Summary:
KDE is known for having a strong view on the client-side decorations vs
server-side decorations issue. The main argument raised against CSD is
that desktop will look less consistent when clients start drawing window
decorations by themselves, which is somewhat true. It all ties to how
well each toolkit is integrated with the desktop environment.
KDE doesn't control the desktop market on Linux. Another big "player"
is GNOME. Both KDE and GNOME have very polarized views on in which
direction desktop should move forward. The KDE community is pushing more
toward server-side decorations while the GNOME community is pushing
more toward client-side decorations. Both communities have developed
great applications and it's not rare to see a GNOME application being
used in KDE Plasma. The only problem is that these different views are
not left behind the curtain and our users pay the price. Resizing GTK
clients in Plasma became practically impossible due to resize borders
having small hit area.
When a client draws its window decoration, it's more likely that it also
draws the drop-shadow around the decoration. The compositor must know
the extents of the shadow so things like snapping and so on work as
expected. And here lies the problem... While the xdg-shell protocol has
a way to specify such things, the NetWM spec doesn't have anything like
that. There's _GTK_FRAME_EXTENTS in the wild, however the problem with
it is that it's a proprietary atom, which is specific only to GTK apps.
Due to that, _GTK_FRAME_EXTENTS wasn't implemented because implementing
anything like that would require major changes in how we think about
geometry.
Recent xdg-shell window geometry patches adjusted geometry abstractions
in kwin to such a degree that it's very easy to add support for client
side decorated clients on X11. We just have to make sure that the
X11Client class provides correct buffer geometry and frame geometry when
the gtk frame extents are set.
Even though the X11 code is feature frozen, I still think it's worth
to have _GTK_FRAME_EXTENTS support in kwin because it will fix the resize
issues. Also, because KWin/Wayland is unfortunately far from becoming
default, it will help us with testing some implementation bits of the
window geometry from xdg-shell.
BUG: 390550
FIXED-IN: 5.18.0
Test Plan:
Things like quick tiling, maximizing, tiling scripts and so on work as
expected with GTK clients.
Reviewers: #kwin, davidedmundson
Reviewed By: #kwin, davidedmundson
Subscribers: cblack, trmdi, kwin
Tags: #kwin
Differential Revision: https://phabricator.kde.org/D24660
KWin is an easy to use, but flexible, composited Window Manager for Xorg windowing systems (Wayland, X11) on Linux. Its primary usage is in conjunction with a Desktop Shell (e.g. KDE Plasma Desktop). KWin is designed to go out of the way; users should not notice that they use a window manager at all. Nevertheless KWin provides a steep learning curve for advanced features, which are available, if they do not conflict with the primary mission. KWin does not have a dedicated targeted user group, but follows the targeted user group of the Desktop Shell using KWin as it's window manager.
KWin is not...
a standalone window manager (c.f. openbox, i3) and does not provide any functionality belonging to a Desktop Shell.
a replacement for window managers designed for use with a specific Desktop Shell (e.g. GNOME Shell)
a minimalistic window manager
designed for use without compositing or for X11 network transparency, though both are possible.
If you are an application developer having questions regarding windowing systems (either X11 or Wayland) please do not hesitate to contact us. Preferable through our mailing list. Ideally subscribe to the mailing list, so that your mail doesn't get stuck in the moderation queue.
End user
Please contact the support channels of your Linux distribution for user support. The KWin development team does not provide end user support.
Please refer to hacking documentation for how to build and start KWin. Further information about KWin's test suite can be found in TESTING.md.
Guidelines for new features
A new Feature can only be added to KWin if:
it does not violate the primary missions as stated at the start of this document
it does not introduce instabilities
it is maintained, that is bugs are fixed in a timely manner (second next minor release) if it is not a corner case.
it works together with all existing features
it supports both single and multi screen (xrandr)
it adds a significant advantage
it is feature complete, that is supports at least all useful features from competitive implementations
it is not a special case for a small user group
it does not increase code complexity significantly
it does not affect KWin's license (GPLv2+)
All new added features are under probation, that is if any of the non-functional requirements as listed above do not hold true in the next two feature releases, the added feature will be removed again.
The same non functional requirements hold true for any kind of plugins (effects, scripts, etc.). It is suggested to use scripted plugins and distribute them separately.
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