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:
     https://bugzilla.gnome.org/show_bug.cgi?id=748498
     https://gitlab.gnome.org/GNOME/gtk/issues/550

     GTK3 windows appear with a black flash:
     https://bugzilla.gnome.org/show_bug.cgi?id=771708
     https://bugzilla.redhat.com/show_bug.cgi?id=1370791

     Black background appears briefly before window gets drawn:
     https://gitlab.gnome.org/GNOME/gtk/issues/550

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."

https://gitlab.gnome.org/GNOME/gtk/commit/2ce63a86ba689aa41eb47409c889c469497478b0

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
http://ftp.gnome.org/pub/gnome/sources/gtk+/3.22/, 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.

Best,
Elle
--
https://ninedegreesbelow.com
Color management and free/libre photography
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