[Intel-gfx] Tearing In Composite XVideo

Garry Bodsworth garry at camvine.com
Tue Jun 2 12:16:08 CEST 2009

On 1 Jun 2009, at 21:36, Carl Worth wrote:

> On Sat, 2009-05-30 at 08:17 +0100, Garry Bodsworth wrote:
>> On 28 May 2009, at 20:36, Garry Bodsworth wrote:
>>> With the 2.7.1 driver compositing an xv surface using OpenGL works
>>> flawlessly, but in the latest git version it has started tearing
>>> again.  This is on an Intel 945GM, so I was wondering if the
>>> commit
>>> 393abc15b76804580bfee0760ddbd1fb77e66c02 could have made this
>>> change?
>>> Thanks,
>>> Garry Bodsworth
>> And I also forgot to mention this commit which does not sync xv
>> surfaces if they are rendered offscreen -
>> 34660fd2df5d61b77ed7041d32ac29053fc94f5a.
>> http://cgit.freedesktop.org/xorg/driver/xf86-video-intel/commit/?id=34660fd2df5d61b77ed7041d32ac29053fc94f5a
>> It sounds a more likely culprit but I am not sure if that code is
>> actually called on an Intel 945GM.
> That commit may have cause problems, yes, but only because it reversed
> the logic of the condition it added. When you tested, did you also  
> have
> this later commit which fixes it?
> commit c3bf8b980134a2761701e4bc18235695a1cb07a4
> Author: Eric Anholt <eric at anholt.net>
> Date:   Thu May 21 11:05:01 2009 -0700
>   Fix backwards logic on whether to sync to vblank or not.
>   Thanks to Michel Dänzer for catching it.
> If so, the next step would probably be to run a quick "git bisect" to
> identify the actual commit which introduces the bug. If you can do  
> that,
> please let us know what you find. Or if you need any help with the git
> bisect, we'll be happy to do that as well.
> By the way, is there some easy way to replicate the bug you're having?
> Running a video player with an OpenGL-based compositing manager or
> something? Let me know what you're doing.
> And, hmm... should that have even worked tear-free before? It seems  
> like
> only recently has Jesse been doing the work that would enable tear- 
> free
> operation in a mode like that.
> -Carl

I think it was sheer dumb luck it wasn't tearing originally.  What I  
will try to do is write a minimal GTK+/Clutter/gstreamer app that will  
demonstrate compositing video because it is easier to check these  
things on their own.

What I am planning on doing now is trying to apply all the swap buffer  
patches from Jesse's blog post.  It sounds to me from what I read it  
does exactly what I am looking for.

Garry Bodsworth

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