@7171al71If what you want to do is apply the effect of a shader only to pixels having a specific colour then you just use a conditional based on that colour, as follows
// Only pixels having the following colour are to be affected
const vec3 TargetColour = vec3(1.0,0.0,1.0);
// Allow a little mismatch with the target colour
const float Threshold = 0.001;
void main ( void )
{
// Default to leaving the pixel unchanged
gl_FragColor = gl_Color;
// If the colour of the pixel is close to the target colour
// then apply whatever transformation you want
if ( distance(gl_Color.rgb,vec3(TargetColour)) <= Threshold )
{ // Put your particular shader code here
}
}
This is a basic Colour Seperation Overlay process - more commonly called Green Screen or Blue Screen depending on the colour being used. Done this crudely it can leave ugly edge effects but whether or not that is a problem depends on what you are using it for.
The target colour and threshold could be passed to the shader as uniform variables rather than hardcoded, then you could specify them in the .scn file.
One ***** thing, the colour (1,0,1) is more commonly called magenta. Red, Green, Blue being the primary colours (R,G,B) and Cyan,Magenta,Yellow (C,M,Y) the secondary colours obtained by adding any two of the primaries.
