Matrix Auto-Update in Three.js

Based on the available documentation, I can provide some clarification about matrix updates in Three.js:

Calling child.updateMatrix()

• When you call child.updateMatrix(), it will only update the child's local matrix, not the parent's matrix.
• The updateMatrix() method updates an object's local transformation matrix based on its position, quaternion, and scale.
• It does not propagate upward to update parent objects.

Difference between matrix and matrixWorld

• matrix: Represents the local transformation of an object relative to its parent.
• matrixWorld: Represents the global transformation of an object in world space.

The matrixWorld is essentially the combination of the object's local matrix with all of its parent matrices. It defines where the object is positioned in the overall scene.

Important Considerations

When you set matrixAutoUpdate = false for both parent and child:

1. You're taking manual control of when matrices are updated
2. You'll need to call updateMatrix() on each object when its transformation changes
3. For the world matrix to be correct, you'll also need to call updateMatrixWorld() after updating the local matrices

For a complete update sequence when manually managing matrices:

JAVASCRIPTCopied
// After changing position, rotation, or scale
parent.updateMatrix();
child.updateMatrix();

// Then update world matrices (typically only needed on the parent)
parent.updateMatrixWorld(true); // true forces update on all children

The updateMatrixWorld(true) call will recursively update all children's world matrices based on their local matrices and parent relationships.