D15071: Don't draw frames and shadows around images with an alpha channel

[Nathaniel Graham]

ngraham created this revision.
ngraham added reviewers: Frameworks, Dolphin, VDG, broulik, cfeck.
Herald added a project: Frameworks.
Herald added a subscriber: kde-frameworks-devel.
ngraham requested review of this revision.

REVISION SUMMARY
  This patch improves and simplifies the criteria for whether or not to draw a frame and a shadow around an image's thumbnail. The old size-based detection code was unreliable and gave false positives as well as false negatives. It is replaced with a simple check for whether the image has an alpha channel, which not only automatically matches all icon files, but also non-icon raster images with transparency, which look better without the frame.
  
  BUG: 258514
  FIXED-IN: 5.50

TEST PLAN
  Verified unchanged:
  
  - SVG icons still have no frame:
  
  - JPEG and PNG images without transparency still have a frame:
  
  Verified changed:
  
  - Non-icon SVG and PNG images with transparency lose their frames. The difference is especially welcome for the cases where the previous set of criteris caused many false positives for folders full of mixed image formats and sizes. For example:
  
  Before:
  
  After:
  
  Before:
  
  After:
  
  Before:
  
  After:

REPOSITORY
  R241 KIO

BRANCH
  thumbnail-frame-refinement (branched from master)

REVISION DETAIL
  https://phabricator.kde.org/D15071

AFFECTED FILES
  src/filewidgets/kfilepreviewgenerator.cpp

To: ngraham, #frameworks, #dolphin, #vdg, broulik, cfeck
Cc: kde-frameworks-devel, michaelh, ngraham, bruns
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