I have set my other problem aside for the time being, and immediately run into another problem.
I’ll try to give enough background information this time:
I’m making a simple rollerblading racing style game, using an XBOX360 controller for input. I’m working on the motion system right now, and have run into a problem with friction along a local axis (wheels roll forwards, but not sideways)
I believe there used to be a friction setting for this, but I think it doesn’t work in bullet.
I’ve managed to use a formula to get the amount of motion along the X axis as a vector in X Y Z format (as opposed to polar coordinates, not sure if this is useful information but I’ll include it in case it is), and I can use the Pythagorean theorem to get it’s magnitude, and apply that as force along the X axis. It works fine, except the pythagorean theorem removes the sign, so friction slows it down if the X velocity is leftwards, but accelerates it if the velocity is rightwards. (that is, the force is always applied in the same local direction, regardless of whether the X velocity vector is facing left or right)
so we get to the request:
how can I tell if two vectors that lie along the same line are pointing the same or opposite directions? if it helps, one vector always has a magnitude of 1 (it being the X axis as taken from the orientation matrix)
 well, I managed to fix the problem all by myself (ego ++)