Visual artifacts in TerminalScreen widget when running under Mutter/GNOME Shell with transparent background about mate-terminal HOT 4 CLOSED

MATE supports running under multiple window managers. We ship Marco, and Compiz is a widely used replacement as it was in the GNOME 2 days. Gnome-shell is simply a combined window manager and panel replacement. A rendering artifact in gnome-shell implies a similar problem may be possible under other window managers too, I suspect Mutter would be affected if nothing else. Since Cinnamon is a gnome-shell fork, it too could be affected though since that fork was long ago there could be different behavior.

I just tested this, and found that on my setup (Debian Unstable) transparency did not work at all in gnome-shell, and in Cinnamon was composited to the desktop background, ignoring all windows between. Both tests were with
gnome-shell --replace and cinnamon --replace respectively, leaving caja managing the desktop

from mate-terminal.

One observation that I want to call out: the code currently does not make use of gtk_widget_app_set_paintable to effect background transparency for the screen widget. Based on discussion in #240, the upshot of the discussion seems to have been that

• solving this issue while preserving the current approach to transparency would require loading-in a CSS fix on startup for the menubar (using either a flat CSS file or gresource)
• using CSS to solve this specific issue would be a hack

I understand the reasoning and agree, but I want to note that gtk_widget_set_app_paintable is the common solution employed by a few of the major GTK3/VTE apps, including tilix, xfce4-terminal, and previously gnome-terminal*, and at least based on my own repeated testing over the past few days, transparency appears to behave as expected for all such applications under GNOME Shell. xfce4-terminal makes use of this approach without needing to load in any resources to ensure menubar opacity.

I suspect it would not be terribly difficult to re-implement this approach without needing a CSS fix for the menubar, but as an interim fix and to ensure consistent behavior, I'm not sure it's the worst possible solution.

* I use a patched gnome-terminal which restores this specific implementation to enable transparency, and I can confirm that it does not display any unusual behavior when running with transparency enabled under GNOME Shell.

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@lukefromdc Thanks very much for testing on your setup, especially confirming Cinnamon behavior.

I've pushed up #434 and am seeing desired behavior when applied to latest master. Not much to it, but any feedback regarding style, implementation, etc. is highly appreciated.

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Closing as apparently fixed by #434.

Happy to contribute further if additional/related transparency issues are surfaced.

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