Subtracting two 4x4 Matrices - is this possible?

Question

I have two 4x4 OPENGL Matrices -

• 1st matrix holds rotation and position of an object at frame 0.

• 2nd matrix holds rotation and position of an object at frame X;

I want to retrieve a movement offset of an object between frame 0 and X, is this enough ( possible ) if I just subtract both?

CMatrix4x4 offsetMatrix = matrixAtFrameX - matrixAtFrame0;

What I am doing is exporting per frame Bone transformation matrix where this matrix is an offset of the transformation between frame 0 of the animation and frame X.

• Can I subtract both matrices ?

• What are the results ?

Answer 1

You'll need to multiply the matrix at frame x with the inverse of the matrix at frame 0.

matrixOffset = inverse(matrixAtFrame0) * matrixAtFrameX

This will give you the relative transformation and rotation between the frames.