;
17 allocInfo.allocationSize = memRequirements.size;
159
18 allocInfo.memoryTypeIndex =
findMemoryType(memRequirements.memoryTypeBits, properties);
19
20 if (vkAllocateMemory(device, &allocInfo, nullptr, &bufferMemory)
!= VK_SUCCESS) {
21 throw std::runtime_error("failed to allocate buffer
memory!");
22 }
23
24 vkBindBufferMemory(device, buffer, bufferMemory, 0);
25 }
Make sure to add parameters for the buffer size, memory properties and usage
so that we can use this function to create many different types of buffers. The
last two parameters are output variables to write the handles to.
You can now remove the buffer creation and memory allocation code from
createVertexBuffer and just call createBuffer instead:
1 void createVertexBuffer() {
2 VkDeviceSize bufferSize = sizeof(vertices[0]) * vertices.size();
3 createBuffer(bufferSize, VK_BUFFER_USAGE_VERTEX_BUFFER_BIT,
VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT |
VK_MEMORY_PROPERTY_HOST_COHERENT_BIT, vertexBuffer,
vertexBufferMemory);
4
5 void* data;
6 vkMapMemory(device, vertexBufferMemory, 0, bufferSize, 0, &data);
7 memcpy(data, vertices.data(), (size_t) bufferSize);
8 vkUnmapMemory(device, vertexBufferMemory);
9 }
Run your program to make sure that the vertex buffer still works properly.
Using a staging buffer
We’re now going to change createVertexBuffer to only use a host visible buffer
as temporary buffer and use a device local one as actual vertex buffer.
1 void createVertexBuffer() {
2 VkDeviceSize bufferSize = sizeof(vertices[0]) * vertices.size();
3
4 VkBuffer stagingBuffer;
5 VkDeviceMemory stagingBufferMemory;
6 createBuffer(bufferSize, VK_BUFFER_USAGE_TRANSFER_SRC_BIT,
VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT |
VK_MEMORY_PROPERTY_HOST_COHERENT_BIT, stagingBuffer,
stagingBufferMemory);
160
7
8 void* data;
9 vkMapMemory(device, stagingBufferMemory, 0, bufferSize, 0,
&data);
10 memcpy(data, vertices.data(), (size_t) bufferSize);
11 vkUnmapMemory(device, stagingBufferMemory);
12
13 createBuffer(bufferSize, VK_BUFFER_USAGE_TRANSFER_DST_BIT |
VK_BUFFER_USAGE_VERTEX_BUFFER_BIT,
VK_MEMORY_PROPERTY_DEVICE_LOCAL_BIT, vertexBuffer,
vertexBufferMemory);
14 }
We’re now using a new stagingBuffer with stagingBufferMemory for mapping
and copying the vertex data. In this chapter we’re going to use two new buffer
usage flags:
• VK_BUFFER_USAGE_TRANSFER_SRC_BIT: Buffer can be used as source in a
memory transfer operation.
• VK_BUFFER_USAGE_TRANSFER_DST_BIT: Buffer can be used as destination
in a memory transfer operation.
The vertexBuffer is now allocated from a memory type that is device local,
which generally means that we’re not able to use vkMapMemory. However, we
can copy data from the stagingBuffer to the vertexBuffer. We have to
indicate that we intend to do that by specifying the transfer source flag for the
stagingBuffer and the transfer destination flag for the vertexBuffer, along
with the vertex buffer usage flag.
We’re now going to write a function to copy the contents from one buffer to
another, called copyBuffer.
1 void copyBuffer(VkBuffer srcBuffer, VkBuffer dstBuffer, VkDeviceSize
size) {
2
3 }
Memory transfer operations are executed using command buffers, just like draw-
ing commands. Therefore we must first allocate a temporary command buffer.
You may wish to create a separate command pool for these kinds of short-lived
buffers, because the implementation may be able to apply memory allocation
optimizations. You should use the VK_COMMAND_POOL_CREATE_TRANSIENT_BIT
flag during command pool generation in that case.
1 void copyBuffer(VkBuffer srcBuffer, VkBuffer dstBuffer, VkDeviceSize
size) {
2 VkCommandBufferAllocateInfo allocInfo{};
3 allocInfo.sType = VK_STRUCTURE_TYPE_COMMAND_BUFFER_ALLOCATE_INFO;
161
4 allocInfo.level = VK_COMMAND_BUFFER_LEVEL_PRIMARY;
5 allocInfo.commandPool = commandPool;
6 allocInfo.commandBufferCount = 1;
7
8 VkCommandBuffer commandBuffer;
9 vkAllocateCommandBuffers(device, &allocInfo, &commandBuffer);
10 }
And immediately start recording the command buffer:
1 VkCommandBufferBeginInfo beginInfo{};
2 beginInfo.sType = VK_STRUCTURE_TYPE_COMMAND_BUFFER_BEGIN_INFO;
3 beginInfo.flags = VK_COMMAND_BUFFER_USAGE_ONE_TIME_SUBMIT_BIT;
4
5 vkBeginCommandBuffer(commandBuffer, &beginInfo);
We’re only going to use the command buffer once and wait with re-
turning from the function until the copy operation has finished exe-
cuting. It’s good practice to tell the driver about our intent using
VK_COMMAND_BUFFER_USAGE_ONE_TIME_SUBMIT_BIT.
1 VkBufferCopy copyRegion{};
2 copyRegion.srcOffset = 0; // Optional
3 copyRegion.dstOffset = 0; // Optional
4 copyRegion.size = size;
5 vkCmdCopyBuffer(commandBuffer, srcBuffer, dstBuffer, 1, ©Region);
Contents of buffers are transferred using the vkCmdCopyBuffer command. It
takes the source and destination buffers as arguments, and an array of regions to
copy. The regions are defined in VkBufferCopy structs and consist of a source
buffer offset, destination buffer offset and size. It is not possible to specify
VK_WHOLE_SIZE here, unlike the vkMapMemory command.
1 vkEndCommandBuffer(commandBuffer);
This command buffer only contains the copy command, so we can stop recording
right after that. Now execute the command buffer to complete the transfer:
1 VkSubmitInfo submitInfo{};
2 submitInfo.sType = VK_STRUCTURE_TYPE_SUBMIT_INFO;
3 submitInfo.commandBufferCount = 1;
4 submitInfo.pCommandBuffers = &commandBuffer;
5
6 vkQueueSubmit(graphicsQueue, 1, &submitInfo, VK_NULL_HANDLE);
7 vkQueueWaitIdle(graphicsQueue);
Unlike the draw commands, there are no events we need to wait on this time.
We just want to execute the transfer on the buffers immediately. There are
162
again two possible ways to wait on this transfer to complete. We could use a
fence and wait with vkWaitForFences, or simply wait for the transfer queue
to become idle with vkQueueWaitIdle. A fence would allow you to schedule
multiple transfers simultaneously and wait for all of them complete, instead
of executing one at a time. That may give the driver more opportunities to
optimize.
1 vkFreeCommandBuffers(device, commandPool, 1, &commandBuffer);
Don’t forget to clean up the command buffer used for the transfer operation.
We can now call copyBuffer from the createVertexBuffer function to move
the vertex data to the device local buffer:
1 createBuffer(bufferSize, VK_BUFFER_USAGE_TRANSFER_DST_BIT |
VK_BUFFER_USAGE_VERTEX_BUFFER_BIT,
VK_MEMORY_PROPERTY_DEVICE_LOCAL_BIT, vertexBuffer,
vertexBufferMemory);
2
3 copyBuffer(stagingBuffer, vertexBuffer, bufferSize);
After copying the data from the staging buffer to the device buffer, we should
clean it up:
1 ...
2
3 copyBuffer(stagingBuffer, vertexBuffer, bufferSize);
4
5 vkDestroyBuffer(device, stagingBuffer, nullptr);
6 vkFreeMemory(device, stagingBufferMemory, nullptr);
7 }
Run your program to verify that you’re seeing the familiar triangle again. The
improvement may not be visible right now, but its vertex data is now being
loaded from high performance memory. This will matter when we’re going to
start rendering more complex geometry.
Conclusion
It should be noted that in a real world application, you’re not supposed
to actually call vkAllocateMemory for every individual buffer. The
maximum number of simultaneous memory allocations is limited by the
maxMemoryAllocationCount physical device limit, which may be as low as
4096 even on high end hardware like an NVIDIA GTX 1080. The right way to
allocate memory for a large number of objects at the same time is to create a
custom allocator that splits up a single allocation among many different objects
by using the offset parameters that we’ve seen in many functions.
163
You can either implement such an allocator yourself, or use the VulkanMem-
oryAllocator library provided by the GPUOpen initiative. However, for this
tutorial it’s okay to use a separate allocation for every resource, because we
won’t come close to hitting any of these limits for now.
C++ code / Vertex shader / Fragment shader
Index buffer
Introduction
The 3D meshes you’ll be rendering in a real world application will often share
vertices between multiple triangles. This already happens even with something
simple like drawing a rectangle:
Drawing a rectangle takes two triangles, which means that we need a vertex
buffer with 6 vertices. The problem is that the data of two vertices needs to be
duplicated resulting in 50% redundancy. It only gets worse with more complex
meshes, where vertices are reused in an average number of 3 triangles. The
solution to this problem is to use an index buffer.
An index buffer is essentially an array of pointers into the vertex buffer. It allows
you to reorder the vertex data, and reuse existing data for multiple vertices. The
illustration above demonstrates what the index buffer would look like for the
rectangle if we have a vertex buffer containing each of the four unique vertices.
The first three indices define the upper-right triangle and the last three indices
define the vertices for the bottom-left triangle.
164
Index buffer creation
In this chapter we’re going to modify the vertex data and add index data to
draw a rectangle like the one in the illustration. Modify the vertex data to
represent the four corners:
1 const std::vector<Vertex> vertices = {
2 {{-0.5f, -0.5f}, {1.0f, 0.0f, 0.0f}},
3 {{0.5f, -0.5f}, {0.0f, 1.0f, 0.0f}},
4 {{0.5f, 0.5f}, {0.0f, 0.0f, 1.0f}},
5 {{-0.5f, 0.5f}, {1.0f, 1.0f, 1.0f}}
6 };
The top-left corner is red, top-right is green, bottom-right is blue and the
bottom-left is white. We’ll add a new array indices to represent the contents
of the index buffer. It should match the indices in the illustration to draw the
upper-right triangle and bottom-left triangle.
1 const std::vector<uint16_t> indices = {
2 0, 1, 2, 2, 3, 0
3 };
It is possible to use either uint16_t or uint32_t for your index buffer depending
on the number of entries in vertices. We can stick to uint16_t for now because
we’re using less than 65535 unique vertices.
Just like the vertex data, the indices need to be uploaded into a VkBuffer for
the GPU to be able to access them. Define two new class members to hold the
resources for the index buffer:
1 VkBuffer vertexBuffer;
2 VkDeviceMemory vertexBufferMemory;
3 VkBuffer indexBuffer;
4 VkDeviceMemory indexBufferMemory;
The createIndexBuffer function that we’ll add now is almost identical to
createVertexBuffer:
1 void initVulkan() {
2 ...
3 createVertexBuffer();
4 createIndexBuffer();
5 ...
6 }
7
8 void createIndexBuffer() {
9 VkDeviceSize bufferSize = sizeof(indices[0]) * indices.size();
10
11 VkBuffer stagingBuffer;
165
12 VkDeviceMemory stagingBufferMemory;
13 createBuffer(bufferSize, VK_BUFFER_USAGE_TRANSFER_SRC_BIT,
VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT |
VK_MEMORY_PROPERTY_HOST_COHERENT_BIT, stagingBuffer,
stagingBufferMemory);
14
15 void* data;
16 vkMapMemory(device, stagingBufferMemory, 0, bufferSize, 0,
&data);
17 memcpy(data, indices.data(), (size_t) bufferSize);
18 vkUnmapMemory(device, stagingBufferMemory);
19
20 createBuffer(bufferSize, VK_BUFFER_USAGE_TRANSFER_DST_BIT |
VK_BUFFER_USAGE_INDEX_BUFFER_BIT,
VK_MEMORY_PROPERTY_DEVICE_LOCAL_BIT, indexBuffer,
indexBufferMemory);
21
22 copyBuffer(stagingBuffer, indexBuffer, bufferSize);
23
24 vkDestroyBuffer(device, stagingBuffer, nullptr);
25 vkFreeMemory(device, stagingBufferMemory, nullptr);
26 }
There are only two notable differences. The bufferSize is now equal to the
number of indices times the size of the index type, either uint16_t or uint32_t.
The usage of the indexBuffer should be VK_BUFFER_USAGE_INDEX_BUFFER_BIT
instead of VK_BUFFER_USAGE_VERTEX_BUFFER_BIT, which makes sense. Other
than that, the process is exactly the same. We create a staging buffer to copy
the contents of indices to and then copy it to the final device local index buffer.
The index buffer should be cleaned up at the end of the program, just like the
vertex buffer:
1 void cleanup() {
2 cleanupSwapChain();
3
4 vkDestroyBuffer(device, indexBuffer, nullptr);
5 vkFreeMemory(device, indexBufferMemory, nullptr);
6
7 vkDestroyBuffer(device, vertexBuffer, nullptr);
8 vkFreeMemory(device, vertexBufferMemory, nullptr);
9
10 ...
11 }
166
Using an index buffer
Using an index buffer for drawing involves two changes to recordCommandBuffer.
We first need to bind the index buffer, just like we did for the vertex buffer.
The difference is that you can only have a single index buffer. It’s unfortunately
not possible to use different indices for each vertex attribute, so we do still
have to completely duplicate vertex data even if just one attribute varies.
1 vkCmdBindVertexBuffers(commandBuffer, 0, 1, vertexBuffers, offsets);
2
3 vkCmdBindIndexBuffer(commandBuffer, indexBuffer, 0,
VK_INDEX_TYPE_UINT16);
An index buffer is bound with vkCmdBindIndexBuffer which has the index
buffer, a byte offset into it, and the type of index data as parameters.
As mentioned before, the possible types are VK_INDEX_TYPE_UINT16 and
VK_INDEX_TYPE_UINT32.
Just binding an index buffer doesn’t change anything yet, we also need to change
the drawing command to tell Vulkan to use the index buffer. Remove the
vkCmdDraw line and replace it with vkCmdDrawIndexed:
1 vkCmdDrawIndexed(commandBuffer,
static_cast<uint32_t>(indices.size()), 1, 0, 0, 0);
A call to this function is very similar to vkCmdDraw. The first two parameters
specify the number of indices and the number of instances. We’re not using
instancing, so just specify 1 instance. The number of indices represents the
number of vertices that will be passed to the vertex shader. The next parameter
specifies an offset into the index buffer, using a value of 1 would cause the
graphics card to start reading at the second index. The second to last parameter
specifies an offset to add to the indices in the index buffer. The final parameter
specifies an offset for instancing, which we’re not using.
Now run your program and you should see the following:
167
You now know how to save memory by reusing vertices with index buffers. This
will become especially important in a future chapter where we’re going to load
complex 3D models.
The previous chapter already mentioned that you should allocate multiple re-
sources like buffers from a single memory allocation, but in fact you should
go a step further. Driver developers recommend that you also store multiple
buffers, like the vertex and index buffer, into a single VkBuffer and use offsets
in commands like vkCmdBindVertexBuffers. The advantage is that your data
is more cache friendly in that case, because it’s closer together. It is even pos-
sible to reuse the same chunk of memory for multiple resources if they are not
used during the same render operations, provided that their data is refreshed,
of course. This is known as aliasing and some Vulkan functions have explicit
flags to specify that you want to do this.
C++ code / Vertex shader / Fragment shader
168
Uniform buffers
Descriptor layout and buffer
Introduction
We’re now able to pass arbitrary attributes to the vertex shader for each ver-
tex, but what about global variables? We’re going to move on to 3D graphics
from this chapter on and that requires a model-view-projection matrix. We
could include it as vertex data, but that’s a waste of memory and it would re-
quire us to update the vertex buffer whenever the transformation changes. The
transformation could easily change every single frame.
The right way to tackle this in Vulkan is to use resource descriptors. A descriptor
is a way for shaders to freely access resources like buffers and images. We’re
going to set up a buffer that contains the transformation matrices and have the
vertex shader access them through a descriptor. Usage of descriptors consists
of three parts:
• Specify a descriptor layout during pipeline creation
• Allocate a descriptor set from a descriptor pool
• Bind the descriptor set during rendering
The descriptor layout specifies the types of resources that are going to be ac-
cessed by the pipeline, just like a render pass specifies the types of attachments
that will be accessed. A descriptor set specifies the actual buffer or image re-
sources that will be bound to the descriptors, just like a framebuffer specifies
the actual image views to bind to render pass attachments. The descriptor
set is then bound for the drawing commands just like the vertex buffers and
framebuffer.
There are many types of descriptors, but in this chapter we’ll work with uniform
buffer objects (UBO). We’ll look at other types of descriptors in future chapters,
but the basic process is the same. Let’s say we have the data we want the vertex
shader to have in a C struct like this:
1 struct UniformBufferObject {
2 glm::mat4 model;
169
3 glm::mat4 view;
4 glm::mat4 proj;
5 };
Then we can copy the data to a VkBuffer and access it through a uniform buffer
object descriptor from the vertex shader like this:
1 layout(binding = 0) uniform UniformBufferObject {
2 mat4 model;
3 mat4 view;
4 mat4 proj;
5 } ubo;
6
7 void main() {
8 gl_Position = ubo.proj * ubo.view * ubo.model * vec4(inPosition,
0.0, 1.0);
9 fragColor = inColor;
10 }
We’re going to update the model, view and projection matrices every frame to
make the rectangle from the previous chapter spin around in 3D.
Vertex shader
Modify the vertex shader to include the uniform buffer object like it was specified
above. I will assume that you are familiar with MVP transformations. If you’re
not, see the resource mentioned in the first chapter.
1 #version 450
2
3 layout(binding = 0) uniform UniformBufferObject {
4 mat4 model;
5 mat4 view;
6 mat4 proj;
7 } ubo;
8
9 layout(location = 0) in vec2 inPosition;
10 layout(location = 1) in vec3 inColor;
11
12 layout(location = 0) out vec3 fragColor;
13
14 void main() {
15 gl_Position = ubo.proj * ubo.view * ubo.model * vec4(inPosition,
0.0, 1.0);
16 fragColor = inColor;
17 }
170
Note that the order of the uniform, in and out declarations doesn’t matter. The
binding directive is similar to the location directive for attributes. We’re going
to reference this binding in the descriptor layout. The line with gl_Position is
changed to use the transformations to compute the final position in clip coordi-
nates. Unlike the 2D triangles, the last component of the clip coordinates may
not be 1, which will result in a division when converted to the final normalized
device coordinates on the screen. This is used in perspective projection as the
perspective division and is essential for making closer objects look larger than
objects that are further away.
Descriptor set layout
The next step is to define the UBO on the C++ side and to tell Vulkan about
this descriptor in the vertex shader.
1 struct UniformBufferObject {
2 glm::mat4 model;
3 glm::mat4 view;
4 glm::mat4 proj;
5 };
We can exactly match the definition in the shader using data types in GLM.
The data in the matrices is binary compatible with the way the shader expects
it, so we can later just memcpy a UniformBufferObject to a VkBuffer.
We need to provide details about every descriptor binding used in the shaders
for pipeline creation, just like we had to do for every vertex attribute and its
location index. We’ll set up a new function to define all of this information
called createDescriptorSetLayout. It should be called right before pipeline
creation, because we’re going to need it there.
1 void initVulkan() {
2 ...
3 createDescriptorSetLayout();
4 createGraphicsPipeline();
5 ...
6 }
7
8 ...
9
10 void createDescriptorSetLayout() {
11
12 }
Every binding needs to be described through a VkDescriptorSetLayoutBinding
struct.
1 void createDescriptorSetLayout() {
171
2 VkDescriptorSetLayoutBinding uboLayoutBinding{};
3 uboLayoutBinding.binding = 0;
4 uboLayoutBinding.descriptorType =
VK_DESCRIPTOR_TYPE_UNIFORM_BUFFER;
5 uboLayoutBinding.descriptorCount = 1;
6 }
The first two fields specify the binding used in the shader and the type of de-
scriptor, which is a uniform buffer object. It is possible for the shader variable
to represent an array of uniform buffer objects, and descriptorCount specifies
the number of values in the array. This could be used to specify a transfor-
mation for each of the bones in a skeleton for skeletal animation, for example.
Our MVP transformation is in a single uniform buffer object, so we’re using a
descriptorCount of 1.
1 uboLayoutBinding.stageFlags = VK_SHADER_STAGE_VERTEX_BIT;
We also need to specify in which shader stages the descriptor is going to be refer-
enced. The stageFlags field can be a combination of VkShaderStageFlagBits
values or the value VK_SHADER_STAGE_ALL_GRAPHICS. In our case, we’re only
referencing the descriptor from the vertex shader.
1 uboLayoutBinding.pImmutableSamplers = nullptr; // Optional
The pImmutableSamplers field is only relevant for image sampling related de-
scriptors, which we’ll look at later. You can leave this to its default value.
All of the descriptor bindings are combined into a single VkDescriptorSetLayout
object. Define a new class member above pipelineLayout:
1 VkDescriptorSetLayout descriptorSetLayout;
2 VkPipelineLayout pipelineLayout;
We can then create it using vkCreateDescriptorSetLayout. This function ac-
cepts a simple VkDescriptorSetLayoutCreateInfo with the array of bindings:
1 VkDescriptorSetLayoutCreateInfo layoutInfo{};
2 layoutInfo.sType =
VK_STRUCTURE_TYPE_DESCRIPTOR_SET_LAYOUT_CREATE_INFO;
3 layoutInfo.bindingCount = 1;
4 layoutInfo.pBindings = &uboLayoutBinding;
5
6 if (vkCreateDescriptorSetLayout(device, &layoutInfo, nullptr,
&descriptorSetLayout) != VK_SUCCESS) {
7 throw std::runtime_error("failed to create descriptor set
layout!");
8 }
172
We need to specify the descriptor set layout during pipeline creation
to tell Vulkan which descriptors the shaders will be using. Descrip-
tor set layouts are specified in the pipeline layout object. Modify the
VkPipelineLayoutCreateInfo to reference the layout object:
1 VkPipelineLayoutCreateInfo pipelineLayoutInfo{};
2 pipelineLayoutInfo.sType =
VK_STRUCTURE_TYPE_PIPELINE_LAYOUT_CREATE_INFO;
3 pipelineLayoutInfo.setLayoutCount = 1;
4 pipelineLayoutInfo.pSetLayouts = &descriptorSetLayout;
You may be wondering why it’s possible to specify multiple descriptor set layouts
here, because a single one already includes all of the bindings. We’ll get back to
that in the next chapter, where we’ll look into descriptor pools and descriptor
sets.
The descriptor layout should stick around while we may create new graphics
pipelines i.e. until the program ends:
1 void cleanup() {
2 cleanupSwapChain();
3
4 vkDestroyDescriptorSetLayout(device, descriptorSetLayout,
nullptr);
5
6 ...
7 }
Uniform buffer
In the next chapter we’ll specify the buffer that contains the UBO data for the
shader, but we need to create this buffer first. We’re going to copy new data
to the uniform buffer every frame, so it doesn’t really make any sense to have a
staging buffer. It would just add extra overhead in this case and likely degrade
performance instead of improving it.
We should have multiple buffers, because multiple frames may be in flight at the
same time and we don’t want to update the buffer in preparation of the next
frame while a previous one is still reading from it! Thus, we need to have as
many uniform buffers as we have frames in flight, and write to a uniform buffer
that is not currently being read by the GPU
To that end, add new class members for uniformBuffers, and uniformBuffersMemory:
1 VkBuffer indexBuffer;
2 VkDeviceMemory indexBufferMemory;
3
4 std::vector<VkBuffer> uniformBuffers;
173
5 std::vector<VkDeviceMemory> uniformBuffersMemory;
6 std::vector<void*> uniformBuffersMapped;
Similarly, create a new function createUniformBuffers that is called after
createIndexBuffer and allocates the buffers:
1 void initVulkan() {
2 ...
3 createVertexBuffer();
4 createIndexBuffer();
5 createUniformBuffers();
6 ...
7 }
8
9 ...
10
11 void createUniformBuffers() {
12 VkDeviceSize bufferSize = sizeof(UniformBufferObject);
13
14 uniformBuffers.resize(MAX_FRAMES_IN_FLIGHT);
15 uniformBuffersMemory.resize(MAX_FRAMES_IN_FLIGHT);
16 uniformBuffersMapped.resize(MAX_FRAMES_IN_FLIGHT);
17
18 for (size_t i = 0; i < MAX_FRAMES_IN_FLIGHT; i++) {
19 createBuffer(bufferSize, VK_BUFFER_USAGE_UNIFORM_BUFFER_BIT,
VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT |
VK_MEMORY_PROPERTY_HOST_COHERENT_BIT, uniformBuffers[i],
uniformBuffersMemory[i]);
20
21 vkMapMemory(device, uniformBuffersMemory[i], 0, bufferSize,
0, &uniformBuffersMapped[i]);
22 }
23 }
We map the buffer right after creation using vkMapMemory to get a pointer
to which we can write the data later on. The buffer stays mapped to this
pointer for the application’s whole lifetime. This technique is called “persistent
mapping” and works on all Vulkan implementations. Not having to map the
buffer every time we need to update it increases performances, as mapping is
not free.
The uniform data will be used for all draw calls, so the buffer containing it
should only be destroyed when we stop rendering.
1 void cleanup() {
2 ...
