Fewer non-opaque ray candidates: opaque BLAS flags and opacity micromaps #1032

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opened 2026-10-25 01:02:05 +00:00 by sky_line · 1 comment

sky_line commented

2026-10-25 01:02:05 +00:00

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Profiled with Nsight Graphics GPU Trace + shader profiler on an RTX 5090 (full GI scene, ~61 FPS, GPU ~16.3 ms/frame). The hottest shader lines are the rayQueryProceedEXT candidate loops (clean_shadow_core.glsl, clean_rt_common.glsl, clean_deferred_light.comp), stalled ~75% waiting on traversal. Every non-opaque candidate goes back to the shader for an alpha test.

Audit BLAS geometry flags: geometry whose materials are fully opaque gets VK_GEOMETRY_OPAQUE_BIT_KHR so the hardware never returns it as a candidate.
Opacity micromaps (VK_EXT_opacity_micromap, where supported) for alpha-tested geometry such as foliage, so the hardware resolves the alpha test itself.

Done when: candidate counts and RT pass timers drop at the same scene with identical shadows and GI.

Profiled with Nsight Graphics GPU Trace + shader profiler on an RTX 5090 (full GI scene, ~61 FPS, GPU ~16.3 ms/frame). The hottest shader lines are the `rayQueryProceedEXT` candidate loops (clean_shadow_core.glsl, clean_rt_common.glsl, clean_deferred_light.comp), stalled ~75% waiting on traversal. Every non-opaque candidate goes back to the shader for an alpha test. 1. Audit BLAS geometry flags: geometry whose materials are fully opaque gets VK_GEOMETRY_OPAQUE_BIT_KHR so the hardware never returns it as a candidate. 2. Opacity micromaps (VK_EXT_opacity_micromap, where supported) for alpha-tested geometry such as foliage, so the hardware resolves the alpha test itself. **Done when:** candidate counts and RT pass timers drop at the same scene with identical shadows and GI.

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2026-10-25 01:02:05 +00:00

sky_line added this to the Slipstream project

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2026-10-25 01:59:11 +00:00