[Algorithms] Re: Portal VS BSP

[Alen L. <ale...@cr...>]

>> Previously I have used BSP because I read that it is more 
>> efficient, perhaps that is no longer the case? "BSPs trade 
>> performance at run-time for a slow preprocessing step 
>> performed when building the world" [1].
> 
> Well, I don't see what the problem with that tradeoff is, unless you have
> incredibly dynamic worlds (i.e. more than just doors opening and closing),
> in which case you should look at more dynamic visibility methods.

This is a matter of content turnover. In our team, we like to 
optimize/eliminate preprocessing as much as possible, so that:
a) artists can check the final results more often, improving their overall 
productivity and
b) in the final stages of production, when it matters the most, new versions 
can be created more quickly. 

So if dynamic visibility buys you extra features (doors...) _and_ removes 
preprocessing, it is very welcome. :) 

> I'm not aware of any that have used the BSP topology to directly extract
> portals (not to say that there aren't any), but quite a few do use the BSP
> for extracting convex regions and then use a sampling method to calculate a
> PVS.

AFAIK, it is just what you do when you are calculating a PVS from a BSP, 
isn't it? You build the portals first, by subdividing bounding polygons 
lying on BSP split planes. It is a very simple and fast method. 

Cheers,
Alen