3
174
4 for (size_t i = 0; i < MAX_FRAMES_IN_FLIGHT; i++) {
5 vkDestroyBuffer(device, uniformBuffers[i], nullptr);
6 vkFreeMemory(device, uniformBuffersMemory[i], nullptr);
7 }
8
9 vkDestroyDescriptorSetLayout(device, descriptorSetLayout,
nullptr);
10
11 ...
12
13 }
Updating uniform data
Create a new function updateUniformBuffer and add a call to it from the
drawFrame function before submitting the next frame:
1 void drawFrame() {
2 ...
3
4 updateUniformBuffer(currentFrame);
5
6 ...
7
8 VkSubmitInfo submitInfo{};
9 submitInfo.sType = VK_STRUCTURE_TYPE_SUBMIT_INFO;
10
11 ...
12 }
13
14 ...
15
16 void updateUniformBuffer(uint32_t currentImage) {
17
18 }
This function will generate a new transformation every frame to make the ge-
ometry spin around. We need to include two new headers to implement this
functionality:
1 #define GLM_FORCE_RADIANS
2 #include <glm/glm.hpp>
3 #include <glm/gtc/matrix_transform.hpp>
4
5 #include <chrono>
175
The glm/gtc/matrix_transform.hpp header exposes functions that can be
used to generate model transformations like glm::rotate, view transforma-
tions like glm::lookAt and projection transformations like glm::perspective.
The GLM_FORCE_RADIANS definition is necessary to make sure that functions like
glm::rotate use radians as arguments, to avoid any possible confusion.
The chrono standard library header exposes functions to do precise timekeeping.
We’ll use this to make sure that the geometry rotates 90 degrees per second
regardless of frame rate.
1 void updateUniformBuffer(uint32_t currentImage) {
2 static auto startTime =
std::chrono::high_resolution_clock::now();
3
4 auto currentTime = std::chrono::high_resolution_clock::now();
5 float time = std::chrono::duration<float,
std::chrono::seconds::period>(currentTime -
startTime).count();
6 }
The updateUniformBuffer function will start out with some logic to calculate
the time in seconds since rendering has started with floating point accuracy.
We will now define the model, view and projection transformations in the uni-
form buffer object. The model rotation will be a simple rotation around the
Z-axis using the time variable:
1 UniformBufferObject ubo{};
2 ubo.model = glm::rotate(glm::mat4(1.0f), time * glm::radians(90.0f),
glm::vec3(0.0f, 0.0f, 1.0f));
The glm::rotate function takes an existing transformation, rotation angle and
rotation axis as parameters. The glm::mat4(1.0f) constructor returns an iden-
tity matrix. Using a rotation angle of time * glm::radians(90.0f) accom-
plishes the purpose of rotation 90 degrees per second.
1 ubo.view = glm::lookAt(glm::vec3(2.0f, 2.0f, 2.0f), glm::vec3(0.0f,
0.0f, 0.0f), glm::vec3(0.0f, 0.0f, 1.0f));
For the view transformation I’ve decided to look at the geometry from above
at a 45 degree angle. The glm::lookAt function takes the eye position, center
position and up axis as parameters.
1 ubo.proj = glm::perspective(glm::radians(45.0f),
swapChainExtent.width / (float) swapChainExtent.height, 0.1f,
10.0f);
I’ve chosen to use a perspective projection with a 45 degree vertical field-of-
view. The other parameters are the aspect ratio, near and far view planes. It
176
is important to use the current swap chain extent to calculate the aspect ratio
to take into account the new width and height of the window after a resize.
1 ubo.proj[1][1] *= -1;
GLM was originally designed for OpenGL, where the Y coordinate of the clip
coordinates is inverted. The easiest way to compensate for that is to flip the
sign on the scaling factor of the Y axis in the projection matrix. If you don’t
do this, then the image will be rendered upside down.
All of the transformations are defined now, so we can copy the data in the
uniform buffer object to the current uniform buffer. This happens in exactly
the same way as we did for vertex buffers, except without a staging buffer. As
noted earlier, we only map the uniform buffer once, so we can directly write to
it without having to map again:
1 memcpy(uniformBuffersMapped[currentImage], &ubo, sizeof(ubo));
Using a UBO this way is not the most efficient way to pass frequently changing
values to the shader. A more efficient way to pass a small buffer of data to
shaders are push constants. We may look at these in a future chapter.
In the next chapter we’ll look at descriptor sets, which will actually bind the
VkBuffers to the uniform buffer descriptors so that the shader can access this
transformation data.
C++ code / Vertex shader / Fragment shader
Descriptor pool and sets
Introduction
The descriptor layout from the previous chapter describes the type of descriptors
that can be bound. In this chapter we’re going to create a descriptor set for
each VkBuffer resource to bind it to the uniform buffer descriptor.
Descriptor pool
Descriptor sets can’t be created directly, they must be allocated from a pool like
command buffers. The equivalent for descriptor sets is unsurprisingly called a
descriptor pool. We’ll write a new function createDescriptorPool to set it up.
1 void initVulkan() {
2 ...
3 createUniformBuffers();
4 createDescriptorPool();
5 ...
6 }
7
177
8 ...
9
10 void createDescriptorPool() {
11
12 }
We first need to describe which descriptor types our descriptor sets are going to
contain and how many of them, using VkDescriptorPoolSize structures.
1 VkDescriptorPoolSize poolSize{};
2 poolSize.type = VK_DESCRIPTOR_TYPE_UNIFORM_BUFFER;
3 poolSize.descriptorCount =
static_cast<uint32_t>(MAX_FRAMES_IN_FLIGHT);
We will allocate one of these descriptors for every frame. This pool size structure
is referenced by the main VkDescriptorPoolCreateInfo:
1 VkDescriptorPoolCreateInfo poolInfo{};
2 poolInfo.sType = VK_STRUCTURE_TYPE_DESCRIPTOR_POOL_CREATE_INFO;
3 poolInfo.poolSizeCount = 1;
4 poolInfo.pPoolSizes = &poolSize;
Aside from the maximum number of individual descriptors that are available,
we also need to specify the maximum number of descriptor sets that may be
allocated:
1 poolInfo.maxSets = static_cast<uint32_t>(MAX_FRAMES_IN_FLIGHT);
The structure has an optional flag similar to command pools that determines if
individual descriptor sets can be freed or not: VK_DESCRIPTOR_POOL_CREATE_FREE_DESCRIPTOR_SET_BIT.
We’re not going to touch the descriptor set after creating it, so we don’t need
this flag. You can leave flags to its default value of 0.
1 VkDescriptorPool descriptorPool;
2
3 ...
4
5 if (vkCreateDescriptorPool(device, &poolInfo, nullptr,
&descriptorPool) != VK_SUCCESS) {
6 throw std::runtime_error("failed to create descriptor pool!");
7 }
Add a new class member to store the handle of the descriptor pool and call
vkCreateDescriptorPool to create it.
Descriptor set
We can now allocate the descriptor sets themselves. Add a createDescriptorSets
function for that purpose:
178
1 void initVulkan() {
2 ...
3 createDescriptorPool();
4 createDescriptorSets();
5 ...
6 }
7
8 ...
9
10 void createDescriptorSets() {
11
12 }
A descriptor set allocation is described with a VkDescriptorSetAllocateInfo
struct. You need to specify the descriptor pool to allocate from, the number of
descriptor sets to allocate, and the descriptor layout to base them on:
1 std::vector<VkDescriptorSetLayout> layouts(MAX_FRAMES_IN_FLIGHT,
descriptorSetLayout);
2 VkDescriptorSetAllocateInfo allocInfo{};
3 allocInfo.sType = VK_STRUCTURE_TYPE_DESCRIPTOR_SET_ALLOCATE_INFO;
4 allocInfo.descriptorPool = descriptorPool;
5 allocInfo.descriptorSetCount =
static_cast<uint32_t>(MAX_FRAMES_IN_FLIGHT);
6 allocInfo.pSetLayouts = layouts.data();
In our case we will create one descriptor set for each frame in flight, all with the
same layout. Unfortunately we do need all the copies of the layout because the
next function expects an array matching the number of sets.
Add a class member to hold the descriptor set handles and allocate them with
vkAllocateDescriptorSets:
1 VkDescriptorPool descriptorPool;
2 std::vector<VkDescriptorSet> descriptorSets;
3
4 ...
5
6 descriptorSets.resize(MAX_FRAMES_IN_FLIGHT);
7 if (vkAllocateDescriptorSets(device, &allocInfo,
descriptorSets.data()) != VK_SUCCESS) {
8 throw std::runtime_error("failed to allocate descriptor sets!");
9 }
You don’t need to explicitly clean up descriptor sets, because they will
be automatically freed when the descriptor pool is destroyed. The call
to vkAllocateDescriptorSets will allocate descriptor sets, each with one
uniform buffer descriptor.
179
1 void cleanup() {
2 ...
3 vkDestroyDescriptorPool(device, descriptorPool, nullptr);
4
5 vkDestroyDescriptorSetLayout(device, descriptorSetLayout,
nullptr);
6 ...
7 }
The descriptor sets have been allocated now, but the descriptors within still
need to be configured. We’ll now add a loop to populate every descriptor:
1 for (size_t i = 0; i < MAX_FRAMES_IN_FLIGHT; i++) {
2
3 }
Descriptors that refer to buffers, like our uniform buffer descriptor, are config-
ured with a VkDescriptorBufferInfo struct. This structure specifies the buffer
and the region within it that contains the data for the descriptor.
1 for (size_t i = 0; i < MAX_FRAMES_IN_FLIGHT; i++) {
2 VkDescriptorBufferInfo bufferInfo{};
3 bufferInfo.buffer = uniformBuffers[i];
4 bufferInfo.offset = 0;
5 bufferInfo.range = sizeof(UniformBufferObject);
6 }
If you’re overwriting the whole buffer, like we are in this case, then it is also
possible to use the VK_WHOLE_SIZE value for the range. The configuration of de-
scriptors is updated using the vkUpdateDescriptorSets function, which takes
an array of VkWriteDescriptorSet structs as parameter.
1 VkWriteDescriptorSet descriptorWrite{};
2 descriptorWrite.sType = VK_STRUCTURE_TYPE_WRITE_DESCRIPTOR_SET;
3 descriptorWrite.dstSet = descriptorSets[i];
4 descriptorWrite.dstBinding = 0;
5 descriptorWrite.dstArrayElement = 0;
The first two fields specify the descriptor set to update and the binding. We
gave our uniform buffer binding index 0. Remember that descriptors can be
arrays, so we also need to specify the first index in the array that we want to
update. We’re not using an array, so the index is simply 0.
1 descriptorWrite.descriptorType = VK_DESCRIPTOR_TYPE_UNIFORM_BUFFER;
2 descriptorWrite.descriptorCount = 1;
We need to specify the type of descriptor again. It’s possible to update multi-
ple descriptors at once in an array, starting at index dstArrayElement. The
descriptorCount field specifies how many array elements you want to update.
180
1 descriptorWrite.pBufferInfo = &bufferInfo;
2 descriptorWrite.pImageInfo = nullptr; // Optional
3 descriptorWrite.pTexelBufferView = nullptr; // Optional
The last field references an array with descriptorCount structs that actually
configure the descriptors. It depends on the type of descriptor which one of the
three you actually need to use. The pBufferInfo field is used for descriptors
that refer to buffer data, pImageInfo is used for descriptors that refer to image
data, and pTexelBufferView is used for descriptors that refer to buffer views.
Our descriptor is based on buffers, so we’re using pBufferInfo.
1 vkUpdateDescriptorSets(device, 1, &descriptorWrite, 0, nullptr);
The updates are applied using vkUpdateDescriptorSets. It accepts two kinds
of arrays as parameters: an array of VkWriteDescriptorSet and an array of
VkCopyDescriptorSet. The latter can be used to copy descriptors to each other,
as its name implies.
Using descriptor sets
We now need to update the recordCommandBuffer function to actually
bind the right descriptor set for each frame to the descriptors in the
shader with vkCmdBindDescriptorSets. This needs to be done before the
vkCmdDrawIndexed call:
1 vkCmdBindDescriptorSets(commandBuffer,
VK_PIPELINE_BIND_POINT_GRAPHICS, pipelineLayout, 0, 1,
&descriptorSets[currentFrame], 0, nullptr);
2 vkCmdDrawIndexed(commandBuffer,
static_cast<uint32_t>(indices.size()), 1, 0, 0, 0);
Unlike vertex and index buffers, descriptor sets are not unique to graphics
pipelines. Therefore we need to specify if we want to bind descriptor sets to
the graphics or compute pipeline. The next parameter is the layout that the
descriptors are based on. The next three parameters specify the index of the
first descriptor set, the number of sets to bind, and the array of sets to bind.
We’ll get back to this in a moment. The last two parameters specify an array
of offsets that are used for dynamic descriptors. We’ll look at these in a future
chapter.
If you run your program now, then you’ll notice that unfortunately nothing is
visible. The problem is that because of the Y-flip we did in the projection matrix,
the vertices are now being drawn in counter-clockwise order instead of clockwise
order. This causes backface culling to kick in and prevents any geometry from
being drawn. Go to the createGraphicsPipeline function and modify the
frontFace in VkPipelineRasterizationStateCreateInfo to correct this:
1 rasterizer.cullMode = VK_CULL_MODE_BACK_BIT;
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2 rasterizer.frontFace = VK_FRONT_FACE_COUNTER_CLOCKWISE;
Run your program again and you should now see the following:
The rectangle has changed into a square because the projection matrix now cor-
rects for aspect ratio. The updateUniformBuffer takes care of screen resizing,
so we don’t need to recreate the descriptor set in recreateSwapChain.
Alignment requirements
One thing we’ve glossed over so far is how exactly the data in the C++ structure
should match with the uniform definition in the shader. It seems obvious enough
to simply use the same types in both:
1 struct UniformBufferObject {
2 glm::mat4 model;
3 glm::mat4 view;
4 glm::mat4 proj;
5 };
6
7 layout(binding = 0) uniform UniformBufferObject {
8 mat4 model;
9 mat4 view;
182
10 mat4 proj;
11 } ubo;
However, that’s not all there is to it. For example, try modifying the struct and
shader to look like this:
1 struct UniformBufferObject {
2 glm::vec2 foo;
3 glm::mat4 model;
4 glm::mat4 view;
5 glm::mat4 proj;
6 };
7
8 layout(binding = 0) uniform UniformBufferObject {
9 vec2 foo;
10 mat4 model;
11 mat4 view;
12 mat4 proj;
13 } ubo;
Recompile your shader and your program and run it and you’ll find that the
colorful square you worked so far has disappeared! That’s because we haven’t
taken into account the alignment requirements.
Vulkan expects the data in your structure to be aligned in memory in a specific
way, for example:
• Scalars have to be aligned by N (= 4 bytes given 32 bit floats).
• A vec2 must be aligned by 2N (= 8 bytes)
• A vec3 or vec4 must be aligned by 4N (= 16 bytes)
• A nested structure must be aligned by the base alignment of its members
rounded up to a multiple of 16.
• A mat4 matrix must have the same alignment as a vec4.
You can find the full list of alignment requirements in the specification.
Our original shader with just three mat4 fields already met the alignment re-
quirements. As each mat4 is 4 x 4 x 4 = 64 bytes in size, model has an offset
of 0, view has an offset of 64 and proj has an offset of 128. All of these are
multiples of 16 and that’s why it worked fine.
The new structure starts with a vec2 which is only 8 bytes in size and therefore
throws off all of the offsets. Now model has an offset of 8, view an offset of 72
and proj an offset of 136, none of which are multiples of 16. To fix this problem
we can use the alignas specifier introduced in C++11:
1 struct UniformBufferObject {
2 glm::vec2 foo;
3 alignas(16) glm::mat4 model;
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4 glm::mat4 view;
5 glm::mat4 proj;
6 };
If you now compile and run your program again you should see that the shader
correctly receives its matrix values once again.
Luckily there is a way to not have to think about these alignment requirements
most of the time. We can define GLM_FORCE_DEFAULT_ALIGNED_GENTYPES right
before including GLM:
1 #define GLM_FORCE_RADIANS
2 #define GLM_FORCE_DEFAULT_ALIGNED_GENTYPES
3 #include <glm/glm.hpp>
This will force GLM to use a version of vec2 and mat4 that has the alignment
requirements already specified for us. If you add this definition then you can
remove the alignas specifier and your program should still work.
Unfortunately this method can break down if you start using nested structures.
Consider the following definition in the C++ code:
1 struct Foo {
2 glm::vec2 v;
3 };
4
5 struct UniformBufferObject {
6 Foo f1;
7 Foo f2;
8 };
And the following shader definition:
1 struct Foo {
2 vec2 v;
3 };
4
5 layout(binding = 0) uniform UniformBufferObject {
6 Foo f1;
7 Foo f2;
8 } ubo;
In this case f2 will have an offset of 8 whereas it should have an offset of 16 since
it is a nested structure. In this case you must specify the alignment yourself:
1 struct UniformBufferObject {
2 Foo f1;
3 alignas(16) Foo f2;
4 };
184
These gotchas are a good reason to always be explicit about alignment. That
way you won’t be caught offguard by the strange symptoms of alignment errors.
1 struct UniformBufferObject {
2 alignas(16) glm::mat4 model;
3 alignas(16) glm::mat4 view;
4 alignas(16) glm::mat4 proj;
5 };
Don’t forget to recompile your shader after removing the foo field.
Multiple descriptor sets
As some of the structures and function calls hinted at, it is actually possible to
bind multiple descriptor sets simultaneously. You need to specify a descriptor
layout for each descriptor set when creating the pipeline layout. Shaders can
then reference specific descriptor sets like this:
1 layout(set = 0, binding = 0) uniform UniformBufferObject { ... }
You can use this feature to put descriptors that vary per-object and descriptors
that are shared into separate descriptor sets. In that case you avoid rebinding
most of the descriptors across draw calls which is potentially more efficient.
C++ code / Vertex shader / Fragment shader
185
Texture mapping
Images
Introduction
The geometry has been colored using per-vertex colors so far, which is a rather
limited approach. In this part of the tutorial we’re going to implement texture
mapping to make the geometry look more interesting. This will also allow us to
load and draw basic 3D models in a future chapter.
Adding a texture to our application will involve the following steps:
• Create an image object backed by device memory
• Fill it with pixels from an image file
• Create an image sampler
• Add a combined image sampler descriptor to sample colors from the tex-
ture
We’ve already worked with image objects before, but those were automatically
created by the swap chain extension. This time we’ll have to create one by
ourselves. Creating an image and filling it with data is similar to vertex buffer
creation. We’ll start by creating a staging resource and filling it with pixel data
and then we copy this to the final image object that we’ll use for rendering.
Although it is possible to create a staging image for this purpose, Vulkan also
allows you to copy pixels from a VkBuffer to an image and the API for this is
actually faster on some hardware. We’ll first create this buffer and fill it with
pixel values, and then we’ll create an image to copy the pixels to. Creating
an image is not very different from creating buffers. It involves querying the
memory requirements, allocating device memory and binding it, just like we’ve
seen before.
However, there is something extra that we’ll have to take care of when working
with images. Images can have different layouts that affect how the pixels are
organized in memory. Due to the way graphics hardware works, simply storing
the pixels row by row may not lead to the best performance, for example. When
performing any operation on images, you must make sure that they have the
186
layout that is optimal for use in that operation. We’ve actually already seen
some of these layouts when we specified the render pass:
• VK_IMAGE_LAYOUT_PRESENT_SRC_KHR: Optimal for presentation
• VK_IMAGE_LAYOUT_COLOR_ATTACHMENT_OPTIMAL: Optimal as attachment
for writing colors from the fragment shader
• VK_IMAGE_LAYOUT_TRANSFER_SRC_OPTIMAL: Optimal as source in a trans-
fer operation, like vkCmdCopyImageToBuffer
• VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL: Optimal as destination in a
transfer operation, like vkCmdCopyBufferToImage
• VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL: Optimal for sampling
from a shader
One of the most common ways to transition the layout of an image is a pipeline
barrier. Pipeline barriers are primarily used for synchronizing access to re-
sources, like making sure that an image was written to before it is read, but they
can also be used to transition layouts. In this chapter we’ll see how pipeline
barriers are used for this purpose. Barriers can additionally be used to transfer
queue family ownership when using VK_SHARING_MODE_EXCLUSIVE.
Image library
There are many libraries available for loading images, and you can even write
your own code to load simple formats like BMP and PPM. In this tutorial we’ll
be using the stb_image library from the stb collection. The advantage of it
is that all of the code is in a single file, so it doesn’t require any tricky build
configuration. Download stb_image.h and store it in a convenient location,
like the directory where you saved GLFW and GLM. Add the location to your
include path.
Visual Studio
Add the directory with stb_image.h in it to the Additional Include
Directories paths.
Makefile
Add the directory with stb_image.h to the include directories for GCC:
187
1 VULKAN_SDK_PATH = /home/user/VulkanSDK/x.x.x.x/x86_64
2 STB_INCLUDE_PATH = /home/user/libraries/stb
3
4 ...
5
6 CFLAGS = -std=c++17 -I$(VULKAN_SDK_PATH)/include
-I$(STB_INCLUDE_PATH)
Loading an image
Include the image library like this:
1 #define STB_IMAGE_IMPLEMENTATION
2 #include <stb_image.h>
The header only defines the prototypes of the functions by default. One code
file needs to include the header with the STB_IMAGE_IMPLEMENTATION definition
to include the function bodies, otherwise we’ll get linking errors.
1 void initVulkan() {
2 ...
3 createCommandPool();
4 createTextureImage();
5 createVertexBuffer();
6 ...
7 }
8
9 ...
10
11 void createTextureImage() {
12
13 }
Create a new function createTextureImage where we’ll load an image and
upload it into a Vulkan image object. We’re going to use command buffers, so
it should be called after createCommandPool.
Create a new directory textures next to the shaders directory to store texture
images in. We’re going to load an image called texture.jpg from that directory.
I’ve chosen to use the following CC0 licensed image resized to 512 x 512 pixels,
but feel free to pick any image you want. The library supports most common
image file formats, like JPEG, PNG, BMP and GIF.
188
Loading an image with this library is really easy:
1 void createTextureImage() {
2 int texWidth, texHeight, texChannels;
3 stbi_uc* pixels = stbi_load("textures/texture.jpg", &texWidth,
&texHeight, &texChannels, STBI_rgb_alpha);
4 VkDeviceSize imageSize = texWidth * texHeight * 4;
5
6 if (!pixels) {
7 throw std::runtime_error("failed to load texture image!");
8 }
9 }
The stbi_load function takes the file path and number of channels to load as
arguments. The STBI_rgb_alpha value forces the image to be loaded with an
alpha channel, even if it doesn’t have one, which is nice for consistency with
other textures in the future. The middle three parameters are outputs for the
189
width, height and actual number of channels in the image. The pointer that is
returned is the first element in an array of pixel values. The pixels are laid out
row by row with 4 bytes per pixel in the case of STBI_rgb_alpha for a total of
texWidth * texHeight * 4 values.
Staging buffer
We’re now going to create a buffer in host visible memory so that we can use
vkMapMemory and copy the pixels to it. Add variables for this temporary buffer
to the createTextureImage function:
1 VkBuffer stagingBuffer;
2 VkDeviceMemory stagingBufferMemory;
The buffer should be in host visible memory so that we can map it and it should
be usable as a transfer source so that we can copy it to an image later on:
1 createBuffer(imageSize, VK_BUFFER_USAGE_TRANSFER_SRC_BIT,
VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT |
VK_MEMORY_PROPERTY_HOST_COHERENT_BIT, stagingBuffer,
stagingBufferMemory);
We can then directly copy the pixel values that we got from the image loading
library to the buffer:
1 void* data;
2 vkMapMemory(device, stagingBufferMemory, 0, imageSize, 0, &data);
3 memcpy(data, pixels, static_cast<size_t>(imageSize));
4 vkUnmapMemory(device, stagingBufferMemory);
Don’t forget to clean up the original pixel array now:
1 stbi_image_free(pixels);
Texture Image
Although we could set up the shader to access the pixel values in the buffer, it’s
better to use image objects in Vulkan for this purpose. Image objects will make
it easier and faster to retrieve colors by allowing us to use 2D coordinates, for
one. Pixels within an image object are known as texels and we’ll use that name
from this point on. Add the following new class members:
1 VkImage textureImage;
2 VkDeviceMemory textureImageMemory;
The parameters for an image are specified in a VkImageCreateInfo struct:
190
1 VkImageCreateInfo imageInfo{};
2 imageInfo.sType = VK_STRUCTURE_TYPE_IMAGE_CREATE_INFO;
3 imageInfo.imageType = VK_IMAGE_TYPE_2D;
4 imageInfo.extent.width = static_cast<uint32_t>(texWidth);
5 imageInfo.extent.height = static_cast<uint32_t>(texHeight);
6 imageInfo.extent.depth = 1;
7 imageInfo.mipLevels = 1;
8 imageInfo.arrayLayers = 1;
The image type, specified in the imageType field, tells Vulkan with what kind
of coordinate system the texels in the image are going to be addressed. It is
possible to create 1D, 2D and 3D images. One dimensional images can be used
to store an array of data or gradient, two dimensional images are mainly used
for textures, and three dimensional images can be used to store voxel volumes,
for example. The extent field specifies the dimensions of the image, basically
how many texels there are on each axis. That’s why depth must be 1 instead
of 0. Our texture will not be an array and we won’t be using mipmapping for
now.
1 imageInfo.format = VK_FORMAT_R8G8B8A8_SRGB;
Vulkan supports many possible image formats, but we should use the same
format for the texels as the pixels in the buffer, otherwise the copy operation
will fail.
