How do I wait for vertical retrace?

[Johan Walles]

2008/5/6 Michel Dänzer <michel at tungstengraphics.com>:
> On Tue, 2008-05-06 at 13:12 +0200, Johan Walles wrote:
>  > 2008/5/6 Samuel Thibault <samuel.thibault at ens-lyon.org>:
>  > > Michel Dänzer, le Tue 06 May 2008 09:37:23 +0200, a écrit :
>  > > > On Mon, 2008-05-05 at 15:43 +0100, Samuel Thibault wrote:
>  > >  > > Michel Dänzer, le Mon 05 May 2008 10:22:19 +0200, a écrit :
>  > >  > > > On Sun, 2008-05-04 at 20:06 +0200, Johan Walles wrote:
>  > >  > > > >
>  > >  > > > > I would like to wait for vertical retrace in an X application.  How
>  > >  > > > > can I do that?
>  > >  > > > >
>  > >  > > > > The point would be to avoid flicker in my app by using double
>  > >  > > > > buffering and update the on-screen image during vertical retrace.
>  > >  > > >
>  > >  > > > There's no mechanism for this yet in X. Your best bet is probably to use
>  > >  > > > OpenGL, e.g. the GLX_SGI_swap_control extension.
>  > >  > >
>  > >  > > Isn't there a more simple double buffering X extension?
>  > >  >
>  > >  > You mean DOUBLE-BUFFER?
>  > >
>  > >  Yes.
>  > >
>  > >  > I'm not really familiar with it, but I know that
>  > >  > at this time it can't synchronize buffer swaps to the refresh.
>  > >
>  > >  Eww, that would be a pity.  At the very beginning of the Extension
>  > >  documentation (Johan: xspecs/Xext/buffer.PS), it is said `Clients should
>  > >  be able to [...] Display a series of buffers in a window in rapid
>  > >  succession to achieve a /smooth/ animation', which is what Johan wants
>  > >  to eventually achieve AIUI (vertical retrace wait being only one method,
>  > >  I don't know whether which others could be possible).
>  >
>  > I don't care about vertical retrace in itself, waiting for vertical
>  > retrace would only be a way for me to achieve flicker-free animation
>  > in a 2D application.  Any other way of doing that would be fine as
>  > well.
>
>  I think the standard technique for double buffering is to use a pixmap
>  as the 'back buffer'.

How would that help achieving flicker-free animation if it doesn't
wait for vertical retrace?

  Regards //Johan