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Prim normals point straight out of their surfaces, caps face out, and a flexible prim rebuilds in place - #556
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The description follows the template's main sections: a Description with detailed changes and a Testing section. It does not include the Related Issues section, which the template asks for, and it doe… | Add a Related Issues entry with a closes or relates-to link, such as an issue for the normals defects or the MAINT-5042 and MAINT-4435 flexi bugs the description names. Add the template's checklist, and tick each item that applies, includin… |
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Check name Status Explanation Title check The title names the main changes: prim normals, cap facing, and in-place flexible prim rebuilds. The changeset covers all three, plus tangent and SIMD work the title omits. The title is 103 characters… Linked Issues check Check skipped because no linked issues were found for this pull request. Out of Scope Changes check Check skipped because no linked issues were found for this pull request. Full details: Title check
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The title names the main changes: prim normals, cap facing, and in-place flexible prim rebuilds. The changeset covers all three, plus tangent and SIMD work the title omits. The title is 103 characters, which is long, but it is specific and not vague.
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A rabbit checks the mesh at dawn
And watches tangent rows stretch on
SIMD paws speed vectors through
Caps and seams align in view
The burrow hums with normals true
Then hops away, its work all done
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This was referenced Oct 23, 2026
RyeMutt
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Review comments at @indra/llmath/llvolume.cpp:
- Around line 5736-5800: Update normalize_grid_normals to check once whether any
vertex is marked as having its own normal before starting donor searches; if
none exists, set every grid normal to +Z and return. Preserve the existing
donor-search behavior for grids with at least one valid normal.
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indra/llmath/alsimdkernels.cppindra/llmath/alsimdkernels.hindra/llmath/alsimdkernels.inlindra/llmath/llvolume.cppindra/llmath/llvolume.hindra/llmath/tests/alsimdkernels_test.cppindra/llmath/tests/llvolume_bench.cppindra/llmath/tests/llvolume_test.cppindra/newview/llvovolume.cpp
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createSide summed each triangle's normal into its corners and then, to "even out quad contributions", added it a second time to the corner both triangles of a quad share. That corner and the one opposite it already had both triangles, so the extra weight made every vertex normal lean around the axis, one way on a face's first row and the other on its last: on a six-sided cylinder by +10.9 and -19.1 degrees, still +2.5 and -4.5 at LOD 3. Under PBR the highlight slanted across every facet. Each grid quad now gives the two corners off its diagonal their own triangle's cross product and the two on it half of each, so a parallelogram weights its four corners alike and no corner takes a normal from a triangle it is not in. The products are taken at the corners off the diagonal, so a quad between copied rows or columns adds exactly nothing and a sculpt's hard edge stays hard. The loop runs over the grid, not the index buffer, so the result does not depend on triangle order. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
The S wrap summed a side's first and last columns whenever the profile counted as closed. On a box those columns are the two edges of one flat side, so a twisted box, tube or prism averaged each side's left and right edges together, and a half cylinder at LOD 2 and 3 added its two opposite rims and turned them over. The T wrap trusted the path's openness, which ignores revolutions and skew: a torus at one and a half turns summed rows half a turn apart, and a skewed circle2 path whose rows meet was never wrapped. A side of two rows was never wrapped at all, since the pole test compared row 0 with itself, leaving the seams of LOD 0 and 1 cylinders 40 to 60 degrees apart. Each face now decides on a full build, from its own positions, whether its first and last columns are one seam and whether its first and last rows are (mJoinsS, mJoinsT), and joins only those. Sculpts keep joining where their stitching samples one column or row of the map. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
A cap took its one normal from the first triangle it emitted, and fell back to +/-Z in profile space when that had no area. A sliver or a flipped first triangle turned the whole cap, the fallback is wrong on any circular path, and the uncut cube cap of a box tapered to a point normalized a zero cross product into NaN. A cap's normal is now its end station's plane normal, row 2 of mRot, signed away from the side of the plane its neighbouring station's ring lies on. The path's direction alone cannot sign it: a twisted sphere's path does not move, and its caps faced into the sphere. Where the sign flips, the cap's winding flips with it. The uncut cube cap takes the same rule. A general cap's centre vertex took its position from the bounding box of its positions and its UV from the bounding box of its UVs, which a twist makes different points, sliding the texture up to 0.22 in UV. Its UV is now mapped from its own position. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