1 imageInfo.tiling = VK_IMAGE_TILING_OPTIMAL;
The tiling field can have one of two values:
• VK_IMAGE_TILING_LINEAR: Texels are laid out in row-major order like our
pixels array
• VK_IMAGE_TILING_OPTIMAL: Texels are laid out in an implementation de-
fined order for optimal access
Unlike the layout of an image, the tiling mode cannot be changed at a later
time. If you want to be able to directly access texels in the memory of the
image, then you must use VK_IMAGE_TILING_LINEAR. We will be using a staging
buffer instead of a staging image, so this won’t be necessary. We will be using
VK_IMAGE_TILING_OPTIMAL for efficient access from the shader.
1 imageInfo.initialLayout = VK_IMAGE_LAYOUT_UNDEFINED;
There are only two possible values for the initialLayout of an image:
• VK_IMAGE_LAYOUT_UNDEFINED: Not usable by the GPU and the very first
transition will discard the texels.
• VK_IMAGE_LAYOUT_PREINITIALIZED: Not usable by the GPU, but the first
transition will preserve the texels.
191
There are few situations where it is necessary for the texels to be preserved
during the first transition. One example, however, would be if you wanted to use
an image as a staging image in combination with the VK_IMAGE_TILING_LINEAR
layout. In that case, you’d want to upload the texel data to it and then transition
the image to be a transfer source without losing the data. In our case, however,
we’re first going to transition the image to be a transfer destination and then
copy texel data to it from a buffer object, so we don’t need this property and
can safely use VK_IMAGE_LAYOUT_UNDEFINED.
1 imageInfo.usage = VK_IMAGE_USAGE_TRANSFER_DST_BIT |
VK_IMAGE_USAGE_SAMPLED_BIT;
The usage field has the same semantics as the one during buffer creation.
The image is going to be used as destination for the buffer copy, so it should
be set up as a transfer destination. We also want to be able to access
the image from the shader to color our mesh, so the usage should include
VK_IMAGE_USAGE_SAMPLED_BIT.
1 imageInfo.sharingMode = VK_SHARING_MODE_EXCLUSIVE;
The image will only be used by one queue family: the one that supports graphics
(and therefore also) transfer operations.
1 imageInfo.samples = VK_SAMPLE_COUNT_1_BIT;
2 imageInfo.flags = 0; // Optional
The samples flag is related to multisampling. This is only relevant for images
that will be used as attachments, so stick to one sample. There are some optional
flags for images that are related to sparse images. Sparse images are images
where only certain regions are actually backed by memory. If you were using
a 3D texture for a voxel terrain, for example, then you could use this to avoid
allocating memory to store large volumes of “air” values. We won’t be using it
in this tutorial, so leave it to its default value of 0.
1 if (vkCreateImage(device, &imageInfo, nullptr, &textureImage) !=
VK_SUCCESS) {
2 throw std::runtime_error("failed to create image!");
3 }
The image is created using vkCreateImage, which doesn’t have any particularly
noteworthy parameters. It is possible that the VK_FORMAT_R8G8B8A8_SRGB for-
mat is not supported by the graphics hardware. You should have a list of
acceptable alternatives and go with the best one that is supported. However,
support for this particular format is so widespread that we’ll skip this step. Us-
ing different formats would also require annoying conversions. We will get back
to this in the depth buffer chapter, where we’ll implement such a system.
1 VkMemoryRequirements memRequirements;
192
2 vkGetImageMemoryRequirements(device, textureImage, &memRequirements);
3
4 VkMemoryAllocateInfo allocInfo{};
5 allocInfo.sType = VK_STRUCTURE_TYPE_MEMORY_ALLOCATE_INFO;
6 allocInfo.allocationSize = memRequirements.size;
7 allocInfo.memoryTypeIndex =
findMemoryType(memRequirements.memoryTypeBits,
VK_MEMORY_PROPERTY_DEVICE_LOCAL_BIT);
8
9 if (vkAllocateMemory(device, &allocInfo, nullptr,
&textureImageMemory) != VK_SUCCESS) {
10 throw std::runtime_error("failed to allocate image memory!");
11 }
12
13 vkBindImageMemory(device, textureImage, textureImageMemory, 0);
Allocating memory for an image works in exactly the same way as allocat-
ing memory for a buffer. Use vkGetImageMemoryRequirements instead of
vkGetBufferMemoryRequirements, and use vkBindImageMemory instead of
vkBindBufferMemory.
This function is already getting quite large and there’ll be a need to create
more images in later chapters, so we should abstract image creation into a
createImage function, like we did for buffers. Create the function and move
the image object creation and memory allocation to it:
1 void createImage(uint32_t width, uint32_t height, VkFormat format,
VkImageTiling tiling, VkImageUsageFlags usage,
VkMemoryPropertyFlags properties, VkImage& image,
VkDeviceMemory& imageMemory) {
2 VkImageCreateInfo imageInfo{};
3 imageInfo.sType = VK_STRUCTURE_TYPE_IMAGE_CREATE_INFO;
4 imageInfo.imageType = VK_IMAGE_TYPE_2D;
5 imageInfo.extent.width = width;
6 imageInfo.extent.height = height;
7 imageInfo.extent.depth = 1;
8 imageInfo.mipLevels = 1;
9 imageInfo.arrayLayers = 1;
10 imageInfo.format = format;
11 imageInfo.tiling = tiling;
12 imageInfo.initialLayout = VK_IMAGE_LAYOUT_UNDEFINED;
13 imageInfo.usage = usage;
14 imageInfo.samples = VK_SAMPLE_COUNT_1_BIT;
15 imageInfo.sharingMode = VK_SHARING_MODE_EXCLUSIVE;
16
17 if (vkCreateImage(device, &imageInfo, nullptr, &image) !=
VK_SUCCESS) {
193
18 throw std::runtime_error("failed to create image!");
19 }
20
21 VkMemoryRequirements memRequirements;
22 vkGetImageMemoryRequirements(device, image, &memRequirements);
23
24 VkMemoryAllocateInfo allocInfo{};
25 allocInfo.sType = VK_STRUCTURE_TYPE_MEMORY_ALLOCATE_INFO;
26 allocInfo.allocationSize = memRequirements.size;
27 allocInfo.memoryTypeIndex =
findMemoryType(memRequirements.memoryTypeBits, properties);
28
29 if (vkAllocateMemory(device, &allocInfo, nullptr, &imageMemory)
!= VK_SUCCESS) {
30 throw std::runtime_error("failed to allocate image memory!");
31 }
32
33 vkBindImageMemory(device, image, imageMemory, 0);
34 }
I’ve made the width, height, format, tiling mode, usage, and memory properties
parameters, because these will all vary between the images we’ll be creating
throughout this tutorial.
The createTextureImage function can now be simplified to:
1 void createTextureImage() {
2 int texWidth, texHeight, texChannels;
3 stbi_uc* pixels = stbi_load("textures/texture.jpg", &texWidth,
&texHeight, &texChannels, STBI_rgb_alpha);
4 VkDeviceSize imageSize = texWidth * texHeight * 4;
5
6 if (!pixels) {
7 throw std::runtime_error("failed to load texture image!");
8 }
9
10 VkBuffer stagingBuffer;
11 VkDeviceMemory stagingBufferMemory;
12 createBuffer(imageSize, VK_BUFFER_USAGE_TRANSFER_SRC_BIT,
VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT |
VK_MEMORY_PROPERTY_HOST_COHERENT_BIT, stagingBuffer,
stagingBufferMemory);
13
14 void* data;
15 vkMapMemory(device, stagingBufferMemory, 0, imageSize, 0, &data);
16 memcpy(data, pixels, static_cast<size_t>(imageSize));
17 vkUnmapMemory(device, stagingBufferMemory);
194
18
19 stbi_image_free(pixels);
20
21 createImage(texWidth, texHeight, VK_FORMAT_R8G8B8A8_SRGB,
VK_IMAGE_TILING_OPTIMAL, VK_IMAGE_USAGE_TRANSFER_DST_BIT |
VK_IMAGE_USAGE_SAMPLED_BIT,
VK_MEMORY_PROPERTY_DEVICE_LOCAL_BIT, textureImage,
textureImageMemory);
22 }
Layout transitions
The function we’re going to write now involves recording and executing a com-
mand buffer again, so now’s a good time to move that logic into a helper function
or two:
1 VkCommandBuffer beginSingleTimeCommands() {
2 VkCommandBufferAllocateInfo allocInfo{};
3 allocInfo.sType = VK_STRUCTURE_TYPE_COMMAND_BUFFER_ALLOCATE_INFO;
4 allocInfo.level = VK_COMMAND_BUFFER_LEVEL_PRIMARY;
5 allocInfo.commandPool = commandPool;
6 allocInfo.commandBufferCount = 1;
7
8 VkCommandBuffer commandBuffer;
9 vkAllocateCommandBuffers(device, &allocInfo, &commandBuffer);
10
11 VkCommandBufferBeginInfo beginInfo{};
12 beginInfo.sType = VK_STRUCTURE_TYPE_COMMAND_BUFFER_BEGIN_INFO;
13 beginInfo.flags = VK_COMMAND_BUFFER_USAGE_ONE_TIME_SUBMIT_BIT;
14
15 vkBeginCommandBuffer(commandBuffer, &beginInfo);
16
17 return commandBuffer;
18 }
19
20 void endSingleTimeCommands(VkCommandBuffer commandBuffer) {
21 vkEndCommandBuffer(commandBuffer);
22
23 VkSubmitInfo submitInfo{};
24 submitInfo.sType = VK_STRUCTURE_TYPE_SUBMIT_INFO;
25 submitInfo.commandBufferCount = 1;
26 submitInfo.pCommandBuffers = &commandBuffer;
27
28 vkQueueSubmit(graphicsQueue, 1, &submitInfo, VK_NULL_HANDLE);
29 vkQueueWaitIdle(graphicsQueue);
30
195
31 vkFreeCommandBuffers(device, commandPool, 1, &commandBuffer);
32 }
The code for these functions is based on the existing code in copyBuffer. You
can now simplify that function to:
1 void copyBuffer(VkBuffer srcBuffer, VkBuffer dstBuffer, VkDeviceSize
size) {
2 VkCommandBuffer commandBuffer = beginSingleTimeCommands();
3
4 VkBufferCopy copyRegion{};
5 copyRegion.size = size;
6 vkCmdCopyBuffer(commandBuffer, srcBuffer, dstBuffer, 1,
©Region);
7
8 endSingleTimeCommands(commandBuffer);
9 }
If we were still using buffers, then we could now write a function to record and
execute vkCmdCopyBufferToImage to finish the job, but this command requires
the image to be in the right layout first. Create a new function to handle layout
transitions:
1 void transitionImageLayout(VkImage image, VkFormat format,
VkImageLayout oldLayout, VkImageLayout newLayout) {
2 VkCommandBuffer commandBuffer = beginSingleTimeCommands();
3
4 endSingleTimeCommands(commandBuffer);
5 }
One of the most common ways to perform layout transitions is using an image
memory barrier. A pipeline barrier like that is generally used to synchronize
access to resources, like ensuring that a write to a buffer completes before read-
ing from it, but it can also be used to transition image layouts and transfer
queue family ownership when VK_SHARING_MODE_EXCLUSIVE is used. There is
an equivalent buffer memory barrier to do this for buffers.
1 VkImageMemoryBarrier barrier{};
2 barrier.sType = VK_STRUCTURE_TYPE_IMAGE_MEMORY_BARRIER;
3 barrier.oldLayout = oldLayout;
4 barrier.newLayout = newLayout;
The first two fields specify layout transition. It is possible to use
VK_IMAGE_LAYOUT_UNDEFINED as oldLayout if you don’t care about the
existing contents of the image.
1 barrier.srcQueueFamilyIndex = VK_QUEUE_FAMILY_IGNORED;
2 barrier.dstQueueFamilyIndex = VK_QUEUE_FAMILY_IGNORED;
196
If you are using the barrier to transfer queue family ownership, then these
two fields should be the indices of the queue families. They must be set to
VK_QUEUE_FAMILY_IGNORED if you don’t want to do this (not the default value!).
1 barrier.image = image;
2 barrier.subresourceRange.aspectMask = VK_IMAGE_ASPECT_COLOR_BIT;
3 barrier.subresourceRange.baseMipLevel = 0;
4 barrier.subresourceRange.levelCount = 1;
5 barrier.subresourceRange.baseArrayLayer = 0;
6 barrier.subresourceRange.layerCount = 1;
The image and subresourceRange specify the image that is affected and the
specific part of the image. Our image is not an array and does not have mipmap-
ping levels, so only one level and layer are specified.
1 barrier.srcAccessMask = 0; // TODO
2 barrier.dstAccessMask = 0; // TODO
Barriers are primarily used for synchronization purposes, so you must specify
which types of operations that involve the resource must happen before the bar-
rier, and which operations that involve the resource must wait on the barrier.
We need to do that despite already using vkQueueWaitIdle to manually syn-
chronize. The right values depend on the old and new layout, so we’ll get back
to this once we’ve figured out which transitions we’re going to use.
1 vkCmdPipelineBarrier(
2 commandBuffer,
3 0 /* TODO */, 0 /* TODO */,
4 0,
5 0, nullptr,
6 0, nullptr,
7 1, &barrier
8 );
All types of pipeline barriers are submitted using the same function. The first pa-
rameter after the command buffer specifies in which pipeline stage the operations
occur that should happen before the barrier. The second parameter specifies the
pipeline stage in which operations will wait on the barrier. The pipeline stages
that you are allowed to specify before and after the barrier depend on how you
use the resource before and after the barrier. The allowed values are listed in this
table of the specification. For example, if you’re going to read from a uniform
after the barrier, you would specify a usage of VK_ACCESS_UNIFORM_READ_BIT
and the earliest shader that will read from the uniform as pipeline stage, for
example VK_PIPELINE_STAGE_FRAGMENT_SHADER_BIT. It would not make sense
to specify a non-shader pipeline stage for this type of usage and the validation
layers will warn you when you specify a pipeline stage that does not match the
type of usage.
197
The third parameter is either 0 or VK_DEPENDENCY_BY_REGION_BIT. The latter
turns the barrier into a per-region condition. That means that the implementa-
tion is allowed to already begin reading from the parts of a resource that were
written so far, for example.
The last three pairs of parameters reference arrays of pipeline barriers of the
three available types: memory barriers, buffer memory barriers, and image
memory barriers like the one we’re using here. Note that we’re not using the
VkFormat parameter yet, but we’ll be using that one for special transitions in
the depth buffer chapter.
Copying buffer to image
Before we get back to createTextureImage, we’re going to write one more
helper function: copyBufferToImage:
1 void copyBufferToImage(VkBuffer buffer, VkImage image, uint32_t
width, uint32_t height) {
2 VkCommandBuffer commandBuffer = beginSingleTimeCommands();
3
4 endSingleTimeCommands(commandBuffer);
5 }
Just like with buffer copies, you need to specify which part of the buffer
is going to be copied to which part of the image. This happens through
VkBufferImageCopy structs:
1 VkBufferImageCopy region{};
2 region.bufferOffset = 0;
3 region.bufferRowLength = 0;
4 region.bufferImageHeight = 0;
5
6 region.imageSubresource.aspectMask = VK_IMAGE_ASPECT_COLOR_BIT;
7 region.imageSubresource.mipLevel = 0;
8 region.imageSubresource.baseArrayLayer = 0;
9 region.imageSubresource.layerCount = 1;
10
11 region.imageOffset = {0, 0, 0};
12 region.imageExtent = {
13 width,
14 height,
15 1
16 };
Most of these fields are self-explanatory. The bufferOffset specifies the byte
offset in the buffer at which the pixel values start. The bufferRowLength and
bufferImageHeight fields specify how the pixels are laid out in memory. For
198
example, you could have some padding bytes between rows of the image. Spec-
ifying 0 for both indicates that the pixels are simply tightly packed like they
are in our case. The imageSubresource, imageOffset and imageExtent fields
indicate to which part of the image we want to copy the pixels.
Buffer to image copy operations are enqueued using the vkCmdCopyBufferToImage
function:
1 vkCmdCopyBufferToImage(
2 commandBuffer,
3 buffer,
4 image,
5 VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL,
6 1,
7 ®ion
8 );
The fourth parameter indicates which layout the image is currently using. I’m
assuming here that the image has already been transitioned to the layout that is
optimal for copying pixels to. Right now we’re only copying one chunk of pixels
to the whole image, but it’s possible to specify an array of VkBufferImageCopy
to perform many different copies from this buffer to the image in one operation.
Preparing the texture image
We now have all of the tools we need to finish setting up the texture image,
so we’re going back to the createTextureImage function. The last thing we
did there was creating the texture image. The next step is to copy the staging
buffer to the texture image. This involves two steps:
• Transition the texture image to VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL
• Execute the buffer to image copy operation
This is easy to do with the functions we just created:
1 transitionImageLayout(textureImage, VK_FORMAT_R8G8B8A8_SRGB,
VK_IMAGE_LAYOUT_UNDEFINED, VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL);
2 copyBufferToImage(stagingBuffer, textureImage,
static_cast<uint32_t>(texWidth),
static_cast<uint32_t>(texHeight));
The image was created with the VK_IMAGE_LAYOUT_UNDEFINED layout, so that
one should be specified as old layout when transitioning textureImage. Re-
member that we can do this because we don’t care about its contents before
performing the copy operation.
To be able to start sampling from the texture image in the shader, we need one
last transition to prepare it for shader access:
199
1 transitionImageLayout(textureImage, VK_FORMAT_R8G8B8A8_SRGB,
VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL,
VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL);
Transition barrier masks
If you run your application with validation layers enabled now, then
you’ll see that it complains about the access masks and pipeline stages in
transitionImageLayout being invalid. We still need to set those based on the
layouts in the transition.
There are two transitions we need to handle:
• Undefined → transfer destination: transfer writes that don’t need to wait
on anything
• Transfer destination → shader reading: shader reads should wait on trans-
fer writes, specifically the shader reads in the fragment shader, because
that’s where we’re going to use the texture
These rules are specified using the following access masks and pipeline stages:
1 VkPipelineStageFlags sourceStage;
2 VkPipelineStageFlags destinationStage;
3
4 if (oldLayout == VK_IMAGE_LAYOUT_UNDEFINED && newLayout ==
VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL) {
5 barrier.srcAccessMask = 0;
6 barrier.dstAccessMask = VK_ACCESS_TRANSFER_WRITE_BIT;
7
8 sourceStage = VK_PIPELINE_STAGE_TOP_OF_PIPE_BIT;
9 destinationStage = VK_PIPELINE_STAGE_TRANSFER_BIT;
10 } else if (oldLayout == VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL &&
newLayout == VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL) {
11 barrier.srcAccessMask = VK_ACCESS_TRANSFER_WRITE_BIT;
12 barrier.dstAccessMask = VK_ACCESS_SHADER_READ_BIT;
13
14 sourceStage = VK_PIPELINE_STAGE_TRANSFER_BIT;
15 destinationStage = VK_PIPELINE_STAGE_FRAGMENT_SHADER_BIT;
16 } else {
17 throw std::invalid_argument("unsupported layout transition!");
18 }
19
20 vkCmdPipelineBarrier(
21 commandBuffer,
22 sourceStage, destinationStage,
23 0,
24 0, nullptr,
200
25 0, nullptr,
26 1, &barrier
27 );
As you can see in the aforementioned table, transfer writes must occur in
the pipeline transfer stage. Since the writes don’t have to wait on anything,
you may specify an empty access mask and the earliest possible pipeline stage
VK_PIPELINE_STAGE_TOP_OF_PIPE_BIT for the pre-barrier operations. It should
be noted that VK_PIPELINE_STAGE_TRANSFER_BIT is not a real stage within the
graphics and compute pipelines. It is more of a pseudo-stage where transfers
happen. See the documentation for more information and other examples of
pseudo-stages.
The image will be written in the same pipeline stage and subsequently read
by the fragment shader, which is why we specify shader reading access in the
fragment shader pipeline stage.
If we need to do more transitions in the future, then we’ll extend the function.
The application should now run successfully, although there are of course no
visual changes yet.
One thing to note is that command buffer submission results in implicit
VK_ACCESS_HOST_WRITE_BIT synchronization at the beginning. Since the
transitionImageLayout function executes a command buffer with only
a single command, you could use this implicit synchronization and set
srcAccessMask to 0 if you ever needed a VK_ACCESS_HOST_WRITE_BIT depen-
dency in a layout transition. It’s up to you if you want to be explicit about it
or not, but I’m personally not a fan of relying on these OpenGL-like “hidden”
operations.
There is actually a special type of image layout that supports all operations,
VK_IMAGE_LAYOUT_GENERAL. The problem with it, of course, is that it doesn’t
necessarily offer the best performance for any operation. It is required for some
special cases, like using an image as both input and output, or for reading an
image after it has left the preinitialized layout.
All of the helper functions that submit commands so far have been set up to
execute synchronously by waiting for the queue to become idle. For practical
applications it is recommended to combine these operations in a single command
buffer and execute them asynchronously for higher throughput, especially the
transitions and copy in the createTextureImage function. Try to experiment
with this by creating a setupCommandBuffer that the helper functions record
commands into, and add a flushSetupCommands to execute the commands that
have been recorded so far. It’s best to do this after the texture mapping works
to check if the texture resources are still set up correctly.
201
Cleanup
Finish the createTextureImage function by cleaning up the staging buffer and
its memory at the end:
1 transitionImageLayout(textureImage, VK_FORMAT_R8G8B8A8_SRGB,
VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL,
VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL);
2
3 vkDestroyBuffer(device, stagingBuffer, nullptr);
4 vkFreeMemory(device, stagingBufferMemory, nullptr);
5 }
The main texture image is used until the end of the program:
1 void cleanup() {
2 cleanupSwapChain();
3
4 vkDestroyImage(device, textureImage, nullptr);
5 vkFreeMemory(device, textureImageMemory, nullptr);
6
7 ...
8 }
The image now contains the texture, but we still need a way to access it from
the graphics pipeline. We’ll work on that in the next chapter.
C++ code / Vertex shader / Fragment shader
Image view and sampler
In this chapter we’re going to create two more resources that are needed for
the graphics pipeline to sample an image. The first resource is one that we’ve
already seen before while working with the swap chain images, but the second
one is new - it relates to how the shader will read texels from the image.
Texture image view
We’ve seen before, with the swap chain images and the framebuffer, that images
are accessed through image views rather than directly. We will also need to
create such an image view for the texture image.
Add a class member to hold a VkImageView for the texture image and create a
new function createTextureImageView where we’ll create it:
1 VkImageView textureImageView;
2
3 ...
202
4
5 void initVulkan() {
6 ...
7 createTextureImage();
8 createTextureImageView();
9 createVertexBuffer();
10 ...
11 }
12
13 ...
14
15 void createTextureImageView() {
16
17 }
The code for this function can be based directly on createImageViews. The
only two changes you have to make are the format and the image:
1 VkImageViewCreateInfo viewInfo{};
2 viewInfo.sType = VK_STRUCTURE_TYPE_IMAGE_VIEW_CREATE_INFO;
3 viewInfo.image = textureImage;
4 viewInfo.viewType = VK_IMAGE_VIEW_TYPE_2D;
5 viewInfo.format = VK_FORMAT_R8G8B8A8_SRGB;
6 viewInfo.subresourceRange.aspectMask = VK_IMAGE_ASPECT_COLOR_BIT;
7 viewInfo.subresourceRange.baseMipLevel = 0;
8 viewInfo.subresourceRange.levelCount = 1;
9 viewInfo.subresourceRange.baseArrayLayer = 0;
10 viewInfo.subresourceRange.layerCount = 1;
I’ve left out the explicit viewInfo.components initialization, because
VK_COMPONENT_SWIZZLE_IDENTITY is defined as 0 anyway. Finish creating the
image view by calling vkCreateImageView:
1 if (vkCreateImageView(device, &viewInfo, nullptr, &textureImageView)
!= VK_SUCCESS) {
2 throw std::runtime_error("failed to create texture image view!");
3 }
Because so much of the logic is duplicated from createImageViews, you may
wish to abstract it into a new createImageView function:
1 VkImageView createImageView(VkImage image, VkFormat format) {
2 VkImageViewCreateInfo viewInfo{};
3 viewInfo.sType = VK_STRUCTURE_TYPE_IMAGE_VIEW_CREATE_INFO;
4 viewInfo.image = image;
5 viewInfo.viewType = VK_IMAGE_VIEW_TYPE_2D;
6 viewInfo.format = format;
203
7 viewInfo.subresourceRange.aspectMask = VK_IMAGE_ASPECT_COLOR_BIT;
8 viewInfo.subresourceRange.baseMipLevel = 0;
9 viewInfo.subresourceRange.levelCount = 1;
10 viewInfo.subresourceRange.baseArrayLayer = 0;
11 viewInfo.subresourceRange.layerCount = 1;
12
13 VkImageView imageView;
14 if (vkCreateImageView(device, &viewInfo, nullptr, &imageView) !=
VK_SUCCESS) {
15 throw std::runtime_error("failed to create texture image
view!");
16 }
17
18 return imageView;
19 }
The createTextureImageView function can now be simplified to:
1 void createTextureImageView() {
2 textureImageView = createImageView(textureImage,
VK_FORMAT_R8G8B8A8_SRGB);
3 }
And createImageViews can be simplified to:
1 void createImageViews() {
2 swapChainImageViews.resize(swapChainImages.size());
3
4 for (uint32_t i = 0; i < swapChainImages.size(); i++) {
5 swapChainImageViews[i] = createImageView(swapChainImages[i],
swapChainImageFormat);
6 }
7 }
Make sure to destroy the image view at the end of the program, right before
destroying the image itself:
1 void cleanup() {
2 cleanupSwapChain();
3
4 vkDestroyImageView(device, textureImageView, nullptr);
5
6 vkDestroyImage(device, textureImage, nullptr);
7 vkFreeMemory(device, textureImageMemory, nullptr);
204
Samplers
It is possible for shaders to read texels directly from images, but that is not very
common when they are used as textures. Textures are usually accessed through
samplers, which will apply filtering and transformations to compute the final
color that is retrieved.
