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/* MipMapDownsamplingShader.frag.txt
*
* Example shader for downsampling during building a OpenGL Mipmap image
* resolution pyramid. This shader can be passed to CreateResolutionPyramid().
*
* This shader computes each "downfiltered" output sample from a 3-by-3 grid
* of neighbouring input samples, weighted by a gaussian filter kernel of
* standard deviation 1.0.
*
* This is a proof-of-concept shader. It demonstrates the principle, but is
* not necessarilly perfect.
*
* (c) 2012 by Mario Kleiner. Licensed under MIT license.
*/
const vec3 ColorToGrayWeights = vec3(0.3, 0.59, 0.11);
uniform sampler2D Image;
uniform vec2 srcSize;
uniform vec2 dstSize;
const mat3 kernel = mat3( 0.075113607954111, 0.123841403152974, 0.075113607954111, 0.123841403152974, 0.204179955571658, 0.123841403152974, 0.075113607954111, 0.123841403152974, 0.075113607954111);
void main()
{
vec2 inpos = gl_TexCoord[0].st;
float dx = 1.0 / srcSize.x;
float dy = 1.0 / srcSize.y;
/* Take 9 weighted samples in a 3x3 grid, to emulate sampling with a gaussian kernel: */
vec4 incolor = vec4(0.0);
incolor += texture2D(Image, inpos + vec2(-dx, -dy)) * kernel[0][0];
incolor += texture2D(Image, inpos + vec2(0.0, -dy)) * kernel[1][0];
incolor += texture2D(Image, inpos + vec2(+dx, -dy)) * kernel[2][0];
incolor += texture2D(Image, inpos + vec2(-dx, 0.0)) * kernel[0][1];
incolor += texture2D(Image, inpos + vec2(0.0, 0.0)) * kernel[1][1];
incolor += texture2D(Image, inpos + vec2(+dx, 0.0)) * kernel[2][1];
incolor += texture2D(Image, inpos + vec2(-dx, +dy)) * kernel[0][2];
incolor += texture2D(Image, inpos + vec2(0.0, +dy)) * kernel[1][2];
incolor += texture2D(Image, inpos + vec2(+dx, +dy)) * kernel[2][2];
/* Optionally convert final RGB sample to grayscale: */
if (true) {
float luminance = dot(incolor.rgb, ColorToGrayWeights);
gl_FragColor.rgb = vec3(luminance);
/* Pass alpha unmodified: */
gl_FragColor.a = incolor.a;
}
else {
/* Simply pass sample unmodified: */
gl_FragColor = incolor;
}
}
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