Why didn't you use a window library like glfw or sdl2? Wouldn't that make it more cross platform? Or is it to simply challenge yourself? I do enjoy game engine programming, but I would never dare to write a renderer on the CPU. Good luck on your journey. I will be following this
Since it doesn't use any graphics API, what tools do you use and how do you make this game cross platform? Do you use glfw or some audio library or do you write that yourself too?