Occlusion Portals - What do they do?

Does anyone have any info on Unity's occlusion portals? I tried looking up stuff about portals, but didn't get much. And on that note, how does one use them? The "open" variable doesn't seem to do anything, and I'm not entirely sure what it's actually supposed to do.

The documentation for it is negligible. I assume it is still in the process of updating.

 

Sounds like it would be used for doors, windows etc. which block visibility between two "occlusion zones", but allow you to see from one zone to another when they are open.

Not really sure as I haven't tried using occlusion culling in any game before.

 

You are quite optimistic

 

Portals do the same thing they did since their first appearance on BSP levels in Quake: the seperate 2 occlusion areas through a confined area that connects them.
In case of unity they can be dynamically opened and closed (so more like physical portals / doors) and are used to 'shut down' whole areas behind them.

 

dreamora - so you mean 'oldschool' portals in that there'd be some precalculated visbility for a 'leaf node' you're standing on and what other leafs in the bsp tree it could see? As I remember, that was the old Q1 style of 'portals' ?

A more dynamic approach, similar to Doom3 portals, could be handy, don't need to compile anything, you've got a discreet set of data (the two 'zones' linked by a planar portal) and you check the fustrum created from your view through the portal for intersections of objects in that other 'zone'... this way it's 100% dynamic, the portal itself can be moving (maybe you have an animated door that slides?) and all objects can be dynamic.

...but that's just a rant, I haven't actually checked out what they're doing in 3.5, but from the sounds of it there's a lot of compiling needed for the occlusion?

 

The portal system in Quake/Doom is different, well not in theory, but the underlying mechanics are very different. In Unity there's no BSP tree that world geometry is partitioned into (nor do we have to build levels out of awkward convex constructive solid brushes), instead I believe Umbra uses an Occlusion Table that is queried to get lists of visible objects.