A side's normals were area sums, made unit length only when tangents were generated, so a prim without tangents put unnormalized normals in its vertex buffer (box sides came out at length 2), and Lengyel's Gram-Schmidt step ran on them before they were normalized, leaving tangents up to 90 degrees off their normals on twisted sides. A vertex whose triangles all had no area kept a zero normal, which the normalize turned into NaN: the copied last column of a cut flat inner side, half circles with square or triangle holes, a sculpt pinch's interior, the empty placeholder. normalize_grid_normals brings every normal to unit length in the accumulation's last pass. A vertex with no normal of its own takes the nearest one up or down its column, then along its row, then around it, only ever one a vertex had of its own. An edge shorter than rounding, as a closed profile's last point to its first, counts as no length, so lone copies no longer take a direction from noise. createTangents no longer normalizes; the mesh path over 65535 vertices normalizes for itself. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
… included Flexible prims rebuild their volume every frame and keep its topology, so the faces are meant to rewrite positions, normals and UVs in place. Over the years the faces stopped agreeing on it: createSide fell back to a full build when its counts grew but not when they shrank (MAINT-4435), createCap's guards were commented out (MAINT-5042), so general caps reallocated their vertices and indices every frame and the uncut cube cap its vertices, and a side kept mTangents through a partial build, so createTangents returned early and the side's tangents stayed at the first frame's pose while the caps' were rebuilt. createVolumeFaces now decides once: a build is partial only when every face's type mask, profile range and path length match the last one. Every face then writes into the buffers it has and keeps its indices, with no allocation, and computes its normals on that path as on the full one. A partial build marks the tangents stale, and genTangents regenerates them in the buffer they already have. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
With the square-hole hollow limit lifted, a square hole above 0.707 in a round profile, and holes in triangle profiles, put their corners past the outer wall (radius 0.53 against 0.5). The cap strip and the inner wall then had no valid layout, and a cylinder with an 0.85 square hole had its caps facing inward. addHole clamps each hole point radially to the outer profile. Where the hole touches the wall, the hollow cap's triangulation treats the strip's rounding-sized triangles as having no area; every profile whose hole does not touch it triangulates as before. The sphere pole override skips cut-end faces, which collapse onto the axis. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
…ects sculptGenerateSpherePlaceholder laid the sphere out transposed against the rows and columns the sphere stitching's pole and seam fix-ups assume, which gave it inverted triangles (127 to 158 degrees). It is now generated in that layout, still facing outward. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
…edges it crosses The normal accumulation computed all four edges of every quad and masked the ones shorter than rounding; it now takes each edge once, passing a quad's right edge on as the next quad's left, and drops a rounding-sized edge with one comparison. addHole's clamp looked for the nearest outer edge along each hole point's ray, and could take an edge the point lies well inside of, on the origin's side, whose line the ray crosses beyond the point; it now skips those. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
A cap with no area, on a pyramid, a cone's tip or the end of a circle2 or tapered half-circle path, has nothing drawn on it, and its station's plane leaves it 70 to 90 degrees from its wall on the last two. Its case now asks for a finite, unit normal facing away from the wall rather than one within 60 degrees of it. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
…at a time Prims and sculpts used Lengyel's tangents: an unweighted sum of face tangents, an invented 1024x ratio for a triangle with no UV area, and a +Z fallback whatever the normal. Mesh assets use MikkTSpace. Prims and sculpts now take the arithmetic of meshoptimizer's default tangent mode: each triangle's tangent by the UV chain rule, projected onto the vertex normal at each corner, weighted by the corner's angle in the tangent plane times the product of its edge lengths, with w from the UV orientation. A prim's or sculpt's vertex is one tangent group, so the sum goes straight to vertices, with no weld, no adjacency and no allocation. alsimd::grid_tangents does a side's grid and alsimd::indexed_tangents a cap, eight lanes wide on AVX2. A triangle adds nothing where its area, in positions or in UVs, is under 1e-5 of its edges squared, so rounding slivers on hollow caps and flat inner seams no longer make noise tangents. Faces cacheOptimize has handled keep their own path. A test holds the kernels to meshopt_generateTangents over the whole sweep and every sculpt, within a rounding bound modelled per vertex. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
- createSide copies its vertices from a per-face column table, about six times faster than the per-vertex index arithmetic it replaces. - alsimd::extents computes a face's position and UV bounds. - alsimd::transform_directions_offset transforms each station's profile into the mesh, bit for bit what rotate plus add gave. - alsimd::normalize3_or_mark normalizes a grid's normals and marks the ones with no length for normalize_grid_normals to fill. - addHole skips its clamp when the hole cannot reach any edge. Positions, UVs and indices are byte-identical to before. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
