False “Invalid mesh topology” warning on the final valid face in `computeSmoothNormals`

utils/src/geometry.cpp の computeSmoothNormals から始め、コミットで固定された UtahTeapot.usd アセットを usdconvert.exe で使用して警告を再現します。最終フェイスの境界条件を確認し、フェイス数がインデックス配列の長さとちょうど一致するメッシュのリグレッションテストカバレッジを追加します。すべてのフェイスが無効なトポロジ警告なしで処理されれば完了です。

Hi Everyone, I found an issue while building a cli tool around around what this repo offers.

Description

When exporting a valid USD mesh to STL, glTF, or GLB using Adobe USD File Format Plugins 2026.07, the exporter emits the following warning:

Invalid mesh topology: offset 4944 into indices for face 1235 is larger than total indices 4944

The source mesh topology is valid:

Faces: 1236
Sum of faceVertexCounts: 4944
Number of faceVertexIndices: 4944

Therefore:

sum(faceVertexCounts) == faceVertexIndices.size()

The warning occurs while processing the final face, where the calculated exclusive end offset is exactly equal to the total number of indices.

The export still completes successfully with exit code 0, but the normal-generation loop appears to stop before processing the final face.

Reproduction asset

The issue reproduces using the unmodified Utah Teapot USD asset from the ASWF USD Assets Working Group repository.

The asset is provided under the Public Domain/CC0 license.

• [Commit-pinned UtahTeapot.usd](https://github.com/usd-wg/assets/blob/0cfdafe7ed4b9507a215553f614e63882907074e/full_assets/Teapot/geo/UtahTeapot.usd)
• [Raw UtahTeapot.usd download](https://raw.githubusercontent.com/usd-wg/assets/0cfdafe7ed4b9507a215553f614e63882907074e/full_assets/Teapot/geo/UtahTeapot.usd)
• [Teapot asset directory](https://github.com/usd-wg/assets/tree/0cfdafe7ed4b9507a215553f614e63882907074e/full_assets/Teapot)
• [Asset README and license information](https://github.com/usd-wg/assets/blob/0cfdafe7ed4b9507a215553f614e63882907074e/full_assets/Teapot/README.md)
• [Upstream asset commit](https://github.com/usd-wg/assets/commit/0cfdafe7ed4b9507a215553f614e63882907074e)

No modifications to the upstream USD file are required to reproduce the warning.

Steps to reproduce

Download the commit-pinned UtahTeapot.usd file and export it to STL:

usdconvert.exe UtahTeapot.usd -o UtahTeapot.stl

The same warning can also be reproduced when exporting to glTF or GLB:

usdconvert.exe UtahTeapot.usd -o UtahTeapot.gltf
usdconvert.exe UtahTeapot.usd -o UtahTeapot.glb

Actual result

The export completes with exit code 0, but emits:

Warning: in computeSmoothNormals at line 762 of utils/src/geometry.cpp
-- Invalid mesh topology: offset 4944 into indices for face 1235 is larger than total indices 4944

The warning is produced for STL, glTF, and GLB exports.

FBX and OBJ exports of the same source mesh complete without this warning.

Expected result

• The mesh should not be reported as having invalid topology.
• The final face should be included in smooth-normal generation.
• No topology warning should be emitted when the exclusive end offset is exactly equal to the total number of indices.

Suspected cause

The current implementation in utils/src/geometry.cpp contains the following condition:

if ((size_t)(faceVertexIndex + numFaceVertices) >= totalNumFaceVertices) {
    TF_WARN(
        "Invalid mesh topology: offset %d into indices for face %zu is larger than "
        "total indices %zu",
        faceVertexIndex + numFaceVertices,
        faceIdx,
        totalNumFaceVertices);
    break;
}

For the final valid face:

faceVertexIndex + numFaceVertices == totalNumFaceVertices

This equality is valid because the calculated value is the exclusive end offset.

The condition appears to reject a valid final face because it uses >=.

A possible correction would be:

if ((size_t)(faceVertexIndex + numFaceVertices) > totalNumFaceVertices) {

The warning text also says the offset is “larger than” the total number of indices, although in this reproduction the two values are equal.

Potential impact

Because the function calls break, normal generation stops before the final face is processed.

Although the export succeeds, the last face may receive incomplete or incorrect generated normal data.

Environment

OS: Windows 10 x64
Adobe USD File Format Plugins: 2026.07
OpenUSD: 25.11
Affected exports: STL, glTF, GLB
Source mesh faces: 1236
Sum of faceVertexCounts: 4944
faceVertexIndices count: 4944

Suggested regression test

Add a valid mesh where the final face ends exactly at the end of the index array:

sum(mesh.faces) == mesh.indices.size()

Verify that:

1. computeSmoothNormals processes every face.
2. No invalid-topology warning is emitted.
3. The generated normals include the final face.

Existing-issue search

I searched the repository’s open and closed issues and pull requests for:

• the exact warning text
• computeSmoothNormals
• faceVertexIndex
• faceVertexIndices
• totalNumFaceVertices
• mesh topology and normal-generation issues
• related STL and glTF reports

I did not find an existing report for this final-face boundary condition.