Improve documentation of area classes
This shall improve the documentation of several area classes,
including NormalizedPoint, NormalizedRect, RegularArea, RegularAreaRect.
This shall also clarify when absolute coordinates and when normalized
coordinates are used.
Describes the normalized coordinate system in NormalizedPoint, with a new term “reference area” do describe mapping.
Page view rotation.
This is not done consistently in Okular, but can be changed later. I think this documentation will help (me) with that then.
Test Plan: Run doxygen
Reviewers: Okular, aacid
Reviewed By: Okular, aacid
Subscribers: aacid, okular-devel
Differential Revision: https://phabricator.kde.org/D21266