[Gtk3] Window decoration defects with native Gtk dialogs

[brlin-tw]

Refer the following screenshots:

Notice:

• The missing shadowing at the edge of the window
• The missing transparency at the corner of the window (rendered as black)

These defects only appear in (seemingly) native Gtk dialogs, control case for comparison:

Also (somewhat) not reproduced in XFCE desktop environment, which seemingly doesn't support some GNOME 3 specific features:

[oSoMoN]

That looks similar to https://launchpad.net/bugs/1755119

[brlin-tw]

@oSoMoN
That looked exactly the same :-/ not sure why still reproduced here.

Are there known fixes for the issue?

[oSoMoN]

Yeah, not sure either… Can you confirm you're not seeing the issue with the chromium snap?

[brlin-tw]

It is reproduced in the Chromium snap as well:

[oSoMoN]

Indeed, I am seeing the issue again with the chromium snap. Re-opening the bug.
The chromium snap from the candidate/from-source channel is not affected though. An obvious difference is that the snap built from source connects to the gtk-common-themes interfaces (gtk-3-themes, icon-themes, sound-themes).

[brlin-tw]

This issue is also reproduced on my demo-gtk-common-themes snap, which is a simple snap for testing gtk-common-themes: https://github.com/Lin-Buo-Ren/demo-gtk-common-themes/blob/master/snap/snapcraft.yaml

I noticed that only the Ambiance and Radiance themes are affected, Adwaita isn't.

[oSoMoN]

@Lin-Buo-Ren: are you still seeing this issue with your snaps? I just tested again with chromium, and the issue seems to be gone.