Michael Hunold (hunold@xxxxxxxxxxxxxx): > In grabbing mode (ie. when the bt8x8 writes the picture to some > offscreen memory), the synchronisation of your incoming picture is not > important. > > What you really need is a way to synchronise the output, ie. a way to > tell your output device: "wait for the next vertical sync, then flip > to the next frame, so I don't get any tearing effects". > > I don't know if X finally has something (ie. a "X vsync extension") > like this, otherwise you need to use some other toolkit like DirectFB > (http:/www.directfb.org) that lets you sync your output to the vsync. Michael, Modern video cards have hardware video overlay engines which scale video and convert from Y'CbCr to RGB. All video cards provide double buffering for overlay surfaces. When a client provides the next video frame, it will page flip to that on the next vertical sync, so you will not get tearing. The X extension to use an overlay surface is called XVIDEO. In tvtime we capture a frame (grabbing) to system RAM. We then process it. We then provide this frame to XVIDEO, which writes it to offscreen video memory. That frame is then shown on the next retrace without tearing. -Billy
