D7440: Turn on Dolphin icon previews by default

[Mark Gaiser]

markg added a comment.


  With all the thumbnailers you turned on, i'd be against it.
  It's probably not going to slow down scrolling speed because the thumbnail generation is done in another process. Thankfully! Otherwise you would be horrible slow :)
  But on large folders it will have an impact on the CPU i think.
  
  But i personally don't like how dolphin handles thumbnailing.
  What it does is:
  
  - Thumbnail the current viewport (so that all you "currently" see is thumbnailed
  - Then stop
  
  If you scroll a bit it does it again. Files that don't have a thumbnail yet are thumbnailed then.
  
  This leads to a very annoying scroll behavior (could just be me...). I tend to scroll a bit, let it generate the thumbnails and scroll a bit further till everything is done.
  Granted, this is only the first time when there are no thumbnails.
  That scrolling i do is only needed because dolphin doesn't do it otherwise.
  
  What i think needs to happen is this:
  
  1. Dolphin should thumbnail the current viewport (it does, no change needed here)
  2. Then continue on with rows above and below it till it's done. OR
  3. If i pump to another part of the view, it should abort the task it had and restart from the new current viewport
  4. In any case, thumbnail everything in a given folder on the background (obviously)
  
  This probably does give another concern.. Like when to stop thumbnailing and the size.
  I don't think size is an issue. When to stop might be, i'd say on a folder change or app exit.
  
  Lastly, there is a performance issue in thumbnailing. I had downloaded a ~4GB file with 1000 QHD wallpapers, just to see how fast it would generate those thumbnails.
  They were all JPG files and roughly 4MB per file. The speed was... not stellar, which is really surprising! My SSD can read about 120 of those files a second (it really can, i tested that!)! Yet the thumbnails only seems to be appearing at a rate of ~10/second (just by looking at it, no specific benchmarks have been done). That tells me that there is lots of room to speed this up! I think that needs to happen first before enabling this, to give the best possible experience to the user.

REPOSITORY
  R318 Dolphin

REVISION DETAIL
  https://phabricator.kde.org/D7440

To: ngraham, #dolphin, #kde_applications, #vdg
Cc: markg, broulik, anthonyfieroni, davidedmundson, ltoscano, dfaure, elvisangelaccio, #konqueror, navarromorales, firef, andrebarros, emmanuelp
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