D8369: Fix rendering issues of subsurfaces by using proper clipping

[Martin Flöser]

graesslin created this revision.
graesslin added reviewers: KWin, Plasma.
Restricted Application added a project: KWin.
Restricted Application added subscribers: kwin, plasma-devel.

REVISION SUMMARY
  Rendering subsurfaces in the OpenGL compositor has always resulted in
  flickering when a subsurface gets repainted and there is a window on top
  of it. Looking at the code this is rather obvious: the clipping of the
  main window is ignored and the complete subsurface is rendered as is and
  thus also rendering above windows where it should not render.
  
  This change passes the clip region and whether hardware clipping is used
  to the rendering of subsurfaces which in turn uses it for rendering the
  texture.
  
  BUG: 385924
  FIXED-IN: 5.11.2

TEST PLAN
  Opened systemsettings, went to decoration KCM, put a window
  partially above and scrolled. Without change: strong flicker, with change:
  no flicker.

REPOSITORY
  R108 KWin

BRANCH
  fix-clipping-subsurfaces-5.11

REVISION DETAIL
  https://phabricator.kde.org/D8369

AFFECTED FILES
  scene_opengl.cpp

To: graesslin, #kwin, #plasma
Cc: plasma-devel, kwin, bwowk, ZrenBot, progwolff, lesliezhai, ali-mohamed, hardening, jensreuterberg, abetts, sebas, apol, mart
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