D27788: Implement EGL_KHR_partial_update and EGL_EXT_swap_buffers_with_damage

[Vlad Zahorodnii]

zzag added a comment.


  The key point about EGL_KHR_partial_update is that the compositor know what parts of the back buffer are going to be updated. So the compositor could specify the damage region _beforehand_ recording command buffers. If the compositor doesn't have a sophisticated effects pipeline, e.g. weston, then it's pretty trivial to determine the buffer damage, but that's not the case for us, unfortunately.
  
  Ideally, a compositing cycle must be split into several phases - pre paint, paint, and maybe post paint. In the pre paint phase, the compositor would do necessary bookkeeping so we know what the damage region for the next frame is.
  
  I really like the idea of having a hook that is called when the scene is about to start recording a command buffer for the next frame, but given the current design of the effects pipeline I am starting to think that we cannot support EGL_KHR_partial_update at the moment. The dirty region for the next frame is computed too late and I don't see how we can fix it because effects have the final say in what area of the screen will be repainted. :/
  
  I would love to be proven wrong, though.

REPOSITORY
  R108 KWin

REVISION DETAIL
  https://phabricator.kde.org/D27788

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