How do I wait for vertical retrace?

[Michel Dänzer]

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).
> 
> Samuel, that sounds like *exactly* what I was after.
> 
> 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.

Interesting choice of subject and initial question then. ;)

I think the standard technique for double buffering is to use a pixmap
as the 'back buffer'.


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Earthling Michel Dänzer           |          http://tungstengraphics.com
Libre software enthusiast         |          Debian, X and DRI developer