These filters are helpful to deal with problems like oversampling. Consider a
texture that is mapped to geometry with more fragments than texels. If you
simply took the closest texel for the texture coordinate in each fragment, then
you would get a result like the first image:
If you combined the 4 closest texels through linear interpolation, then you would
get a smoother result like the one on the right. Of course your application may
have art style requirements that fit the left style more (think Minecraft), but
the right is preferred in conventional graphics applications. A sampler object
automatically applies this filtering for you when reading a color from the texture.
Undersampling is the opposite problem, where you have more texels than frag-
ments. This will lead to artifacts when sampling high frequency patterns like a
checkerboard texture at a sharp angle:
205
As shown in the left image, the texture turns into a blurry mess in the dis-
tance. The solution to this is anisotropic filtering, which can also be applied
automatically by a sampler.
Aside from these filters, a sampler can also take care of transformations. It
determines what happens when you try to read texels outside the image through
its addressing mode. The image below displays some of the possibilities:
We will now create a function createTextureSampler to set up such a sampler
object. We’ll be using that sampler to read colors from the texture in the shader
later on.
1 void initVulkan() {
2 ...
3 createTextureImage();
4 createTextureImageView();
5 createTextureSampler();
6 ...
7 }
8
9 ...
10
11 void createTextureSampler() {
12
13 }
206
Samplers are configured through a VkSamplerCreateInfo structure, which spec-
ifies all filters and transformations that it should apply.
1 VkSamplerCreateInfo samplerInfo{};
2 samplerInfo.sType = VK_STRUCTURE_TYPE_SAMPLER_CREATE_INFO;
3 samplerInfo.magFilter = VK_FILTER_LINEAR;
4 samplerInfo.minFilter = VK_FILTER_LINEAR;
The magFilter and minFilter fields specify how to interpolate texels that
are magnified or minified. Magnification concerns the oversampling problem
describes above, and minification concerns undersampling. The choices are
VK_FILTER_NEAREST and VK_FILTER_LINEAR, corresponding to the modes
demonstrated in the images above.
1 samplerInfo.addressModeU = VK_SAMPLER_ADDRESS_MODE_REPEAT;
2 samplerInfo.addressModeV = VK_SAMPLER_ADDRESS_MODE_REPEAT;
3 samplerInfo.addressModeW = VK_SAMPLER_ADDRESS_MODE_REPEAT;
The addressing mode can be specified per axis using the addressMode fields.
The available values are listed below. Most of these are demonstrated in the
image above. Note that the axes are called U, V and W instead of X, Y and Z.
This is a convention for texture space coordinates.
• VK_SAMPLER_ADDRESS_MODE_REPEAT: Repeat the texture when going be-
yond the image dimensions.
• VK_SAMPLER_ADDRESS_MODE_MIRRORED_REPEAT: Like repeat, but inverts
the coordinates to mirror the image when going beyond the dimensions.
• VK_SAMPLER_ADDRESS_MODE_CLAMP_TO_EDGE: Take the color of the edge
closest to the coordinate beyond the image dimensions.
• VK_SAMPLER_ADDRESS_MODE_MIRROR_CLAMP_TO_EDGE: Like clamp to edge,
but instead uses the edge opposite to the closest edge.
• VK_SAMPLER_ADDRESS_MODE_CLAMP_TO_BORDER: Return a solid color
when sampling beyond the dimensions of the image.
It doesn’t really matter which addressing mode we use here, because we’re not
going to sample outside of the image in this tutorial. However, the repeat mode
is probably the most common mode, because it can be used to tile textures like
floors and walls.
1 samplerInfo.anisotropyEnable = VK_TRUE;
2 samplerInfo.maxAnisotropy = ???;
These two fields specify if anisotropic filtering should be used. There is no reason
not to use this unless performance is a concern. The maxAnisotropy field limits
the amount of texel samples that can be used to calculate the final color. A
lower value results in better performance, but lower quality results. To figure
out which value we can use, we need to retrieve the properties of the physical
device like so:
207
1 VkPhysicalDeviceProperties properties{};
2 vkGetPhysicalDeviceProperties(physicalDevice, &properties);
If you look at the documentation for the VkPhysicalDeviceProperties struc-
ture, you’ll see that it contains a VkPhysicalDeviceLimits member named
limits. This struct in turn has a member called maxSamplerAnisotropy and
this is the maximum value we can specify for maxAnisotropy. If we want to go
for maximum quality, we can simply use that value directly:
1 samplerInfo.maxAnisotropy = properties.limits.maxSamplerAnisotropy;
You can either query the properties at the beginning of your program and
pass them around to the functions that need them, or query them in the
createTextureSampler function itself.
1 samplerInfo.borderColor = VK_BORDER_COLOR_INT_OPAQUE_BLACK;
The borderColor field specifies which color is returned when sampling beyond
the image with clamp to border addressing mode. It is possible to return black,
white or transparent in either float or int formats. You cannot specify an arbi-
trary color.
1 samplerInfo.unnormalizedCoordinates = VK_FALSE;
The unnormalizedCoordinates field specifies which coordinate system you
want to use to address texels in an image. If this field is VK_TRUE, then you
can simply use coordinates within the [0, texWidth) and [0, texHeight)
range. If it is VK_FALSE, then the texels are addressed using the [0, 1) range
on all axes. Real-world applications almost always use normalized coordinates,
because then it’s possible to use textures of varying resolutions with the exact
same coordinates.
1 samplerInfo.compareEnable = VK_FALSE;
2 samplerInfo.compareOp = VK_COMPARE_OP_ALWAYS;
If a comparison function is enabled, then texels will first be compared to a value,
and the result of that comparison is used in filtering operations. This is mainly
used for percentage-closer filtering on shadow maps. We’ll look at this in a
future chapter.
1 samplerInfo.mipmapMode = VK_SAMPLER_MIPMAP_MODE_LINEAR;
2 samplerInfo.mipLodBias = 0.0f;
3 samplerInfo.minLod = 0.0f;
4 samplerInfo.maxLod = 0.0f;
All of these fields apply to mipmapping. We will look at mipmapping in a later
chapter, but basically it’s another type of filter that can be applied.
The functioning of the sampler is now fully defined. Add a class member to hold
the handle of the sampler object and create the sampler with vkCreateSampler:
208
1 VkImageView textureImageView;
2 VkSampler textureSampler;
3
4 ...
5
6 void createTextureSampler() {
7 ...
8
9 if (vkCreateSampler(device, &samplerInfo, nullptr,
&textureSampler) != VK_SUCCESS) {
10 throw std::runtime_error("failed to create texture
sampler!");
11 }
12 }
Note the sampler does not reference a VkImage anywhere. The sampler is a
distinct object that provides an interface to extract colors from a texture. It
can be applied to any image you want, whether it is 1D, 2D or 3D. This is
different from many older APIs, which combined texture images and filtering
into a single state.
Destroy the sampler at the end of the program when we’ll no longer be accessing
the image:
1 void cleanup() {
2 cleanupSwapChain();
3
4 vkDestroySampler(device, textureSampler, nullptr);
5 vkDestroyImageView(device, textureImageView, nullptr);
6
7 ...
8 }
Anisotropy device feature
If you run your program right now, you’ll see a validation layer message like
this:
That’s because anisotropic filtering is actually an optional device feature. We
need to update the createLogicalDevice function to request it:
1 VkPhysicalDeviceFeatures deviceFeatures{};
2 deviceFeatures.samplerAnisotropy = VK_TRUE;
209
And even though it is very unlikely that a modern graphics card will not support
it, we should update isDeviceSuitable to check if it is available:
1 bool isDeviceSuitable(VkPhysicalDevice device) {
2 ...
3
4 VkPhysicalDeviceFeatures supportedFeatures;
5 vkGetPhysicalDeviceFeatures(device, &supportedFeatures);
6
7 return indices.isComplete() && extensionsSupported &&
swapChainAdequate && supportedFeatures.samplerAnisotropy;
8 }
The vkGetPhysicalDeviceFeatures repurposes the VkPhysicalDeviceFeatures
struct to indicate which features are supported rather than requested by setting
the boolean values.
Instead of enforcing the availability of anisotropic filtering, it’s also possible to
simply not use it by conditionally setting:
1 samplerInfo.anisotropyEnable = VK_FALSE;
2 samplerInfo.maxAnisotropy = 1.0f;
In the next chapter we will expose the image and sampler objects to the shaders
to draw the texture onto the square.
C++ code / Vertex shader / Fragment shader
Combined image sampler
Introduction
We looked at descriptors for the first time in the uniform buffers part of the
tutorial. In this chapter we will look at a new type of descriptor: combined
image sampler. This descriptor makes it possible for shaders to access an im-
age resource through a sampler object like the one we created in the previous
chapter.
We’ll start by modifying the descriptor layout, descriptor pool and descriptor set
to include such a combined image sampler descriptor. After that, we’re going
to add texture coordinates to Vertex and modify the fragment shader to read
colors from the texture instead of just interpolating the vertex colors.
Updating the descriptors
Browse to the createDescriptorSetLayout function and add a VkDescriptorSetLayoutBinding
for a combined image sampler descriptor. We’ll simply put it in the binding
after the uniform buffer:
210
1 VkDescriptorSetLayoutBinding samplerLayoutBinding{};
2 samplerLayoutBinding.binding = 1;
3 samplerLayoutBinding.descriptorCount = 1;
4 samplerLayoutBinding.descriptorType =
VK_DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER;
5 samplerLayoutBinding.pImmutableSamplers = nullptr;
6 samplerLayoutBinding.stageFlags = VK_SHADER_STAGE_FRAGMENT_BIT;
7
8 std::array<VkDescriptorSetLayoutBinding, 2> bindings =
{uboLayoutBinding, samplerLayoutBinding};
9 VkDescriptorSetLayoutCreateInfo layoutInfo{};
10 layoutInfo.sType =
VK_STRUCTURE_TYPE_DESCRIPTOR_SET_LAYOUT_CREATE_INFO;
11 layoutInfo.bindingCount = static_cast<uint32_t>(bindings.size());
12 layoutInfo.pBindings = bindings.data();
Make sure to set the stageFlags to indicate that we intend to use the combined
image sampler descriptor in the fragment shader. That’s where the color of the
fragment is going to be determined. It is possible to use texture sampling in
the vertex shader, for example to dynamically deform a grid of vertices by a
heightmap.
We must also create a larger descriptor pool to make room for the alloca-
tion of the combined image sampler by adding another VkPoolSize of type
VK_DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER to the VkDescriptorPoolCreateInfo.
Go to the createDescriptorPool function and modify it to include a
VkDescriptorPoolSize for this descriptor:
1 std::array<VkDescriptorPoolSize, 2> poolSizes{};
2 poolSizes[0].type = VK_DESCRIPTOR_TYPE_UNIFORM_BUFFER;
3 poolSizes[0].descriptorCount =
static_cast<uint32_t>(MAX_FRAMES_IN_FLIGHT);
4 poolSizes[1].type = VK_DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER;
5 poolSizes[1].descriptorCount =
static_cast<uint32_t>(MAX_FRAMES_IN_FLIGHT);
6
7 VkDescriptorPoolCreateInfo poolInfo{};
8 poolInfo.sType = VK_STRUCTURE_TYPE_DESCRIPTOR_POOL_CREATE_INFO;
9 poolInfo.poolSizeCount = static_cast<uint32_t>(poolSizes.size());
10 poolInfo.pPoolSizes = poolSizes.data();
11 poolInfo.maxSets = static_cast<uint32_t>(MAX_FRAMES_IN_FLIGHT);
Inadequate descriptor pools are a good example of a problem that the vali-
dation layers will not catch: As of Vulkan 1.1, vkAllocateDescriptorSets
may fail with the error code VK_ERROR_POOL_OUT_OF_MEMORY if the pool is not
sufficiently large, but the driver may also try to solve the problem internally.
This means that sometimes (depending on hardware, pool size and allocation
211
size) the driver will let us get away with an allocation that exceeds the limits
of our descriptor pool. Other times, vkAllocateDescriptorSets will fail and
return VK_ERROR_POOL_OUT_OF_MEMORY. This can be particularly frustrating if
the allocation succeeds on some machines, but fails on others.
Since Vulkan shifts the responsiblity for the allocation to the driver, it is no
longer a strict requirement to only allocate as many descriptors of a certain
type (VK_DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER, etc.) as specified
by the corresponding descriptorCount members for the creation of the
descriptor pool. However, it remains best practise to do so, and in the future,
VK_LAYER_KHRONOS_validation will warn about this type of problem if you
enable Best Practice Validation.
The final step is to bind the actual image and sampler resources to the descrip-
tors in the descriptor set. Go to the createDescriptorSets function.
1 for (size_t i = 0; i < MAX_FRAMES_IN_FLIGHT; i++) {
2 VkDescriptorBufferInfo bufferInfo{};
3 bufferInfo.buffer = uniformBuffers[i];
4 bufferInfo.offset = 0;
5 bufferInfo.range = sizeof(UniformBufferObject);
6
7 VkDescriptorImageInfo imageInfo{};
8 imageInfo.imageLayout = VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL;
9 imageInfo.imageView = textureImageView;
10 imageInfo.sampler = textureSampler;
11
12 ...
13 }
The resources for a combined image sampler structure must be specified in a
VkDescriptorImageInfo struct, just like the buffer resource for a uniform buffer
descriptor is specified in a VkDescriptorBufferInfo struct. This is where the
objects from the previous chapter come together.
1 std::array<VkWriteDescriptorSet, 2> descriptorWrites{};
2
3 descriptorWrites[0].sType = VK_STRUCTURE_TYPE_WRITE_DESCRIPTOR_SET;
4 descriptorWrites[0].dstSet = descriptorSets[i];
5 descriptorWrites[0].dstBinding = 0;
6 descriptorWrites[0].dstArrayElement = 0;
7 descriptorWrites[0].descriptorType =
VK_DESCRIPTOR_TYPE_UNIFORM_BUFFER;
8 descriptorWrites[0].descriptorCount = 1;
9 descriptorWrites[0].pBufferInfo = &bufferInfo;
10
11 descriptorWrites[1].sType = VK_STRUCTURE_TYPE_WRITE_DESCRIPTOR_SET;
12 descriptorWrites[1].dstSet = descriptorSets[i];
212
13 descriptorWrites[1].dstBinding = 1;
14 descriptorWrites[1].dstArrayElement = 0;
15 descriptorWrites[1].descriptorType =
VK_DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER;
16 descriptorWrites[1].descriptorCount = 1;
17 descriptorWrites[1].pImageInfo = &imageInfo;
18
19 vkUpdateDescriptorSets(device,
static_cast<uint32_t>(descriptorWrites.size()),
descriptorWrites.data(), 0, nullptr);
The descriptors must be updated with this image info, just like the buffer. This
time we’re using the pImageInfo array instead of pBufferInfo. The descriptors
are now ready to be used by the shaders!
Texture coordinates
There is one important ingredient for texture mapping that is still missing, and
that’s the actual coordinates for each vertex. The coordinates determine how
the image is actually mapped to the geometry.
1 struct Vertex {
2 glm::vec2 pos;
3 glm::vec3 color;
4 glm::vec2 texCoord;
5
6 static VkVertexInputBindingDescription getBindingDescription() {
7 VkVertexInputBindingDescription bindingDescription{};
8 bindingDescription.binding = 0;
9 bindingDescription.stride = sizeof(Vertex);
10 bindingDescription.inputRate = VK_VERTEX_INPUT_RATE_VERTEX;
11
12 return bindingDescription;
13 }
14
15 static std::array<VkVertexInputAttributeDescription, 3>
getAttributeDescriptions() {
16 std::array<VkVertexInputAttributeDescription, 3>
attributeDescriptions{};
17
18 attributeDescriptions[0].binding = 0;
19 attributeDescriptions[0].location = 0;
20 attributeDescriptions[0].format = VK_FORMAT_R32G32_SFLOAT;
21 attributeDescriptions[0].offset = offsetof(Vertex, pos);
22
23 attributeDescriptions[1].binding = 0;
213
24 attributeDescriptions[1].location = 1;
25 attributeDescriptions[1].format = VK_FORMAT_R32G32B32_SFLOAT;
26 attributeDescriptions[1].offset = offsetof(Vertex, color);
27
28 attributeDescriptions[2].binding = 0;
29 attributeDescriptions[2].location = 2;
30 attributeDescriptions[2].format = VK_FORMAT_R32G32_SFLOAT;
31 attributeDescriptions[2].offset = offsetof(Vertex, texCoord);
32
33 return attributeDescriptions;
34 }
35 };
Modify the Vertex struct to include a vec2 for texture coordinates. Make sure
to also add a VkVertexInputAttributeDescription so that we can use access
texture coordinates as input in the vertex shader. That is necessary to be able
to pass them to the fragment shader for interpolation across the surface of the
square.
1 const std::vector<Vertex> vertices = {
2 {{-0.5f, -0.5f}, {1.0f, 0.0f, 0.0f}, {1.0f, 0.0f}},
3 {{0.5f, -0.5f}, {0.0f, 1.0f, 0.0f}, {0.0f, 0.0f}},
4 {{0.5f, 0.5f}, {0.0f, 0.0f, 1.0f}, {0.0f, 1.0f}},
5 {{-0.5f, 0.5f}, {1.0f, 1.0f, 1.0f}, {1.0f, 1.0f}}
6 };
In this tutorial, I will simply fill the square with the texture by using coordinates
from 0, 0 in the top-left corner to 1, 1 in the bottom-right corner. Feel free to
experiment with different coordinates. Try using coordinates below 0 or above
1 to see the addressing modes in action!
Shaders
The final step is modifying the shaders to sample colors from the texture. We
first need to modify the vertex shader to pass through the texture coordinates
to the fragment shader:
1 layout(location = 0) in vec2 inPosition;
2 layout(location = 1) in vec3 inColor;
3 layout(location = 2) in vec2 inTexCoord;
4
5 layout(location = 0) out vec3 fragColor;
6 layout(location = 1) out vec2 fragTexCoord;
7
8 void main() {
9 gl_Position = ubo.proj * ubo.view * ubo.model * vec4(inPosition,
0.0, 1.0);
214
10 fragColor = inColor;
11 fragTexCoord = inTexCoord;
12 }
Just like the per vertex colors, the fragTexCoord values will be smoothly inter-
polated across the area of the square by the rasterizer. We can visualize this by
having the fragment shader output the texture coordinates as colors:
1 #version 450
2
3 layout(location = 0) in vec3 fragColor;
4 layout(location = 1) in vec2 fragTexCoord;
5
6 layout(location = 0) out vec4 outColor;
7
8 void main() {
9 outColor = vec4(fragTexCoord, 0.0, 1.0);
10 }
You should see something like the image below. Don’t forget to recompile the
shaders!
The green channel represents the horizontal coordinates and the red channel
the vertical coordinates. The black and yellow corners confirm that the tex-
215
ture coordinates are correctly interpolated from 0, 0 to 1, 1 across the square.
Visualizing data using colors is the shader programming equivalent of printf
debugging, for lack of a better option!
A combined image sampler descriptor is represented in GLSL by a sampler
uniform. Add a reference to it in the fragment shader:
1 layout(binding = 1) uniform sampler2D texSampler;
There are equivalent sampler1D and sampler3D types for other types of images.
Make sure to use the correct binding here.
1 void main() {
2 outColor = texture(texSampler, fragTexCoord);
3 }
Textures are sampled using the built-in texture function. It takes a sampler
and coordinate as arguments. The sampler automatically takes care of the
filtering and transformations in the background. You should now see the texture
on the square when you run the application:
Try experimenting with the addressing modes by scaling the texture coordinates
to values higher than 1. For example, the following fragment shader produces
the result in the image below when using VK_SAMPLER_ADDRESS_MODE_REPEAT:
216
1 void main() {
2 outColor = texture(texSampler, fragTexCoord * 2.0);
3 }
You can also manipulate the texture colors using the vertex colors:
1 void main() {
2 outColor = vec4(fragColor * texture(texSampler,
fragTexCoord).rgb, 1.0);
3 }
I’ve separated the RGB and alpha channels here to not scale the alpha channel.
217
You now know how to access images in shaders! This is a very powerful technique
when combined with images that are also written to in framebuffers. You can
use these images as inputs to implement cool effects like post-processing and
camera displays within the 3D world.
C++ code / Vertex shader / Fragment shader
218
Depth buffering
Introduction
The geometry we’ve worked with so far is projected into 3D, but it’s still com-
pletely flat. In this chapter we’re going to add a Z coordinate to the position to
prepare for 3D meshes. We’ll use this third coordinate to place a square over
the current square to see a problem that arises when geometry is not sorted by
depth.
3D geometry
Change the Vertex struct to use a 3D vector for the position, and update the
format in the corresponding VkVertexInputAttributeDescription:
1 struct Vertex {
2 glm::vec3 pos;
3 glm::vec3 color;
4 glm::vec2 texCoord;
5
6 ...
7
8 static std::array<VkVertexInputAttributeDescription, 3>
getAttributeDescriptions() {
9 std::array<VkVertexInputAttributeDescription, 3>
attributeDescriptions{};
10
11 attributeDescriptions[0].binding = 0;
12 attributeDescriptions[0].location = 0;
13 attributeDescriptions[0].format = VK_FORMAT_R32G32B32_SFLOAT;
14 attributeDescriptions[0].offset = offsetof(Vertex, pos);
15
16 ...
17 }
18 };
219
Next, update the vertex shader to accept and transform 3D coordinates as input.
Don’t forget to recompile it afterwards!
1 layout(location = 0) in vec3 inPosition;
2
3 ...
4
5 void main() {
6 gl_Position = ubo.proj * ubo.view * ubo.model * vec4(inPosition,
1.0);
7 fragColor = inColor;
8 fragTexCoord = inTexCoord;
9 }
Lastly, update the vertices container to include Z coordinates:
1 const std::vector<Vertex> vertices = {
2 {{-0.5f, -0.5f, 0.0f}, {1.0f, 0.0f, 0.0f}, {0.0f, 0.0f}},
3 {{0.5f, -0.5f, 0.0f}, {0.0f, 1.0f, 0.0f}, {1.0f, 0.0f}},
4 {{0.5f, 0.5f, 0.0f}, {0.0f, 0.0f, 1.0f}, {1.0f, 1.0f}},
5 {{-0.5f, 0.5f, 0.0f}, {1.0f, 1.0f, 1.0f}, {0.0f, 1.0f}}
6 };
If you run your application now, then you should see exactly the same result as
before. It’s time to add some extra geometry to make the scene more interest-
ing, and to demonstrate the problem that we’re going to tackle in this chapter.
Duplicate the vertices to define positions for a square right under the current
one like this:
Use Z coordinates of -0.5f and add the appropriate indices for the extra square:
1 const std::vector<Vertex> vertices = {
2 {{-0.5f, -0.5f, 0.0f}, {1.0f, 0.0f, 0.0f}, {0.0f, 0.0f}},
220
3 {{0.5f, -0.5f, 0.0f}, {0.0f, 1.0f, 0.0f}, {1.0f, 0.0f}},
4 {{0.5f, 0.5f, 0.0f}, {0.0f, 0.0f, 1.0f}, {1.0f, 1.0f}},
5 {{-0.5f, 0.5f, 0.0f}, {1.0f, 1.0f, 1.0f}, {0.0f, 1.0f}},
6
7 {{-0.5f, -0.5f, -0.5f}, {1.0f, 0.0f, 0.0f}, {0.0f, 0.0f}},
8 {{0.5f, -0.5f, -0.5f}, {0.0f, 1.0f, 0.0f}, {1.0f, 0.0f}},
9 {{0.5f, 0.5f, -0.5f}, {0.0f, 0.0f, 1.0f}, {1.0f, 1.0f}},
10 {{-0.5f, 0.5f, -0.5f}, {1.0f, 1.0f, 1.0f}, {0.0f, 1.0f}}
11 };
12
13 const std::vector<uint16_t> indices = {
14 0, 1, 2, 2, 3, 0,
15 4, 5, 6, 6, 7, 4
16 };
Run your program now and you’ll see something resembling an Escher illustra-
tion:
The problem is that the fragments of the lower square are drawn over the frag-
ments of the upper square, simply because it comes later in the index array.
There are two ways to solve this:
• Sort all of the draw calls by depth from back to front
221
• Use depth testing with a depth buffer
The first approach is commonly used for drawing transparent objects, because
order-independent transparency is a difficult challenge to solve. However, the
problem of ordering fragments by depth is much more commonly solved using a
depth buffer. A depth buffer is an additional attachment that stores the depth for
every position, just like the color attachment stores the color of every position.
Every time the rasterizer produces a fragment, the depth test will check if the
new fragment is closer than the previous one. If it isn’t, then the new fragment
is discarded. A fragment that passes the depth test writes its own depth to the
depth buffer. It is possible to manipulate this value from the fragment shader,
just like you can manipulate the color output.
1 #define GLM_FORCE_RADIANS
2 #define GLM_FORCE_DEPTH_ZERO_TO_ONE
3 #include <glm/glm.hpp>
4 #include <glm/gtc/matrix_transform.hpp>
The perspective projection matrix generated by GLM will use the OpenGL
depth range of -1.0 to 1.0 by default. We need to configure it to use the Vulkan
range of 0.0 to 1.0 using the GLM_FORCE_DEPTH_ZERO_TO_ONE definition.
