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Prims, sculpts, GLTF primitives and avatar meshes are ordered for the vertex cache - #560
A prim side's quads were written row by row, so on a side wider than the vertex cache, each row missed what the row before it had brought in. GLTF primitives and avatar meshes were drawn in the order they were authored. This PR orders all of them for the cache. It also leaves out the triangles with no area that a sculpt's pinches make.
This is part 5 of a stack of 7. Merge them in order: each PR is based on the one before it and shows only its own commits.
Prims and sculpts (createSide): quads are now written in an order a 16-entry FIFO cache reuses, worked out from the grid's layout alone.
A grid of up to 7 rows goes a column at a time.
A taller grid goes in near-equal bands of quads, each band row by row, with every other band written from its last row back to its first.
A flat inner side, doubled at its corners, orders each run between corners as a grid of its own.
This takes no meshoptimizer and no allocation. Vertices keep the grid's order, and a partial build writes the same indices as the full build before it. The band rows and columns are written through alsimd's 16-bit lanes.
Sculpt pinches: a sculpt map's pinched rows and columns, a sphere's poles, or any run of one colour make triangles with two corners at one point. Shared volumes now leave those triangles out.
They are found by 24-bit codes, eight quads at a time under AVX2, and each one is confirmed on the positions.
Normals are summed before any triangle is dropped, so points and normals are unchanged and only the index count shrinks.
A band of 7 quads fills a 16-entry cache exactly, and thrashes after a row that drops triangles. So bands are at most 6 across, unless a single band of up to 7 covers the whole side.
GLTF primitives (Primitive::prep): triangles are ordered with meshopt_optimizeVertexCache. The vertices are then reordered for fetch, with every attribute moving alike.
Avatar meshes (LLPolyMeshSharedData::loadMesh): each .llm file's faces are ordered for the cache once, as the file loads, after every index has been checked against the mesh's vertices. Morphs and skin weights address vertices, which keep their order.
Results
Vertices transformed per triangle, before → after:
shape
before
after
sphere, LOD 3
1.091
0.657
torus, LOD 3
1.042
0.605
sculpt, LOD 3
1.031
0.598
64 × 32 GLTF sphere
1.048
0.656
rigged GLTF sphere
1.205
0.737
Avatar meshes: over all 29 meshes, 21,686 triangles, vertices transformed fall from 20,012 to 16,665.
Prim sides: over 21,640 sides, every side of the sweep, the flexible prims and the sculpts transforms at most 5% more vertices per triangle than meshoptimizer's own cache order would. The worst is about 1.02. A test holds that bound.
Sculpt pinches: the test shapes lose 3,926 triangles, on 73 faces. A sphere sculpt at LOD 3 draws 1,984 triangles instead of 2,048.
Build times:
spheres and tori at LOD 2 and 3 build 3 to 5% faster;
small prims are up to 1.5% slower per call;
flexible prims are at or below what they were;
a sculpt at LOD 0 is 9 to 19% slower, because of the pinch search, and about 1% faster at LOD 3.
Testing
llmath_tests, shuffled: 422 cases. 421 pass and 1 is skipped. The cases include the cache and fetch bounds over the sweep, the flexible prims and the sculpts.
GLTF ordering:Primitive::prep is out of the tests' reach. Its steps, run over the mesh test corpus, keep every triangle's corners as they were.
Shuffled:llprimitive_tests passes all 48 cases. llcommon_tests has 723 cases: 720 pass and 3 are skipped.
Viewer: not yet checked. To check: sculpts of each stitching type, one with a pinch and one with hard edges; a GLTF scene; avatars.
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Reviewing files that changed from the base of the PR and between ad8510c and 6fb648f.
