Okay,

I have a very simple project set up specifically for this question. It's just a 3D shape centered in the origin. I've been looking everywhere for a way to rotate that object by any two points.
So let's say the object was a gun and there was a character behind it with the gun mesh in its hand. I'd want to have the character and the gun to rotate around the same point so that the character and the gun it was carrying could rotate as a whole. But I'd also like to be able to tilt the gun around its own origin so that I could maybe make it point a little up in the character's hand. So I'd need to rotate it around the character's center and the gun's center.
I'm sure this problem's come up a lot. I'm fine with just links to tutorials or other threads where this was explained in this forum.

I have a pretty good understanding of matrices and their transformations, but I am completely lost with quaternions so links for those would be great too.

Thanks

First create the rotation matrix for the gun.
second, place the gun at the hand
third, make the rotation & translation matrix for the player
fourth, mulitiply the gun matrix by the player matrix.

something like this..

gun_matrix = Matrix.Identity * Matrix.CreateRotationXXX( rotations )

gun_matrix.Translation = position_of_players_hand

player_matrix = Matrix.identity * Matrix.createrotationsxxxx(player rotations)

player_matrix.Translation = position_of_player

//now rotate the gun by the player matrix, which will also move it relative to the player

gun_matrix *= player_matrix


best,
Byron

Thanks that works great.