Hi. To calculate a portal i check the intersection of the bounding boxes of the cells. So if there is n cells the check is n^2. I converted a Quake2 map in a bsp tree but the map have many cells (bsp leaf nodes). About ~ 3800 so 3800^2 is a very large number. Is there a way where i can check it fast? What is the best way to check if a portal is transparent i.e. there's no polygon in the middle like a wall. I'm using a lot of line visibility. Thanks in advance.

It sounds like you could use quad/octrees to solve your problem more quickly.