Files selected for processing: 11
indra/llappearance/llpolymesh.cpp
indra/llcommon/alsimd.h
indra/llcommon/tests/alsimd_test.cpp
indra/llmath/alsimdkernels.cpp
indra/llmath/alsimdkernels.h
indra/llmath/alsimdkernels.inl
indra/llmath/llvolume.cpp
indra/llmath/tests/alsimdkernels_test.cpp
indra/llmath/tests/llvolume_bench.cpp
indra/llmath/tests/llvolume_test.cpp
indra/newview/gltf/primitive.cpp
📝 Summary
Summary by CodeRabbit
Performance
Improved 3D mesh processing and rendering efficiency, particularly for complex objects and sculpted shapes.
Bug Fixes
Sculpted shapes with overlapping vertices now avoid generating unnecessary zero-area triangles when valid alternatives are available.
Meshes with invalid index data retain their existing processing behavior.
Testing
Expanded coverage for mesh geometry, triangle generation, and performance across a range of shape types and detail levels.
This change adds SIMD kernels for sculpt-grid processing, updates volume index generation to omit confirmed pinched triangles, and applies vertex-cache ordering to avatar meshes and eligible glTF primitives. Tests and benchmarks cover the new kernels, sculpt output, transformed-vertex counts, and index ordering.
Changes: Mesh Generation and Cache Ordering
Layer / File(s)
Summary
SIMD kernels for sculpt grids indra/llcommon/alsimd.h, indra/llcommon/tests/alsimd_test.cpp, indra/llmath/alsimdkernels.*, indra/llmath/tests/alsimdkernels_test.cpp
Adds signed 32-bit SIMD operations and kernels that encode point coordinates and flag coincident sculpt-grid triangles. Tests cover lane operations, packing, code generation, and triangle flags.
Volume index generation and validation indra/llmath/llvolume.cpp, indra/llmath/tests/llvolume_test.cpp, indra/llmath/tests/llvolume_bench.cpp
Changes grid traversal and bounded index writing. Eligible sculpt faces omit confirmed pinched triangles when some, but not all, triangles are pinched. Tests compare sculpt triangles and transformed-vertex counts; benchmarks compare index orders.
Cache ordering for loaded meshes and glTF primitives indra/llappearance/llpolymesh.cpp, indra/newview/gltf/primitive.cpp
Avatar mesh loading reorders valid face indices. Eligible glTF primitives reorder indices and remap vertex attributes into fetch order, removing unused vertices.
sequenceDiagram
participant Volume as LLVolumeFace
participant Codes as unit_cube_codes
participant Flags as grid_coincident_triangles
Volume->>Codes: Encode sculpt vertex coordinates
Codes-->>Volume: Return packed vertex codes
Volume->>Flags: Pass codes and grid dimensions
Flags-->>Volume: Return coincident-triangle flags
Volume->>Volume: Confirm pinches and write selected indices
Loading
Possibly related PRs
AlchemyViewer/Alchemy#559: Establishes meshoptimizer and ALScratchArena integration used by the cache-ordering changes.
AlchemyViewer/Alchemy#557: Omits zero-area triangles from collapsed rows and columns; this PR also omits triangles with coincident sculpt vertices.
AlchemyViewer/Alchemy#556: Adds SIMD and volume-generation infrastructure extended by the sculpt-grid kernels and index-generation changes.
Merge Risk: Low · up to ad851
A malformed glTF triangle list can stop a debug viewer build during preparation. Add the index-count guard before merging, or accept this bounded risk.
Pre-merge checks: 4 · 1
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The title clearly and concisely identifies the main vertex-cache ordering changes for prims, sculpts, GLTF primitives, and avatar meshes.
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Write docstrings for the functions missing them to satisfy the coverage threshold.
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A rabbit packed the bytes just right, Then hopped through grids in bands of light. Pinched triangles left the scene, While cached vertices stayed lean. “Good mesh,” it cheered, and nibbled greens.
Comment @coderabbitai help to get the list of available commands.
…es it
createSide wrote each side's quads row by row, so on a side wider than
the cache every row missed what the row before it brought in. It now
writes them in an order a 16-entry FIFO cache reuses, from the grid's
layout alone:
- a grid of up to 7 rows goes a column at a time, so a column's right
edge is still cached when the next takes it as its left;
- a taller grid goes in near-equal bands of at most 7 quads across, each
row by row, every other band from its last row back to its first;
- a flat inner side doubled at its corners orders each run between
corners as a grid of its own, since two runs share no vertex.
