SLERP & skeletal animation interpolation help!

Question

I had skeletal animation in my program working fine, but I was interpolating between the 4x4 matrices stored for each bone between frames in a linear way, i.e.

bMatrix bMathbMathInterpolate(bMatrix const * const p_a,bMatrix const * const p_b, float p_delta)
{
    bMatrix l_mat;

   for(unsigned char i = 0;i lessthan (edit: sorry less than symbol break it) 16;i++)
         l_mat.m_values[i] = bMathInterpolate(p_a->m_values[i], p_b->m_values[i], p_delta);

   return l_mat;
}

Which is O.K. unless of course there is a large amount of rotation in the matrix - the model becomes slightly squashed between keyframes.

So, I made a separate interpolation algorithm than converts the rotation part only of a 4x4 matrix into a quaternion, performs SLERP, and replaces the rotation part only of the matrix with the matrix version of the quaternion. For the translation part of the matrix, I just interpolated it in a linear way.

Looking at the results, this is obviously wrong!!! :'(

If you understand all this very well (unlike myself), you're probably thinking "No! That's not how you do it!" - if so, please tell me what I'm doing wrong!!

I don't know what to do with the translation part of the matrix, because I can only find resources that tell you how to convert back and forth between a quaternion and 3x3 matrix.

Any help will be much appreciated!!!!

Answer 1

You should be able to convert the translation component of the matrices to vectors, and then linearly interpolate them, and then convert the rotation component to a quaternion, and slerp (or lerp, or nlerp) them, and then recombine the resulting vector and quaterion back into a matrix.