double buffering is only half the answer, the other havl is doing the "buffer flop" on the verticle retrace. Not sure how to check for this in SDL however ): ----- Original Message ----- From: "Henry Gomersall" <whg21 at cam.ac.uk> To: <sdl at libsdl.org> Sent: Wednesday, November 20, 2002 2:42 PM Subject: [SDL] colour blocks