Compatibility problems with latest GTK+ applications
mgraesslin at kde.org
Wed May 7 09:11:37 BST 2014
I need some advice. The new GTK+ release introduced and enforces client-side-
decorations (CSD) and that is causing severe compatibility problems with
Plasma Workspaces (especially the stable release which we cannot adjust any
more). I'll give a list of issues below.
I'm not sure what we can do about it. I think we need to do something about
it, because this looks like a road back to "GTK apps can only be used in GNOME
Shell" resulting in "KDE apps can only be used in Plasma". Because of that I
think the compatibility problems matters to everyone also our application
developers. I think the right thing is to contact the GTK+ developers and
point out the problems, but I am probably the wrong person for it as I'm a
known opponent of CSD and fear that my feedback would be ignored. As a
fallback strategy we could enforce server-side-decorations (SSD) for all GTK+
applications which would look strange  but at least no loss in
Of course there are things we can do in KWin to improve compatibility, but
4.11 is feature frozen and these would require new code and we have certainly
more important things to do than to fix client breakage (we don't do that in
It would be way easier if GTK+ would detect whether the environment supports
CSD and use a normal application design if that's not supported. This would
not only be relevant for us, but especially for tiling window managers.
List of issues I noticed:
* A hung window can no longer be closed or moved. Technical explanation: there
is a ping protocol to detect hung applications. KWin only sends ping requests
when the window is being closed from the window manager (e.g. decoration close
button or Alt+F4).
* quick tiling broken, see . It includes the shadow in calculation.
* black shadows around window if compositing gets disabled after the window
got opened . Technical explanation: GTK+ doesn't detect that compositing
gets enabled/disabled. Other direction is broken, too.
* double borders if window gets opened when compositing is disabled .
Technical explanation: GTK+ uses the Motif Window Manager Hints to tell how
the decoration should look like. KWin is not the Motif Window Manager and does
not fully support the hints. Fun fact our code has a comment that we follow
Metacity to only support those hints which are not stupid.
* double border if decorations on KWin side are enforced  (Alt+F3 -> More
Actions -> No Border). Technical explanation: GTK+ doesn't detect the re-
parenting and doesn't hide it's own deco and shadow
* Wrong resize cursor is shown on edges 
* Windows don't have a maximize and minimize button although configured in the
* Incorrect drag delay: KWin uses either a drag delay on distance or on time
for starting move or resize. GTK+ only has a drag delay on distance for moving
and none for resizing. That's an important accessibility feature to have that
* Windows can no longer be shaded
* Windows can no longer be put into window tabs
* Dialogs don't have a close button  (unless run without compositing)
* Ignores the configured mouse actions, uses (hard coded?) actions. Defaulting
to lower window on middle click while we use window tab drag on middle click
* no visual distinction between active and inactive application
* Broken window snapping: window snaps to shadow 
* Mismatching application window menu . Note our menu could be invoked
through DBus. I consider this as a big problem as that's the only way to e.g.
add windows to activities (which is also broken now) or to access the advanced
window manager features GNOME doesn't know of.
That list I figured out in less than 10 min usage of a new GTK+ application. I
assume and fear that the list is much longer.
Any advice on how to handle this situation is appreciated.
-------------- next part --------------
A non-text attachment was scrubbed...
Size: 198 bytes
Desc: This is a digitally signed message part.
More information about the kde-core-devel