> And before that, 2D games (side-scrolling platformers were not a thing on PC hardware until Carmack did it, iirc). I think his main thing is balancing clarity

> And before that, 2D games (side-scrolling platformers were not a thing on PC hardware until Carmack did it, iirc). I think his main thing is balancing clarity - what happens when and in what order - with maintainability. Smooth side-scrollers did exist on the PC before Keen (An early one would be the PC port of Defender). Moon Patrol even had jumping in the early '80s. Furthermore other contemporaries of Carmack were making full-fledged side-scrolling platformers in ways different from how Keen did it (there were many platformers released in 1990). They all involved various limitations on level design (as did what Keen used), but I don't believe any of them allowed both X and Y scrolling like the Keen games did.