This is an example of how to structure a render-time independent main game loop, as inspired by Glenn Fiedler (http://gafferongames.com/game-physics/fix-your-timestep/). Essentially, this allows your engine to accurately take variable amounts of steps relative to the speed that frames are being rendered, regardless of what the current render speed is. This means that frame-rate drops have minimal effect on engine speed.
There's also some quick and dirty code to render a tiled gutter pattern on the edges of the game window to maintain a constant aspect ratio when users resize the game window.