Do exact portals have to be a flat plane? I know they have to correlate to actual edges in the map as if you were making glass or something, but I just need to know if they have to be flat or if they can weave a bit.

That tutorial only used flat, but i think you dont have to use flats.

Well the problem with the tutorial map is it is the basic of basics that basic can be.
Too simple of geometry to be useful as a tutorial IMO to begin with.

Well, my advice is to play with it, experiment. There's a few things at stake here. I use exact portals a lot for interiors but you can import Bungie's own portals into 3ds max to see how bungie did it. Sometimes, they seem to wrap even full valleys into Exact portals.


Then again, the key is experimentation. Make your portals, compile your level then look for the errors like "no area divided by portal" or something alike. Look into the .WRL it'll highlight in yellow the faulty portal. Also, use rastertizer_wireframe 1 while in game to test how your portal behaves and if it actually culls properly the rooms behind.

Essential to any high poly BSP, you will also need regular portals to divide your land masses properly. These can also be tricky but will help a long way getting rid of visual error even though they are not as efficient as Exact portals.