SDL retains everything you've drawn to the screen in backing store. You need to do an SDL_Flip (1.2) or SDL_RenderPresent/SDL_UpdateWindowSurface (2.0) to commit what's in the back buffer to the screen.
SDL retains everything you've drawn to the screen in backing store. You need to do an SDL_Flip (1.2) or SDL_RenderPresent/SDL_UpdateWindowSurface (2.0) to commit what's in the back buffer to the screen.