Decoration (possibly) breaks gtk applications.

[developer91234]

The headerbar height increases as the gtk theme attempts to inject material window buttons into gtk.

Result: scrambled window buttons and narrow elongated buttons in the CSD. (degree of breakage depends on the theme).

(sorry I don't have a screenshot, I observed this on my previous install and don't want to break my current one). Moreover, the breakage persisted even after switching back to breeze default. Just something to keep an eye on - I could be wrong and it could have been caused by something else.

Maybe if the decoration just followed the upstream breeze style, there would be less potential for bugs (and greater visual consistency throughout the system - material style looks foreign on KDE).

[Zren]

This is probably an upstream bug in kde-gtk-config. Breeze GTK theme literally renders the buttons of this kdecoration plugin as SVGs to be used in the Breeze GTK theme. See these for details:

• ~/.config/gtk-3.0/assets/
• Issue Close, maximize and minimize buttons are very small in gtk apps with CSDs since Plasma 5.20 #22
• https://bugs.kde.org/show_bug.cgi?id=426670

When I checked checked ~/.config/gtk-3.0/assets/, the buttons seem to be properly rendered to SVG.

When I tried to reproduce this, I noticed that my GTK window decorations were stuck with breeze buttons. I ran gnome-chess from the terminal and noticed that it's now using GTK 4 in Manjaro!

$ gnome-chess 
(gnome-chess:933824): Gtk-WARNING **: 12:30:55.072: Unknown key gtk-button-images in /home/chris/.config/gtk-4.0/settings.ini
$ pacman -Ss gnome-chess
extra/gnome-chess 40.1-1 (gnome-extra) [installed]    Play the classic two-player boardgame of chess

It's likely that the migration (if there is one) from GTK 3 to GTK 4 only happens once. So it's possible that it copied some GTK 3.0 stuff to the GTK 4.0 config folder. However, it seems the kde-gtk-config is still rendering just the GTK 3.0 theme.

• https://invent.kde.org/plasma/kde-gtk-config/-/blob/master/kded/kwin_bridge/decorationpainter.cpp
• https://invent.kde.org/plasma/kde-gtk-config/-/blob/master/kded/gtkconfig.cpp#L155
• https://invent.kde.org/plasma/kde-gtk-config/-/blob/master/kded/configeditor.cpp#L154

TODO: File a new bug report at https://bugs.kde.org/buglist.cgi?list_id=1870348&product=kde-gtk-config