I'm trying to create the simplest animation scenario, 12 vertices and 2 bones.

enter image description here

Both bones has a 4x4 matrix. When both are set to "Identity", the model looks correct, like in the picture above (default pose).

When I rotate the root joint, the whole mesh rotates, as expected (child joint rotates with root joint, child joint matrix is pre-multiplied by the root joint's matrix).

However, when I rotate the child joint only, it seems like the vertices it affects rotate around the root joint's origin, effectively stretching the vertices - instead of rotating around the child joint's origin.

So the question is, what would be the correct matrices for this basic example?

Identity matrices for the joints:

1 0 0 0
0 1 0 0
0 0 1 0
0 0 0 1

Joint transforms are calculated as:

Joint 0 matrix = Joint 0 matrix;
Joint 1 matrix = Joint 0 matrix * Joint 1 matrix;


When I store positional data in the Child joint, Row 4 (0, 2, 0, 1) - the vertices affected by it are stretched in the Y direction.


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