D22498: Introduce a simple frame rendered statistic

graesslin created this revision.
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REVISION SUMMARY
  One of the main gripes with KWin's composite support over the years is
  for me the FPS effect. For developers it doesn't provide useful
  information as it triggers constant repaints. This just doesn't match
  how KWin actually renders. For users it's also not a good solution as it
  shows multiple problems:
  
  - due to being graphical it influences the measurement
  - it is capped at 100 Hz which is not sufficient for 144 Hz screens
  - it is integrated into the effects system which is not deep enough to
  
  properly measure
  
  While the 100 Hz problem is solvable the general problem remains: the
  fps effect is not showing the reality and this is unsolvable. Also we
  see that users reference this effect a lot in bug reports and this is to
  me a problem.
  
  With this patch I try to address the problem by properly recording the
  rendered frames in the compositor. It's kept simple and just puts the
  timestamp in a queue with a max size of 5 sec at 144 Hz. In practice
  this captures a longer time frame as KWin doesn't render that many
  frames.
  
  For a start the information is put into support information, but not as
  fps. Fps makes IMHO no sense in KWin. So it shows the number of frames
  and the duration in msec. A user could calculate the fps from it, but as
  said, that's pretty useless. To indicate this an explanation text is
  added.
  
  The chosen architecture allows to do more in future. One could for
  example extract the framerate of the last second or constantly updating
  the fps as a sliding average. The current implementation is inspired by
  glxgears which just prints out the number of frames over the last five
  seconds.

REPOSITORY
  R108 KWin

BRANCH
  frame-rendered-statistics

REVISION DETAIL
  https://phabricator.kde.org/D22498

AFFECTED FILES
  CMakeLists.txt
  composite.cpp
  composite.h
  frame_statistics.cpp
  frame_statistics.h
  workspace.cpp

To: graesslin, #kwin
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