D4963: Add scaling support into BlurEffect::doBlur

[David Edmundson]

davidedmundson created this revision.
Restricted Application added a project: Plasma.
Restricted Application added a subscriber: plasma-devel.

REVISION SUMMARY
  This patch caputres from the framebuffer using the framebuffer's
  geometry, factoring in scale. We then keep the current normal DPI
  framebuffer causing it to downsample there.
  
  This is good because:
  
  - it keeps the code very simple
  - it's a performance optimisation. Blurring on 4k is naturally more
  
  expensive than at regular DPI. Downsampling keeps it the same - and you
  can't see a difference given it's high DPI and you're going to blur it
  anwyay.
  
  - it keeps kernel sizes somewhat resolution independent so it will look
  
  just as blurry across multiple screens.
  
  ::doCachedBlur still needs doing.

TEST PLAN
  Ran an app
  Ran the kwindowsystem blur test
  Observed the right part of the window being blurred

BRANCH
  scaling_final

REVISION DETAIL
  https://phabricator.kde.org/D4963

AFFECTED FILES
  effects/blur/blur.cpp

To: davidedmundson, #plasma
Cc: plasma-devel, progwolff, lesliezhai, ali-mohamed, jensreuterberg, abetts, sebas, apol
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