Depth image and view
A depth attachment is based on an image, just like the color attachment. The
difference is that the swap chain will not automatically create depth images for
us. We only need a single depth image, because only one draw operation is
running at once. The depth image will again require the trifecta of resources:
image, memory and image view.
1 VkImage depthImage;
2 VkDeviceMemory depthImageMemory;
3 VkImageView depthImageView;
Create a new function createDepthResources to set up these resources:
1 void initVulkan() {
2 ...
3 createCommandPool();
4 createDepthResources();
5 createTextureImage();
6 ...
7 }
8
9 ...
10
11 void createDepthResources() {
222
12
13 }
Creating a depth image is fairly straightforward. It should have the same resolu-
tion as the color attachment, defined by the swap chain extent, an image usage
appropriate for a depth attachment, optimal tiling and device local memory.
The only question is: what is the right format for a depth image? The format
must contain a depth component, indicated by _D??_ in the VK_FORMAT_.
Unlike the texture image, we don’t necessarily need a specific format, because we
won’t be directly accessing the texels from the program. It just needs to have
a reasonable accuracy, at least 24 bits is common in real-world applications.
There are several formats that fit this requirement:
• VK_FORMAT_D32_SFLOAT: 32-bit float for depth
• VK_FORMAT_D32_SFLOAT_S8_UINT: 32-bit signed float for depth and 8 bit
stencil component
• VK_FORMAT_D24_UNORM_S8_UINT: 24-bit float for depth and 8 bit stencil
component
The stencil component is used for stencil tests, which is an additional test that
can be combined with depth testing. We’ll look at this in a future chapter.
We could simply go for the VK_FORMAT_D32_SFLOAT format, because support
for it is extremely common (see the hardware database), but it’s nice to add
some extra flexibility to our application where possible. We’re going to write a
function findSupportedFormat that takes a list of candidate formats in order
from most desirable to least desirable, and checks which is the first one that is
supported:
1 VkFormat findSupportedFormat(const std::vector<VkFormat>&
candidates, VkImageTiling tiling, VkFormatFeatureFlags features)
{
2
3 }
The support of a format depends on the tiling mode and usage, so we must also
include these as parameters. The support of a format can be queried using the
vkGetPhysicalDeviceFormatProperties function:
1 for (VkFormat format : candidates) {
2 VkFormatProperties props;
3 vkGetPhysicalDeviceFormatProperties(physicalDevice, format,
&props);
4 }
The VkFormatProperties struct contains three fields:
• linearTilingFeatures: Use cases that are supported with linear tiling
223
• optimalTilingFeatures: Use cases that are supported with optimal
tiling
• bufferFeatures: Use cases that are supported for buffers
Only the first two are relevant here, and the one we check depends on the tiling
parameter of the function:
1 if (tiling == VK_IMAGE_TILING_LINEAR && (props.linearTilingFeatures
& features) == features) {
2 return format;
3 } else if (tiling == VK_IMAGE_TILING_OPTIMAL &&
(props.optimalTilingFeatures & features) == features) {
4 return format;
5 }
If none of the candidate formats support the desired usage, then we can either
return a special value or simply throw an exception:
1 VkFormat findSupportedFormat(const std::vector<VkFormat>&
candidates, VkImageTiling tiling, VkFormatFeatureFlags features)
{
2 for (VkFormat format : candidates) {
3 VkFormatProperties props;
4 vkGetPhysicalDeviceFormatProperties(physicalDevice, format,
&props);
5
6 if (tiling == VK_IMAGE_TILING_LINEAR &&
(props.linearTilingFeatures & features) == features) {
7 return format;
8 } else if (tiling == VK_IMAGE_TILING_OPTIMAL &&
(props.optimalTilingFeatures & features) == features) {
9 return format;
10 }
11 }
12
13 throw std::runtime_error("failed to find supported format!");
14 }
We’ll use this function now to create a findDepthFormat helper function to se-
lect a format with a depth component that supports usage as depth attachment:
1 VkFormat findDepthFormat() {
2 return findSupportedFormat(
3 {VK_FORMAT_D32_SFLOAT, VK_FORMAT_D32_SFLOAT_S8_UINT,
VK_FORMAT_D24_UNORM_S8_UINT},
4 VK_IMAGE_TILING_OPTIMAL,
5 VK_FORMAT_FEATURE_DEPTH_STENCIL_ATTACHMENT_BIT
6 );
224
7 }
Make sure to use the VK_FORMAT_FEATURE_ flag instead of VK_IMAGE_USAGE_ in
this case. All of these candidate formats contain a depth component, but the
latter two also contain a stencil component. We won’t be using that yet, but we
do need to take that into account when performing layout transitions on images
with these formats. Add a simple helper function that tells us if the chosen
depth format contains a stencil component:
1 bool hasStencilComponent(VkFormat format) {
2 return format == VK_FORMAT_D32_SFLOAT_S8_UINT || format ==
VK_FORMAT_D24_UNORM_S8_UINT;
3 }
Call the function to find a depth format from createDepthResources:
1 VkFormat depthFormat = findDepthFormat();
We now have all the required information to invoke our createImage and
createImageView helper functions:
1 createImage(swapChainExtent.width, swapChainExtent.height,
depthFormat, VK_IMAGE_TILING_OPTIMAL,
VK_IMAGE_USAGE_DEPTH_STENCIL_ATTACHMENT_BIT,
VK_MEMORY_PROPERTY_DEVICE_LOCAL_BIT, depthImage,
depthImageMemory);
2 depthImageView = createImageView(depthImage, depthFormat);
However, the createImageView function currently assumes that the subresource
is always the VK_IMAGE_ASPECT_COLOR_BIT, so we will need to turn that field
into a parameter:
1 VkImageView createImageView(VkImage image, VkFormat format,
VkImageAspectFlags aspectFlags) {
2 ...
3 viewInfo.subresourceRange.aspectMask = aspectFlags;
4 ...
5 }
Update all calls to this function to use the right aspect:
1 swapChainImageViews[i] = createImageView(swapChainImages[i],
swapChainImageFormat, VK_IMAGE_ASPECT_COLOR_BIT);
2 ...
3 depthImageView = createImageView(depthImage, depthFormat,
VK_IMAGE_ASPECT_DEPTH_BIT);
4 ...
5 textureImageView = createImageView(textureImage,
VK_FORMAT_R8G8B8A8_SRGB, VK_IMAGE_ASPECT_COLOR_BIT);
225
That’s it for creating the depth image. We don’t need to map it or copy another
image to it, because we’re going to clear it at the start of the render pass like
the color attachment.
Explicitly transitioning the depth image
We don’t need to explicitly transition the layout of the image to a depth at-
tachment because we’ll take care of this in the render pass. However, for com-
pleteness I’ll still describe the process in this section. You may skip it if you
like.
Make a call to transitionImageLayout at the end of the createDepthResources
function like so:
1 transitionImageLayout(depthImage, depthFormat,
VK_IMAGE_LAYOUT_UNDEFINED,
VK_IMAGE_LAYOUT_DEPTH_STENCIL_ATTACHMENT_OPTIMAL);
The undefined layout can be used as initial layout, because there are no existing
depth image contents that matter. We need to update some of the logic in
transitionImageLayout to use the right subresource aspect:
1 if (newLayout == VK_IMAGE_LAYOUT_DEPTH_STENCIL_ATTACHMENT_OPTIMAL) {
2 barrier.subresourceRange.aspectMask = VK_IMAGE_ASPECT_DEPTH_BIT;
3
4 if (hasStencilComponent(format)) {
5 barrier.subresourceRange.aspectMask |=
VK_IMAGE_ASPECT_STENCIL_BIT;
6 }
7 } else {
8 barrier.subresourceRange.aspectMask = VK_IMAGE_ASPECT_COLOR_BIT;
9 }
Although we’re not using the stencil component, we do need to include it in the
layout transitions of the depth image.
Finally, add the correct access masks and pipeline stages:
1 if (oldLayout == VK_IMAGE_LAYOUT_UNDEFINED && newLayout ==
VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL) {
2 barrier.srcAccessMask = 0;
3 barrier.dstAccessMask = VK_ACCESS_TRANSFER_WRITE_BIT;
4
5 sourceStage = VK_PIPELINE_STAGE_TOP_OF_PIPE_BIT;
6 destinationStage = VK_PIPELINE_STAGE_TRANSFER_BIT;
7 } else if (oldLayout == VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL &&
newLayout == VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL) {
8 barrier.srcAccessMask = VK_ACCESS_TRANSFER_WRITE_BIT;
226
9 barrier.dstAccessMask = VK_ACCESS_SHADER_READ_BIT;
10
11 sourceStage = VK_PIPELINE_STAGE_TRANSFER_BIT;
12 destinationStage = VK_PIPELINE_STAGE_FRAGMENT_SHADER_BIT;
13 } else if (oldLayout == VK_IMAGE_LAYOUT_UNDEFINED && newLayout ==
VK_IMAGE_LAYOUT_DEPTH_STENCIL_ATTACHMENT_OPTIMAL) {
14 barrier.srcAccessMask = 0;
15 barrier.dstAccessMask =
VK_ACCESS_DEPTH_STENCIL_ATTACHMENT_READ_BIT |
VK_ACCESS_DEPTH_STENCIL_ATTACHMENT_WRITE_BIT;
16
17 sourceStage = VK_PIPELINE_STAGE_TOP_OF_PIPE_BIT;
18 destinationStage = VK_PIPELINE_STAGE_EARLY_FRAGMENT_TESTS_BIT;
19 } else {
20 throw std::invalid_argument("unsupported layout transition!");
21 }
The depth buffer will be read from to perform depth tests to see if a fragment
is visible, and will be written to when a new fragment is drawn. The reading
happens in the VK_PIPELINE_STAGE_EARLY_FRAGMENT_TESTS_BIT stage and the
writing in the VK_PIPELINE_STAGE_LATE_FRAGMENT_TESTS_BIT. You should
pick the earliest pipeline stage that matches the specified operations, so that it
is ready for usage as depth attachment when it needs to be.
Render pass
We’re now going to modify createRenderPass to include a depth attachment.
First specify the VkAttachmentDescription:
1 VkAttachmentDescription depthAttachment{};
2 depthAttachment.format = findDepthFormat();
3 depthAttachment.samples = VK_SAMPLE_COUNT_1_BIT;
4 depthAttachment.loadOp = VK_ATTACHMENT_LOAD_OP_CLEAR;
5 depthAttachment.storeOp = VK_ATTACHMENT_STORE_OP_DONT_CARE;
6 depthAttachment.stencilLoadOp = VK_ATTACHMENT_LOAD_OP_DONT_CARE;
7 depthAttachment.stencilStoreOp = VK_ATTACHMENT_STORE_OP_DONT_CARE;
8 depthAttachment.initialLayout = VK_IMAGE_LAYOUT_UNDEFINED;
9 depthAttachment.finalLayout =
VK_IMAGE_LAYOUT_DEPTH_STENCIL_ATTACHMENT_OPTIMAL;
The format should be the same as the depth image itself. This time we don’t
care about storing the depth data (storeOp), because it will not be used after
drawing has finished. This may allow the hardware to perform additional op-
timizations. Just like the color buffer, we don’t care about the previous depth
contents, so we can use VK_IMAGE_LAYOUT_UNDEFINED as initialLayout.
227
1 VkAttachmentReference depthAttachmentRef{};
2 depthAttachmentRef.attachment = 1;
3 depthAttachmentRef.layout =
VK_IMAGE_LAYOUT_DEPTH_STENCIL_ATTACHMENT_OPTIMAL;
Add a reference to the attachment for the first (and only) subpass:
1 VkSubpassDescription subpass{};
2 subpass.pipelineBindPoint = VK_PIPELINE_BIND_POINT_GRAPHICS;
3 subpass.colorAttachmentCount = 1;
4 subpass.pColorAttachments = &colorAttachmentRef;
5 subpass.pDepthStencilAttachment = &depthAttachmentRef;
Unlike color attachments, a subpass can only use a single depth (+stencil) at-
tachment. It wouldn’t really make any sense to do depth tests on multiple
buffers.
1 std::array<VkAttachmentDescription, 2> attachments =
{colorAttachment, depthAttachment};
2 VkRenderPassCreateInfo renderPassInfo{};
3 renderPassInfo.sType = VK_STRUCTURE_TYPE_RENDER_PASS_CREATE_INFO;
4 renderPassInfo.attachmentCount =
static_cast<uint32_t>(attachments.size());
5 renderPassInfo.pAttachments = attachments.data();
6 renderPassInfo.subpassCount = 1;
7 renderPassInfo.pSubpasses = &subpass;
8 renderPassInfo.dependencyCount = 1;
9 renderPassInfo.pDependencies = &dependency;
Next, update the VkSubpassDependency struct to refer to both attachments.
1 dependency.srcStageMask =
VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT |
VK_PIPELINE_STAGE_EARLY_FRAGMENT_TESTS_BIT;
2 dependency.dstStageMask =
VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT |
VK_PIPELINE_STAGE_EARLY_FRAGMENT_TESTS_BIT;
3 dependency.dstAccessMask = VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT |
VK_ACCESS_DEPTH_STENCIL_ATTACHMENT_WRITE_BIT;
Finally, we need to extend our subpass dependencies to make sure that there
is no conflict between the transitioning of the depth image and it being cleared
as part of its load operation. The depth image is first accessed in the early
fragment test pipeline stage and because we have a load operation that clears,
we should specify the access mask for writes.
228
Framebuffer
The next step is to modify the framebuffer creation to bind the depth image
to the depth attachment. Go to createFramebuffers and specify the depth
image view as second attachment:
1 std::array<VkImageView, 2> attachments = {
2 swapChainImageViews[i],
3 depthImageView
4 };
5
6 VkFramebufferCreateInfo framebufferInfo{};
7 framebufferInfo.sType = VK_STRUCTURE_TYPE_FRAMEBUFFER_CREATE_INFO;
8 framebufferInfo.renderPass = renderPass;
9 framebufferInfo.attachmentCount =
static_cast<uint32_t>(attachments.size());
10 framebufferInfo.pAttachments = attachments.data();
11 framebufferInfo.width = swapChainExtent.width;
12 framebufferInfo.height = swapChainExtent.height;
13 framebufferInfo.layers = 1;
The color attachment differs for every swap chain image, but the same depth
image can be used by all of them because only a single subpass is running at
the same time due to our semaphores.
You’ll also need to move the call to createFramebuffers to make sure that it
is called after the depth image view has actually been created:
1 void initVulkan() {
2 ...
3 createDepthResources();
4 createFramebuffers();
5 ...
6 }
Clear values
Because we now have multiple attachments with VK_ATTACHMENT_LOAD_OP_CLEAR,
we also need to specify multiple clear values. Go to recordCommandBuffer and
create an array of VkClearValue structs:
1 std::array<VkClearValue, 2> clearValues{};
2 clearValues[0].color = {{0.0f, 0.0f, 0.0f, 1.0f}};
3 clearValues[1].depthStencil = {1.0f, 0};
4
5 renderPassInfo.clearValueCount =
static_cast<uint32_t>(clearValues.size());
229
6 renderPassInfo.pClearValues = clearValues.data();
The range of depths in the depth buffer is 0.0 to 1.0 in Vulkan, where 1.0 lies
at the far view plane and 0.0 at the near view plane. The initial value at each
point in the depth buffer should be the furthest possible depth, which is 1.0.
Note that the order of clearValues should be identical to the order of your
attachments.
Depth and stencil state
The depth attachment is ready to be used now, but depth testing still
needs to be enabled in the graphics pipeline. It is configured through the
VkPipelineDepthStencilStateCreateInfo struct:
1 VkPipelineDepthStencilStateCreateInfo depthStencil{};
2 depthStencil.sType =
VK_STRUCTURE_TYPE_PIPELINE_DEPTH_STENCIL_STATE_CREATE_INFO;
3 depthStencil.depthTestEnable = VK_TRUE;
4 depthStencil.depthWriteEnable = VK_TRUE;
The depthTestEnable field specifies if the depth of new fragments should
be compared to the depth buffer to see if they should be discarded. The
depthWriteEnable field specifies if the new depth of fragments that pass the
depth test should actually be written to the depth buffer.
1 depthStencil.depthCompareOp = VK_COMPARE_OP_LESS;
The depthCompareOp field specifies the comparison that is performed to keep
or discard fragments. We’re sticking to the convention of lower depth = closer,
so the depth of new fragments should be less.
1 depthStencil.depthBoundsTestEnable = VK_FALSE;
2 depthStencil.minDepthBounds = 0.0f; // Optional
3 depthStencil.maxDepthBounds = 1.0f; // Optional
The depthBoundsTestEnable, minDepthBounds and maxDepthBounds fields are
used for the optional depth bound test. Basically, this allows you to only keep
fragments that fall within the specified depth range. We won’t be using this
functionality.
1 depthStencil.stencilTestEnable = VK_FALSE;
2 depthStencil.front = {}; // Optional
3 depthStencil.back = {}; // Optional
The last three fields configure stencil buffer operations, which we also won’t
be using in this tutorial. If you want to use these operations, then you will
have to make sure that the format of the depth/stencil image contains a stencil
component.
230
1 pipelineInfo.pDepthStencilState = &depthStencil;
Update the VkGraphicsPipelineCreateInfo struct to reference the depth sten-
cil state we just filled in. A depth stencil state must always be specified if the
render pass contains a depth stencil attachment.
If you run your program now, then you should see that the fragments of the
geometry are now correctly ordered:
Handling window resize
The resolution of the depth buffer should change when the window is resized to
match the new color attachment resolution. Extend the recreateSwapChain
function to recreate the depth resources in that case:
1 void recreateSwapChain() {
2 int width = 0, height = 0;
3 while (width == 0 || height == 0) {
4 glfwGetFramebufferSize(window, &width, &height);
5 glfwWaitEvents();
6 }
7
8 vkDeviceWaitIdle(device);
231
9
10 cleanupSwapChain();
11
12 createSwapChain();
13 createImageViews();
14 createDepthResources();
15 createFramebuffers();
16 }
The cleanup operations should happen in the swap chain cleanup function:
1 void cleanupSwapChain() {
2 vkDestroyImageView(device, depthImageView, nullptr);
3 vkDestroyImage(device, depthImage, nullptr);
4 vkFreeMemory(device, depthImageMemory, nullptr);
5
6 ...
7 }
Congratulations, your application is now finally ready to render arbitrary 3D
geometry and have it look right. We’re going to try this out in the next chapter
by drawing a textured model!
C++ code / Vertex shader / Fragment shader
232
Loading models
Introduction
Your program is now ready to render textured 3D meshes, but the current
geometry in the vertices and indices arrays is not very interesting yet. In
this chapter we’re going to extend the program to load the vertices and indices
from an actual model file to make the graphics card actually do some work.
Many graphics API tutorials have the reader write their own OBJ loader in a
chapter like this. The problem with this is that any remotely interesting 3D
application will soon require features that are not supported by this file format,
like skeletal animation. We will load mesh data from an OBJ model in this
chapter, but we’ll focus more on integrating the mesh data with the program
itself rather than the details of loading it from a file.
Library
We will use the tinyobjloader library to load vertices and faces from an OBJ file.
It’s fast and it’s easy to integrate because it’s a single file library like stb_image.
Go to the repository linked above and download the tiny_obj_loader.h file to
a folder in your library directory.
Visual Studio
Add the directory with tiny_obj_loader.h in it to the Additional Include
Directories paths.
233
Makefile
Add the directory with tiny_obj_loader.h to the include directories for GCC:
1 VULKAN_SDK_PATH = /home/user/VulkanSDK/x.x.x.x/x86_64
2 STB_INCLUDE_PATH = /home/user/libraries/stb
3 TINYOBJ_INCLUDE_PATH = /home/user/libraries/tinyobjloader
4
5 ...
6
7 CFLAGS = -std=c++17 -I$(VULKAN_SDK_PATH)/include
-I$(STB_INCLUDE_PATH) -I$(TINYOBJ_INCLUDE_PATH)
Sample mesh
In this chapter we won’t be enabling lighting yet, so it helps to use a sample
model that has lighting baked into the texture. An easy way to find such
models is to look for 3D scans on Sketchfab. Many of the models on that site
are available in OBJ format with a permissive license.
For this tutorial I’ve decided to go with the Viking room model by nigelgoh (CC
BY 4.0). I tweaked the size and orientation of the model to use it as a drop in
replacement for the current geometry:
• viking_room.obj
• viking_room.png
Feel free to use your own model, but make sure that it only consists of one
material and that is has dimensions of about 1.5 x 1.5 x 1.5 units. If it is larger
than that, then you’ll have to change the view matrix. Put the model file in
a new models directory next to shaders and textures, and put the texture
image in the textures directory.
Put two new configuration variables in your program to define the model and
texture paths:
1 const uint32_t WIDTH = 800;
234
2 const uint32_t HEIGHT = 600;
3
4 const std::string MODEL_PATH = "models/viking_room.obj";
5 const std::string TEXTURE_PATH = "textures/viking_room.png";
And update createTextureImage to use this path variable:
1 stbi_uc* pixels = stbi_load(TEXTURE_PATH.c_str(), &texWidth,
&texHeight, &texChannels, STBI_rgb_alpha);
Loading vertices and indices
We’re going to load the vertices and indices from the model file now, so you
should remove the global vertices and indices arrays now. Replace them
with non-const containers as class members:
1 std::vector<Vertex> vertices;
2 std::vector<uint32_t> indices;
3 VkBuffer vertexBuffer;
4 VkDeviceMemory vertexBufferMemory;
You should change the type of the indices from uint16_t to uint32_t, because
there are going to be a lot more vertices than 65535. Remember to also change
the vkCmdBindIndexBuffer parameter:
1 vkCmdBindIndexBuffer(commandBuffer, indexBuffer, 0,
VK_INDEX_TYPE_UINT32);
The tinyobjloader library is included in the same way as STB libraries. Include
the tiny_obj_loader.h file and make sure to define TINYOBJLOADER_IMPLEMENTATION
in one source file to include the function bodies and avoid linker errors:
1 #define TINYOBJLOADER_IMPLEMENTATION
2 #include <tiny_obj_loader.h>
We’re now going to write a loadModel function that uses this library to populate
the vertices and indices containers with the vertex data from the mesh. It
should be called somewhere before the vertex and index buffers are created:
1 void initVulkan() {
2 ...
3 loadModel();
4 createVertexBuffer();
5 createIndexBuffer();
6 ...
7 }
8
235
9 ...
10
11 void loadModel() {
12
13 }
A model is loaded into the library’s data structures by calling the
tinyobj::LoadObj function:
1 void loadModel() {
2 tinyobj::attrib_t attrib;
3 std::vector<tinyobj::shape_t> shapes;
4 std::vector<tinyobj::material_t> materials;
5 std::string warn, err;
6
7 if (!tinyobj::LoadObj(&attrib, &shapes, &materials, &warn, &err,
MODEL_PATH.c_str())) {
8 throw std::runtime_error(warn + err);
9 }
10 }
An OBJ file consists of positions, normals, texture coordinates and faces. Faces
consist of an arbitrary amount of vertices, where each vertex refers to a position,
normal and/or texture coordinate by index. This makes it possible to not just
reuse entire vertices, but also individual attributes.
The attrib container holds all of the positions, normals and texture coordinates
in its attrib.vertices, attrib.normals and attrib.texcoords vectors. The
shapes container contains all of the separate objects and their faces. Each face
consists of an array of vertices, and each vertex contains the indices of the
position, normal and texture coordinate attributes. OBJ models can also define
a material and texture per face, but we will be ignoring those.
The err string contains errors and the warn string contains warnings that oc-
curred while loading the file, like a missing material definition. Loading only
really failed if the LoadObj function returns false. As mentioned above, faces
in OBJ files can actually contain an arbitrary number of vertices, whereas our
application can only render triangles. Luckily the LoadObj has an optional
parameter to automatically triangulate such faces, which is enabled by default.
We’re going to combine all of the faces in the file into a single model, so just
iterate over all of the shapes:
1 for (const auto& shape : shapes) {
2
3 }
236
The triangulation feature has already made sure that there are three vertices per
face, so we can now directly iterate over the vertices and dump them straight
into our vertices vector:
1 for (const auto& shape : shapes) {
2 for (const auto& index : shape.mesh.indices) {
3 Vertex vertex{};
4
5 vertices.push_back(vertex);
6 indices.push_back(indices.size());
7 }
8 }
For simplicity, we will assume that every vertex is unique for now, hence the sim-
ple auto-increment indices. The index variable is of type tinyobj::index_t,
which contains the vertex_index, normal_index and texcoord_index mem-
bers. We need to use these indices to look up the actual vertex attributes in the
attrib arrays:
1 vertex.pos = {
2 attrib.vertices[3 * index.vertex_index + 0],
3 attrib.vertices[3 * index.vertex_index + 1],
4 attrib.vertices[3 * index.vertex_index + 2]
5 };
6
7 vertex.texCoord = {
8 attrib.texcoords[2 * index.texcoord_index + 0],
9 attrib.texcoords[2 * index.texcoord_index + 1]
10 };
11
12 vertex.color = {1.0f, 1.0f, 1.0f};
Unfortunately the attrib.vertices array is an array of float values instead
of something like glm::vec3, so you need to multiply the index by 3. Similarly,
there are two texture coordinate components per entry. The offsets of 0, 1 and
2 are used to access the X, Y and Z components, or the U and V components
in the case of texture coordinates.
