title: How to center fullscreen window
body: <p>I have a 16:9 display where I'd like to show fullscreen SDL window which is in 4:3 mode.<code>SDL_SetWindowFullscreen(window, SDL_WINDOW_FULLSCREEN)</code> sets the window to the left side of the screen and leaves a big black bar to the right. </p>
  
  <p>I'd like to center the window and have black bars on the left and the right side. </p>
  
  <p>It seems that <code>SDL_SetWindowPosition(window, x, y)</code> has no effect on window when it is in fullscreen mode. Can I center the fullscreen window in SDL2?</p>