Writing mental ray shaders: Quantization Part II

Intro

Here I will combine my two previous posts into one shader, the uv_as_colors_banding shader. I'll implement the rounding function as demonstrated in the wikipedia article. I did not understand some of the source code from the book

Methodology

1. Implement uv as colors

2. Define u_count, which is the amount of banding in the u direction

3. Define v_count, which is the amount of banding in the v direction

4. Implement the quantize function. 

MI Source

declare shader
 color "uv_as_colors_banding" (
  integer "u_count" default 4,
  integer "v_count" default 4,
 )
apply material
end declare

C Source

#include "shader.h"

struct uv_as_colors_banding{
 miInteger u_count;
 miInteger v_count;
 };

miScalar quantize(miScalar value, miInteger m) {
 miScalar q = (miScalar)m;
 return (miScalar)(((int)(value * q)) / q);
 }

miBoolean uv_as_colors_banding(miColor *result, miState *state, struct uv_as_colors_banding *params) {
 result->r = quantize(state->tex_list[0].x, *mi_eval_integer(¶ms->u_count));
 result->g = quantize(state->tex_list[0].y, *mi_eval_integer(¶ms->v_count));
 result->b = 0;
 return miTRUE;
 }