Squad takes four quaternions. Where do I get the four quaternions from? With slerp there are only two because you go from one spot to another, but why are there four with squad? Anyone know a good article to demystify the squad algorithm? Thanks.

My guess is that you need two more to fully establish the boundary conditions, i.e. the initial and final ''velocities'' of the interpolation, just like with splines.

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Stolen from Magmai Kai Holmlor, who held it from Oluseyi, who was inspired by Kylotan...

From the directx documentation for D3DXQuaternionSquad:


"This function uses the following sequence of spherical linear interpolation operations: Slerp(Slerp(pQ1, pC, t), Slerp(pA, pB, t), 2t(1 - t))"

where the argument order is

pOut, pQ1, pA, pB, pC, t

Try working out what it does as t goes from 0 to 1 to visualise it.