I have been playing around with SDL 2.0 but after searching I haven't found anything online about how to support retina macs. When creating a window using the following code.
gWindow = SDL_CreateWindow("SDL Tutorial", SDL_WINDOWPOS_UNDEFINED,
SDL_WINDOWPOS_UNDEFINED, 500, 500, SDL_WINDOW_SHOWN);
It creates a window that has an actual size of 1000 * 1000. This isn't really an issue because it's how apps are supposed to work using a hidpi screen. However, when loading images I can't seem to find a way to load images that are 2x as big for retina screens and my images always look blurry.