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[FIX] Fix glTF node matrix decomposition with negative scale #8329

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Merged
willeastcott merged 1 commit into from
Jan 6, 2026
Merged

[FIX] Fix glTF node matrix decomposition with negative scale #8329

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10 changes: 8 additions & 2 deletions src/framework/parsers/glb-parser.js
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Original file line number Diff line number Diff line change
Expand Up @@ -1517,6 +1517,7 @@ const createAnimation = (gltfAnimation, animationIndex, gltfAccessors, bufferVie

const tempMat = new Mat4();
const tempVec = new Vec3();
const tempQuat = new Quat();

const createNode = (gltfNode, nodeIndex, nodeInstancingMap) => {
const entity = new GraphNode();
Expand All @@ -1532,9 +1533,14 @@ const createNode = (gltfNode, nodeIndex, nodeInstancingMap) => {
tempMat.data.set(gltfNode.matrix);
tempMat.getTranslation(tempVec);
entity.setLocalPosition(tempVec);
tempMat.getEulerAngles(tempVec);
entity.setLocalEulerAngles(tempVec);
// Use Quat.setFromMat4 which properly handles negative determinant (mirrored matrices)
// by normalizing the rotation before extraction
tempQuat.setFromMat4(tempMat);
entity.setLocalRotation(tempQuat);
tempMat.getScale(tempVec);
// Apply negative sign to X scale if the matrix is mirrored (negative determinant).
// This matches the convention used in Quat.setFromMat4 which flips the X axis.
tempVec.x *= tempMat.scaleSign;
entity.setLocalScale(tempVec);
}

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