D29131: [scene] Generate window quads for sub-surfaces

zzag created this revision.
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REVISION SUMMARY
  No window quads are generated for sub-surfaces right now. This means that
  effects that operate on window quads are not able to transform
  sub-surfaces. Furthermore, the OpenGL scene needs window quads to clip
  windows without using the scissor test.
  
  The best (imho) way to render sub-surfaces would be with some help from a
  scene graph. Unfortunately, KDE hasn't developed any scene graph
  implementation that we could plug inti kwin and let the scene graph do
  its magic. As a short term solution, this patch adjusts relevant parts of
  the scene to make it generate window quads for sub-surfaces.
  
  In order to build window quads, we traverse the current window pixmap
  tree in DFS manner. When we enter a pixmap, we generate window quads. An
  id is assigned to each quad that can be later used to match a list of
  window quads against some particular window pixmap.
  
  With the proposed change, no changes to effects are required. Effects see
  window quads for sub-surfaces as regular WindowQuadContents quads.
  
  Cross-fading is still kind of broken. In order to cross-fade between two
  window pixmap trees, we need to render each tree in a texture, then
  cross-fade between those two textures in a shader. Unfortunately, this is
  not easy to do with the current design, so I only left a FIXME comment.
  Although it should be pretty straightforward with a scene graph.
  
  BUG: 387313

TEST PLAN
  Enabled the wobbly windows effect, moved weston-subsurfaces
  around on the screen.

REPOSITORY
  R108 KWin

BRANCH
  subsurface-quads

REVISION DETAIL
  https://phabricator.kde.org/D29131

AFFECTED FILES
  CMakeLists.txt
  platformsupport/scenes/opengl/abstract_egl_backend.cpp
  plugins/scenes/opengl/scene_opengl.cpp
  plugins/scenes/opengl/scene_opengl.h
  plugins/scenes/qpainter/scene_qpainter.cpp
  plugins/scenes/qpainter/scene_qpainter.h
  scene.cpp
  scene.h
  subsurfacemonitor.cpp
  subsurfacemonitor.h

To: zzag, #kwin
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