Modifying OpenGL axis system

Question

I\'m using OpenGL with gluPerspective, what would I need to do to make it use an axis-system which the origin is top left instead of bottom left?

Answer 1

I would say direct operating on the projection matrix is a clean way for this operation. But if by any chance you need an alternative:

You can just use glScalef(1.f, -1.f, 1.f) to flip the axis.

This is also just an operation on the GL_MODELVIEW or GL_PROJECTION matrix (whatever is currently active).