How to find out, how many tiles ca be rendered on the screen.

I have Plane made of tiles in opengl. I start drawing them at (0, 0, -20) after that i do my translations so that the view is rotated somewhat similar to an isometric (kind of) perspective.

I’d now like to know, how many tiles are visible in each direction. So what i need to know basicly is, which coordinates (int the “before translation” - space) are now visible in the translated view.

The “tiles” before the translations" (for example in x direction there are 14 tiles visible):

Image Here

And after the translations ( now there are 28 tiles visible in “old” x direction):

Image Here

As far as i know right now from my tries to do this i don’t think that frustum culling will do the job. I also posted my question at gamedev here: Link herethere are some advices in the discussions that i already tried with no success. Maybe unprojecting some points myself (without gluUnproject) would to the trick since gluUnproject just won’t work. But i’m missing an explanaition of how to unproject a point manually.

Mhm… btw. This is my first post allthough i read the posting guidelines i can’t explain why this board won’t let me post the two images (which are important to explain my problem). Any help on that?

Thanks for any help!