After creating a BSP tree from the CSG'ed World, i'm having major difficulties creating automatic portals. And the documents are a little bit contradictionary. Some said pre-splitting the portals agains all the nodes planes ( this is very slow! ) This is what happens right now: -The portal generator builds large polygons of every node that encompassed that data set. -These portals are then send down the tree, starting at the node that the portals plane lies on( is this correct ) or should i start at the very root of the BSP tree? -the sending down of the portals goes like this, 1.if the portal lies in front of the node, recurse with the front node. the same apllies for the back node. 2.if it splits the node's plane, split the portal in two portals and either recurse with the front and back node's 3.if it is on the plane( right now immmediatly the 'root node' ) create a copy of the portal and recurse with front and back node 4. eventually we'll pop out into a leaf node, so add the portals to the correpsponding leaf. Does the leaf right now contains all the potential portals?! If so i believe i have to split the portals against all the leafs planes( polygons ) after this has completed we have our portal with the right dimensions. Is this correct or should another approach be taken?