src/opengl/util/composition_mode_darken.glsl
author Alex Gilkes <alex.gilkes@nokia.com>
Mon, 11 Jan 2010 14:00:40 +0000
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// Dca' = min(Sca.Da, Dca.Sa) + Sca.(1 - Da) + Dca.(1 - Sa)
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// Da'  = Sa + Da - Sa.Da 
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vec4 composite(vec4 src, vec4 dst)
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{
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    vec4 result;
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    result.rgb = min(src.rgb * dst.a, dst.rgb * src.a) + src.rgb * (1.0 - dst.a) + dst.rgb * (1.0 - src.a);
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    result.a = src.a + dst.a - src.a * dst.a;
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    return result;
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}