Just a quick update this week. I learnt some cool stuff to do with building matrixes...or matrices. Yea..matrices.
As far as I can tell thus far in my investigations, you need the following basic ingredients to start with:
1) A unit vector
2) The normalized cross product of 1) and any vector that isn't a scalar of 1) *
3) The cross product of the vector from 1) and 2). Again, needs to be normalized
4) A point
I picked up a good maths intro series from Chad Vernon to which he alluded how to build something that resembles the classic rivet constraint. It was an interesting challenge to take on as I only had some clues to go by, not a step by step guide. I'm glad I stuck with it and got something working in the end.
I've tested it on a skinned mesh with blendshapes and its doing the job so far. Yea..I can't believe it either.
Thanks http://www.hippydrome.com/ for the free model.
* I wonder what happens when you take the cross product of a and -a...