How do I wait for vertical retrace?

Chuck Robey chuckr at
Tue May 6 10:02:56 PDT 2008

Hash: SHA1

Samuel Thibault wrote:
> Carsten Haitzler, le Wed 07 May 2008 00:50:46 +0800, a écrit :
>> On Tue, 6 May 2008 18:43:52 +0200 Nicolas George
>> < at> babbled:
>>> L'octidi 18 floréal, an CCXVI, Johan Walles a écrit :
>>>> 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.
>>> DOUBLE-BUFFER is no good for that: when used for continuous animation (such
>>> as video), it causes exactly as much tearing as a simple bitmap copy. At
>>> least it was true in November 2006.
>> it's been pretty much true as long as i have done anything with x (since about
>> 1995...). i have yet to see is not tear...
> He may be fine with tears, which are not like flickers.

I'm obviously too new at this, haven';t seen a screen tear since I stopped doing
 any video effects work, so I'm sorry if I misinterpreted you (I'm glad now I
took that tone, else I'd REALLY be apologizing, wouldn't I?)  There, it was only
a matter of making sure that all of your multiple video inputs were time synced,
and that was accomplished by great stacks of digital time delay boxes, one for
every possible input to those big effects boards, and the time syncing was
finely tuned enough so that the color sync never was more than a nsec or two
off, among maybe 50 to 200 different inputs.  Running those effects boards in a
full-feedback mode was REALLY psychedelic, nice way to waste slow nights!

Sorry, I will go away on this now (although I think I was right about my OpenGL

> Samuel
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