Ok, so would you check the players bounds against all of the cell bounding boxes each frame? or would you need to keep track of the players movement through portals to speed this up?
So when you project the corners of the portal into screen space and build a 2D bounding box from them how do you project the objects to screen space and get a 2D box from those? Would you take the corners of the objects bounding box and project them to screen space and then create the smallest 2D box from the 8 corners?