/* 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 vec3 ColorToGrayWeights = vec3(0.3, 0.59, 0.11); 
uniform sampler2DRect Image;

void main()
{
    vec4 incolor = texture2DRect(Image, gl_TexCoord[0].st);
    float luminance = dot(incolor.rgb, ColorToGrayWeights);
    gl_FragColor.a = incolor.a;
    gl_FragColor.rgb = vec3(luminance);
}
