Writing mental ray shaders: UV Chooser

Intro
Here is a shader that loads a texture, and chooses which UV set to use. There's an equivalent node in Maya, but it requires setting the input values in hypershade, which isn't intuitive for the avg user. In 3ds max the same thing is set with UV channels. Multi texture layering is an important technique when dealing repetitive textures, by using 5 1k textures, i can create a better looking texture than a single 5k texture. Not sure why maya is making it so hard for avg users.

MI Source

declare shader
 color "uv_chooser" (
  color texture "tex",
  integer "uv_sets"
 )
apply material
end declare

C Source

#include "shader.h"

struct uv_chooser{
 miTag tex;
 miInteger uv_sets;
 };

miBoolean uv_chooser(miColor *result, miState *state, struct uv_chooser *params) {
 miTag tex = *mi_eval_tag(&params->tex);
 miInteger uv_sets = *mi_eval_integer(&params->uv_sets);
 int i = uv_sets;
 mi_lookup_color_texture(result, state, tex, &state->tex_list[i]);
 return miTRUE;
 }

 

Writing mental ray shaders: Mosaic Tiles

Introduction

Here is a little something thats detours from the book. Combining quantization and texture uv, I can create a mosaic effect. 

Methodology

1. Have an input texture

2. quantize the uv_coordinates

3. use the quantized_uv_coordinates inside mi_lookup_texture_color

From top to bottom: Original, tile = 20, tile = 10, Porn?!