Fix app icon button in window decos with high DPI in previews.

Authored by davidedmundson on Jul 28 2017, 8:49 AM.

Description

Fix app icon button in window decos with high DPI in previews.

Summary:
With both Qt devicePixelRatio > 1 and Qt::AA_UseHighDpiPixmaps set
QIcon.pixmap() will return a bigger image than the size requested, with
the relevant devicePixelRatio set.

This code is trying to center an icon within a bounding rect, (like
QStyle::drawItemPixmap) and so positioning should use normalised pixels,
not actual pixmap pixels.

This affected Systemsettings previews but not kwin.

Reviewers: Plasma, mart

Reviewed By: Plasma, mart

Subscribers: mart, plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D6763

Details