Identifying linear skinning problems
To get an idea of the problem, Figure 9.9 shows a simple box, twisted in the middle:
Figure 9.9: A noticeable volume loss in the middle when twisting the model
We can see that the twist leads to volume loss, a phenomenon we thought we had solved by using the joints affecting the vertices, and the weights of the joints per vertex. Apparently, something in the calculation is still going wrong.
Particularly on a sharp bend or twist, the linear interpolation may lead to wrong results. This is because linear interpolation uses the shortest path between the vertices:
Figure 9.10: Shortest path for linear interpolation using matrices
If we use quaternion interpolation instead of linear interpolation, the paths of the connection between the vertices will be located on an arc between the two locations, keeping the virtual volume of the model in this place:
Figure 9...
