glRotatef and billiard balls

Thanx for the reply.

Well, the 'physics' is pretty simple.
Angle of reflection = angle of incidence.
eg get the angle of direction relative to the normal to the edge, then the reflected angle will be the negative of this.

let y axis = up, and x axis = right

eg vector of ball going to edge at right of screen = (x=1, y=1), then vector after hitting edge will be (-1, 1).

example 2: vector of ball (1, 4), and hits edge at top of screen then vector after hitting edge will be (1, -4).

example 3: vector of ball going to edge = (-1, 5), and hits edge on left of screen then vector after hitting edge will be (1, 5).

example 4: vector of ball going to edge = (1, -3), and hits edge on bottom of screen then vector after hitting edge will be (1, 3).

After hitting edge you'd also want to to decrease the magnitude of the velocity due to friction.

1) Check out matrices in OpenGL... google, etc.

2) Each update, add a "rotate" matrix onto the balls' matrix.

3) Render each ball with their corresponding rotation-matrix.

Cheers!

You could keep track of your rotations in a vector (or better a quaternion) and create a rotation matrix each frame (you would be doing that anyway). That would help you reduce the precision errors that come along with matrix multiplications.

Thanx for all the replies. Now I have a lot of work ahead of me...

Have been reading a lot about Matrices and Quaternions on the Internet. Phew! I think I have a basic understanding of what they do now.

Tell me if I'm going in the wrong direction...

1. Set where to rotate in a matrix
2. Add that matrix to the quaternion
3. Show the result

Read about rotation matrices, but still don't understand how to get my normalised vector that I've used before for rotating, into a matrix. And how do I add that matrix to a quaternion? Any Rotating-For-Dummies webpage that explains that? ... In a very simple way ;)

[Edited by - toto1919 on September 21, 2006 3:26:52 AM]

Try this article: http://www.gamedev.net/reference/articles/article1095.asp.

You should keep a quaternion Q for your ball, add the delta rotation (in form of a quaternion) to Q each frame, then convert Q into a matrix and add it to the modelview matrix (e.g. glMultMatrixf(Q->toMatrix()).

For Q->toMatrix() see the article.

Wow! Thanx for the quick reply.

The webpage looks "easy" enough for me to grasp... Looking in to it now...

Works fine now!

Thanx for all your valuable input.