[KDE/Mac] Qt4-Mac differences and KDE apps

[Ian Wadham]

This is to let you know that some problems in KDE apps on OS X may
be due to code accidentally using non-portable features of Qt.

Usually Qt does an excellent job of making code portable across
platforms and it is easy, when programming, to assume that the
Qt portability is perfect.  But there are occasional exceptions … :-(

Marko has just reported a bug in Palapeli (a KDE app for jigsaw
puzzles) where rubber-band selection does not work.  The pieces
are selected, but the rubber-band is invisible or severely distorted.

I noticed another case in which one of the KDE Games (KBounce)
displays a message as black-on-black and there is a similar sounding
bug (re QML Components) in Marko's list on:
https://trac.macports.org/wiki/KDEProblems

The KBounce black-on-black case is definitely down to differences in Qt4
between platforms, which in turn are down to differences in the underlying
operating system or graphics that Qt is unable to smooth over.  See:
http://qt-project.org/doc/qt-4.8/qpainter.html#CompositionMode-enum
for some fine print on an example of this, which relates to the KBounce case.

I think there have also been decisions by the Qt team not to support
every last Qt feature on every platform.  And I think maybe the way the
rubber-band is implemented in Palapeli uses one of those non-portable
features … :-(

The solution, to both types of Qt non-portability, is for the KDE author or
maintainer to re-program using some more portable feature of Qt or KDE.

Cheers, Ian W.

P.S.
I should have fixed the KBounce black-on-black problem.  I found it
about two years ago, when I was mentoring a GSoC student who was
upgrading the game, but had to postpone fixing it until after he finished.
Somehow I forgot to get back to it.  Mea culpa …

I will be addressing the Palapeli and KBounce bugs as soon as possible.
My former GSoC student is maintainer of KBounce and I am maintainer
of Palapeli … :-)