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).

Thanks.