Pixel-Composer/shaders/sh_combine_rgb/sh_combine_rgb.fsh

//
// Simple passthrough fragment shader
//
varying vec2 v_vTexcoord;
varying vec4 v_vColour;

uniform float base;
uniform int mode;
uniform sampler2D samplerR;
uniform sampler2D samplerG;
uniform sampler2D samplerB;
uniform sampler2D samplerA;

uniform int useR;
uniform int useG;
uniform int useB;
uniform int useA;

float sample(vec4 col, int ch) {
	if(mode == 0) return (col[0] + col[1] + col[2]) / 3. * col[3];
	return col[ch];
}

void main() {
	float r = (useR == 1)? sample(texture2D( samplerR, v_vTexcoord ), 0) : base;
	float g = (useG == 1)? sample(texture2D( samplerG, v_vTexcoord ), 1) : base;
	float b = (useB == 1)? sample(texture2D( samplerB, v_vTexcoord ), 2) : base;
	float a = (useA == 1)? sample(texture2D( samplerA, v_vTexcoord ), 3) : 1.;
	
	gl_FragColor = vec4(r, g, b, a);
}