[RyeMutt]

Now that a straight, untwisted, untapered prim gets one quad per profile edge, a box, a prism, or a hollow, cut, tapered or sheared box builds exactly the same geometry at all four LODs. Today each LOD is still built separately, and an LOD change still rebuilds the volume and its spatial group's buffers. With this PR, such a shape is built once, and its LOD changes rebuild nothing.

This is part 3 of a stack of 7. Merge them in order: each PR is based on the one before it and shows only its own commits.

1. Prim normals point straight out of their surfaces, caps face out, and a flexible prim rebuilds in place #556 prim normals
2. A straight prim gets one quad per profile edge, and rows its parameters collapse emit no triangles #557 vertex reduction
3. A prim every LOD builds alike is generated once, and its LOD changes rebuild nothing #558 LOD-invariant prims ← this PR
4. Mesh and GLTF tangents come from meshoptimizer's MikkTSpace mode, welded and ordered in one pass #559 mesh tangents
5. Prims, sculpts, GLTF primitives and avatar meshes are ordered for the vertex cache #560 vertex cache order
6. Planar texgen maps a face that faces one way as one plane, and its normal map takes the planar frame #561 planar texgen
7. The uploader's LODs and normals come from meshoptimizer's attribute-aware simplifier #562 uploader LODs and normals

Changes

• LLVolume::isLODInvariant(params): answers from the parameters whether every LOD builds the shape alike. The split rule generate applies is now profile_split(), so the check and the generator can't drift apart.

  • A hole that the clamp pulls in to its wall keeps its split points, so it varies by LOD. The check lays the profile out once to see that, when a parameter set's LOD group is made.
  • Sculpts, meshes, flexible prims, and the unique single-face volume a sculpt unload makes are never LOD-invariant.

• LLVolumeLODGroup::refLOD: hands out one volume, the LOD 3 one, for every LOD of an invariant shape. derefLOD already finds a volume by pointer, so the counts stay consistent.

• LLVOVolume::updateLOD: an invariant volume now takes the path of an LOD that didn't change. mLOD still moves, for the LOD display, object weights and streaming cost, but nothing is refetched or rebuilt. LLPrimitive::setVolume also returns early for the same invariant parameters, so that a later setVolume doesn't report a change.

• Tracy plots, per frame:

  • "volume LOD moves";
  • "volume LOD rebuilds";
  • "volume LOD change faces";
  • "volume group rebuilds".

  Two captures of the same camera sweep can compare rebuilds directly.

Testing

• llmath_tests, shuffled: 411 cases. 410 pass and 1 is skipped.
  • Every sweep shape the predicate accepts builds byte-identical positions, normals, UVs, tangents, indices and faces at all four LODs.
  • Every shape it rejects differs at some LOD.
  • refLOD and derefLOD in mixed order leave the group clean.
• llprimitive_tests: all 48 cases pass.
• Viewer: not yet checked. A Tracy capture of a camera sweep over a box-heavy region, before and after, would measure the rebuilds this saves.

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📥 Commits

Reviewing files that changed from the base of the PR and between 327b53f and c93b7cf.

📒 Files selected for processing: 9

• indra/llmath/llvolume.cpp
• indra/llmath/llvolume.h
• indra/llmath/llvolumemgr.cpp
• indra/llmath/llvolumemgr.h
• indra/llmath/tests/llvolume_bench.cpp
• indra/llmath/tests/llvolume_test.cpp
• indra/llprimitive/llprimitive.cpp
• indra/llprimitive/tests/llprimitive_test.cpp
• indra/newview/llvovolume.cpp

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