Hmmm... the ScrollAreas ::paintEvent() opens the painter on it's viewprt 
::widget(), but i don't grep special Qt::WA_WState_InPaintEvent handling for 
QAbstractScrollArea (or any gui/widgets) - sure that's legal?

I mean, shouldn't the paint code be reimplemented in the actual viewport 
widget then? (i.e. in viewportEvent what oddly seems to be 
KHTMLView::widgetEvent(QEvent* e))

In doubt you could just un/set the Attribute around the painting, but afaik 
that's no very good idea...

Thomas

Am Monday 18 January 2010 schrieb Thiago Macieira:
> 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+0x146)
> > [0x7fe439a9c206] 3:
> > /opt/kde4/lib/libkhtml.so.5(_ZN9KHTMLView10paintEventEP11QPaintEvent+0x39
> >) [0x7fe429d4fd99] 4:
> > /opt/kde4/lib/libkhtml.so.5(_ZN9KHTMLView13viewportEventEP6QEvent+0xfa)
> > [0x7fe429d4841a] 5:
> > /usr/lib/qt4.5/lib/libQtCore.so.4(_ZN23QCoreApplicationPrivate29sendThrou
> >g 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.
> 
> This is where I get lost
> 
> #9  0xb6dbc837 in qt_message_output (msgType=QtWarningMsg, buf=0x977ae98
> "QPainter::begin: Widget painting can only begin as a result of a
>  paintEvent") at
>  /home/thiago/src/troll/qt-4.6/src/corelib/global/qglobal.cpp:2227 #10
>  0xb6dbc9f9 in qt_message (msgType=QtWarningMsg, msg=0xb6a6aeac
>  "QPainter::begin: Widget painting can only begin as a result of a
>  paintEvent", ap=0xbf8eda74 "��\216�")
>     at /home/thiago/src/troll/qt-4.6/src/corelib/global/qglobal.cpp:2273
> #11 0xb6dbca81 in qWarning (msg=0xb6a6aeac "QPainter::begin: Widget
>  painting can only begin as a result of a paintEvent") at
> /home/thiago/src/troll/qt-4.6/src/corelib/global/qglobal.cpp:2355
> #12 0xb63d6aa4 in QPainter::begin (this=0xbf8edc54, pd=0x94594b8) at
> /home/thiago/src/troll/qt-4.6/src/gui/painting/qpainter.cpp:1799
> #13 0xb63d583f in QPainter (this=0xbf8edc54, pd=0x94594b8) at
> /home/thiago/src/troll/qt-4.6/src/gui/painting/qpainter.cpp:1480
> #14 0xb335c6a5 in KHTMLView::paintEvent (this=0x94688e0, e=0xbf8edcfc) at
> /home/tmacieir/src/kde4/KDE/kdelibs/khtml/khtmlview.cpp:878
> #15 0xb33639cc in KHTMLView::viewportEvent (this=0x94688e0, e=0xbf8ee2a8)
>  at /home/tmacieir/src/kde4/KDE/kdelibs/khtml/khtmlview.cpp:2129
> #16 0xb67e073b in QAbstractScrollAreaPrivate::viewportEvent
>  (this=0x9468ea8, event=0xbf8ee2a8) at
> /home/thiago/src/troll/qt-4.6/src/gui/widgets/qabstractscrollarea_p.h:100
> #17 0xb67e0822 in QAbstractScrollAreaFilter::eventFilter (this=0x94584a0,
> o=0x8ebd098, e=0xbf8ee2a8) at
> /home/thiago/src/troll/qt-4.6/src/gui/widgets/qabstractscrollarea_p.h:116
> #18 0xb6edea1f in QCoreApplicationPrivate::sendThroughObjectEventFilters
> (this=0x8aa98b0, receiver=0x8ebd098, event=0xbf8ee2a8)
>     at
