NIR Texture Instructions¶
Even though texture instructions could be supported as intrinsics, the vast number of combinations mean that doing so is practically impossible. Instead, NIR has a dedicated texture instruction. There are several texture operations:
doxygenenum: Cannot find file: /home/user/documentation/docs/mesa/repository/docs/doxygen_xml/index.xml
As with other instruction types, there is still an array of sources, except that each source also has a type associated with it. There are various source types, each corresponding to a piece of information that the different texture operations require.
doxygenenum: Cannot find file: /home/user/documentation/docs/mesa/repository/docs/doxygen_xml/index.xml
Of particular interest are the texture/sampler deref/index/handle source types. First, note that textures and samplers are specified separately in NIR. While not required for OpenGL, this is required for Vulkan and OpenCL. Some OpenGL [ES] drivers have to deal with hardware that does not have separate samplers and textures. While not recommended, an OpenGL-only driver may assume that the texture and sampler derefs will always point to the same resource, if needed. Note that this pretty well paints your compiler into a corner and makes any future port to Vulkan or OpenCL harder, so such assumptions should really only be made if targeting OpenGL ES 2.0 era hardware.
Also, like a lot of other resources, there are multiple ways to represent a
texture in NIR. It can be referenced by a variable dereference, an index, or a
bindless handle. When using an index or a bindless handle, the texture type
information is generally not available. To handle this, various information
from the type is redundantly stored in the nir_tex_instr itself.
doxygenstruct: Cannot find file: /home/user/documentation/docs/mesa/repository/docs/doxygen_xml/index.xml
doxygenstruct: Cannot find file: /home/user/documentation/docs/mesa/repository/docs/doxygen_xml/index.xml
Texture instruction helpers¶
There are a number of helper functions for working with NIR texture instructions. They are documented here in no particular order.
doxygenfunction: Cannot find file: /home/user/documentation/docs/mesa/repository/docs/doxygen_xml/index.xml
doxygenfunction: Cannot find file: /home/user/documentation/docs/mesa/repository/docs/doxygen_xml/index.xml
doxygenfunction: Cannot find file: /home/user/documentation/docs/mesa/repository/docs/doxygen_xml/index.xml
doxygenfunction: Cannot find file: /home/user/documentation/docs/mesa/repository/docs/doxygen_xml/index.xml
doxygenfunction: Cannot find file: /home/user/documentation/docs/mesa/repository/docs/doxygen_xml/index.xml
doxygenfunction: Cannot find file: /home/user/documentation/docs/mesa/repository/docs/doxygen_xml/index.xml
doxygenfunction: Cannot find file: /home/user/documentation/docs/mesa/repository/docs/doxygen_xml/index.xml
doxygenfunction: Cannot find file: /home/user/documentation/docs/mesa/repository/docs/doxygen_xml/index.xml
doxygenfunction: Cannot find file: /home/user/documentation/docs/mesa/repository/docs/doxygen_xml/index.xml
doxygenfunction: Cannot find file: /home/user/documentation/docs/mesa/repository/docs/doxygen_xml/index.xml
doxygenfunction: Cannot find file: /home/user/documentation/docs/mesa/repository/docs/doxygen_xml/index.xml
Texture instruction lowering¶
Because most hardware only supports some subset of all possible GLSL/SPIR-V texture operations, NIR provides a quite powerful lowering pass which is able to implement more complex texture operations in terms of simpler ones.
doxygenfunction: Cannot find file: /home/user/documentation/docs/mesa/repository/docs/doxygen_xml/index.xml
doxygenstruct: Cannot find file: /home/user/documentation/docs/mesa/repository/docs/doxygen_xml/index.xml
doxygenenum: Cannot find file: /home/user/documentation/docs/mesa/repository/docs/doxygen_xml/index.xml