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Lumen follow-up: true octahedral corner wrap for WSRC borders #23

@proggeramlug

Description

@proggeramlug

Ticket 014 V11 landed true octahedral silhouette wrap for the 4 edges of each probe's padded 10×10 octel slab. Corners (padded (0,0), (0,9), (9,0), (9,9)) were left as edge-extend — the double fold at a corner has two valid mirror interpretations, and bilinear weight at the exact corner is tiny, so the visual impact was deemed negligible.

When to do this

  • If a scene appears where the sampler's bilinear tap lands squarely on a corner texel at a silhouette-equatorial direction and produces a visible artifact.
  • If WSRC quality ever becomes load-bearing for visual parity tests.

Scope

  • WSRC_BAKE_WGSL / WSRC_BAKE_HW_WGSL corner branch: instead of edge-extend (reuse nearest inside octel), write the double-mirror neighbour. The standard convention: corner (0, 0) = nearest inside (7, 7); (0, 9) = (7, 0); etc.
  • Verify sample weights behave correctly at the corner — the bilinear tap there combines 1 corner + 2 edge + 1 inside texel with tiny weights on the corner.

Why deferred

Bilinear weight at a corner texel is at most 1/16 when the sample point sits at the cube-corner's uv — and probe silhouette-edge directions are rare targets for miss rays (most rays point into meaningful world directions, not at the octahedral "poles"). See docs/perf/014-lumen-mesh-sdfs.md §V15 closure.

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