96 lines
2.9 KiB
HLSL
96 lines
2.9 KiB
HLSL
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#ifndef UNITY_POSTFX_EXPOSURE_HISTOGRAM
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#define UNITY_POSTFX_EXPOSURE_HISTOGRAM
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// Don't forget to update 'LogHistogram.cs' if you change these values !
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#define HISTOGRAM_BINS 128
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#define HISTOGRAM_TEXELS HISTOGRAM_BINS / 4
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#if SHADER_API_GLES3 || SHADER_API_METAL
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#define HISTOGRAM_THREAD_X 8
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#define HISTOGRAM_THREAD_Y 8
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#define HISTOGRAM_REDUCTION_THREAD_X 8
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#define HISTOGRAM_REDUCTION_THREAD_Y 8
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#define HISTOGRAM_REDUCTION_ALT_PATH 1
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#else
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#define HISTOGRAM_THREAD_X 16
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#define HISTOGRAM_THREAD_Y 16
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#define HISTOGRAM_REDUCTION_THREAD_X HISTOGRAM_THREAD_X
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#define HISTOGRAM_REDUCTION_THREAD_Y HISTOGRAM_BINS / HISTOGRAM_THREAD_Y
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#define HISTOGRAM_REDUCTION_ALT_PATH 0
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#endif
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#define HISTOGRAM_REDUCTION_BINS HISTOGRAM_REDUCTION_THREAD_X * HISTOGRAM_REDUCTION_THREAD_Y
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float GetHistogramBinFromLuminance(float value, float2 scaleOffset)
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{
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return saturate(log2(value) * scaleOffset.x + scaleOffset.y);
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}
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float GetLuminanceFromHistogramBin(float bin, float2 scaleOffset)
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{
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return exp2((bin - scaleOffset.y) / scaleOffset.x);
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}
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float GetBinValue(StructuredBuffer<uint> buffer, uint index, float maxHistogramValue)
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{
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return float(buffer[index]) * maxHistogramValue;
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}
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float FindMaxHistogramValue(StructuredBuffer<uint> buffer)
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{
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uint maxValue = 0u;
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for (uint i = 0; i < HISTOGRAM_BINS; i++)
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{
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uint h = buffer[i];
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maxValue = max(maxValue, h);
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}
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return float(maxValue);
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}
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void FilterLuminance(StructuredBuffer<uint> buffer, uint i, float maxHistogramValue, float2 scaleOffset, inout float4 filter)
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{
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float binValue = GetBinValue(buffer, i, maxHistogramValue);
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// Filter dark areas
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float offset = min(filter.z, binValue);
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binValue -= offset;
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filter.zw -= offset.xx;
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// Filter highlights
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binValue = min(filter.w, binValue);
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filter.w -= binValue;
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// Luminance at the bin
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float luminance = GetLuminanceFromHistogramBin(float(i) / float(HISTOGRAM_BINS), scaleOffset);
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filter.xy += float2(luminance * binValue, binValue);
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}
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float GetAverageLuminance(StructuredBuffer<uint> buffer, float4 params, float maxHistogramValue, float2 scaleOffset)
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{
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// Sum of all bins
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uint i;
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float totalSum = 0.0;
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UNITY_UNROLL
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for (i = 0; i < HISTOGRAM_BINS; i++)
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totalSum += GetBinValue(buffer, i, maxHistogramValue);
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// Skip darker and lighter parts of the histogram to stabilize the auto exposure
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// x: filtered sum
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// y: accumulator
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// zw: fractions
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float4 filter = float4(0.0, 0.0, totalSum * params.xy);
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UNITY_UNROLL
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for (i = 0; i < HISTOGRAM_BINS; i++)
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FilterLuminance(buffer, i, maxHistogramValue, scaleOffset, filter);
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// Clamp to user brightness range
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return clamp(filter.x / max(filter.y, EPSILON), params.z, params.w);
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}
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#endif // UNITY_POSTFX_EXPOSURE_HISTOGRAM
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