[Differential] [Request, 202 lines] D3413: Introduce a KWin/Wayland image grabber

[graesslin (Martin Gräßlin)]

graesslin created this revision.
graesslin added reviewers: Plasma on Wayland, bgupta.
Restricted Application added a subscriber: plasma-devel.
Restricted Application added a project: Plasma on Wayland.

REVISION SUMMARY
  This new ImageGrabber makes use of the new DBus interface introduced
  with https://phabricator.kde.org/D3412 in KWin.
  
  Taking a screen shot on Wayland is significantly different to how
  screenshot taking on X11 works. No application is able to access a
  window buffer or even able to figure out which window is at a given
  mouse position.
  
  Due to that the complete interaction needs to go through the compositor.
  The only supported mode is thus window under cursor with click. There is
  no other mode available. The idea is to keep the user always under
  control of the screen shot taking - a security feature.
  
  Full screen shot or screen region shot is currently not yet supported.
  
  Explaining the dbus interaction: spectacle creates a pipe fd which gets
  passed to the compositor through the dbus call. It starts to read from
  the pipe in a dedicated thread (to keep gui thread responsive) with a
  timeout of 30 sec. Spectacle doesn't know when the user clicks, so a
  reasonable timeout is required.
  
  In case the user cancels the selection or clicks a "non window"
  spectacle cannot know that and will read an empty image from the pipe.

REPOSITORY
  rSPECTACLE Spectacle

BRANCH
  kwin-wayland

REVISION DETAIL
  https://phabricator.kde.org/D3413

AFFECTED FILES
  CMakeLists.txt
  src/CMakeLists.txt
  src/PlatformBackends/KWinWaylandImageGrabber.cpp
  src/PlatformBackends/KWinWaylandImageGrabber.h
  src/SpectacleCore.cpp

EMAIL PREFERENCES
  https://phabricator.kde.org/settings/panel/emailpreferences/

To: graesslin, #plasma_on_wayland, bgupta
Cc: plasma-devel, lesliezhai, ali-mohamed, jensreuterberg, abetts, sebas
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