At certain times, extra rooms are added to Black Annex during game-play. I actually cut this from the design doc about six months ago, but I was finally able to add it back in by piggy-backing on the system I build for spawning in enemies. It works in a much more complex way than the enemy spawn-in. With enemy spawn, there’s just an AI entity that’s invisible until it hears someone call for help.
When creating a new room, the clipping plane needs to be dramatically modified, and the zBuffer needs to be rebuilt as the room is spawning-in as well (the zBuffer typically only considers walls and static objects once when the level loads, and then never again because they don’t change.). There’s also the issue of “joining” tiles needing to appear to connect old rooms to the new ones, so certain wall tiles need to “listen” for a spawning room, and switch to a different type to connect to the new room.
In the video below, see how the new room actually “connects” to the old room, and a new window appears in one of the offices which wasn’t there before.