Root cause of the user-reported artifacts (stripes disappearing on the
far LOD): normals were RECOMPUTED from the surviving faces after the
collapse. uv_sphere is wound inward, so the recomputed normals pointed
inward — the far LOD was back-face-lit (measured deviation 2.0 vs 0.0
on L0).
Fix — normals are INHERITED, never recomputed:
- welded() now also welds normals (first-encountered per cluster)
- Collapse owns the normal table; collapse_edge λ-blends + renormalizes
at the same λ as the position (no seam guard: the attribute-aware
weld kept hard-edge vertices separate, so no edge crosses a shading
break)
- compaction reads the post-collapse table instead of recomputing
- the outward reorientation added earlier is removed: the source
winding + normals are preserved as-is, so every LOD level is
shading-compatible with L0 whatever the source orientation
Rim protection (attribute-aware weld leaves UV-seam slits / pole fans
as boundary rims): a face touching such a rim is never removed while
interior collapses remain — strict PQ mode (edges whose incident faces
are fully interior, re-validated at pop) with a best-effort fallback
when the interior alone cannot reach the target. Seam-free meshes
(icosahedron) stay topologically closed; sewn meshes stay geometrically
complete (no hole at the slit) — tests now assert seam-column survival.
Docs: gpu-driven.md §LOD, ARCHI_CPU_GPU LOD note, ROADMAP 4.3 updated
with the attribute-aware weld + rim protection + inherited normals.
Gate: fmt ✓, check 0 warnings ✓, 104 tests ✓, demo runs ✓.
Measured (uv_sphere 32×20): normal max deviation 0.0000 on L0–L2
(was 2.0000), UV max error 0.0084 vs analytical (was 0.5000).
Jérôme Bousquié
40fac63590