D19190: [RFC] Improve scroll wheel speed

[Nathaniel Graham]

ngraham created this revision.
ngraham added reviewers: Dolphin, elvisangelaccio.
Herald added a project: Dolphin.
Herald added a subscriber: kfm-devel.
ngraham requested review of this revision.

REVISION SUMMARY
  Dolphin currently scrolls by the height of three items at a time per "step" when
  using a scroll wheel. Because item height is highly variable, this leads to scroll
  speed being inconsistent between views, and generally far too fast when using
  icon view with icons larger than 22px size.
  
  This patch makes the size of the scroll step consistent at roughly the height of
  three text labels + their padding, which feels much better to me when using a
  scroll wheel mouse, and better matches the scroll speed in other KDE apps.
  
  RFC because currently the step size is determined using a magic number, when it
  should really use a multiple of the the item labels' fontmetrics height. I 
  couldn't figure out how to do that though. Help is appreciated.
  
  BUG: 386379
  FIXED-IN: 19.04.0

TEST PLAN
  Use a mouse with a scroll wheel and scroll in Dolphin item views with list view, 
  details view, icon view, etc, using different item sizes. Speed should be 
  consistent in all views now, and also feel consistent with other KDE apps.
  
  Also try with multiple scale factors to make sure the behavior does not change.

REPOSITORY
  R318 Dolphin

BRANCH
  improve-scrollwheel-speed (branched from master)

REVISION DETAIL
  https://phabricator.kde.org/D19190

AFFECTED FILES
  src/kitemviews/kitemlistcontainer.cpp

To: ngraham, #dolphin, elvisangelaccio
Cc: kfm-devel, alexde, feverfew, spoorun, navarromorales, firef, andrebarros, emmanuelp, mikesomov
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