D12385: Thumbnail smooth scaling in filepicker

[Henrik Fehlauer]

rkflx accepted this revision.
rkflx added a comment.


  Thanks Kai, great questions. I think I can answer them:
  
  In D12385#250511 <https://phabricator.kde.org/D12385#250511>, @broulik wrote:
  
  > What's the performance penalty of that?
  
  
  I don't see any performance issues, both when testing the perceived performance, as well as when looking at the code.
  
  > Does the file dialog request the correct size from the preview job?
  
  It's always scaling down 128px icons (i.e. the "normal" thumbnail size) and never touches 256px icons ("large"), because 128px is the maximum setting of the slider (icon sizes verified with `qDebug`). (For HiDPI, thumbnail handling is broken like everywhere, sadly.)
  
  > It shouldn't have to end up in this codepath that often, I //think//.
  
  This code path is called once per item upon entering directories, switching view modes or changing zoom levels, as well as when hovering over an item.
  
  ---
  
  I'd say the patch is okay. We get better visuals with no perceived slow-down (maybe a theoretical performance loss, but not really relevant for those tiny thumbnails, apparently).
  
  As for the intermittent issues described above: Maybe recreating the cache due to 371e523f5d7e <https://phabricator.kde.org/R241:371e523f5d7ee0e37934135db6499eff3b976162> is the reason while comparing patched version and system version of the file dialog?

REPOSITORY
  R241 KIO

BRANCH
  image_smooth_downscale (branched from master)

REVISION DETAIL
  https://phabricator.kde.org/D12385

To: anemeth, #frameworks, #vdg, ngraham, elvisangelaccio, rkflx
Cc: cfeck, broulik, ngraham, #frameworks, michaelh, bruns
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