Template Files

The text that ppmtoarbtxt generates from a template file is the literal text of the template file, except with substitution specifier replaced with something else. The program recognizes a substitution specifier as text of the form #(...).

ppmtoarbtxt treats white space in the template files the same as any other characters, placing it in the output, with one exception: If the template file ends with a newline character, ppmtoarbtxt ignores it -- it does not include it in the output.

Many substitution specifiers use format strings (another form of template) to specify the substitution. You should make these format strings as minimal as possible, placing literal text outside the substitution specifier instead of inside the format string. For example,

Wrong: #(flum %%%2.2f 0 1)

Right: %#(flum %2.2f 0 1)

The valid substitution specifiers are as follows. Text that has the form of a substitution specifier but is not actually valid (e.g. #(random junk) usually just specifies its literal value, but if it is close enough to something valid, ppmtoarbtxt assumes you made a mistake and fails.

Useful in a body template, to do substitutions based on a particular pixel:

#(ired format blackref whiteref)

generates an integer in the range blackref to whiteref in a format specified by format representing the red intensity of the pixel. A red intensity of 0 becomes blackref; a red intensity of maxval becomes whiteref, with the rest linearly interpolated in between.

format is a printf-like format specifier like "%d". ppmtoarbtxt uses as the entire format string to a fprintf POSIX library call whose only other argument is the red itensity as an integer data type. ppmtoarbtxt does not necessarily verify that your format string makes sense; there are values you could specify that could even crash the program. To avoid unexpected behavior, keep format strings simple and hardcoded, and never include a per cent sign or newline.

#(ired) is equivalent to #(ired %d 0 255).

#(igreen format blackref whiteref)

Same as #(ired..., but for green.

#(iblue format blackref whiteref)

Same as #(ired..., but for blue.

#(ilum format blackref whiteref)

Same as #(ired..., but representing the luminance value (0.299*red + 0.587*green + 0.114*blue) of the pixel.

#(fred format blackref whiteref)

Same as #(ired..., but generates a floating point number instead of an integer.

In this case, the second argument to the fprintf that uses format has a double precision floating point data type.

#(fred) is equivalent to #(fred %f 0.0 1.0).

#(fgreen format blackref whiteref)

Same as #(fred..., but for green.

#(fblue format blackref whiteref)

Same as #(fred..., but for blue.

#(flum format blackref whiteref)

Same as #(fred..., but representing the luminance value (0.299*red + 0.587*green + 0.114*blue) of the pixel.

#(posx format)

Generates the horizontal position of the pixel, in pixels from the left edge of the image.

The second argument to the fprintf that uses format has an unsigned integer data type.

format defaults to %u

#(posy format)

Same as #(width..., but for the vertical position.

If you use any of the above substitution specifiers in a head or tail template, the result is undefined.

Useful in a head or tail template, to do substitutions based on whole-image attributes:

#(width format)

Generates the width in pixels of the image.

The second argument to the fprintf that uses format has an unsigned integer data type.

format defaults to %u

#(height format)

Same as #(width..., but for the height of the image.

gray inversion

Here we generate a PGM plain-format image with gray inversion (like ppmtopgm | pnminvert).

Contents of our head template file:

P2
#(width) #(height)
255

Contents of our body skeleton file:

#(ilum %d 255 0)

povray file

Here we generate a povray file where each pixel is represented by a sphere at location (x,y,z) = (posx,height-posy,luminance). The color of the sphere is the color of the pixel.

Contents of our head skeleton:

#include "colors.inc"
#include "textures.inc"
camera {


   location  <#(width) * 0.6, #(height) * 0.7, 80>


   look_at   <#(width) * 0.5, #(height) * 0.5, 0>
}
light_source { <#(width) * 0.5, #(height) * 0.5, 25> color White
}

Contents of our body skeleton:

sphere { <#(posx),#(height)-#(posy),#(ilum %d 0 10)>, 0.5


  texture {


    pigment {


      color rgb <#(fred),#(fgreen),#(fblue)>


    }


    finish {


      phong 1


    }


  }
}