Tonemap / grade: 3D lookup table #820

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opened 2026-10-17 18:10:01 +00:00 by sky_line · 1 comment

sky_line commented

2026-10-17 18:10:01 +00:00

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The tonemap does per-pixel pow / exp grading and curve work; a 32^3 table baked when the grade changes replaces it. Likely ~0.1-0.2 ms at 4K; imperceptible. Needs measurement.

Context: measured on a GTX 1080 (Pascal) at 4K with the test-control channel and the shader clock (RenderVKShaderClockLighting) / pipeline stats (RenderVKPipelineStats). The frame is GPU-bound but not bandwidth-bound (memory controller ~36% busy on the 1080, ~14% on a 5090): it is latency / occupancy bound, so trading a little memory traffic for fewer registers and fewer dependent loads should help every GPU generation.

The tonemap does per-pixel pow / exp grading and curve work; a 32^3 table baked when the grade changes replaces it. Likely ~0.1-0.2 ms at 4K; imperceptible. Needs measurement. Context: measured on a GTX 1080 (Pascal) at 4K with the test-control channel and the shader clock (RenderVKShaderClockLighting) / pipeline stats (RenderVKPipelineStats). The frame is GPU-bound but not bandwidth-bound (memory controller ~36% busy on the 1080, ~14% on a 5090): it is latency / occupancy bound, so trading a little memory traffic for fewer registers and fewer dependent loads should help every GPU generation.

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2026-10-17 18:10:01 +00:00

sky_line added this to the Slipstream project

2026-10-17 18:10:01 +00:00

sky_line referenced this issue from a commit

2026-10-22 19:32:55 +00:00

#820: tonemap / grade tail as a baked 3D lookup table (RenderVKTonemapLut)