More on this topic:
Build engine also cannot do full room over room, because the map is still 2D. There are ingenious tricks in the engine that allow the feeling of room over room.
One is silent teleporters that basically take you to a different place in the map (this is what happens every time you dive under water – check it).
The second key element has to do with the way the engine renders sectors – it does not care about their absolute position in space, only the connections between them. So two sectors can really overlap or occupy the same area in space, as long as they are not visible at the same time. So you can “feel” room over room, but you can never see room over room.
The latter feature allows some amazing things that are almost unheard of in 3D games. I encourage you guys playing it right now to check the following secret levels to understand what I’m talking about and to be deeply impressed:
E2L11 – Lunatic Fringe (exit from E2L08 – Dark Side)
http://legacy.3drealms.com/duke3d/walkthrough/e2m9.html
E3L10 – Tier Drops (exit from E3L05 – Movie Set)
http://legacy.3drealms.com/duke3d/walkthrough/e3m5.html
