So I was thinking about the NODES structure of levels ( http://doomwiki.org/wiki/Node ) and how part of the structure is defining the bounding box surrounding each of the child nodes. This bounding box is used for a quick-n-dirty visibility calculation for the back side of a partition line. The engine takes the two appropriate corners of the bounding box and calculates if any part of that bounding box is even in the player's field of view; if not, it skips descending that part of t