[Algorithms] Portal VS BSP

[De B. <be...@ii...>]

I read that call of duty uses a portal rendering algorithm rather than BSP.
They state that "to help designers, we switched to a portal based renderer".
Isn't placing portals an extra burden on artists? I know BSP just has the
annoying preprocessing, but is there any other reason? It would be
interesting to know how many FPS games don't use BSP.

I assume the portal rendering just for indoor areas since "portal technology
effectively confines us to render interior scenes only" [1].

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].

What I need is a system to draw architectural buildings + their surroundings
for large architectural projects (which have fairly large landscapes). I
have decided to use terrain algs for the terrain, LOD for vegetation and LOD
for outside buildings, and either BSP or portal for inside buildings. 

I suppose I will do both and use whatever seems easiest throughout the whole
development process.

The scary thing before was that you had to place portals manually. But in
the buildings I am working with defining where rooms and portals are is
hard. Sometimes there are so many windows and voids you could almost say
there is one room. Do artists still have to manually place portals? I know
that you can do "glass shader" = portal, but manually placing the rest still
seems like too much work.

Do any games use a bsp like algorithm to determine portals for the portal
rendering algorithm? or some other automated portal placement?

I read a new paper on portal rendering that works for indoor and outdoor
scenes (well very limited outdoor scenes) called "breaking the walls",
released this year. It had automatic portal placement that is supposed to be
better than the bsp automatic placement of portals.

I also read that doom3 uses portals to connect areas. HL2 uses the usual bsp
for indoors and some advanced real-time occlusion for outdoors. So I guess
FPS games can successfully use either portals or bsps for their indoor
parts. And I am still unsure whether I should go the bsp route again or the
portal route.

[1]
http://www.medialab.chalmers.se/c2c/doc/portals.html

-Ryan De Boer