glRotate rotates about the origin, so if you want to rotate the quad about it's center, you have to move it's center to the origin.

Since the quad extends from [x, y] to [x+w, y+h], the center is located at [x+w/2, y+h/2]. So first translate the center to the origin, rotate, and translate back. Something like this.

glTranslate(x+w/2, y+h/2, 0);glRotate(whatever);glTranslate(-x-w/2, -y-h/2, 0);

Thank you! Thank you that works fine if I use single quads! :)

But what about if I want to rotate the full scene?

Here a screenshot what I mean:
http://members.chello.at/ennemoser/tile_rotation.jpg

Is it possible to do that without those black "holes"?
What must I rotate the quads about? window_w/2 - window_h/2 ? hmm..

how about:
glTranslatef( window_w/2, window_h/2, 0);
glRotatef( angle, 0.0f, 0.0f, 1.0f);
glTranslatef( - window_w/2, -window_h/2, 0);


Thank you again ^^

[Edited by - rakoon2 on September 4, 2004 5:03:08 AM]

What you see in that jpg is not the scene rotating, but each individual tile rotating around it's own center. That is why there is black space.

Yes I know. :)

glTranslatef( window_w/2, window_h/2, 0);
glRotatef( angle, 0.0f, 0.0f, 1.0f);
glTranslatef( - window_w/2, -window_h/2, 0);

is right. :p