The order takes no meshoptimizer and no allocation, vertices keep the
grid's order, and a partial build writes the indices of the full build
before it. Whole band rows and columns are written as vectors through
alsimd's 16-bit lanes, from offsets made once a side, and the order is
called out of line so createSide's own loops keep their layout.
Every side of the sweep, the flexible prims and the sculpts transforms
at most 5% more vertices a triangle than meshoptimizer's cache order of
the same triangles (the worst about 1.02, over 21,640 sides), and a test
holds it there. At LOD 3 a sphere transforms 0.657 vertices a triangle
where it took 1.091, a torus 0.605 for 1.042 and a sculpt 0.598 for
1.031; overfetch is unchanged, and every stream but the indices is bit
for bit what it was. Builds, as rdtsc medians over four code layouts:
spheres and tori at LOD 2-3 3-5% faster, sculpts at LOD 2-3 about 2%,
small prims up to 1.5% slower for the call, flexible prims at or below
what they were.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
A sculpt map's pinched rows and columns, a sphere's poles or any run of
one colour, make triangles with no area that the GPU still transforms
and sets up. createSide now finds them on sculpts of shared volumes:
- unit_cube_codes gives each point a 24-bit code: its bytes, for a point
a map gave, and otherwise its position rounded and clamped to them;
- grid_coincident_triangles flags a row at a time each quad's triangles
with two corners of one code, eight quads a step under AVX2 and four
through alsimd's new 32-bit integer lanes;
- the flags are confirmed on the positions themselves.
Normals are summed before any triangle is left out, so points and
normals are as they were and only the index count shrinks; a face always
keeps a triangle. Unique and flexible volumes, which build in part, keep
every triangle.
A band of 7 quads fills a 16-entry cache with nothing to spare, and
thrashes after a row with triangles left out, so bands are at most 6
across unless one band of up to 7 covers the side. Sculpts without
pinches transform about 2% more vertices for it (1,224 to 1,249 at
LOD 3); prims are unchanged.
Over the test shapes 3,926 triangles go, on 73 faces. A sphere sculpt at
LOD 3 draws 1,984 triangles for 2,048 and transforms 1,242 vertices,
2,112 before the cache order. The bounds test records the vertices
transformed rather than the figure a triangle, which rises when
triangles that cost nothing go. Finding the pinches costs about 1.8k
cycles on a 33 by 33 sculpt: builds at LOD 0 are 9-19% slower, at
LOD 1 5-10%, at LOD 2 1-3%, and at LOD 3 about 1% faster.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
…etch
Primitive::prep orders a triangle list's triangles with
meshopt_optimizeVertexCache, then its vertices in the order those
triangles first take them, moving positions, normals, tangents, both UV
sets, colours, weights and joints alike, before the octree and the
vertex buffer are made from them. A vertex no triangle takes is dropped.
The remap and meshoptimizer's scratch come from the thread's arena. A
primitive that is not a triangle list, or whose attributes are not one
value a vertex, is left as it is.
Nothing in the tests reaches Primitive::prep; its steps run over the
mesh test corpus keep every triangle's corners as they were. A 64 by 32
UV sphere transforms 0.656 vertices a triangle where it took 1.048, a
rigged sphere 0.737 for 1.205. A 128 by 64 sphere already in sequential
order overfetches 2.6% more at a 92-byte vertex.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
LLPolyMeshSharedData::loadMesh orders each .llm file's faces with
meshopt_optimizeVertexCache, in place, once every index is checked to be
within the mesh's vertices; a file with one outside keeps its order.
Every avatar shares the file's faces, which
LLViewerJointMesh::updateFaceData copies to the GPU as they are. Morphs
and skin weights address vertices, which keep their order, and an LOD
file's faces are its own.
