Games using the id Tech 1 graphics engine (formerly known as the "DOOM engine") (original or modified) by iD Software, Inc..
Some facts:
It was the first 3D game engine that allowed variable heights for floors and ceilings. However, it only allowed one floor or ceiling per area, making multi-storied levels impossible.
John Carmack experimented with 16 bit textures, but found the overhead unacceptable for the game.
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