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List:       kwin
Subject:    Re: Support for _NET_WM_DONT_BYPASS_COMPOSITOR hints
From:       Martin =?ISO-8859-1?Q?Gr=E4=DFlin?= <mgraesslin () kde ! org>
Date:       2012-08-30 10:39:58
Message-ID: 14636891.mgPpKGugd1 () martin-desktop
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Hi,

sorry for having not answered your mail on the wm-spec mailing list, I somehow 
missed it.

KDE has supported such a hint since our July release last year: 
_KDE_NET_WM_BLOCK_COMPOSITING

We implement it in a different way as we do not use unredirection for it, but 
stop the compositing completely when there is a window with such a hint. There 
are multiple reasons to do so:
* performance is still largely affected if the compositor still has an OpenGL 
context
* unredirection mostly makes only sense for fullscreen windows which doesn't 
take into account e.g. a video player you want to interact with (opening a 
menu would redirect it again) or do not have on fullscreen
* unredirection is causing quite some pain with certain combinations of 
Distributions and drivers - that bad that we have considered removing 
unredirection support overall.

When we added the hint we did not propose it for the NET_WM spec as we are (to 
my knowledge) the only window manager which still is able to be run without 
compositing.

If such a hint is added to the spec, I would like it to be written in a way 
that it would also cover our blocks compositing usecase. That is that the 
compositor can decide whether to unredirect or stop compositing completely.

Another suggested would be to add a further hint to the _NET_SUPPORTED section 
and adjust the text to say that a compositor MUST support the hint if it is 
announced in _NET_SUPPORTED. That way a Client can actually know whether it 
will have full resources or not.

Best Regards
Martin Gräßlin

On Thursday 30 August 2012 12:00:44 drago01 wrote:
> Hi,
> 
> I have proposed [1] some new _NET_WM hints that allow applications to
> ask the compositor to unredirect them (games might want that to not
> take a performance hit) or
> to ask the compositor to never unredirect them (i.e not performance
> critical so unredirecting will do more harm then good for them).
> 
> I'd like to add support for that in mutter [2] but I'd rather want to
> agree with you guys on the hints / language of the spec before using
> the NET_WM namespace. Having this in _NET_WM would
> also make it easier for applications as they don't have to support
> multiple implementations but just set one hint.
> 
> Looking forward to feedback from you.
> 
> Thanks
> 
> [1] https://mail.gnome.org/archives/wm-spec-list/2012-February/msg00010.html
> [2] https://bugzilla.gnome.org/show_bug.cgi?id=683020
> _______________________________________________
> kwin mailing list
> kwin@kde.org
> https://mail.kde.org/mailman/listinfo/kwin

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