VRAM (later): quantize skinned positions (16-bit per-instance box) as a pressure-only ladder rung #617

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opened 2026-10-10 01:20:14 +00:00 by sky_line · 0 comments

sky_line commented

2026-10-10 01:20:14 +00:00

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What it costs

Precision: ~0.03 mm on a 2 m avatar, ~0.3 mm on a 20 m giant / vehicle: well under clothing gaps (1-5 mm), so it does not cause poking by itself. (fp16 is not an option: positions are eye-relative and fp16 has 6 cm steps at 64-128 m.)
RT: acceleration-structure builds do not take unorm positions; needs snorm16 with a per-geometry transform (awkward for the grouped rigged BLAS) or a float copy for the BLAS (gives memory back).
Motion vectors: current and previous positions quantized separately add sub-0.1 mm motion noise (TAA / FSR would ignore it, but it is not zero).
Rig weld: welded vertices on different meshes quantize in different boxes, so seams could reopen by ~0.05 mm (sub-pixel); "exact" becomes "near".
Previous positions (12 B) and the optional history (24 B) could follow.

Decide later, after #616 and the other VRAM work (#614, #615) are measured.

Follow-up to #616 (which takes the skinned output from 48 B to 20 B losslessly). Further: quantize skinned positions from fp32 (12 B) to 16-bit unorm inside each instance's bounding box (6 B + 2 pad): 20 B -> 16 B per vertex (48 -> 16 overall, -67%). Considered as an optional VRAM-ladder rung (only under pressure), not the default. ## What it costs - Precision: ~0.03 mm on a 2 m avatar, ~0.3 mm on a 20 m giant / vehicle: well under clothing gaps (1-5 mm), so it does not cause poking by itself. (fp16 is not an option: positions are eye-relative and fp16 has 6 cm steps at 64-128 m.) - **RT:** acceleration-structure builds do not take unorm positions; needs snorm16 with a per-geometry transform (awkward for the grouped rigged BLAS) or a float copy for the BLAS (gives memory back). - **Motion vectors:** current and previous positions quantized separately add sub-0.1 mm motion noise (TAA / FSR would ignore it, but it is not zero). - **Rig weld:** welded vertices on different meshes quantize in different boxes, so seams could reopen by ~0.05 mm (sub-pixel); "exact" becomes "near". - Previous positions (12 B) and the optional history (24 B) could follow. Decide later, after #616 and the other VRAM work (#614, #615) are measured.

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