I'm not super familiar with meson so I was having trouble building.. I'm guessing that you need to set the option somehow for what engine you want to build, but I wasn't able to figure out how.

I managed to build the sdl2 engine by hacking the meson.build file, but could you tell me how you're supposed to do this?

Looks really cool! I did a similar from scratch side-scroller game for a project in college that was a lot of fun. Thanks for sharing!