This is just a mini list of "regressions" to track GTK2 behaviours that are still missing/broken in GTK3.
Most notably, these are differences since the last GTK2 release of Ubuntu MATE - which was 16.04.
Themes: Cannot change colour
GTK3's theming engine had completely changed and no longer supports this option.
You can technically modify any theme by changing its colour values in a text editor.
If you use the Ambiant-MATE family or Yaru-MATE of themes, ubuntu-mate-colours provides other colours and a mechanism to generate a custom colours if desired.
Upstream bug report requesting functionality
Treeviews: No alternate rows colours
GTK2 vs GTK3
gtk3-classic patches this! Requires an additional step.
Upstream bug report
Middle click dragging in Caja
A content menu is supposed to appear, but it currently performs the primary action (left click)
Bug reports
Scrolling over tabs
It use to be possible to scroll over tabs to change them. The feature was removed from GtkNotebook in GTK3, and as a result, every program will need to implement the same feature again.
MATE Issues (mostly fixed)
- https://github.com/mate-desktop/mate-terminal/issues/133
- https://github.com/mate-desktop/pluma/issues/271
- https://github.com/mate-desktop/caja/issues/896
- https://github.com/mate-desktop/mate-control-center/issues/445
- https://github.com/mate-desktop/mate-power-manager/issues/282
- https://github.com/mate-desktop/mate-applets/issues/398
- https://github.com/mate-desktop/mate-panel/issues/967
- https://github.com/mate-desktop/mate-media/issues/130
- https://github.com/mate-desktop/mate-system-monitor/issues/166
gtk3-classic patches this (for GtkNotebook controls)
Overlay/momentium scroll bar behaviour
Not a regression as such, but the default behaviour is debatable.
gtk3-classic patches this by changing the defaults.
Traditional dialogs for logging out / shutting down in MATE
See mate-session-manager#261, it wasn't accepted upstream, but you could patch your copy of mate-session-manager
locally and use this diff.