I'm drawing 2D, on different layers, dealing with real coordinates [(0,0), (screenWidth, screenHeight)] instead of the standard [-1,1]. And everything is ok when using gluOrtho2D(0, w, h, 0).
However, I want to be able to render those layers in a 3D space, so the user can merge in the scene. The problem is: with gluPerspective, all my coordinates are changed, and for the reason I'd have to change them all in my code, this is strictly unwanted.
So, is there a (simple) way to solve my thing?