RT VRAM: exclude tiny distant objects from the TLAS #579

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opened 2026-10-09 01:49:13 +00:00 by sky_line · 0 comments

sky_line commented

2026-10-09 01:49:13 +00:00

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Measured in a heavy region (2026-10-09): RT acceleration structures (rt-as) are about 1.7 GB, as much as all the geometry, and the opacity micromaps (rt-mask) are 354 MB. Follow-up to #573.

Idea

Skip instances whose projected size is below a few pixels (or below a world-size threshold at distance) when building the TLAS, and let their BLAS age out.

Trade-offs

Tiny distant objects lose their RT shadows and reflections. Shadow maps or AO could still cover them if needed.
Use hysteresis so objects don't flicker in and out as the camera moves.

Done when

Instance count and BLAS memory drop in dense scenes with no visible change in near-field shadows.

Measured in a heavy region (2026-10-09): RT acceleration structures (`rt-as`) are about 1.7 GB, as much as all the geometry, and the opacity micromaps (`rt-mask`) are 354 MB. Follow-up to #573. ## Idea Skip instances whose projected size is below a few pixels (or below a world-size threshold at distance) when building the TLAS, and let their BLAS age out. ## Trade-offs - Tiny distant objects lose their RT shadows and reflections. Shadow maps or AO could still cover them if needed. - Use hysteresis so objects don't flicker in and out as the camera moves. ## Done when Instance count and BLAS memory drop in dense scenes with no visible change in near-field shadows.

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sky_line added this to the Slipstream project

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