Hey,

Just for reference I am attaching a small patch that takes advantage of glXGetVideoSyncSGI (from the SGI_video_sync extension). On a compatible X11 setup (which may highly depend on the hardware *and* the drivers used) it can be used for proper VSync without slowing down a game (e.g. if a DOS game tries to output about 70fps while the host display's refresh rate is 60Hz).

Note that (at least for simplicity and maybe not just that) when this feature is in use, DOSBox does *not* take advantage of the ARB Pixel Buffer Object related functions. (In fact I think that these aren't available here for testing anyway; Not that it's truly relevant.)