Summary:
Building upon the generic X Selection support this patch establishes another
selection class representing the XDND selection and provides interfaces
to communicate drags originating from Xwayland windows to the Wayland
server KWin and drags originating from Wayland native drags to Xwayland.
For Wayland native drags KWin will claim the XDND selection as owner and
will simply translate all relevant events to the XDND protocol and receive
alike messages by X clients.
When an X client claims the XDND selection KWin is notified via the X protocol
and it decides if it allows the X drag to transcend into the Wayland protocol.
If this is the case the mouse position is tracked and on entering a Wayland
native window a proxy X Window is mapped to the top of the window stack. This
proxy window acts as a drag destination for the drag origin window and again
X messages will be translated into respective Wayland protocol calls. If the
cursor leaves the Wayland window geometry before a drop is registered, the
proxy window is unmapped, what triggers a subsequent drag leave event.
In both directions the necessary core integration is minimal. There is a single
call to be done in the drag and drop event filter through the Xwayland
interface class.
From my tests this patch facilitates drags between any Qt/KDE apps. What needs
extra care are the browsers, which use target formats, that are not directly
compatible with the Wayland protocol's MIME representation. For Chromium an
additional integration step must be done in order to provide it with a net
window stack containing the proxy window.
Test Plan: Manually. Auto tests planned.
Reviewers: #kwin
Subscribers: zzag, kwin, alexde
Tags: #kwin
Maniphest Tasks: T4611
Differential Revision: https://phabricator.kde.org/D15627
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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