Lighting: skip the split shadow pass when nothing casts #823

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opened 2026-10-17 18:10:02 +00:00 by sky_line · 0 comments

sky_line commented

2026-10-17 18:10:02 +00:00

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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.

With sun shadows off and no shadowed projectors the split lighting's shadow pass still decodes the G-buffer and writes a constant 1.0 visibility that the combine reads back (~0.8 ms at 4K on a GTX 1080). Skip it under that specialisation key and make the combine's sun visibility a constant. 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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