GTK3 "empty black window"/"black flash" bug that affects GIMP-2.99

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GTK3 "empty black window"/"black flash" bug that affects GIMP-2.99

Elle Stone
Hi All,

This is just an FYI for anyone who encounters the issue and doesn't
already know about this bug.

There is a long-standing GTK3 bug - that's recently been fixed in GTK
git master - that does affect GIMP-2.99. I noticed it yesterday when I
tried for the first time to use GIMP-2.99 for actual editing.

This bug causes an empty black window to briefly appear when opening
editing dialog windows such as "Filters/Blur/Gaussian Blur".

FWIW, this GTK3 bug was reported back in 2015 for GTK3 version 3.22.x,
and there is a trail of bug reports on various OS's running various
desktops, including:

     Black background appears briefly before window gets drawn:

     GTK3 windows appear with a black flash:

     Black background appears briefly before window gets drawn:

The fix was committed here, three months ago:

     x11: Set a transparent background on windows by default
     "This avoids black flicker on compositing WMs when a window is
first shown."

I noticed the "empty black window" bug when opening GIMP-2.99 editing
dialogs such as "Curves" and "Gaussian Blur", on both Gentoo (updated a
couple of week ago) and OpenSUSE Tumbleweed (updated today). Both of
these OS's use GTK3 version 3.30.

Checking the latest 3.30 tarball from, it appears the fix
hasn't been incorporated into any actual GTK3 releases.

So I downloaded the latest GTK3 tarball, applied the fix (involves
adding a couple of extra lines of code to gdk/x11/gdkwindow-x11.c), and
compiled/installed it in my GIMP-2.99 prefix. This fix does indeed get
rid of the "black flash" problem.

Color management and free/libre photography
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