uniform sampler2D colorTexture;
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uniform float avgLuminance;
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uniform float threshold;
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uniform float offset;
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varying vec2 v_textureCoordinates;
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float key(float avg)
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{
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float guess = 1.5 - (1.5 / (avg * 0.1 + 1.0));
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return max(0.0, guess) + 0.1;
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}
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// See section 9. "The bright-pass filter" of Realtime HDR Rendering
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// http://www.cg.tuwien.ac.at/research/publications/2007/Luksch_2007_RHR/Luksch_2007_RHR-RealtimeHDR%20.pdf
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void main()
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{
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vec4 color = texture2D(colorTexture, v_textureCoordinates);
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vec3 xyz = czm_RGBToXYZ(color.rgb);
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float luminance = xyz.r;
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float scaledLum = key(avgLuminance) * luminance / avgLuminance;
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float brightLum = max(scaledLum - threshold, 0.0);
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float brightness = brightLum / (offset + brightLum);
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xyz.r = brightness;
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gl_FragColor = vec4(czm_XYZToRGB(xyz), 1.0);
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}
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