Identifying the triangle to which the given fragment belongs

jaeho · April 7, 2016, 1:57pm

Suppose there is an instance of ofMesh whose mode is OF_PRIMITIVE_TRIANGLES. The mesh is a polygon made up with some given vertices and indices.

I’m wondering if there is any way to know to which triangle the given fragment belongs in a fragment shader?

kashim · April 7, 2016, 2:01pm

perhaps it can be useful to look at this:
https://www.opengl.org/wiki/Tessellation_Control_Shader
https://www.opengl.org/wiki/Tessellation_Evaluation_Shader

and:

github.com

kashimAstro/ofxShaderSelect/blob/master/example/bin/data/shader.glsl

-- VERTEX
in vec4 Position;
out vec3 vPosition;

void main(){
    vPosition = Position.xyz;
}

-- FRAGMENT
out vec4 FragColor;
in vec3 gFacetNormal;
in vec3 gTriDistance;
in vec3 gPatchDistance;
in float gPrimitive;
uniform vec3 LightPosition;
uniform vec3 DiffuseMaterial;
uniform vec3 AmbientMaterial;

float amplify(float d, float scale, float offset)
{

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