mlookatup expression function
Computes the transformation matrix of a lookat from one vector to another, with an up vector.
See also: mlookat
mlookatup(v1, v2, upv)
Computes a transform matrix specifying a lookat from vector v1 to the vector v2, taking up vector upv into consideration.
The vectors are converted to 3 vectors for this computation. The resulting matrix will be a 3×3 matrix.
Computes the lookat matrix and returns the rotation value for RX.