KDirOperator: Use a fixed line height for scroll speed
Summary:
This patch intends to do mostly the same as D19190, but for KDirOperator.
This uses the font's line height multiplied by the amount of scroll lines
from QApplication as a scroll speed for views. This makes the scroll speed
not depend on the icon size, which greatly improves scrolling behaviour.
For more details, see the linked review.
Test Plan:
Run tests/kfilewidgettest_gui and go to a directory with a lot of items.
Scroll around, then change icon size and see that scrolling speed remains
the same.
Reviewers: ngraham, elvisangelaccio
Reviewed By: ngraham, elvisangelaccio
Subscribers: ngraham, kde-frameworks-devel
Tags: Frameworks
Differential Revision: https://phabricator.kde.org/D25683