What is "multi portal masking (a special type of portal system, doesn't need a BSP, but creates recursive occlusion masks from the portals instead)"? It's a notion by Yann (http://www.gamedev.net/community/forums/topic.asp?topic_id=130479) Anyone got ANY clue? Aren't BSPs in Portal Rendering Engines a bad form of implementing automated portal generation? [edited by - mux on May 26, 2004 4:00:27 AM]

I believe it''s a system where you render the current cell/area. Then if a portal is visible in the frustum you render the other cell, the one that is on the other side. Then you use recursion, if that cell has portals you test them as well. But not against the whole frustum but against the (much narrower) frustum formed by the camera position and the 4 corners of the portal.

Since it speaks of masks, I assume it doesn''t work with frustums but with the screen space projection of the 4 corner points of the portal. If the screen space projection of the second portal overlaps the first portal, then you recurse further, otherwise the third cell is invisible and can be skipped.