It's fast because you start with the portalzone the camera occupies and work your way outwards in a recursive function. You can usually only see 1 or 2 portalzones away, so as soon as the portals start coming up as being occluded, the function returns. I haven't seen a need for any precompiled vis data, other than splitting the geometry up into portalzones.
Of course, in some situations using portalzone occlusion would actually slow the scene down. It's all about how you set the portals up, and how many polygons and objects you want the world to consist of.
3D World Studio 5.47 comes with an example scene of a large warehouse complex. This is probably the most demanding kind of scene you can render, because it combines large areas of terrain with high-poly interior structures. I set portalzones up inside all the buildings, and added portals at the building entrances. Then all the objects inside the warehouse structures only have to be drawn if the entrance to that building is visible. The speed gains are definitely worthwhile, even when no dynamic lights or shadows are being processed.
Of course, in some situations using portalzone occlusion would actually slow the scene down. It's all about how you set the portals up, and how many polygons and objects you want the world to consist of.
3D World Studio 5.47 comes with an example scene of a large warehouse complex. This is probably the most demanding kind of scene you can render, because it combines large areas of terrain with high-poly interior structures. I set portalzones up inside all the buildings, and added portals at the building entrances. Then all the objects inside the warehouse structures only have to be drawn if the entrance to that building is visible. The speed gains are definitely worthwhile, even when no dynamic lights or shadows are being processed.