Count of rendered polygons

Once upon a time, I dabbled in programming Homebrew for the Nintendo DS. During testing of the 3D hardware, you could pull a count of currently rendered polygons from a hardware register. I was doing this to confirm how many, appr开发者_开发百科oximately, of a certain model would be rendered at various angles because there was a max of 2048 triangles allowed.

I'm hoping this isn't a completely stupid question... but here it goes. Is there anyway to get the number of polygons that are actually being rendered each frame (not being omitted by depth buffering) in OpenGL? Specifically, OpenGL ES 1.1?

You could just run each triangle through an algorithm to determine if it inside the view frustrum by treating the viewing area as four planes. Then it's just a matter of checking which side of the plane each triangle is on, and making sure you only add up triangles that are on the correct side of all four planes. This wouldn't be good for rendering speed, but it would give you an accurate count on how many polygons are being rendered for each viewing angle. This website Graphics Gems contains a lot of good source code that can help you with the math portion of things if you need it. It contains the source code for a series of five books that contain graphics algorithms such as ray triangle intersection, etc.

Edit:

I didn't notice your comment about depth buffering, the above description is for all triangles in the viewing window. You could just add two more planes at your depth buffer distances and use those to further filter out visible polygons.