Annotations

shaders/lut-apply/shader.slang

@@ -7,6 +7,8 @@ float3 sampleLutCell(float3 index)
     float g = floor(index.g + 0.5);
     float b = floor(index.b + 0.5);
 
+    // The 33^3 cube is packed as blue slices laid horizontally, with red across
+    // each slice and green down the atlas.
     float atlasWidth = LUT_SIZE * LUT_SIZE;
     float2 lutUv;
     lutUv.x = (r + b * LUT_SIZE + 0.5) / atlasWidth;
@@ -30,6 +32,9 @@ float3 applyLut33(float3 color)
     float3 c011 = sampleLutCell(float3(baseIndex.r, nextIndex.g, nextIndex.b));
     float3 c111 = sampleLutCell(float3(nextIndex.r, nextIndex.g, nextIndex.b));
 
+    // Tetrahedral interpolation chooses one of six paths through the cube.
+    // This avoids the muddy diagonals that simple trilinear LUT sampling can
+    // introduce for strong grades.
     if (blend.r > blend.g)
     {
         if (blend.g > blend.b)
@@ -55,6 +60,8 @@ float hash12(float2 value)
 
 float3 outputDither(float2 pixel)
 {
+    // Subtract paired hashes to center the dither around zero, then scale to
+    // roughly one 8-bit code value.
     float r = hash12(pixel + float2(17.0, 31.0)) - hash12(pixel + float2(83.0, 47.0));
     float g = hash12(pixel + float2(29.0, 71.0)) - hash12(pixel + float2(53.0, 19.0));
     float b = hash12(pixel + float2(61.0, 11.0)) - hash12(pixel + float2(7.0, 97.0));