I am doing some view box culling. These are my steps:
-setup PROJECTION matrix
-setup MODELVIEW matrix
-get projection & modelview matrices from opengl. Multiply.
-Project the coords of the bounding box using this matrix.
-Test whether the projected point will be mapped to the screen or not. (*)
Opengl will take this coord and map it into window coords.
My question is:
What coords at * should I test for. It appears -1 < x < 1 and -1<y<1 are correct. What about the z coord?
What projected coords are mapped into the viewport?
Does this depend on the projection? (I really dont think it does).