Maya quaternion & matrix operation order

Here are some pointers I had to learn the hard way, and don’t ever want to forget.

MQuaternion(MVector a, MVector b)

constructs the rotation to go from B to A!
So if you have an arbitrary aim vector and wish to go from world space to that aim vector use something like

MQuaternion(aimVector, MVector::xAxis)

The documentation is very ambiguous about this. Or rather, it makes you think the opposite!

If you wish to combine matrices in maya think of how children and parents relate in the 3D scene to determine the order of multiplication. Childs go first, e.g.

(leafMatrix * parentMatrix) * rootMatrix

Another way to think about it is adding rotations. So if you have a rotation and you wish to add some rotation to it, you generally parent an empty group to it and rotate that, so you again get this relationship of

additionalRotation * existingRotation

A little note: not sure if adding quaternion rotations works in the same way; should check!

More conventions to come hopefully!

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