Normalize skin weights possible?

[Olaf-Wolf3D]

Hey! Is there a way to normalize skin weights with gltf-transform? To get rid of ACCESSOR_WEIGHTS_NON_NORMALIZED errors.
Limiting number of weights to top 4 most influential and then normalizing would also be great.
I didn't find a function for that in the docs.

[donmccurdy]

Hi @Olaf-Wolf3D! I did implement a function to normalize skin weights, though it is only used internally and not exported currently:

glTF-Transform/packages/functions/src/quantize.ts

Lines 434 to 468 in 18c4757

	function normalizeWeights(prim: Primitive | PrimitiveTarget): void {
	const vertexCount = prim.getAttribute('POSITION')!.getCount();
	const weightsEl: number[] = [];
	for (let i = 0; i < vertexCount; i++) {
	let vertexWeightsSum = 0;
	let leastWeight = Infinity;
	let leastIndex = -1;
	let leastAttribute: Accessor | null = null;
	let weights: Accessor | null;
	let attributeIndex = 0;
	// Find sum of weights and the joint with the lowest non-zero weight.
	while ((weights = prim.getAttribute(`WEIGHTS_${attributeIndex++}`))) {
	weights.getElement(i, weightsEl);
	for (let j = 0; j < weightsEl.length; j++) {
	vertexWeightsSum += weightsEl[j];
	if (weightsEl[j] > 0 && weightsEl[j] < leastWeight) {
	leastAttribute = weights;
	leastWeight = weightsEl[j];
	leastIndex = j;
	}
	}
	}
	// Normalize by updating least-significant joint weight.
	if (leastAttribute && vertexWeightsSum !== 1) {
	leastAttribute.getElement(i, weightsEl);
	weightsEl[leastIndex] += 1 - vertexWeightsSum;
	leastAttribute.setElement(i, weightsEl);
	}
	}
	}

Sorting the weights (so the highest weights are all in WEIGHT_0) and then dropping WEIGHTS_1+ could be done very similarly. Feel free to open a 'feature request' issue or PR for this if you'd like these exported from the /functions package.

[donmccurdy]

Updating my previous answer for the latest release after #670 —

const limit = 4;

for (const mesh of document.getRoot().listMeshes()) {
  for (const prim of mesh.listPrimitives()) {
    sortPrimitiveWeights(prim, limit);
  }
}