I'm writing a 3d program using meshes moving only along x,y, with z=0 at all times. I say 3-d because it uses lighting and rotations.

I'd like to calculate the screen bounds in world space as a float value, given just fovy, screen ratio, and z distance of the camera.

Can anyone who's better than me at math (i.e. anyone at all) help me do this without calculating frustum planes? I think frustum planes are overkill if there's no movement along the z-axis, right?