https://www.pcgamer.com/omdo-is-what-happens-when-you-turn-doom-into-a-magic-eye-puzzle/

If you've never come across one of the Magic Eye books, then the picture above might just look like a random collection of dots. But if you know how to squint at it just right—and go cross-eyed in the process—then a familiar scene from DOOM will present itself in 3D, with the gun model at the bottom of the image and two pillars in the distance (at least, that's what my unpracticed eyes see).

That's what you get in OMDO, which is identical to DOOM except every frame is a random dot autostereogram (like the one above). Some people prefer going cross-eyed to see them in 3D, while some prefer going wall-eyed—OMDO caters for both by letting you switch between parallel convergence and cross-eyed convergence from the main menu.