# Dang 3D Math!

Ok, I’m trying to make bones with my models, but I can’t come up with an equation to express where the new vertex points lie based on the rotation of the bone.

So I have 2 bone points (ends of the bone) and one vertex point which are based on the model. What rotations do I use for moving the vertex with respect to the two bone poinnts?

You mean one bone?
You need to move the vertices to the bone’s coordinate system, rotate them as the bone is rotated, move them as the bone is translated and move them to their old position (the first step exactly backwards I would believe) AFAIK.

Of course that is possible through just one matrix multiplication with the vertices after you calculated that transformation matrix.

Originally posted by Nick_Weihs:
[b]Ok, I’m trying to make bones with my models, but I can’t come up with an equation to express where the new vertex points lie based on the rotation of the bone.

So I have 2 bone points (ends of the bone) and one vertex point which are based on the model. What rotations do I use for moving the vertex with respect to the two bone poinnts?[/b]

You should represent your bones as a 3-vector and a Quaternion (both relative to the parent). Animation becomes a simple SLERP between keys for the orientation and for most cases you don’t change the bone position. Store the vertices in bone-space, then convert all bones to a 4x4 matrix and transform the vertices for that bone (with weight if you want).