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fix: gracefully handle mixed-material OBJ models instead of crashing #8666

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fix: gracefully handle mixed-material OBJ models instead of crashing #8666

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82122e1
fix: gracefully handle mixed-material OBJ models instead of crashing
Nixxx19 Mar 22, 2026
fea06a0
support mixed material coloring using sentinel for uncolored vertices
Nixxx19 Apr 17, 2026
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6 changes: 3 additions & 3 deletions src/webgl/loading.js
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Original file line number Diff line number Diff line change
Expand Up @@ -631,6 +631,7 @@ function loading(p5, fn){
model.vertexColors.push(1);
} else {
hasColorlessVertices = true;
model.vertexColors.push(-1, -1, -1, -1);
}
} else {
face.push(usedVerts[vertString][currentMaterial]);
Expand All @@ -652,9 +653,8 @@ function loading(p5, fn){
if (model.vertexNormals.length === 0) {
model.computeNormals();
}
if (hasColoredVertices === hasColorlessVertices) {
// If both are true or both are false, throw an error because the model is inconsistent
throw new Error('Model coloring is inconsistent. Either all vertices should have colors or none should.');
if (!hasColoredVertices) {
model.vertexColors = [];
}

return model;
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26 changes: 21 additions & 5 deletions test/unit/io/loadModel.js
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Expand Up @@ -79,11 +79,27 @@ suite('loadModel', function() {
assert.deepEqual(model.vertexColors, expectedColors);
});

test('inconsistent vertex coloring throws error', async function() {
// Attempt to load the model and catch the error
await expect(mockP5Prototype.loadModel(inconsistentColorObjFile))
.rejects
.toThrow('Model coloring is inconsistent. Either all vertices should have colors or none should.');
test('mixed material coloring loads model with sentinel colors for uncolored vertices', async function() {
const model = await mockP5Prototype.loadModel(inconsistentColorObjFile);
assert.instanceOf(model, Geometry);
assert.equal(
model.vertexColors.length,
model.vertices.length * 4,
'vertexColors should have four entries per vertex'
);
const hasSentinel = model.vertexColors.some(
(_, i) =>
i % 4 === 0 &&
model.vertexColors[i] === -1 &&
model.vertexColors[i + 1] === -1 &&
model.vertexColors[i + 2] === -1 &&
model.vertexColors[i + 3] === -1
);
const hasRealColor = model.vertexColors.some(
(_, i) => i % 4 === 0 && model.vertexColors[i] !== -1
);
assert.isTrue(hasSentinel, 'Uncolored vertices should have sentinel color');
assert.isTrue(hasRealColor, 'Colored vertices should retain their color');
});

test('missing MTL file shows OBJ model without vertexColors', async function() {
Expand Down