…s in its normal's plane A circle path's stations step around it, and the steps add up with rounding: genNGon could place a station a rounding short of the end cut, leaving a row with no height before the end's on twisted circle paths. A station within a hundredth of a step of the end is now the end's own. The point counts ARC reads are left as they were. Lengyel's tangents, which a mesh LOD too large for meshoptimizer's weld still takes, gave a vertex no triangle gives a direction (0, 0, 1) whatever its normal. It now takes +x, or +y where the normal is within 45 degrees of x, put in the plane of its normal. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
getApproximateFaceNormal summed the face's normals into a second ret declared inside its if, and returned the outer one, always zero, so media focus always fell back to the camera's direction. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
… not need A flexible prim now regenerates its tangents with its frames, which it never did before, and with meshoptimizer's weighting that cost up to 50% on a flexi frame. A flexible face (mFlexible) takes cheap tangents on every build instead, so they do not change in kind between its first build and its frames: a side's by central difference along its rows, made orthogonal to the normal (alsimd::grid_tangents_central), with a neighbour's where that has no length; a cap's the one tangent its end station's frame gives (mCapTangent). Caps and straight sides agree with the weighted tangent to within 0.004 degrees; on a bent path the two differ by up to the path's turn per section. Every flexi frame is now faster than before these changes. Line-path and flexible caps take their facing from the path's direction and skip the neighbouring-ring test. addHole's pre-test compares the distance to each edge's line, so it also skips on clockwise profiles. The hollow cap strip compares edge lengths only when both of its candidate triangles qualify. Box at LOD 0 and 1 builds within a few percent of before. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Streaming cost and ARC count a circle2 path's points with getNumNGonPoints, which walks the stations as genNGon places them. Since genNGon now takes a station within a hundredth of a step of the end cut as the end's own, the count did not: a circle2 path whose end cut lands on a step counted one point more than it built, as a torus cut to 8 to 13 of its 24 sides at LOD 3 did. The count stops at the same place. Circle paths count their points by a formula of the side count, not by walking the stations, and are unchanged. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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…t to another meshopt_generateTangents welds vertices whose positions, normals and UVs compare equal and sums the corners of all of them, where createTangents sums each vertex's own. A flat inner side's copied columns share a position and a UV, and on a circle path the two copies of a straight column take normals that differ only by rounding. Where that rounding leaves them equal to the last bit, meshoptimizer gives each copy the sum of both sides, at its station's own angle, while each copy's tangent leans a quarter of a step toward its own side: 3.4 degrees at LOD 3 and 5.2 at LOD 2 on a square hole's inner side. Which pairs weld is the compiler's rounding, so the check failed on Clang, GCC and MSVC ARM64 and passed on MSVC x64. A vertex meshoptimizer joins to another with corners of its own now counts as split and is not compared. Forcing every such pair to weld on MSVC x64 failed the check 90 times before this and none after, and it still compares 1.66 million vertices. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Prim generation was written for vertex lighting, and its normals have defects that per-pixel lighting shows:
This PR fixes the normals without changing a single vertex count. It also gives prim and sculpt tangents meshoptimizer's arithmetic, eight lanes at a time.
This is part 1 of a stack of 7. Merge them in order: each PR is based on the one before it and shows only its own commits.
Changes
Normals
createSide): an "even out quad contributions" pass added each triangle a second time at the corner its quad's two triangles share. That leaned every normal around the axis: by +10.9° and −19.1° on a 6-sided cylinder, and still by +2.5° and −4.5° at LOD 3. Each grid quad now weights its four corners alike. A quad between copied rows or columns adds nothing, so a sculpt's hard edge stays hard.mJoinsS,mJoinsT). Before:normalize_grid_normals), so no normal is zero or NaN. Before, box sides came out at length 2 when tangents weren't made, and Lengyel's Gram-Schmidt step ran on unnormalized normals.getNumNGonPoints, which ARC and streaming cost read) now counts the stations it builds. A torus cut to 8 to 13 of its 24 sides at LOD 3 counted one point more than it built.getApproximateFaceNormalsummed into a shadowed variable and returned zero, so media focus always faced the camera instead of the face.Flexible prims
createVolumeFacesnow decides once whether a build is partial. On a partial build, every face rewrites its buffers in place, with no allocation. Before:createCap's guards were commented out (MAINT-5042);createSidefell back to a full build only when its counts grew (MAINT-4435);Tangents and speed
alsimd::grid_tangents,alsimd::indexed_tangents) and replaces Lengyel's unweighted sum, invented ratios and +Z fallback. Mesh LODs too large for the weld still use Lengyel's generator; its fallback tangent now lies in its normal's plane.Testing
llmath_tests, shuffled: 406 cases. 405 pass and 1 is skipped. Each fix has its own case inllvolume_test.cpp, run over the shape sweep and the sculpt maps. A further case holds the tangent kernels tomeshopt_generateTangents.llvolume_bench.cpp: prim, sculpt and flexi build times. These figures are in the commit messages.🤖 Generated with Claude Code