How are you storing the rotation? Are you using an angle? If so, you need to apply an identical transform to the forward vector, then simply add the forward vector times a scalar speed to your current position. Alternatively you could use a separate velocity vector (not necessarily the same as forward) which allows you to do things like skidding. Of course, since you are in 2D, you can forgoe the vector transform entirely and just use trig to update your position:

x += cos (angle) * speed;
y += sin (angle) * speed;

However, i think if you want something like GTA, you are going to need some physics modeling (velocity, collision and friction on 2 axels at least) or you are not going to get the same kind of motion as you do in GTA.

I know www.gametutorials.com has a nice couple tutorials that are good for vector based movement I would look at those they''re in the opengl section I learned a lot from them.

quote:Original post by samosa
hey, thanks alot, that works, i am not using angles, im just making it rotate based on spin which is a GLfloat variable (ex 1.0f) it moves around, but it only occasionally moves in the direction its facing, how could i find the angle?

If you are using a GLfloat with glRotatef, you are indeed using an angle (which is actually specified in degrees and NOT in radians as the C++ cos and sin functions or MS sinf and cosf functions are). You need to convert from degrees to radians. 180 degrees equals PI radians (where PI is approximately 3.1415926). So to convert from degrees to radians you multiply:

AngleInRadians = AngleInDegrees * PI / 180;