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/* Shader for conversion of RGB textures into Grayscale textures.
* Uses standard formula for conversion:
* (w)2006 by Mario Kleiner. Licensed under MIT license.
*/
#extension GL_ARB_texture_rectangle : enable
const vec4 ColorToGrayWeights = { 0.3, 0.59, 0.11, 0.0 };
uniform sampler2DRect Image;
void main()
{
vec4 leftcolor = texture2DRect(Image, gl_TexCoord[0].st);
vec4 rightcolor = texture2DRect(Image, gl_TexCoord[0].st + vec2(1.0, 0.0));
float leftlum = dot(leftcolor, ColorToGrayWeights);
float rightlum = dot(rightcolor, ColorToGrayWeights);
gl_FragColor.a = 255.0;
gl_FragColor.rgb = max(leftlum - rightlum, 0.0) * 1;
}
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