D6464: Prevent endless loop in checkGLError due to GL_CONTEXT_LOST

[Martin Flöser]

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

REVISION SUMMARY
  The GL_CONTEXT_LOST flag is not reset when calling glGetError. This of
  course bites with: "Thus, glGetError should always be called in a loop,
  until it returns GL_NO_ERROR, if all error flags are to be reset."
  (see https://www.khronos.org/registry/OpenGL-Refpages/gl4/html/glGetError.xhtml)
  
  As KWin calls checkGLError from init call it can result in a freeze of
  KWin. This is a regression reported multiple times since the release of
  5.10.3 which enabled GLX_NV_robustness_video_memory_purge extension.
  
  Please note that I am not able to test this change. I do not have an
  NVIDIA card and are not hiting the problem. I have no way to simulate
  the code. I do not know whether the change will fix the problem, it is
  based on what others do. Inspiration for this change is mostly from
  mutter: https://git.gnome.org/browse/mutter/commit/?id=d4d2bf0f6c1737256b921c4f1dedd3a95138cab9
  
  BUG: 381870
  FIXED-IN: 5.10.3.1

TEST PLAN
  See above, I can only compile check the change

REPOSITORY
  R108 KWin

BRANCH
  check-context-lost

REVISION DETAIL
  https://phabricator.kde.org/D6464

AFFECTED FILES
  libkwineffects/kwinglutils.cpp

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