[joakleaf]

Actually, this was sort of a thing already back in the 90s...

There is an alpha of Duke Nukem 3D (LameDuke) which had some screen space reflections. As I recall, the game crashed when you look up or down on the reflections, likely because of a pixel read beyond screen boundaries.

Discussion here: https://forums.duke4.net/topic/1329-lameduke/

[tripzilch]

IIRC, and I don't know if it's the same with this alpha version, but I remember messing around in a level editor for the original Duke Nukem 3D, and mirrors were done simply by having an adjacent room with mirrored geometry :)

(and, I assume marking the wall between as a mirror so it knows to also render the dynamic objects mirrored--but I don't know for sure, I was quite young and didn't have a lot of success with this level editor because I didn't understand it fully)

[pandaman]

Those are not screen space reflections. For one, they are impossible to do without a z-buffer (which that game did not have), not to mention it would be an extremely stupid idea to do such an expensive computation for a flat mirror.