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List:       freedesktop-xorg
Subject:    Direct access to window off-screen buffer
From:       Troll Berserker <berserker.troll () yandex ! com>
Date:       2018-02-04 2:50:50
Message-ID: 289c8437-fa47-863f-4703-83e8c40a1e07 () yandex ! com
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Hi all,

Is is possible to directly (using MIT-SHM) access the off-screen storage of the \
redirected (using Composite extension) window? I've tried (using \
XCompositeNameWindowPixmap + XShmCreatePixmap) and it seems that the modifying the \
memory doesn't modify window's content, so I won't post the code here. Someone may \
guess that I don't see changes because my compositor doesn't get Damage event and \
doesn't update screen, but this is not the case. I've slightly modified xcompmgr and \
try to get the SHMed Pixmap and modify it shortly before it calls XRenderComposite.

I've thought a bit and I now I'm thinking that there is should be no surprise that \
XShmCreatePixmap doesn't work. It expects segment of already allocated memory, but \
the off-screen is already allocated somewhere else.

So, if I understand everything correctly and it is not possible to directly access \
the off-screen buffer of the window, the question: what is the fastest way to access \
its contents? Using XShmCreateImage+XShmGetImage? \
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