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Comment by torginus | Hacker News Reader

This looks like portals. Essentially how FPS games of that era worked is that they had rooms stitched together by doorways (or 'portals') as a way of occlusion culling. While perfectly capable of representing sensible geometry, it was actually not a requirement that the geometry should make sense in any shape or form and allowed arbitrary connections between rooms.

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The Marathon 1+2 engine back in the 90s allowed for "5D space", ie. "Spatial" Rooms that were capable of overlapping each other, because the engine only defined the floor polygon with a given height and these floor polys were connected to each other at the vertices to create the actual level spaces.

So even though you were in the same absolute space coordinate as another player, you were not necessarily in the same room.

Good times. <:o)

Huh I never knew that. I just knew you couldn’t have two floors directly above each other while also having both floors visible to the player at the same time. All of my Mara 1 maps I built would crash when I tried this. I wonder if what you just explained is why.

I don't know how they actually did it but conceptually I thought about it as traversing the map's segments depth first in 2D starting at one edge of the viewport & the currently occupied polygon. Simple, and allows freedom like overlapping rooms, but would go sideways in cases like the one you describe.

Doom actually didn't permit overlapping rooms like Duke3d and some other games did, although some source ports of Doom do allow it (notably used by the trendy MyHouse.wad)

Some vanilla Doom levels get exceptionally close to simulating it using portals and other tricks.

And bridges and such, but I'd put the line on Boom compatible engines.

FPS games of that era were usually either in the portals camp or the BSP camp, BSP being the "OG" way to do it precisely because Doom did it that way.

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