perf(sky): ~10x cheaper night-sky lattice — one-round cell hash, 2x2x2 block, bit-sliced stars

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The owner measured 63% GPU at night vs 28% by day: the starfield
lattice was the whole difference. Three lossless cuts:
- one packed-multiply hash round per cell instead of ~9 chained PCG
  rounds (position/presence bit-sliced from one result, brightness/tint
  from a second);
- the 3x3x3 neighbourhood sweep becomes the 2x2x2 block around the
  sample — a star's visible footprint (a few px) is far smaller than a
  lattice cell on screen, so any star outside that block is over a full
  cell (>=15 px) away and contributes nothing;
- background mottle drops its invisible third octave.

Same densities, sizes, colours, and look; star positions reshuffle
(procedural layout, not authored). sky.frag.spv re-pinned.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

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Erik 2026-08-23 18:31:39 +02:00

parent 9fcc3f4870

commit 9cf15e1f13

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