This seems like a clear improvement to the current situation and I'm okay with approving it (although I won't for the time being, as you mention a new test and I'd like to see it first :slight_smile:).
I was thinking, maybe it makes sense to add a WARN() if we get in `glxdrv_wglSwapBuffers()` without a GL context? Probably not, now that I look at it in detail. The implicit flush in `glXSwapBuffers()` only happens when a GL context is current. win32's `SwapBuffers()` doesn't say, of course, but it would be sensible if it did the same, which means that the application gives up to the implicit flush by calling `wglMakeCurrent(NULL)`. Also we're currently printing no messages when `GLX_OML_sync_control` is not supported, so it's probably fine as is.