Doom does some weird stuff with FOV and how it renders the environment though; newer FPS games have "real" 3D graphics, Doom used some interesting tricks to make things look 3D. The Quake engine was iirc the first "real" 3D engine.
Quake was the first widely popular "real" 3D engine, but ironically the first game in the series being discussed in this thread, Descent, pre-dated it by around a year with fully 3D graphics in 1995.
> The Quake engine was iirc the first "real" 3D engine.
There were many 3D engines before Quake. You had a bunch of Micropose combat flight sims, a ton of 3d driving games, even Elite on the BBC micro.
Hell, I'd written some 3D graphics on the Atari ST before Quake.
Quake was the first 3D texture mapped, dynamically lit, first person shooter...maybe...depending on your definition. It was certainly one of the first to have that ran at frame rates around 30fps.
As others have said, Descent was also around the same time too.