Run your program now with optimization enabled (e.g. Release mode in Visual
Studio and with the -O3 compiler flag for GCC‘). This is necessary, because
otherwise loading the model will be very slow. You should see something like
the following:
237
Great, the geometry looks correct, but what’s going on with the texture? The
OBJ format assumes a coordinate system where a vertical coordinate of 0 means
the bottom of the image, however we’ve uploaded our image into Vulkan in a
top to bottom orientation where 0 means the top of the image. Solve this by
flipping the vertical component of the texture coordinates:
1 vertex.texCoord = {
2 attrib.texcoords[2 * index.texcoord_index + 0],
3 1.0f - attrib.texcoords[2 * index.texcoord_index + 1]
4 };
When you run your program again, you should now see the correct result:
238
All that hard work is finally beginning to pay off with a demo like this!
As the model rotates you may notice that the rear (backside of the
walls) looks a bit funny. This is normal and is simply because the
model is not really designed to be viewed from that side.
Vertex deduplication
Unfortunately we’re not really taking advantage of the index buffer yet. The
vertices vector contains a lot of duplicated vertex data, because many vertices
are included in multiple triangles. We should keep only the unique vertices and
use the index buffer to reuse them whenever they come up. A straightforward
way to implement this is to use a map or unordered_map to keep track of the
unique vertices and respective indices:
1 #include <unordered_map>
2
3 ...
4
5 std::unordered_map<Vertex, uint32_t> uniqueVertices{};
6
7 for (const auto& shape : shapes) {
8 for (const auto& index : shape.mesh.indices) {
239
9 Vertex vertex{};
10
11 ...
12
13 if (uniqueVertices.count(vertex) == 0) {
14 uniqueVertices[vertex] =
static_cast<uint32_t>(vertices.size());
15 vertices.push_back(vertex);
16 }
17
18 indices.push_back(uniqueVertices[vertex]);
19 }
20 }
Every time we read a vertex from the OBJ file, we check if we’ve already seen a
vertex with the exact same position and texture coordinates before. If not, we
add it to vertices and store its index in the uniqueVertices container. After
that we add the index of the new vertex to indices. If we’ve seen the exact
same vertex before, then we look up its index in uniqueVertices and store that
index in indices.
The program will fail to compile right now, because using a user-defined type
like our Vertex struct as key in a hash table requires us to implement two
functions: equality test and hash calculation. The former is easy to implement
by overriding the == operator in the Vertex struct:
1 bool operator==(const Vertex& other) const {
2 return pos == other.pos && color == other.color && texCoord ==
other.texCoord;
3 }
A hash function for Vertex is implemented by specifying a template special-
ization for std::hash<T>. Hash functions are a complex topic, but cpprefer-
ence.com recommends the following approach combining the fields of a struct
to create a decent quality hash function:
1 namespace std {
2 template<> struct hash<Vertex> {
3 size_t operator()(Vertex const& vertex) const {
4 return ((hash<glm::vec3>()(vertex.pos) ^
5 (hash<glm::vec3>()(vertex.color) << 1)) >> 1) ^
6 (hash<glm::vec2>()(vertex.texCoord) << 1);
7 }
8 };
9 }
This code should be placed outside the Vertex struct. The hash functions for
the GLM types need to be included using the following header:
240
1 #define GLM_ENABLE_EXPERIMENTAL
2 #include <glm/gtx/hash.hpp>
The hash functions are defined in the gtx folder, which means that it is tech-
nically still an experimental extension to GLM. Therefore you need to define
GLM_ENABLE_EXPERIMENTAL to use it. It means that the API could change with
a new version of GLM in the future, but in practice the API is very stable.
You should now be able to successfully compile and run your program. If
you check the size of vertices, then you’ll see that it has shrunk down from
1,500,000 to 265,645! That means that each vertex is reused in an average
number of ~6 triangles. This definitely saves us a lot of GPU memory.
C++ code / Vertex shader / Fragment shader
241
Generating Mipmaps
Introduction
Our program can now load and render 3D models. In this chapter, we will add
one more feature, mipmap generation. Mipmaps are widely used in games and
rendering software, and Vulkan gives us complete control over how they are
created.
Mipmaps are precalculated, downscaled versions of an image. Each new image
is half the width and height of the previous one. Mipmaps are used as a form of
Level of Detail or LOD. Objects that are far away from the camera will sample
their textures from the smaller mip images. Using smaller images increases the
rendering speed and avoids artifacts such as Moiré patterns. An example of
what mipmaps look like:
242
Image creation
In Vulkan, each of the mip images is stored in different mip levels of a VkImage.
Mip level 0 is the original image, and the mip levels after level 0 are commonly
referred to as the mip chain.
The number of mip levels is specified when the VkImage is created. Up until
now, we have always set this value to one. We need to calculate the number of
mip levels from the dimensions of the image. First, add a class member to store
this number:
1 ...
2 uint32_t mipLevels;
3 VkImage textureImage;
4 ...
The value for mipLevels can be found once we’ve loaded the texture in
createTextureImage:
1 int texWidth, texHeight, texChannels;
2 stbi_uc* pixels = stbi_load(TEXTURE_PATH.c_str(), &texWidth,
&texHeight, &texChannels, STBI_rgb_alpha);
3 ...
4 mipLevels =
static_cast<uint32_t>(std::floor(std::log2(std::max(texWidth,
texHeight)))) + 1;
This calculates the number of levels in the mip chain. The max function se-
lects the largest dimension. The log2 function calculates how many times that
dimension can be divided by 2. The floor function handles cases where the
largest dimension is not a power of 2. 1 is added so that the original image has
a mip level.
To use this value, we need to change the createImage, createImageView, and
transitionImageLayout functions to allow us to specify the number of mip
levels. Add a mipLevels parameter to the functions:
1 void createImage(uint32_t width, uint32_t height, uint32_t
mipLevels, VkFormat format, VkImageTiling tiling,
VkImageUsageFlags usage, VkMemoryPropertyFlags properties,
VkImage& image, VkDeviceMemory& imageMemory) {
2 ...
3 imageInfo.mipLevels = mipLevels;
4 ...
5 }
1 VkImageView createImageView(VkImage image, VkFormat format,
VkImageAspectFlags aspectFlags, uint32_t mipLevels) {
2 ...
243
3 viewInfo.subresourceRange.levelCount = mipLevels;
4 ...
1 void transitionImageLayout(VkImage image, VkFormat format,
VkImageLayout oldLayout, VkImageLayout newLayout, uint32_t
mipLevels) {
2 ...
3 barrier.subresourceRange.levelCount = mipLevels;
4 ...
Update all calls to these functions to use the right values:
1 createImage(swapChainExtent.width, swapChainExtent.height, 1,
depthFormat, VK_IMAGE_TILING_OPTIMAL,
VK_IMAGE_USAGE_DEPTH_STENCIL_ATTACHMENT_BIT,
VK_MEMORY_PROPERTY_DEVICE_LOCAL_BIT, depthImage,
depthImageMemory);
2 ...
3 createImage(texWidth, texHeight, mipLevels, VK_FORMAT_R8G8B8A8_SRGB,
VK_IMAGE_TILING_OPTIMAL, VK_IMAGE_USAGE_TRANSFER_DST_BIT |
VK_IMAGE_USAGE_SAMPLED_BIT, VK_MEMORY_PROPERTY_DEVICE_LOCAL_BIT,
textureImage, textureImageMemory);
1 swapChainImageViews[i] = createImageView(swapChainImages[i],
swapChainImageFormat, VK_IMAGE_ASPECT_COLOR_BIT, 1);
2 ...
3 depthImageView = createImageView(depthImage, depthFormat,
VK_IMAGE_ASPECT_DEPTH_BIT, 1);
4 ...
5 textureImageView = createImageView(textureImage,
VK_FORMAT_R8G8B8A8_SRGB, VK_IMAGE_ASPECT_COLOR_BIT, mipLevels);
1 transitionImageLayout(depthImage, depthFormat,
VK_IMAGE_LAYOUT_UNDEFINED,
VK_IMAGE_LAYOUT_DEPTH_STENCIL_ATTACHMENT_OPTIMAL, 1);
2 ...
3 transitionImageLayout(textureImage, VK_FORMAT_R8G8B8A8_SRGB,
VK_IMAGE_LAYOUT_UNDEFINED, VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL,
mipLevels);
Generating Mipmaps
Our texture image now has multiple mip levels, but the staging buffer can only
be used to fill mip level 0. The other levels are still undefined. To fill these
levels we need to generate the data from the single level that we have. We will
244
use the vkCmdBlitImage command. This command performs copying, scaling,
and filtering operations. We will call this multiple times to blit data to each
level of our texture image.
vkCmdBlitImage is considered a transfer operation, so we must inform Vulkan
that we intend to use the texture image as both the source and destination
of a transfer. Add VK_IMAGE_USAGE_TRANSFER_SRC_BIT to the texture image’s
usage flags in createTextureImage:
1 ...
2 createImage(texWidth, texHeight, mipLevels, VK_FORMAT_R8G8B8A8_SRGB,
VK_IMAGE_TILING_OPTIMAL, VK_IMAGE_USAGE_TRANSFER_SRC_BIT |
VK_IMAGE_USAGE_TRANSFER_DST_BIT | VK_IMAGE_USAGE_SAMPLED_BIT,
VK_MEMORY_PROPERTY_DEVICE_LOCAL_BIT, textureImage,
textureImageMemory);
3 ...
Like other image operations, vkCmdBlitImage depends on the layout
of the image it operates on. We could transition the entire image to
VK_IMAGE_LAYOUT_GENERAL, but this will most likely be slow. For optimal per-
formance, the source image should be in VK_IMAGE_LAYOUT_TRANSFER_SRC_OPTIMAL
and the destination image should be in VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL.
Vulkan allows us to transition each mip level of an image independently. Each
blit will only deal with two mip levels at a time, so we can transition each level
into the optimal layout between blits commands.
transitionImageLayout only performs layout transitions on the entire
image, so we’ll need to write a few more pipeline barrier commands. Remove
the existing transition to VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL in
createTextureImage:
1 ...
2 transitionImageLayout(textureImage, VK_FORMAT_R8G8B8A8_SRGB,
VK_IMAGE_LAYOUT_UNDEFINED, VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL,
mipLevels);
3 copyBufferToImage(stagingBuffer, textureImage,
static_cast<uint32_t>(texWidth),
static_cast<uint32_t>(texHeight));
4 //transitioned to VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL while
generating mipmaps
5 ...
This will leave each level of the texture image in VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL.
Each level will be transitioned to VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL
after the blit command reading from it is finished.
We’re now going to write the function that generates the mipmaps:
245
1 void generateMipmaps(VkImage image, int32_t texWidth, int32_t
texHeight, uint32_t mipLevels) {
2 VkCommandBuffer commandBuffer = beginSingleTimeCommands();
3
4 VkImageMemoryBarrier barrier{};
5 barrier.sType = VK_STRUCTURE_TYPE_IMAGE_MEMORY_BARRIER;
6 barrier.image = image;
7 barrier.srcQueueFamilyIndex = VK_QUEUE_FAMILY_IGNORED;
8 barrier.dstQueueFamilyIndex = VK_QUEUE_FAMILY_IGNORED;
9 barrier.subresourceRange.aspectMask = VK_IMAGE_ASPECT_COLOR_BIT;
10 barrier.subresourceRange.baseArrayLayer = 0;
11 barrier.subresourceRange.layerCount = 1;
12 barrier.subresourceRange.levelCount = 1;
13
14 endSingleTimeCommands(commandBuffer);
15 }
We’re going to make several transitions, so we’ll reuse this VkImageMemoryBarrier.
The fields set above will remain the same for all barriers. subresourceRange.miplevel,
oldLayout, newLayout, srcAccessMask, and dstAccessMask will be changed
for each transition.
1 int32_t mipWidth = texWidth;
2 int32_t mipHeight = texHeight;
3
4 for (uint32_t i = 1; i < mipLevels; i++) {
5
6 }
This loop will record each of the VkCmdBlitImage commands. Note that the
loop variable starts at 1, not 0.
1 barrier.subresourceRange.baseMipLevel = i - 1;
2 barrier.oldLayout = VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL;
3 barrier.newLayout = VK_IMAGE_LAYOUT_TRANSFER_SRC_OPTIMAL;
4 barrier.srcAccessMask = VK_ACCESS_TRANSFER_WRITE_BIT;
5 barrier.dstAccessMask = VK_ACCESS_TRANSFER_READ_BIT;
6
7 vkCmdPipelineBarrier(commandBuffer,
8 VK_PIPELINE_STAGE_TRANSFER_BIT, VK_PIPELINE_STAGE_TRANSFER_BIT,
0,
9 0, nullptr,
10 0, nullptr,
11 1, &barrier);
First, we transition level i - 1 to VK_IMAGE_LAYOUT_TRANSFER_SRC_OPTIMAL.
This transition will wait for level i - 1 to be filled, either from the previous
246
blit command, or from vkCmdCopyBufferToImage. The current blit command
will wait on this transition.
1 VkImageBlit blit{};
2 blit.srcOffsets[0] = { 0, 0, 0 };
3 blit.srcOffsets[1] = { mipWidth, mipHeight, 1 };
4 blit.srcSubresource.aspectMask = VK_IMAGE_ASPECT_COLOR_BIT;
5 blit.srcSubresource.mipLevel = i - 1;
6 blit.srcSubresource.baseArrayLayer = 0;
7 blit.srcSubresource.layerCount = 1;
8 blit.dstOffsets[0] = { 0, 0, 0 };
9 blit.dstOffsets[1] = { mipWidth > 1 ? mipWidth / 2 : 1, mipHeight >
1 ? mipHeight / 2 : 1, 1 };
10 blit.dstSubresource.aspectMask = VK_IMAGE_ASPECT_COLOR_BIT;
11 blit.dstSubresource.mipLevel = i;
12 blit.dstSubresource.baseArrayLayer = 0;
13 blit.dstSubresource.layerCount = 1;
Next, we specify the regions that will be used in the blit operation. The source
mip level is i - 1 and the destination mip level is i. The two elements of
the srcOffsets array determine the 3D region that data will be blitted from.
dstOffsets determines the region that data will be blitted to. The X and Y
dimensions of the dstOffsets[1] are divided by two since each mip level is
half the size of the previous level. The Z dimension of srcOffsets[1] and
dstOffsets[1] must be 1, since a 2D image has a depth of 1.
1 vkCmdBlitImage(commandBuffer,
2 image, VK_IMAGE_LAYOUT_TRANSFER_SRC_OPTIMAL,
3 image, VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL,
4 1, &blit,
5 VK_FILTER_LINEAR);
Now, we record the blit command. Note that textureImage is used for both
the srcImage and dstImage parameter. This is because we’re blitting between
different levels of the same image. The source mip level was just transitioned
to VK_IMAGE_LAYOUT_TRANSFER_SRC_OPTIMAL and the destination level is still
in VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL from createTextureImage.
Beware if you are using a dedicated transfer queue (as suggested in Vertex
buffers): vkCmdBlitImage must be submitted to a queue with graphics capabil-
ity.
The last parameter allows us to specify a VkFilter to use in the blit. We have
the same filtering options here that we had when making the VkSampler. We
use the VK_FILTER_LINEAR to enable interpolation.
1 barrier.oldLayout = VK_IMAGE_LAYOUT_TRANSFER_SRC_OPTIMAL;
2 barrier.newLayout = VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL;
247
3 barrier.srcAccessMask = VK_ACCESS_TRANSFER_READ_BIT;
4 barrier.dstAccessMask = VK_ACCESS_SHADER_READ_BIT;
5
6 vkCmdPipelineBarrier(commandBuffer,
7 VK_PIPELINE_STAGE_TRANSFER_BIT,
VK_PIPELINE_STAGE_FRAGMENT_SHADER_BIT, 0,
8 0, nullptr,
9 0, nullptr,
10 1, &barrier);
This barrier transitions mip level i - 1 to VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL.
This transition waits on the current blit command to finish. All sampling
operations will wait on this transition to finish.
1 ...
2 if (mipWidth > 1) mipWidth /= 2;
3 if (mipHeight > 1) mipHeight /= 2;
4 }
At the end of the loop, we divide the current mip dimensions by two. We check
each dimension before the division to ensure that dimension never becomes 0.
This handles cases where the image is not square, since one of the mip dimensions
would reach 1 before the other dimension. When this happens, that dimension
should remain 1 for all remaining levels.
1 barrier.subresourceRange.baseMipLevel = mipLevels - 1;
2 barrier.oldLayout = VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL;
3 barrier.newLayout = VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL;
4 barrier.srcAccessMask = VK_ACCESS_TRANSFER_WRITE_BIT;
5 barrier.dstAccessMask = VK_ACCESS_SHADER_READ_BIT;
6
7 vkCmdPipelineBarrier(commandBuffer,
8 VK_PIPELINE_STAGE_TRANSFER_BIT,
VK_PIPELINE_STAGE_FRAGMENT_SHADER_BIT, 0,
9 0, nullptr,
10 0, nullptr,
11 1, &barrier);
12
13 endSingleTimeCommands(commandBuffer);
14 }
Before we end the command buffer, we insert one more pipeline barrier. This bar-
rier transitions the last mip level from VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL
to VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL. This wasn’t handled by
the loop, since the last mip level is never blitted from.
Finally, add the call to generateMipmaps in createTextureImage:
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1 transitionImageLayout(textureImage, VK_FORMAT_R8G8B8A8_SRGB,
VK_IMAGE_LAYOUT_UNDEFINED, VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL,
mipLevels);
2 copyBufferToImage(stagingBuffer, textureImage,
static_cast<uint32_t>(texWidth),
static_cast<uint32_t>(texHeight));
3 //transitioned to VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL while
generating mipmaps
4 ...
5 generateMipmaps(textureImage, texWidth, texHeight, mipLevels);
Our texture image’s mipmaps are now completely filled.
Linear filtering support
It is very convenient to use a built-in function like vkCmdBlitImage to generate
all the mip levels, but unfortunately it is not guaranteed to be supported on all
platforms. It requires the texture image format we use to support linear filter-
ing, which can be checked with the vkGetPhysicalDeviceFormatProperties
function. We will add a check to the generateMipmaps function for this.
First add an additional parameter that specifies the image format:
1 void createTextureImage() {
2 ...
3
4 generateMipmaps(textureImage, VK_FORMAT_R8G8B8A8_SRGB, texWidth,
texHeight, mipLevels);
5 }
6
7 void generateMipmaps(VkImage image, VkFormat imageFormat, int32_t
texWidth, int32_t texHeight, uint32_t mipLevels) {
8
9 ...
10 }
In the generateMipmaps function, use vkGetPhysicalDeviceFormatProperties
to request the properties of the texture image format:
1 void generateMipmaps(VkImage image, VkFormat imageFormat, int32_t
texWidth, int32_t texHeight, uint32_t mipLevels) {
2
3 // Check if image format supports linear blitting
4 VkFormatProperties formatProperties;
5 vkGetPhysicalDeviceFormatProperties(physicalDevice, imageFormat,
&formatProperties);
6
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7 ...
The VkFormatProperties struct has three fields named linearTilingFeatures,
optimalTilingFeatures and bufferFeatures that each describe how
the format can be used depending on the way it is used. We create
a texture image with the optimal tiling format, so we need to check
optimalTilingFeatures. Support for the linear filtering feature can be
checked with the VK_FORMAT_FEATURE_SAMPLED_IMAGE_FILTER_LINEAR_BIT:
1 if (!(formatProperties.optimalTilingFeatures &
VK_FORMAT_FEATURE_SAMPLED_IMAGE_FILTER_LINEAR_BIT)) {
2 throw std::runtime_error("texture image format does not support
linear blitting!");
3 }
There are two alternatives in this case. You could implement a function that
searches common texture image formats for one that does support linear blitting,
or you could implement the mipmap generation in software with a library like
stb_image_resize. Each mip level can then be loaded into the image in the
same way that you loaded the original image.
It should be noted that it is uncommon in practice to generate the mipmap
levels at runtime anyway. Usually they are pregenerated and stored in the
texture file alongside the base level to improve loading speed. Implementing
resizing in software and loading multiple levels from a file is left as an exercise
to the reader.
Sampler
While the VkImage holds the mipmap data, VkSampler controls how that data is
read while rendering. Vulkan allows us to specify minLod, maxLod, mipLodBias,
and mipmapMode (“Lod” means “Level of Detail”). When a texture is sampled,
the sampler selects a mip level according to the following pseudocode:
1 lod = getLodLevelFromScreenSize(); //smaller when the object is
close, may be negative
2 lod = clamp(lod + mipLodBias, minLod, maxLod);
3
4 level = clamp(floor(lod), 0, texture.mipLevels - 1); //clamped to
the number of mip levels in the texture
5
6 if (mipmapMode == VK_SAMPLER_MIPMAP_MODE_NEAREST) {
7 color = sample(level);
8 } else {
9 color = blend(sample(level), sample(level + 1));
10 }
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If samplerInfo.mipmapMode is VK_SAMPLER_MIPMAP_MODE_NEAREST, lod selects
the mip level to sample from. If the mipmap mode is VK_SAMPLER_MIPMAP_MODE_LINEAR,
lod is used to select two mip levels to be sampled. Those levels are sampled
and the results are linearly blended.
The sample operation is also affected by lod:
1 if (lod <= 0) {
2 color = readTexture(uv, magFilter);
3 } else {
4 color = readTexture(uv, minFilter);
5 }
If the object is close to the camera, magFilter is used as the filter. If the object
is further from the camera, minFilter is used. Normally, lod is non-negative,
and is only 0 when close the camera. mipLodBias lets us force Vulkan to use
lower lod and level than it would normally use.
To see the results of this chapter, we need to choose values for our
textureSampler. We’ve already set the minFilter and magFilter to
use VK_FILTER_LINEAR. We just need to choose values for minLod, maxLod,
mipLodBias, and mipmapMode.
1 void createTextureSampler() {
2 ...
3 samplerInfo.mipmapMode = VK_SAMPLER_MIPMAP_MODE_LINEAR;
4 samplerInfo.minLod = 0.0f; // Optional
5 samplerInfo.maxLod = static_cast<float>(mipLevels);
6 samplerInfo.mipLodBias = 0.0f; // Optional
7 ...
8 }
To allow the full range of mip levels to be used, we set minLod to 0.0f, and
maxLod to the number of mip levels. We have no reason to change the lod value
, so we set mipLodBias to 0.0f.
Now run your program and you should see the following:
251
It’s not a dramatic difference, since our scene is so simple. There are subtle
differences if you look closely.
The most noticeable difference is the writing on the papers. With mipmaps, the
writing has been smoothed. Without mipmaps, the writing has harsh edges and
252
gaps from Moiré artifacts.
You can play around with the sampler settings to see how they affect mipmap-
ping. For example, by changing minLod, you can force the sampler to not use
the lowest mip levels:
1 samplerInfo.minLod = static_cast<float>(mipLevels / 2);
These settings will produce this image:
This is how higher mip levels will be used when objects are further away from
the camera.
C++ code / Vertex shader / Fragment shader
253
Multisampling
Introduction
Our program can now load multiple levels of detail for textures which fixes
artifacts when rendering objects far away from the viewer. The image is now
a lot smoother, however on closer inspection you will notice jagged saw-like
patterns along the edges of drawn geometric shapes. This is especially visible
in one of our early programs when we rendered a quad:
This undesired effect is called “aliasing” and it’s a result of a limited numbers
of pixels that are available for rendering. Since there are no displays out there
254
with unlimited resolution, it will be always visible to some extent. There’s a
number of ways to fix this and in this chapter we’ll focus on one of the more
popular ones: Multisample anti-aliasing (MSAA).
In ordinary rendering, the pixel color is determined based on a single sample
point which in most cases is the center of the target pixel on screen. If part
of the drawn line passes through a certain pixel but doesn’t cover the sample
point, that pixel will be left blank, leading to the jagged “staircase” effect.
What MSAA does is it uses multiple sample points per pixel (hence the name)
to determine its final color. As one might expect, more samples lead to better
results, however it is also more computationally expensive.
In our implementation, we will focus on using the maximum available sample
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count. Depending on your application this may not always be the best approach
and it might be better to use less samples for the sake of higher performance if
the final result meets your quality demands.
Getting available sample count
Let’s start off by determining how many samples our hardware can use. Most
modern GPUs support at least 8 samples but this number is not guaranteed to
be the same everywhere. We’ll keep track of it by adding a new class member:
1 ...
2 VkSampleCountFlagBits msaaSamples = VK_SAMPLE_COUNT_1_BIT;
3 ...
By default we’ll be using only one sample per pixel which is equivalent to no mul-
tisampling, in which case the final image will remain unchanged. The exact max-
imum number of samples can be extracted from VkPhysicalDeviceProperties
associated with our selected physical device. We’re using a depth buffer, so we
have to take into account the sample count for both color and depth. The high-
est sample count that is supported by both (&) will be the maximum we can
support. Add a function that will fetch this information for us:
1 VkSampleCountFlagBits getMaxUsableSampleCount() {
2 VkPhysicalDeviceProperties physicalDeviceProperties;
3 vkGetPhysicalDeviceProperties(physicalDevice,
&physicalDeviceProperties);
4
5 VkSampleCountFlags counts =
physicalDeviceProperties.limits.framebufferColorSampleCounts
&
physicalDeviceProperties.limits.framebufferDepthSampleCounts;
6 if (counts & VK_SAMPLE_COUNT_64_BIT) { return
VK_SAMPLE_COUNT_64_BIT; }
7 if (counts & VK_SAMPLE_COUNT_32_BIT) { return
VK_SAMPLE_COUNT_32_BIT; }
8 if (counts & VK_SAMPLE_COUNT_16_BIT) { return
VK_SAMPLE_COUNT_16_BIT; }
9 if (counts & VK_SAMPLE_COUNT_8_BIT) { return
VK_SAMPLE_COUNT_8_BIT; }
10 if (counts & VK_SAMPLE_COUNT_4_BIT) { return
VK_SAMPLE_COUNT_4_BIT; }
11 if (counts & VK_SAMPLE_COUNT_2_BIT) { return
VK_SAMPLE_COUNT_2_BIT; }
12
13 return VK_SAMPLE_COUNT_1_BIT;
14 }
256
We will now use this function to set the msaaSamples variable during the
physical device selection process. For this, we have to slightly modify the
pickPhysicalDevice function:
1 void pickPhysicalDevice() {
2 ...
