QPainter logs in stdout

[Thomas Lübking]

The backtrace hints that paintEvent is called from the eventdispatcher. That's 
probably not it. The painter is simply not opened on the widget (viewport) the 
paintevent was called for (scrollarea) - w/o some special treatment (i don't 
see) that won't work.

Am Monday 18 January 2010 schrieb Ingo Klöcker:
> On Monday 18 January 2010, Thiago Macieira wrote:
> > Em Segunda-feira 18. Janeiro 2010, às 20.50.12, Jaime Torres escreveu:
> > > I have much more info now.
> > >
> > > I've modified Qt4.6.1 (yes, installed in /usr/lib/qt4.5) to include
> > > a kbactrace after every qwarning in QPaint, and here you are why it
> > > happens. But I get lost and can not fix it.
> > >
> > >
> > > QPainter::begin: Widget painting can only begin as a result of a
> > > paintEvent [
> > > 0: /usr/lib/qt4.5/lib/libQtGui.so.4 [0x7fe439a965d8]
> > > 1:
> > > /usr/lib/qt4.5/lib/libQtGui.so.4(_ZN8QPainter5beginEP12QPaintDevice
> > >+0x5ea) [0x7fe439a9ba9a] 2:
> > > /usr/lib/qt4.5/lib/libQtGui.so.4(_ZN8QPainterC1EP12QPaintDevice+0x1
> > >46) [0x7fe439a9c206] 3:
> > > /opt/kde4/lib/libkhtml.so.5(_ZN9KHTMLView10paintEventEP11QPaintEven
> > >t+0x39) [0x7fe429d4fd99] 4:
> > > /opt/kde4/lib/libkhtml.so.5(_ZN9KHTMLView13viewportEventEP6QEvent+0
> > >xfa) [0x7fe429d4841a] 5:
> > > /usr/lib/qt4.5/lib/libQtCore.so.4(_ZN23QCoreApplicationPrivate29sen
> > >dThroug hObjectEventFiltersEP7QObjectP6QEvent+0xc0) [0x7fe43af16900]
> > > 6:
> >
> > Here's the same as a backtrace in gdb. To reproduce:
> >
> > QT_FATAL_WARNINGS=1 konqueror http://qt.nokia.com
> >
> > As you can see from the backtrace, KHTMLView::viewportEvent creates a
> > QPaintEvent and calls paintEvent. That's what causes the issue.
> >
> > However, given the documentation for
> > QAbstractScrollArea::viewportEvent as well as the implementation in
> > Qt, it would seem that paint events are allowed.
> 
> Is this supposed to trigger an immediate repaint? If yes, then IIRC in a
> similar situation (on Windows) we also tried to use paintEvent(). It
> didn't work. After digging into Qt's sources we finally resorted to
> something like
>   QEvent event( QEvent::UpdateRequest );
>   QCoreApplication::postEvent( viewport, &event );
> instead.
> 
> 
> Regards,
> Ingo
>