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List:       xfree-xpert
Subject:    Re: [Xpert] periodic (1.4 second) YUV overlay glitch on DVD application
From:       Mark Vojkovich <mvojkovich () valinux ! com>
Date:       2000-11-30 20:47:06
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On 30 Nov 2000, Emmanuel Michon wrote:

> I'm using X4.0.1 on an ATI Rage128 card using the V.Dergachev r128_drv.o
> driver from GATOS CVS sep 11th 2000 --- for the YUV overlay feature.

   That module is not supplied by the XFree86 project.  There is
some Rage128 Xv support in the latest CVS, however.  I'm still working
on some clipping gliches in that though.  I've never used the
GATOS driver.

> What does exactly XSync?

   XSync stalls until the XServer has processed everything in the
X pipeline that preceeds it.  It's probably not something you
want to be using in a performance critical application because
it will not return until the YUV data is transfered to the overlay
and your application will be strongly linked to scheduling of the
X Server.  You should call XFlush after every Put to flush the
buffer but at that time it's usually not safe to touch the buffer
because the X-Server isn't through with it.  You either have to
wait for the ShmCompletionEvent or cycle through enough buffers
so that you are more-or-less assured that the server is through
with a buffer by the time you render to it.  Of course, waiting
for a ShmCompletionEvent right after the put is pretty much
the same thing as calling XSync.  If you are using ShmCompletionEvents
it would be wise to still have at least two buffers and postpone
waiting for the even until right before you need to use the buffer. 



				Mark.

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