3 for (const auto& device : devices) {
4 if (isDeviceSuitable(device)) {
5 physicalDevice = device;
6 msaaSamples = getMaxUsableSampleCount();
7 break;
8 }
9 }
10 ...
11 }
Setting up a render target
In MSAA, each pixel is sampled in an offscreen buffer which is then rendered
to the screen. This new buffer is slightly different from regular images we’ve
been rendering to - they have to be able to store more than one sample per
pixel. Once a multisampled buffer is created, it has to be resolved to the default
framebuffer (which stores only a single sample per pixel). This is why we have
to create an additional render target and modify our current drawing process.
We only need one render target since only one drawing operation is active at a
time, just like with the depth buffer. Add the following class members:
1 ...
2 VkImage colorImage;
3 VkDeviceMemory colorImageMemory;
4 VkImageView colorImageView;
5 ...
This new image will have to store the desired number of samples per pixel, so
we need to pass this number to VkImageCreateInfo during the image creation
process. Modify the createImage function by adding a numSamples parameter:
1 void createImage(uint32_t width, uint32_t height, uint32_t
mipLevels, VkSampleCountFlagBits numSamples, VkFormat format,
VkImageTiling tiling, VkImageUsageFlags usage,
VkMemoryPropertyFlags properties, VkImage& image,
VkDeviceMemory& imageMemory) {
2 ...
3 imageInfo.samples = numSamples;
4 ...
257
For now, update all calls to this function using VK_SAMPLE_COUNT_1_BIT - we
will be replacing this with proper values as we progress with implementation:
1 createImage(swapChainExtent.width, swapChainExtent.height, 1,
VK_SAMPLE_COUNT_1_BIT, depthFormat, VK_IMAGE_TILING_OPTIMAL,
VK_IMAGE_USAGE_DEPTH_STENCIL_ATTACHMENT_BIT,
VK_MEMORY_PROPERTY_DEVICE_LOCAL_BIT, depthImage,
depthImageMemory);
2 ...
3 createImage(texWidth, texHeight, mipLevels, VK_SAMPLE_COUNT_1_BIT,
VK_FORMAT_R8G8B8A8_SRGB, VK_IMAGE_TILING_OPTIMAL,
VK_IMAGE_USAGE_TRANSFER_SRC_BIT |
VK_IMAGE_USAGE_TRANSFER_DST_BIT | VK_IMAGE_USAGE_SAMPLED_BIT,
VK_MEMORY_PROPERTY_DEVICE_LOCAL_BIT, textureImage,
textureImageMemory);
We will now create a multisampled color buffer. Add a createColorResources
function and note that we’re using msaaSamples here as a function parameter
to createImage. We’re also using only one mip level, since this is enforced by
the Vulkan specification in case of images with more than one sample per pixel.
Also, this color buffer doesn’t need mipmaps since it’s not going to be used as
a texture:
1 void createColorResources() {
2 VkFormat colorFormat = swapChainImageFormat;
3
4 createImage(swapChainExtent.width, swapChainExtent.height, 1,
msaaSamples, colorFormat, VK_IMAGE_TILING_OPTIMAL,
VK_IMAGE_USAGE_TRANSIENT_ATTACHMENT_BIT |
VK_IMAGE_USAGE_COLOR_ATTACHMENT_BIT,
VK_MEMORY_PROPERTY_DEVICE_LOCAL_BIT, colorImage,
colorImageMemory);
5 colorImageView = createImageView(colorImage, colorFormat,
VK_IMAGE_ASPECT_COLOR_BIT, 1);
6 }
For consistency, call the function right before createDepthResources:
1 void initVulkan() {
2 ...
3 createColorResources();
4 createDepthResources();
5 ...
6 }
Now that we have a multisampled color buffer in place it’s time to take care
of depth. Modify createDepthResources and update the number of samples
used by the depth buffer:
258
1 void createDepthResources() {
2 ...
3 createImage(swapChainExtent.width, swapChainExtent.height, 1,
msaaSamples, depthFormat, VK_IMAGE_TILING_OPTIMAL,
VK_IMAGE_USAGE_DEPTH_STENCIL_ATTACHMENT_BIT,
VK_MEMORY_PROPERTY_DEVICE_LOCAL_BIT, depthImage,
depthImageMemory);
4 ...
5 }
We have now created a couple of new Vulkan resources, so let’s not forget to
release them when necessary:
1 void cleanupSwapChain() {
2 vkDestroyImageView(device, colorImageView, nullptr);
3 vkDestroyImage(device, colorImage, nullptr);
4 vkFreeMemory(device, colorImageMemory, nullptr);
5 ...
6 }
And update the recreateSwapChain so that the new color image can be recre-
ated in the correct resolution when the window is resized:
1 void recreateSwapChain() {
2 ...
3 createImageViews();
4 createColorResources();
5 createDepthResources();
6 ...
7 }
We made it past the initial MSAA setup, now we need to start using this new
resource in our graphics pipeline, framebuffer, render pass and see the results!
Adding new attachments
Let’s take care of the render pass first. Modify createRenderPass and update
color and depth attachment creation info structs:
1 void createRenderPass() {
2 ...
3 colorAttachment.samples = msaaSamples;
4 colorAttachment.finalLayout =
VK_IMAGE_LAYOUT_COLOR_ATTACHMENT_OPTIMAL;
5 ...
6 depthAttachment.samples = msaaSamples;
7 ...
259
You’ll notice that we have changed the finalLayout from VK_IMAGE_LAYOUT_PRESENT_SRC_KHR
to VK_IMAGE_LAYOUT_COLOR_ATTACHMENT_OPTIMAL. That’s because multisam-
pled images cannot be presented directly. We first need to resolve them to a
regular image. This requirement does not apply to the depth buffer, since it
won’t be presented at any point. Therefore we will have to add only one new
attachment for color which is a so-called resolve attachment:
1 ...
2 VkAttachmentDescription colorAttachmentResolve{};
3 colorAttachmentResolve.format = swapChainImageFormat;
4 colorAttachmentResolve.samples = VK_SAMPLE_COUNT_1_BIT;
5 colorAttachmentResolve.loadOp = VK_ATTACHMENT_LOAD_OP_DONT_CARE;
6 colorAttachmentResolve.storeOp = VK_ATTACHMENT_STORE_OP_STORE;
7 colorAttachmentResolve.stencilLoadOp =
VK_ATTACHMENT_LOAD_OP_DONT_CARE;
8 colorAttachmentResolve.stencilStoreOp =
VK_ATTACHMENT_STORE_OP_DONT_CARE;
9 colorAttachmentResolve.initialLayout = VK_IMAGE_LAYOUT_UNDEFINED;
10 colorAttachmentResolve.finalLayout =
VK_IMAGE_LAYOUT_PRESENT_SRC_KHR;
11 ...
The render pass now has to be instructed to resolve multisampled color image
into regular attachment. Create a new attachment reference that will point to
the color buffer which will serve as the resolve target:
1 ...
2 VkAttachmentReference colorAttachmentResolveRef{};
3 colorAttachmentResolveRef.attachment = 2;
4 colorAttachmentResolveRef.layout =
VK_IMAGE_LAYOUT_COLOR_ATTACHMENT_OPTIMAL;
5 ...
Set the pResolveAttachments subpass struct member to point to the newly
created attachment reference. This is enough to let the render pass define a
multisample resolve operation which will let us render the image to screen:
1 ...
2 subpass.pResolveAttachments = &colorAttachmentResolveRef;
3 ...
Now update render pass info struct with the new color attachment:
1 ...
2 std::array<VkAttachmentDescription, 3> attachments =
{colorAttachment, depthAttachment, colorAttachmentResolve};
3 ...
260
With the render pass in place, modify createFramebuffers and add the new
image view to the list:
1 void createFramebuffers() {
2 ...
3 std::array<VkImageView, 3> attachments = {
4 colorImageView,
5 depthImageView,
6 swapChainImageViews[i]
7 };
8 ...
9 }
Finally, tell the newly created pipeline to use more than one sample by modifying
createGraphicsPipeline:
1 void createGraphicsPipeline() {
2 ...
3 multisampling.rasterizationSamples = msaaSamples;
4 ...
5 }
Now run your program and you should see the following:
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Just like with mipmapping, the difference may not be apparent straight away.
On a closer look you’ll notice that the edges are not as jagged anymore and the
whole image seems a bit smoother compared to the original.
The difference is more noticable when looking up close at one of the edges:
Quality improvements
There are certain limitations of our current MSAA implementation which may
impact the quality of the output image in more detailed scenes. For exam-
ple, we’re currently not solving potential problems caused by shader aliasing,
262
i.e. MSAA only smoothens out the edges of geometry but not the interior filling.
This may lead to a situation when you get a smooth polygon rendered on screen
but the applied texture will still look aliased if it contains high contrasting col-
ors. One way to approach this problem is to enable Sample Shading which will
improve the image quality even further, though at an additional performance
cost:
1 void createLogicalDevice() {
2 ...
3 deviceFeatures.sampleRateShading = VK_TRUE; // enable sample
shading feature for the device
4 ...
5 }
6
7 void createGraphicsPipeline() {
8 ...
9 multisampling.sampleShadingEnable = VK_TRUE; // enable sample
shading in the pipeline
10 multisampling.minSampleShading = .2f; // min fraction for sample
shading; closer to one is smoother
11 ...
12 }
In this example we’ll leave sample shading disabled but in certain scenarios the
quality improvement may be noticeable:
Conclusion
It has taken a lot of work to get to this point, but now you finally have a good
base for a Vulkan program. The knowledge of the basic principles of Vulkan
263
that you now possess should be sufficient to start exploring more of the features,
like:
• Push constants
• Instanced rendering
• Dynamic uniforms
• Separate images and sampler descriptors
• Pipeline cache
• Multi-threaded command buffer generation
• Multiple subpasses
• Compute shaders
The current program can be extended in many ways, like adding Blinn-Phong
lighting, post-processing effects and shadow mapping. You should be able to
learn how these effects work from tutorials for other APIs, because despite
Vulkan’s explicitness, many concepts still work the same.
C++ code / Vertex shader / Fragment shader
264
Compute Shader
Introduction
In this bonus chapter we’ll take a look at compute shaders. Up until now
all previous chapters dealt with the traditional graphics part of the Vulkan
pipeline. But unlike older APIs like OpenGL, compute shader support in Vulkan
is mandatory. This means that you can use compute shaders on every Vulkan
implementation available, no matter if it’s a high-end desktop GPU or a low-
powered embedded device.
This opens up the world of general purpose computing on graphics processor
units (GPGPU), no matter where your application is running. GPGPU means
that you can do general computations on your GPU, something that has tra-
ditionally been a domain of CPUs. But with GPUs having become more and
more powerful and more flexible, many workloads that would require the general
purpose capabilities of a CPU can now be done on the GPU in realtime.
A few examples of where the compute capabilities of a GPU can be used are
image manipulation, visibility testing, post processing, advanced lighting calcu-
lations, animations, physics (e.g. for a particle system) and much more. And it’s
even possible to use compute for non-visual computational only work that does
not require any graphics output, e.g. number crunching or AI related things.
This is called “headless compute”.
Advantages
Doing computationally expensive calculations on the GPU has several advan-
tages. The most obvious one is offloading work from the CPU. Another one
is not requiring moving data between the CPU’s main memory and the GPU’s
memory. All of the data can stay on the GPU without having to wait for slow
transfers from main memory.
Aside from these, GPUs are heavily parallelized with some of them having tens
of thousands of small compute units. This often makes them a better fit for
highly parallel workflows than a CPU with a few large compute units.
265
The Vulkan pipeline
It’s important to know that compute is completely separated from the graphics
part of the pipeline. This is visible in the following block diagram of the Vulkan
pipeline from the official specification:
In this diagram we can see the traditional graphics part of the pipeline on the
left, and several stages on the right that are not part of this graphics pipeline,
including the compute shader (stage). With the compute shader stage being
detached from the graphics pipeline we’ll be able to use it anywhere we see fit.
This is very different from e.g. the fragment shader which is always applied to
the transformed output of the vertex shader.
The center of the diagram also shows that e.g. descriptor sets are also used by
compute, so everything we learned about descriptors layouts, descriptor sets
and descriptors also applies here.
An example
An easy to understand example that we will implement in this chapter is a
GPU based particle system. Such systems are used in many games and often
consist of thousands of particles that need to be updated at interactive frame
rates. Rendering such a system requires 2 main components: vertices, passed
as vertex buffers, and a way to update them based on some equation.
The “classical” CPU based particle system would store particle data in the sys-
tem’s main memory and then use the CPU to update them. After the update,
the vertices need to be transferred to the GPU’s memory again so it can dis-
play the updated particles in the next frame. The most straight-forward way
would be recreating the vertex buffer with the new data for each frame. This
is obviously very costly. Depending on your implementation, there are other
266
options like mapping GPU memory so it can be written by the CPU (called
“resizable BAR” on desktop systems, or unified memory on integrated GPUs)
or just using a host local buffer (which would be the slowest method due to
PCI-E bandwidth). But no matter what buffer update method you choose, you
always require a “round-trip” to the CPU to update the particles.
With a GPU based particle system, this round-trip is no longer required. Ver-
tices are only uploaded to the GPU at the start and all updates are done in the
GPU’s memory using compute shaders. One of the main reasons why this is
faster is the much higher bandwidth between the GPU and it’s local memory.
In a CPU based scenario, you’d be limited by main memory and PCI-express
bandwidth, which is often just a fraction of the GPU’s memory bandwidth.
When doing this on a GPU with a dedicated compute queue, you can update
particles in parallel to the rendering part of the graphics pipeline. This is called
“async compute”, and is an advanced topic not covered in this tutorial.
Here is a screenshot from this chapter’s code. The particles shown here are up-
dated by a compute shader directly on the GPU, without any CPU interaction:
267
Data manipulation
In this tutorial we already learned about different buffer types like vertex and
index buffers for passing primitives and uniform buffers for passing data to a
shader. And we also used images to do texture mapping. But up until now, we
always wrote data using the CPU and only did reads on the GPU.
An important concept introduced with compute shaders is the ability to arbi-
trarily read from and write to buffers. For this, Vulkan offers two dedicated
storage types.
Shader storage buffer objects (SSBO)
A shader storage buffer (SSBO) allows shaders to read from and write to a buffer.
Using these is similar to using uniform buffer objects. The biggest differences are
that you can alias other buffer types to SSBOs and that they can be arbitrarily
large.
Going back to the GPU based particle system, you might now wonder how to
deal with vertices being updated (written) by the compute shader and read
(drawn) by the vertex shader, as both usages would seemingly require different
buffer types.
But that’s not the case. In Vulkan you can specify multiple usages for buffers
and images. So for the particle vertex buffer to be used as a vertex buffer (in
the graphics pass) and as a storage buffer (in the compute pass), you simply
create the buffer with those two usage flags:
1 VkBufferCreateInfo bufferInfo{};
2 ...
3 bufferInfo.usage = VK_BUFFER_USAGE_VERTEX_BUFFER_BIT |
VK_BUFFER_USAGE_STORAGE_BUFFER_BIT |
VK_BUFFER_USAGE_TRANSFER_DST_BIT;
4 ...
5
6 if (vkCreateBuffer(device, &bufferInfo, nullptr,
&shaderStorageBuffers[i]) != VK_SUCCESS) {
7 throw std::runtime_error("failed to create vertex buffer!");
8 }
The two flags VK_BUFFER_USAGE_VERTEX_BUFFER_BIT and VK_BUFFER_USAGE_STORAGE_BUFFER_BIT
set with bufferInfo.usage tell the implementation that we want to use this
buffer for two different scenarios: as a vertex buffer in the vertex shader and as a
store buffer. Note that we also added the VK_BUFFER_USAGE_TRANSFER_DST_BIT
flag in here so we can transfer data from the host to the GPU. This is cru-
cial as we want the shader storage buffer to stay in GPU memory only
(VK_MEMORY_PROPERTY_DEVICE_LOCAL_BIT) we need to to transfer data from
the host to this buffer.
268
Here is the same code using using the createBuffer helper function:
1 createBuffer(bufferSize, VK_BUFFER_USAGE_STORAGE_BUFFER_BIT |
VK_BUFFER_USAGE_VERTEX_BUFFER_BIT |
VK_BUFFER_USAGE_TRANSFER_DST_BIT,
VK_MEMORY_PROPERTY_DEVICE_LOCAL_BIT, shaderStorageBuffers[i],
shaderStorageBuffersMemory[i]);
The GLSL shader declaration for accessing such a buffer looks like this:
1 struct Particle {
2 vec2 position;
3 vec2 velocity;
4 vec4 color;
5 };
6
7 layout(std140, binding = 1) readonly buffer ParticleSSBOIn {
8 Particle particlesIn[ ];
9 };
10
11 layout(std140, binding = 2) buffer ParticleSSBOOut {
12 Particle particlesOut[ ];
13 };
In this example we have a typed SSBO with each particle having a position and
velocity value (see the Particle struct). The SSBO then contains an unbound
number of particles as marked by the []. Not having to specify the number of
elements in an SSBO is one of the advantages over e.g. uniform buffers. std140
is a memory layout qualifier that determines how the member elements of the
shader storage buffer are aligned in memory. This gives us certain guarantees,
required to map the buffers between the host and the GPU.
Writing to such a storage buffer object in the compute shader is straight-forward
and similar to how you’d write to the buffer on the C++ side:
1 particlesOut[index].position = particlesIn[index].position +
particlesIn[index].velocity.xy * ubo.deltaTime;
Storage images
Note that we won’t be doing image manipulation in this chapter. This paragraph
is here to make readers aware that compute shaders can also be used for image
manipulation.
A storage image allows you read from and write to an image. Typical use cases
are applying image effects to textures, doing post processing (which in turn is
very similar) or generating mip-maps.
This is similar for images:
269
1 VkImageCreateInfo imageInfo {};
2 ...
3 imageInfo.usage = VK_IMAGE_USAGE_SAMPLED_BIT |
VK_IMAGE_USAGE_STORAGE_BIT;
4 ...
5
6 if (vkCreateImage(device, &imageInfo, nullptr, &textureImage) !=
VK_SUCCESS) {
7 throw std::runtime_error("failed to create image!");
8 }
The two flags VK_IMAGE_USAGE_SAMPLED_BIT and VK_IMAGE_USAGE_STORAGE_BIT
set with imageInfo.usage tell the implementation that we want to use this
image for two different scenarios: as an image sampled in the fragment shader
and as a storage image in the computer shader;
The GLSL shader declaration for storage image looks similar to sampled images
used e.g. in the fragment shader:
1 layout (binding = 0, rgba8) uniform readonly image2D inputImage;
2 layout (binding = 1, rgba8) uniform writeonly image2D outputImage;
A few differences here are additional attributes like rgba8 for the format of the
image, the readonly and writeonly qualifiers, telling the implementation that
we will only read from the input image and write to the output image. And last
but not least we need to use the image2D type to declare a storage image.
Reading from and writing to storage images in the compute shader is then done
using imageLoad and imageStore:
1 vec3 pixel = imageLoad(inputImage,
ivec2(gl_GlobalInvocationID.xy)).rgb;
2 imageStore(outputImage, ivec2(gl_GlobalInvocationID.xy), pixel);
Compute queue families
In the physical device and queue families chapter we already learned about queue
families and how to select a graphics queue family. Compute uses the queue
family properties flag bit VK_QUEUE_COMPUTE_BIT. So if we want to do compute
work, we need to get a queue from a queue family that supports compute.
Note that Vulkan requires an implementation which supports graphics opera-
tions to have at least one queue family that supports both graphics and compute
operations, but it’s also possible that implementations offer a dedicated com-
pute queue. This dedicated compute queue (that does not have the graphics
bit) hints at an asynchronous compute queue. To keep this tutorial beginner
270
friendly though, we’ll use a queue that can do both graphics and compute opera-
tions. This will also save us from dealing with several advanced synchronization
mechanisms.
For our compute sample we need to change the device creation code a bit:
1 uint32_t queueFamilyCount = 0;
2 vkGetPhysicalDeviceQueueFamilyProperties(device, &queueFamilyCount,
nullptr);
3
4 std::vector<VkQueueFamilyProperties> queueFamilies(queueFamilyCount);
5 vkGetPhysicalDeviceQueueFamilyProperties(device, &queueFamilyCount,
queueFamilies.data());
6
7 int i = 0;
8 for (const auto& queueFamily : queueFamilies) {
9 if ((queueFamily.queueFlags & VK_QUEUE_GRAPHICS_BIT) &&
(queueFamily.queueFlags & VK_QUEUE_COMPUTE_BIT)) {
10 indices.graphicsAndComputeFamily = i;
11 }
12
13 i++;
14 }
The changed queue family index selection code will now try to find a queue
family that supports both graphics and compute.
We can then get a compute queue from this queue family in createLogicalDevice:
1 vkGetDeviceQueue(device, indices.graphicsAndComputeFamily.value(),
0, &computeQueue);
The compute shader stage
In the graphics samples we have used different pipeline stages to load shaders
and access descriptors. Compute shaders are accessed in a similar way by
using the VK_SHADER_STAGE_COMPUTE_BIT pipeline. So loading a compute
shader is just the same as loading a vertex shader, but with a different shader
stage. We’ll talk about this in detail in the next paragraphs. Compute also
introduces a new binding point type for descriptors and pipelines named
VK_PIPELINE_BIND_POINT_COMPUTE that we’ll have to use later on.
Loading compute shaders
Loading compute shaders in our application is the same as loading any
other other shader. The only real difference is that we’ll need to use the
VK_SHADER_STAGE_COMPUTE_BIT mentioned above.
271
1 auto computeShaderCode = readFile("shaders/compute.spv");
2
3 VkShaderModule computeShaderModule =
createShaderModule(computeShaderCode);
4
5 VkPipelineShaderStageCreateInfo computeShaderStageInfo{};
6 computeShaderStageInfo.sType =
VK_STRUCTURE_TYPE_PIPELINE_SHADER_STAGE_CREATE_INFO;
7 computeShaderStageInfo.stage = VK_SHADER_STAGE_COMPUTE_BIT;
8 computeShaderStageInfo.module = computeShaderModule;
9 computeShaderStageInfo.pName = "main";
10 ...
Preparing the shader storage buffers
Earlier on we learned that we can use shader storage buffers to pass arbitrary
data to compute shaders. For this example we will upload an array of particles
to the GPU, so we can manipulate it directly in the GPU’s memory.
In the frames in flight chapter we talked about duplicating resources per frame
in flight, so we can keep the CPU and the GPU busy. First we declare a vector
for the buffer object and the device memory backing it up:
1 std::vector<VkBuffer> shaderStorageBuffers;
2 std::vector<VkDeviceMemory> shaderStorageBuffersMemory;
In the createShaderStorageBuffers we then resize those vectors to match the
max. number of frames in flight:
1 shaderStorageBuffers.resize(MAX_FRAMES_IN_FLIGHT);
2 shaderStorageBuffersMemory.resize(MAX_FRAMES_IN_FLIGHT);
With this setup in place we can start to move the initial particle information to
the GPU. We first initialize a vector of particles on the host side:
1 // Initialize particles
2 std::default_random_engine rndEngine((unsigned)time(nullptr));
3 std::uniform_real_distribution<float> rndDist(0.0f, 1.0f);
4
5 // Initial particle positions on a circle
6 std::vector<Particle> particles(PARTICLE_COUNT);
7 for (auto& particle : particles) {
8 float r = 0.25f * sqrt(rndDist(rndEngine));
9 float theta = rndDist(rndEngine) * 2 *
3.14159265358979323846;
10 float x = r * cos(theta) * HEIGHT / WIDTH;
11 float y = r * sin(theta);
272
12 particle.position = glm::vec2(x, y);
13 particle.velocity = glm::normalize(glm::vec2(x,y)) *
0.00025f;
14 particle.color = glm::vec4(rndDist(rndEngine),
rndDist(rndEngine), rndDist(rndEngine), 1.0f);
15 }
We then create a staging buffer in the host’s memory to hold the initial particle
properties:
1 VkDeviceSize bufferSize = sizeof(Particle) * PARTICLE_COUNT;
2
3 VkBuffer stagingBuffer;
4 VkDeviceMemory stagingBufferMemory;
5 createBuffer(bufferSize, VK_BUFFER_USAGE_TRANSFER_SRC_BIT,
VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT |
VK_MEMORY_PROPERTY_HOST_COHERENT_BIT, stagingBuffer,
stagingBufferMemory);
6
7 void* data;
8 vkMapMemory(device, stagingBufferMemory, 0, bufferSize, 0,
&data);
9 memcpy(data, particles.data(), (size_t)bufferSize);
10 vkUnmapMemory(device, stagingBufferMemory);
Using this staging buffer as a source we then create the per-frame shader storage
buffers and copy the particle properties from the staging buffer to each of these:
1 for (size_t i = 0; i < MAX_FRAMES_IN_FLIGHT; i++) {
2 createBuffer(bufferSize, VK_BUFFER_USAGE_STORAGE_BUFFER_BIT
| VK_BUFFER_USAGE_VERTEX_BUFFER_BIT |
VK_BUFFER_USAGE_TRANSFER_DST_BIT,
VK_MEMORY_PROPERTY_DEVICE_LOCAL_BIT,
shaderStorageBuffers[i], shaderStorageBuffersMemory[i]);
3 // Copy data from the staging buffer (host) to the shader
storage buffer (GPU)
4 copyBuffer(stagingBuffer, shaderStorageBuffers[i],
bufferSize);
5 }
6 }
Descriptors
Setting up descriptors for compute is almost identical to graphics. The only
difference is that descriptors need to have the VK_SHADER_STAGE_COMPUTE_BIT
set to make them accessible by the compute stage:
273
1 std::array<VkDescriptorSetLayoutBinding, 3> layoutBindings{};
2 layoutBindings[0].binding = 0;
3 layoutBindings[0].descriptorCount = 1;
4 layoutBindings[0].descriptorType = VK_DESCRIPTOR_TYPE_UNIFORM_BUFFER;
5 layoutBindings[0].pImmutableSamplers = nullptr;
6 layoutBindings[0].stageFlags = VK_SHADER_STAGE_COMPUTE_BIT;
7 ...
