Check out UnrealEd sometime for clues. ;-p

IIRC, Unreal is largely BSP based. It supports portals, too. I seem to remember reading in an interview with Tim Sweeney, that the Unreal engine favours a sparsely populated BSP tree, although I cannot remember a source to cite.

From what I''ve read, the Unreal engine now features a separate layered heightmap terrain engine, on which BSP-based maps can sit. If it works, thats a really neat sounding technology! (I think LithTech can do it too, but its from Monolith so it can be assumed that 90% of listed features are either broken or not included.....)

How exactly do you make the BSP favour outdoor terrain? I mean, in outdoor terrain there isn''t much occlusion of polygons so it seems that the BSP tree method is a big wad of hot air? It''s much better for areas where there is lots of polygons being hidden from view.
And what about Quake? That didn''t even use BSP sorting for HSR, and that seemed to be able to handle high polygon scene with low occlusion, I tried to understand what abrash was saying in his real-time ramblings but couldn''t catch on?

Portals do suck for outdoors, although they can make an effective way to represent transitions from outdoors to indoors (ie. doors/windows).

From what I can tell (doing Unreal - as opposed to UT - editing), the outdoor scenes only work because they are kept to a relatively low polycount (you can see the facets on the cliffs if you lower texture detail). The classic outdoor area used to represent the Unreal engine always used to be the area you enter just after escaping from the spaceship (where you first meet the Brutes). You have a large area with huts, the spaceship itself is crashed into a mountain, and a panoramic view of an area with a waterfall tumbling down into a REALLY big lake (really big for the time). Its worth loading this level into UnrealEd, one can learn a lot from it. For one thing, the outdoor areas - for all their vastness - never actually demands all that many polys, due to clever map design. The Quake engine, however, still couldn''t do a level like that, simply because its subdivision routines are heavily optimized for enclosed, claustrophobic spaces. (Ever notice with the Unreal engine that there is less of a performance benefit for making a tightly enclosed map?) I think that part of this is related to the way each engine subdivides the map; Quake tends to have very low polycounts at each node of a very deep BSP tree. This is ideal for very high performance indoors. Unreal BSP trees aren''t very deep at all (hence the quick compilation times), but this means a bit less computation for open regions. Unreal also sectorizes maps, and you can sometimes get a performance boost by moving an outdoor region into its own sector.

The Q3 engine may be a bit better than previous iterations of Quake for outdoor areas (although I still wouldn''t want to try and write Deus Ex in it!). Some of Q3''s deathmatch arenas are relatively open (albeit small).

As for the rocks in Unreal''s new outdoor engine, I read in an interview with CliffyB that this is a deliberate attempt to move away from the Tribes feeling of huge, empty landscapes. He also kept talking about how beautiful his trees are, so its entirely possible that he''d just had too much coffee that day!

Hrm - when you say subdivision in Quake do you mean polygon's being subdivided for the sake of maintaining the bsp? Because from what I read that's not how they decided to do things with the quake engine because they didn't want high polygon counts? (which meant more edges being calculated thus lower framerate due to hardware limitations)

Edited by - Maitrek on July 9, 2000 12:01:01 AM

Hrm - Quake used BSP trees for drawing of the terrain but what about moving parts like doors and models? Doesn''t matter anyway - unreal''s the topic here. ANd also at one stage during the production of Quake they tried 1/z and said that it was good but they couldn''t quite get it working.