How to determine if a mesh is on screen.

Hello there!

I would like to do some post-processing on the scene after it is rendered (OnPostRender) using the GL class, and for that to work, I'd need to iterate over all meshes that are visible on screen. Is there any performant way to do that? Is there any way, for example, to know whether a face/mesh has been culled?

Also will GL class be able to do its builtin z-sorting tests for me? Thanks! Cau