enable vsync synchronization

src/Main.hs

@@ -54,6 +54,9 @@ main = do
   -- window should be a window, not fullscreen or so
   SDL.setWindowMode window SDL.Windowed
 
+  -- synchronize buffer swapping with monitor's vsync
+  SDL.swapInterval $= SDL.SynchronizedUpdates
+
   -- show the window
   SDL.showWindow window