Over the 29 meshes, 21,686 triangles, vertices transformed fall from
20,012 to 16,665: the upper body from 0.918 a triangle to 0.708, the
head from 0.893 to 0.725. avatar_eye_1, 70 triangles, takes one more.
The largest file costs about 1.9 million cycles as it loads.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Actionable comments posted: 1
🪄 Fix comments: Fix CodeRabbit comments on this PR
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Inline comments:
Review comments at @indra/newview/gltf/primitive.cpp:
- Line 308: Update the guard in Primitive::prep to reject TRIANGLES primitives
whose index_count is not divisible by three before calling
meshopt_optimizeVertexCache, while preserving the existing checks for primitive
mode, minimum count, and vertex count.
After applying the fix, consider running `coderabbit review --agent` for local
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Commits
Reviewing files that changed from the base of the PR and between 7dc2043 and ad8510c.
Files selected for processing: 11
indra/llappearance/llpolymesh.cpp
indra/llcommon/alsimd.h
indra/llcommon/tests/alsimd_test.cpp
indra/llmath/alsimdkernels.cpp
indra/llmath/alsimdkernels.h
indra/llmath/alsimdkernels.inl
indra/llmath/llvolume.cpp
indra/llmath/tests/alsimdkernels_test.cpp
indra/llmath/tests/llvolume_bench.cpp
indra/llmath/tests/llvolume_test.cpp
indra/newview/gltf/primitive.cpp
Included review availability: This review used your included allowance. Your plan provides up to 1 included review per hour; 0 remain after this review.
…order
Primitive::prep trims a triangle list to whole triangles only where it
generates normals or tangents. An asset that carries both, with an index
count that three does not divide, reached meshopt_optimizeVertexCache,
which asserts that it does. Such a primitive is now left in the order it
came in, as one whose attributes are not one value a vertex is.
Reported by CodeRabbit on #560.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
alsimd_test's ints() built four int32 lanes by passing each value's bits
through set() as a float. A lane of the sign bit alone is then -0, and
/fp:fast need not keep the sign of a zero: MSVC's arm64 build, whose
set() is a chain of vsetq_lane_f32, made it +0, so the case holding
cmpeq_i32 to whole lanes found 0x80000000 equal to 0 there. ints() now
loads the values with loadu_i32. The kernels' own integer lanes come
from integer loads and were never affected.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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A prim side's quads were written row by row, so on a side wider than the vertex cache, each row missed what the row before it had brought in. GLTF primitives and avatar meshes were drawn in the order they were authored. This PR orders all of them for the cache. It also leaves out the triangles with no area that a sculpt's pinches make.
This is part 5 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
Prims and sculpts (
createSide): quads are now written in an order a 16-entry FIFO cache reuses, worked out from the grid's layout alone.This takes no meshoptimizer and no allocation. Vertices keep the grid's order, and a partial build writes the same indices as the full build before it. The band rows and columns are written through alsimd's 16-bit lanes.
Sculpt pinches: a sculpt map's pinched rows and columns, a sphere's poles, or any run of one colour make triangles with two corners at one point. Shared volumes now leave those triangles out.
GLTF primitives (
Primitive::prep): triangles are ordered withmeshopt_optimizeVertexCache. The vertices are then reordered for fetch, with every attribute moving alike.Avatar meshes (
LLPolyMeshSharedData::loadMesh): each.llmfile's faces are ordered for the cache once, as the file loads, after every index has been checked against the mesh's vertices. Morphs and skin weights address vertices, which keep their order.Results
Vertices transformed per triangle, before → after:
Testing
llmath_tests, shuffled: 422 cases. 421 pass and 1 is skipped. The cases include the cache and fetch bounds over the sweep, the flexible prims and the sculpts.Primitive::prepis out of the tests' reach. Its steps, run over the mesh test corpus, keep every triangle's corners as they were.llprimitive_testspasses all 48 cases.llcommon_testshas 723 cases: 720 pass and 3 are skipped.🤖 Generated with Claude Code