57 lines
2.5 KiB
Plaintext
57 lines
2.5 KiB
Plaintext
#version 430 core // Need SSBOs and atomic counters
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// Input Texture (the processed image ready for display)
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// Binding = 0 matches glBindImageTexture unit
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// Use rgba8 format as we assume display texture is 8-bit sRGB (adjust if needed)
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layout(binding = 0, rgba8) uniform readonly image2D InputTexture;
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// Output Histogram Buffer (SSBO)
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// Binding = 1 matches glBindBufferBase index
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// Contains 256 bins for R, 256 for G, 256 for B sequentially (total 768 uints)
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layout(std430, binding = 1) buffer HistogramBuffer {
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uint bins[]; // Use an unsized array
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} histogram;
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// Workgroup size (adjust based on GPU architecture for performance, 16x16 is often reasonable)
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layout (local_size_x = 16, local_size_y = 16, local_size_z = 1) in;
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// Helper to convert linear float (potentially HDR 0.0+) to 0-255 bin index
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// Applies an approximate gamma curve for perceptual binning.
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uint linearToVisualBin(float linearVal) {
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// Clamp linear value to 0.0-1.0 range before gamma/binning
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// This histograms the displayable range after processing.
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float clampedVal = clamp(linearVal, 0.0, 1.0);
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// Apply approximate sRGB gamma for perceptual brightness mapping
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float displayApprox = pow(clampedVal, 1.0/2.2);
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// Convert 0.0-1.0 display value to 0-255 bin index
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return uint(displayApprox * 255.999); // Use 255.999 to ensure 1.0 maps to 255
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}
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void main() {
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// Get the global invocation ID (like pixel coordinates)
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ivec2 pixelCoord = ivec2(gl_GlobalInvocationID.xy);
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ivec2 textureSize = imageSize(InputTexture);
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// Boundary check: Don't process outside the image bounds
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if (pixelCoord.x >= textureSize.x || pixelCoord.y >= textureSize.y) {
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return;
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}
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// Load the pixel color (values are normalized float 0.0-1.0 from rgba8 image load)
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vec4 pixelColor = imageLoad(InputTexture, pixelCoord);
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// Calculate bin indices (0-255)
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// We clamp just in case, although imageLoad from rgba8 should be in range.
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uint rBin = linearToVisualBin(pixelColor.r);
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uint gBin = linearToVisualBin(pixelColor.g);
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uint bBin = linearToVisualBin(pixelColor.b);
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// Atomically increment the counters in the SSBO
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// Offset Green bins by 256, Blue bins by 512
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atomicAdd(histogram.bins[rBin], 1u);
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atomicAdd(histogram.bins[gBin + 256u], 1u);
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atomicAdd(histogram.bins[bBin + 512u], 1u);
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// Optional: Track Max Value (more complex, requires another SSBO or different strategy)
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// Example: atomicMax(histogram.maxBinValue, histogram.bins[rBin]); // Needs careful sync
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} |