Note that you can combine shader stages here, so if you want the descriptor to
be accessible from the vertex and compute stage, e.g. for a uniform buffer with
parameters shared across them, you simply set the bits for both stages:
1 layoutBindings[0].stageFlags = VK_SHADER_STAGE_VERTEX_BIT |
VK_SHADER_STAGE_COMPUTE_BIT;
Here is the descriptor setup for our sample. The layout looks like this:
1 std::array<VkDescriptorSetLayoutBinding, 3> layoutBindings{};
2 layoutBindings[0].binding = 0;
3 layoutBindings[0].descriptorCount = 1;
4 layoutBindings[0].descriptorType = VK_DESCRIPTOR_TYPE_UNIFORM_BUFFER;
5 layoutBindings[0].pImmutableSamplers = nullptr;
6 layoutBindings[0].stageFlags = VK_SHADER_STAGE_COMPUTE_BIT;
7
8 layoutBindings[1].binding = 1;
9 layoutBindings[1].descriptorCount = 1;
10 layoutBindings[1].descriptorType = VK_DESCRIPTOR_TYPE_STORAGE_BUFFER;
11 layoutBindings[1].pImmutableSamplers = nullptr;
12 layoutBindings[1].stageFlags = VK_SHADER_STAGE_COMPUTE_BIT;
13
14 layoutBindings[2].binding = 2;
15 layoutBindings[2].descriptorCount = 1;
16 layoutBindings[2].descriptorType = VK_DESCRIPTOR_TYPE_STORAGE_BUFFER;
17 layoutBindings[2].pImmutableSamplers = nullptr;
18 layoutBindings[2].stageFlags = VK_SHADER_STAGE_COMPUTE_BIT;
19
20 VkDescriptorSetLayoutCreateInfo layoutInfo{};
21 layoutInfo.sType =
VK_STRUCTURE_TYPE_DESCRIPTOR_SET_LAYOUT_CREATE_INFO;
22 layoutInfo.bindingCount = 3;
23 layoutInfo.pBindings = layoutBindings.data();
24
25 if (vkCreateDescriptorSetLayout(device, &layoutInfo, nullptr,
&computeDescriptorSetLayout) != VK_SUCCESS) {
26 throw std::runtime_error("failed to create compute descriptor
set layout!");
27 }
274
Looking at this setup, you might wonder why we have two layout bindings for
shader storage buffer objects, even though we’ll only render a single particle
system. This is because the particle positions are updated frame by frame
based on a delta time. This means that each frame needs to know about the
last frames’ particle positions, so it can update them with a new delta time and
write them to it’s own SSBO:
For that, the compute shader needs to have access to the last and cur-
rent frame’s SSBOs. This is done by passing both to the compute
shader in our descriptor setup. See the storageBufferInfoLastFrame
and storageBufferInfoCurrentFrame:
1 for (size_t i = 0; i < MAX_FRAMES_IN_FLIGHT; i++) {
2 VkDescriptorBufferInfo uniformBufferInfo{};
3 uniformBufferInfo.buffer = uniformBuffers[i];
4 uniformBufferInfo.offset = 0;
5 uniformBufferInfo.range = sizeof(UniformBufferObject);
6
7 std::array<VkWriteDescriptorSet, 3> descriptorWrites{};
8 ...
9
10 VkDescriptorBufferInfo storageBufferInfoLastFrame{};
11 storageBufferInfoLastFrame.buffer = shaderStorageBuffers[(i - 1)
% MAX_FRAMES_IN_FLIGHT];
12 storageBufferInfoLastFrame.offset = 0;
13 storageBufferInfoLastFrame.range = sizeof(Particle) *
PARTICLE_COUNT;
14
15 descriptorWrites[1].sType =
VK_STRUCTURE_TYPE_WRITE_DESCRIPTOR_SET;
16 descriptorWrites[1].dstSet = computeDescriptorSets[i];
17 descriptorWrites[1].dstBinding = 1;
18 descriptorWrites[1].dstArrayElement = 0;
19 descriptorWrites[1].descriptorType =
275
VK_DESCRIPTOR_TYPE_STORAGE_BUFFER;
20 descriptorWrites[1].descriptorCount = 1;
21 descriptorWrites[1].pBufferInfo = &storageBufferInfoLastFrame;
22
23 VkDescriptorBufferInfo storageBufferInfoCurrentFrame{};
24 storageBufferInfoCurrentFrame.buffer = shaderStorageBuffers[i];
25 storageBufferInfoCurrentFrame.offset = 0;
26 storageBufferInfoCurrentFrame.range = sizeof(Particle) *
PARTICLE_COUNT;
27
28 descriptorWrites[2].sType =
VK_STRUCTURE_TYPE_WRITE_DESCRIPTOR_SET;
29 descriptorWrites[2].dstSet = computeDescriptorSets[i];
30 descriptorWrites[2].dstBinding = 2;
31 descriptorWrites[2].dstArrayElement = 0;
32 descriptorWrites[2].descriptorType =
VK_DESCRIPTOR_TYPE_STORAGE_BUFFER;
33 descriptorWrites[2].descriptorCount = 1;
34 descriptorWrites[2].pBufferInfo = &storageBufferInfoCurrentFrame;
35
36 vkUpdateDescriptorSets(device, 3, descriptorWrites.data(), 0,
nullptr);
37 }
Remember that we also have to request the descriptor types for the SSBOs from
our descriptor pool:
1 std::array<VkDescriptorPoolSize, 2> poolSizes{};
2 ...
3
4 poolSizes[1].type = VK_DESCRIPTOR_TYPE_STORAGE_BUFFER;
5 poolSizes[1].descriptorCount =
static_cast<uint32_t>(MAX_FRAMES_IN_FLIGHT) * 2;
We need to double the number of VK_DESCRIPTOR_TYPE_STORAGE_BUFFER types
requested from the pool by two because our sets reference the SSBOs of the last
and current frame.
Compute pipelines
As compute is not a part of the graphics pipeline, we can’t use vkCreateGraphicsPipelines.
Instead we need to create a dedicated compute pipeline with vkCreateComputePipelines
for running our compute commands. Since a compute pipeline does not touch
any of the rasterization state, it has a lot less state than a graphics pipeline:
1 VkComputePipelineCreateInfo pipelineInfo{};
276
2 pipelineInfo.sType = VK_STRUCTURE_TYPE_COMPUTE_PIPELINE_CREATE_INFO;
3 pipelineInfo.layout = computePipelineLayout;
4 pipelineInfo.stage = computeShaderStageInfo;
5
6 if (vkCreateComputePipelines(device, VK_NULL_HANDLE, 1,
&pipelineInfo, nullptr, &computePipeline) != VK_SUCCESS) {
7 throw std::runtime_error("failed to create compute pipeline!");
8 }
The setup is a lot simpler, as we only require one shader stage and a pipeline
layout. The pipeline layout works the same as with the graphics pipeline:
1 VkPipelineLayoutCreateInfo pipelineLayoutInfo{};
2 pipelineLayoutInfo.sType =
VK_STRUCTURE_TYPE_PIPELINE_LAYOUT_CREATE_INFO;
3 pipelineLayoutInfo.setLayoutCount = 1;
4 pipelineLayoutInfo.pSetLayouts = &computeDescriptorSetLayout;
5
6 if (vkCreatePipelineLayout(device, &pipelineLayoutInfo, nullptr,
&computePipelineLayout) != VK_SUCCESS) {
7 throw std::runtime_error("failed to create compute pipeline
layout!");
8 }
Compute space
Before we get into how a compute shader works and how we submit compute
workloads to the GPU, we need to talk about two important compute concepts:
work groups and invocations. They define an abstract execution model for
how compute workloads are processed by the compute hardware of the GPU in
three dimensions (x, y, and z).
Work groups define how the compute workloads are formed and processed by
the the compute hardware of the GPU. You can think of them as work items the
GPU has to work through. Work group dimensions are set by the application
at command buffer time using a dispatch command.
And each work group then is a collection of invocations that execute the same
compute shader. Invocations can potentially run in parallel and their dimensions
are set in the compute shader. Invocations within a single workgroup have access
to shared memory.
This image shows the relation between these two in three dimensions:
277
The number of dimensions for work groups (defined by vkCmdDispatch) and
invocations depends (defined by the local sizes in the compute shader) on how
input data is structured. If you e.g. work on a one-dimensional array, like we
do in this chapter, you only have to specify the x dimension for both.
As an example: If we dispatch a work group count of [64, 1, 1] with a compute
shader local size of [32, 32, ,1], our compute shader will be invoked 64 x 32 x 32
= 65,536 times.
Note that the maximum count for work groups and local sizes differs from
implementation to implementation, so you should always check the compute
related maxComputeWorkGroupCount, maxComputeWorkGroupInvocations and
maxComputeWorkGroupSize limits in VkPhysicalDeviceLimits.
Compute shaders
Now that we have learned about all the parts required to setup a compute
shader pipeline, it’s time to take a look at compute shaders. All of the things
we learned about using GLSL shaders e.g. for vertex and fragment shaders also
applies to compute shaders. The syntax is the same, and many concepts like
passing data between the application and the shader are the same. But there
are some important differences.
A very basic compute shader for updating a linear array of particles may look
like this:
1 #version 450
2
3 layout (binding = 0) uniform ParameterUBO {
4 float deltaTime;
5 } ubo;
6
7 struct Particle {
8 vec2 position;
278
9 vec2 velocity;
10 vec4 color;
11 };
12
13 layout(std140, binding = 1) readonly buffer ParticleSSBOIn {
14 Particle particlesIn[ ];
15 };
16
17 layout(std140, binding = 2) buffer ParticleSSBOOut {
18 Particle particlesOut[ ];
19 };
20
21 layout (local_size_x = 256, local_size_y = 1, local_size_z = 1) in;
22
23 void main()
24 {
25 uint index = gl_GlobalInvocationID.x;
26
27 Particle particleIn = particlesIn[index];
28
29 particlesOut[index].position = particleIn.position +
particleIn.velocity.xy * ubo.deltaTime;
30 particlesOut[index].velocity = particleIn.velocity;
31 ...
32 }
The top part of the shader contains the declarations for the shader’s input.
First is a uniform buffer object at binding 0, something we already learned
about in this tutorial. Below we declare our Particle structure that matches the
declaration in the C++ code. Binding 1 then refers to the shader storage buffer
object with the particle data from the last frame (see the descriptor setup), and
binding 2 points to the SSBO for the current frame, which is the one we’ll be
updating with this shader.
An interesting thing is this compute-only declaration related to the compute
space:
1 layout (local_size_x = 256, local_size_y = 1, local_size_z = 1) in;
This defines the number invocations of this compute shader in the current work
group. As noted earlier, this is the local part of the compute space. Hence the
local_ prefix. As we work on a linear 1D array of particles we only need to
specify a number for x dimension in local_size_x.
The main function then reads from the last frame’s SSBO and writes the updated
particle position to the SSBO for the current frame. Similar to other shader
types, compute shaders have their own set of builtin input variables. Built-ins
279
are always prefixed with gl_. One such built-in is gl_GlobalInvocationID, a
variable that uniquely identifies the current compute shader invocation across
the current dispatch. We use this to index into our particle array.
Running compute commands
Dispatch
Now it’s time to actually tell the GPU to do some compute. This is done by
calling vkCmdDispatch inside a command buffer. While not perfectly true, a
dispatch is for compute as a draw call like vkCmdDraw is for graphics. This
dispatches a given number of compute work items in at max. three dimensions.
1 VkCommandBufferBeginInfo beginInfo{};
2 beginInfo.sType = VK_STRUCTURE_TYPE_COMMAND_BUFFER_BEGIN_INFO;
3
4 if (vkBeginCommandBuffer(commandBuffer, &beginInfo) != VK_SUCCESS) {
5 throw std::runtime_error("failed to begin recording command
buffer!");
6 }
7
8 ...
9
10 vkCmdBindPipeline(commandBuffer, VK_PIPELINE_BIND_POINT_COMPUTE,
computePipeline);
11 vkCmdBindDescriptorSets(commandBuffer,
VK_PIPELINE_BIND_POINT_COMPUTE, computePipelineLayout, 0, 1,
&computeDescriptorSets[i], 0, 0);
12
13 vkCmdDispatch(computeCommandBuffer, PARTICLE_COUNT / 256, 1, 1);
14
15 ...
16
17 if (vkEndCommandBuffer(commandBuffer) != VK_SUCCESS) {
18 throw std::runtime_error("failed to record command buffer!");
19 }
The vkCmdDispatch will dispatch PARTICLE_COUNT / 256 local work groups in
the x dimension. As our particles array is linear, we leave the other two dimen-
sions at one, resulting in a one-dimensional dispatch. But why do we divide
the number of particles (in our array) by 256? That’s because in the previous
paragraph we defined that every compute shader in a work group will do 256
invocations. So if we were to have 4096 particles, we would dispatch 16 work
groups, with each work group running 256 compute shader invocations. Getting
the two numbers right usually takes some tinkering and profiling, depending
on your workload and the hardware you’re running on. If your particle size
280
would be dynamic and can’t always be divided by e.g. 256, you can always use
gl_GlobalInvocationID at the start of your compute shader and return from
it if the global invocation index is greater than the number of your particles.
And just as was the case for the compute pipeline, a compute command buffer
contains a lot less state then a graphics command buffer. There’s no need to
start a render pass or set a viewport.
Submitting work
As our sample does both compute and graphics operations, we’ll be doing two
submits to both the graphics and compute queue per frame (see the drawFrame
function):
1 ...
2 if (vkQueueSubmit(computeQueue, 1, &submitInfo, nullptr) !=
VK_SUCCESS) {
3 throw std::runtime_error("failed to submit compute command
buffer!");
4 };
5 ...
6 if (vkQueueSubmit(graphicsQueue, 1, &submitInfo,
inFlightFences[currentFrame]) != VK_SUCCESS) {
7 throw std::runtime_error("failed to submit draw command
buffer!");
8 }
The first submit to the compute queue updates the particle positions using the
compute shader, and the second submit will then use that updated data to draw
the particle system.
Synchronizing graphics and compute
Synchronization is an important part of Vulkan, even more so when doing com-
pute in conjunction with graphics. Wrong or lacking synchronization may result
in the vertex stage starting to draw (=read) particles while the compute shader
hasn’t finished updating (=write) them (read-after-write hazard), or the com-
pute shader could start updating particles that are still in use by the vertex part
of the pipeline (write-after-read hazard).
So we must make sure that those cases don’t happen by properly synchronizing
the graphics and the compute load. There are different ways of doing so, de-
pending on how you submit your compute workload but in our case with two
separate submits, we’ll be using semaphores and fences to ensure that the ver-
tex shader won’t start fetching vertices until the compute shader has finished
updating them.
281
This is necessary as even though the two submits are ordered one-after-another,
there is no guarantee that they execute on the GPU in this order. Adding in
wait and signal semaphores ensures this execution order.
So we first add a new set of synchronization primitives for the compute work
in createSyncObjects. The compute fences, just like the graphics fences, are
created in the signaled state because otherwise, the first draw would time out
while waiting for the fences to be signaled as detailed here:
1 std::vector<VkFence> computeInFlightFences;
2 std::vector<VkSemaphore> computeFinishedSemaphores;
3 ...
4 computeInFlightFences.resize(MAX_FRAMES_IN_FLIGHT);
5 computeFinishedSemaphores.resize(MAX_FRAMES_IN_FLIGHT);
6
7 VkSemaphoreCreateInfo semaphoreInfo{};
8 semaphoreInfo.sType = VK_STRUCTURE_TYPE_SEMAPHORE_CREATE_INFO;
9
10 VkFenceCreateInfo fenceInfo{};
11 fenceInfo.sType = VK_STRUCTURE_TYPE_FENCE_CREATE_INFO;
12 fenceInfo.flags = VK_FENCE_CREATE_SIGNALED_BIT;
13
14 for (size_t i = 0; i < MAX_FRAMES_IN_FLIGHT; i++) {
15 ...
16 if (vkCreateSemaphore(device, &semaphoreInfo, nullptr,
&computeFinishedSemaphores[i]) != VK_SUCCESS ||
17 vkCreateFence(device, &fenceInfo, nullptr,
&computeInFlightFences[i]) != VK_SUCCESS) {
18 throw std::runtime_error("failed to create compute
synchronization objects for a frame!");
19 }
20 }
We then use these to synchronize the compute buffer submission with the graph-
ics submission:
1 // Compute submission
2 vkWaitForFences(device, 1, &computeInFlightFences[currentFrame],
VK_TRUE, UINT64_MAX);
3
4 updateUniformBuffer(currentFrame);
5
6 vkResetFences(device, 1, &computeInFlightFences[currentFrame]);
7
8 vkResetCommandBuffer(computeCommandBuffers[currentFrame],
/*VkCommandBufferResetFlagBits*/ 0);
9 recordComputeCommandBuffer(computeCommandBuffers[currentFrame]);
282
10
11 submitInfo.commandBufferCount = 1;
12 submitInfo.pCommandBuffers = &computeCommandBuffers[currentFrame];
13 submitInfo.signalSemaphoreCount = 1;
14 submitInfo.pSignalSemaphores =
&computeFinishedSemaphores[currentFrame];
15
16 if (vkQueueSubmit(computeQueue, 1, &submitInfo,
computeInFlightFences[currentFrame]) != VK_SUCCESS) {
17 throw std::runtime_error("failed to submit compute command
buffer!");
18 };
19
20 // Graphics submission
21 vkWaitForFences(device, 1, &inFlightFences[currentFrame], VK_TRUE,
UINT64_MAX);
22
23 ...
24
25 vkResetFences(device, 1, &inFlightFences[currentFrame]);
26
27 vkResetCommandBuffer(commandBuffers[currentFrame],
/*VkCommandBufferResetFlagBits*/ 0);
28 recordCommandBuffer(commandBuffers[currentFrame], imageIndex);
29
30 VkSemaphore waitSemaphores[] = {
computeFinishedSemaphores[currentFrame],
imageAvailableSemaphores[currentFrame] };
31 VkPipelineStageFlags waitStages[] = {
VK_PIPELINE_STAGE_VERTEX_INPUT_BIT,
VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT };
32 submitInfo = {};
33 submitInfo.sType = VK_STRUCTURE_TYPE_SUBMIT_INFO;
34
35 submitInfo.waitSemaphoreCount = 2;
36 submitInfo.pWaitSemaphores = waitSemaphores;
37 submitInfo.pWaitDstStageMask = waitStages;
38 submitInfo.commandBufferCount = 1;
39 submitInfo.pCommandBuffers = &commandBuffers[currentFrame];
40 submitInfo.signalSemaphoreCount = 1;
41 submitInfo.pSignalSemaphores =
&renderFinishedSemaphores[currentFrame];
42
43 if (vkQueueSubmit(graphicsQueue, 1, &submitInfo,
inFlightFences[currentFrame]) != VK_SUCCESS) {
44 throw std::runtime_error("failed to submit draw command
283
buffer!");
45 }
Similar to the sample in the semaphores chapter, this setup will immediately
run the compute shader as we haven’t specified any wait semaphores. This is
fine, as we are waiting for the compute command buffer of the current frame
to finish execution before the compute submission with the vkWaitForFences
command.
The graphics submission on the other hand needs to wait for the compute
work to finish so it doesn’t start fetching vertices while the compute buffer
is still updating them. So we wait on the computeFinishedSemaphores
for the current frame and have the graphics submission wait on the
VK_PIPELINE_STAGE_VERTEX_INPUT_BIT stage, where vertices are consumed.
But it also needs to wait for presentation so the fragment shader won’t
output to the color attachments until the image has been presented. So we
also wait on the imageAvailableSemaphores on the current frame at the
VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT stage.
Drawing the particle system
Earlier on, we learned that buffers in Vulkan can have multiple use-cases and so
we created the shader storage buffer that contains our particles with both the
shader storage buffer bit and the vertex buffer bit. This means that we can use
the shader storage buffer for drawing just as we used “pure” vertex buffers in
the previous chapters.
We first setup the vertex input state to match our particle structure:
1 struct Particle {
2 ...
3
4 static std::array<VkVertexInputAttributeDescription, 2>
getAttributeDescriptions() {
5 std::array<VkVertexInputAttributeDescription, 2>
attributeDescriptions{};
6
7 attributeDescriptions[0].binding = 0;
8 attributeDescriptions[0].location = 0;
9 attributeDescriptions[0].format = VK_FORMAT_R32G32_SFLOAT;
10 attributeDescriptions[0].offset = offsetof(Particle,
position);
11
12 attributeDescriptions[1].binding = 0;
13 attributeDescriptions[1].location = 1;
284
14 attributeDescriptions[1].format =
VK_FORMAT_R32G32B32A32_SFLOAT;
15 attributeDescriptions[1].offset = offsetof(Particle, color);
16
17 return attributeDescriptions;
18 }
19 };
Note that we don’t add velocity to the vertex input attributes, as this is only
used by the compute shader.
We then bind and draw it like we would with any vertex buffer:
1 vkCmdBindVertexBuffers(commandBuffer, 0, 1,
&shaderStorageBuffer[currentFrame], offsets);
2
3 vkCmdDraw(commandBuffer, PARTICLE_COUNT, 1, 0, 0);
Conclusion
In this chapter, we learned how to use compute shaders to offload work from the
CPU to the GPU. Without compute shaders, many effects in modern games and
applications would either not be possible or would run a lot slower. But even
more than graphics, compute has a lot of use-cases, and this chapter only gives
you a glimpse of what’s possible. So now that you know how to use compute
shaders, you may want to take look at some advanced compute topics like:
• Shared memory
• Asynchronous compute
• Atomic operations
• Subgroups
You can find some advanced compute samples in the official Khronos Vulkan
Samples repository.
C++ code / Vertex shader / Fragment shader / Compute shader
285
FAQ
This page lists solutions to common problems that you may encounter while
developing Vulkan applications.
I get an access violation error in the core valida-
tion layer
Make sure that MSI Afterburner / RivaTuner Statistics Server is not running,
because it has some compatibility problems with Vulkan.
I don’t see any messages from the validation lay-
ers / Validation layers are not available
First make sure that the validation layers get a chance to print errors by keeping
the terminal open after your program exits. You can do this from Visual Studio
by running your program with Ctrl-F5 instead of F5, and on Linux by executing
your program from a terminal window. If there are still no messages and you
are sure that validation layers are turned on, then you should ensure that your
Vulkan SDK is correctly installed by following the “Verify the Installation” in-
structions on this page. Also ensure that your SDK version is at least 1.1.106.0
to support the VK_LAYER_KHRONOS_validation layer.
vkCreateSwapchainKHR triggers an error in
SteamOverlayVulkanLayer64.dll
This appears to be a compatibility problem in the Steam client beta. There
are a few possible workarounds: * Opt out of the Steam beta program. *
Set the DISABLE_VK_LAYER_VALVE_steam_overlay_1 environment variable
to 1 * Delete the Steam overlay Vulkan layer entry in the registry under
HKEY_LOCAL_MACHINE\SOFTWARE\Khronos\Vulkan\ImplicitLayers
Example:
286
vkCreateInstance fails with VK_ERROR_INCOMPATIBLE_DRIV
If you are using MacOS with the latest MoltenVK SDK then vkCreateInstance
may return the VK_ERROR_INCOMPATIBLE_DRIVER error. This is be-
cause Vulkan SDK version 1.3.216 or newer requires you to enable the
VK_KHR_PORTABILITY_subset extension to use MoltenVK, because it is
currently not fully conformant.
You have to add the VK_INSTANCE_CREATE_ENUMERATE_PORTABILITY_BIT_KHR
flag to your VkInstanceCreateInfo and add VK_KHR_PORTABILITY_ENUMERATION_EXTENSION_NAME
to your instance extension list.
Code example:
1 ...
2
3 std::vector<const char*> requiredExtensions;
4
5 for(uint32_t i = 0; i < glfwExtensionCount; i++) {
6 requiredExtensions.emplace_back(glfwExtensions[i]);
7 }
8
9 requiredExtensions.emplace_back(VK_KHR_PORTABILITY_ENUMERATION_EXTENSION_NAME);
10
11 createInfo.flags |= VK_INSTANCE_CREATE_ENUMERATE_PORTABILITY_BIT_KHR;
12
13 createInfo.enabledExtensionCount = (uint32_t)
requiredExtensions.size();
14 createInfo.ppEnabledExtensionNames = requiredExtensions.data();
15
16 if (vkCreateInstance(&createInfo, nullptr, &instance) != VK_SUCCESS)
{
17 throw std::runtime_error("failed to create instance!");
18 }
287