Review Request 115910: Screenedge show support for Clients

Martin Gräßlin mgraesslin at
Fri Feb 21 07:21:04 UTC 2014

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(Updated Feb. 21, 2014, 8:21 a.m.)

Review request for kwin and Plasma.


Adjusted to the suggested changes. It's now based on property instead of client messages, which means:
* survives KWin restart
* supports self restoring from Client (see adjusted test app)
* uses a protocol to specify the edge

Repository: kde-workspace

Description (updated)

Screenedge show support for Clients

This provides a new protocol intended to be used by auto-hiding panels
to make use of the centralized screen edges. To use it a Client can
set an X11 property of type _KDE_NET_WM_SCREEN_EDGE_SHOW to KWin.
As value it takes:
* 0: top edge
* 1: right edge
* 2: bottom edge
* 3: left edge

KWin will hide the Client (hide because unmap or minimize would break
it) and create an Edge. If that Edge gets triggered the Client is shown
again and the property gets deleted. If the Client doesn't border the
specified screen edge the Client gets shown immediately so that we
never end in a situation that we cannot unhide the auto-hidden panel
again. The exact process is described in the documentation of
ScreenEdges. The Client can request to be shown again by deleting the

If KWin gets restarted the state is read from the property and it is
tried to create the edge as described.

As this is a KWin specific extension we need to discuss what it means
for Clients using this feature with other WMs: it does nothing. As
the Client gets hidden by KWin and not by the Client, it just doesn't
get hidden if the WM doesn't provide the feature. In case of an
auto-hiding panel this seems like a good solution given that we don't
want to hide it if we cannot unhide it. Of course there's the option
for the Client to provide that feature itself and if that's wanted we
would need to announce the feature in the _NET_SUPPORTED atom. At the
moment that doesn't sound like being needed as Plasma doesn't want to
provide an own implementation.

The implementation comes with a small test application showing how
the feature is intended to be used.

Diffs (updated)

  kwin/screenedge.h 60f5fd669ccc5eb627feffa460552558d1765b31 
  kwin/screenedge.cpp 04cf0d6d5262ab84d88559b6dc85e099efec77bf 
  kwin/tests/CMakeLists.txt 3fa16f21c617a8f4b39b2bbd39b534b6a11e8d14 
  kwin/tests/screenedgeshowtest.cpp PRE-CREATION 
  kwin/atoms.h 1690067c5d1da59f38f9e77ef64eacfbc1faa0cf 
  kwin/atoms.cpp 904f5efe4a32e3673dae9e6da92bf4336def660d 
  kwin/client.h 6a0dbe4f45f9bb6c58de8c045488cec990e95118 
  kwin/client.cpp 36431bfc33418a207de12fa8cc95a35539256366 
  kwin/events.cpp 1fa6e425d4dac7d661612e5d090c3c9c8f4b1a18 
  kwin/manage.cpp 3e385cd6aeceee3c3bff4e09be2aee130856201f 




Martin Gräßlin

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