So a little over a month ago, I thought it would be cool to try out emscripten and WebAssembly with one of my students. We had previously done some "hello world" type graphics programs and a simple game port and I thought it'd be fun to see how easy (or not) it was to get those to run in the browser.
While I think it was a good exercise, and emscripten is much better than it was a couple years ago, I don't think it's ready for primetime yet. You cannot simply compile your existing graphics/game code and expect it to work. If you're lucky you only have to make a few minor changes and with an #ifdef you can use the same code for your regular executable to. If you're not, you might have to re-do your whole program because of the limitations emscripten (which are really the limitations of the browser/DOM rendering model. These include turning infinite loops into callback functions and restricting yourself to OpenGL ES 2/3 which gets translated to WebGL 1/2.
In any case, here are our results:
For some reason we could not get file loading to work and the movement in sdl2_interactive is very inconsistent for no reason that we could determine. We originally wanted to port simulate which we had previously already ported to C but due to the mainloop callback requirement, it would have required a complete redesign.