> /home/thiago/src/troll/qt-4.6/src/corelib/kernel/qcoreapplication.cpp:819
> #19 0xb6245c8e in QApplicationPrivate::notify_helper (this=0x8aa98b0,
> receiver=0x8ebd098, e=0xbf8ee2a8) at
> /home/thiago/src/troll/qt-4.6/src/gui/kernel/qapplication.cpp:4294
> #20 0xb6245b17 in QApplication::notify (this=0xbf8f0b5c,
>  receiver=0x8ebd098, e=0xbf8ee2a8) at
> /home/thiago/src/troll/qt-4.6/src/gui/kernel/qapplication.cpp:4263
> #21 0xb7521497 in KApplication::notify (this=0xbf8f0b5c,
>  receiver=0x8ebd098, event=0xbf8ee2a8) at
> /home/tmacieir/src/kde4/KDE/kdelibs/kdeui/kernel/kapplication.cpp:302
> #22 0xb6ede741 in QCoreApplication::notifyInternal (this=0xbf8f0b5c,
> receiver=0x8ebd098, event=0xbf8ee2a8) at
> /home/thiago/src/troll/qt-4.6/src/corelib/kernel/qcoreapplication.cpp:704
> #23 0xb6248475 in QCoreApplication::sendSpontaneousEvent
>  (receiver=0x8ebd098, event=0xbf8ee2a8) at
> ../../include/QtCore/../../../../../src/troll/qt-4.6/src/corelib/kernel/qco
> reapplication.h:218 #24 0xb62aa437 in QWidgetPrivate::drawWidget
>  (this=0x9421e98, pdev=0x8f8a7d4, rgn=@0xbf8ee408, offset=@0xbf8ee454,
>  flags=4, sharedPainter=0x0,
> backingStore=0x8f8a818)
>     at /home/thiago/src/troll/qt-4.6/src/gui/kernel/qwidget.cpp:5322
> #25 0xb62aace1 in QWidgetPrivate::paintSiblingsRecursive (this=0x9468ea8,
> pdev=0x8f8a7d4, siblings=@0x9468eb4, index=0, rgn=@0xbf8ee628,
> offset=@0xbf8ee674, flags=4, sharedPainter=0x0,
>     backingStore=0x8f8a818) at
> /home/thiago/src/troll/qt-4.6/src/gui/kernel/qwidget.cpp:5435
> #26 0xb62aa8a1 in QWidgetPrivate::drawWidget (this=0x9468ea8,
>  pdev=0x8f8a7d4, rgn=@0xbf8ee628, offset=@0xbf8ee674, flags=4,
>  sharedPainter=0x0,
> backingStore=0x8f8a818)
>     at /home/thiago/src/troll/qt-4.6/src/gui/kernel/qwidget.cpp:5371
> #27 0xb62aace1 in QWidgetPrivate::paintSiblingsRecursive (this=0x946c7e0,
> pdev=0x8f8a7d4, siblings=@0x946c7ec, index=2, rgn=@0xbf8ee848,
> offset=@0xbf8ee894, flags=4, sharedPainter=0x0,
>     backingStore=0x8f8a818) at
> /home/thiago/src/troll/qt-4.6/src/gui/kernel/qwidget.cpp:5435
> #28 0xb62aa8a1 in QWidgetPrivate::drawWidget (this=0x946c7e0,
>  pdev=0x8f8a7d4, rgn=@0xbf8ee848, offset=@0xbf8ee894, flags=4,
>  sharedPainter=0x0,
> backingStore=0x8f8a818)
>     at /home/thiago/src/troll/qt-4.6/src/gui/kernel/qwidget.cpp:5371
> #29 0xb62aace1 in QWidgetPrivate::paintSiblingsRecursive (this=0x8ec42d8,
> pdev=0x8f8a7d4, siblings=@0x8ec42e4, index=0, rgn=@0xbf8eea68,
> offset=@0xbf8eeab4, flags=4, sharedPainter=0x0,
>     backingStore=0x8f8a818) at
> /home/thiago/src/troll/qt-4.6/src/gui/kernel/qwidget.cpp:5435
> #30 0xb62aa8a1 in QWidgetPrivate::drawWidget (this=0x8ec42d8,
>  pdev=0x8f8a7d4, rgn=@0xbf8eea68, offset=@0xbf8eeab4, flags=4,
>  sharedPainter=0x0,
> backingStore=0x8f8a818)
>     at /home/thiago/src/troll/qt-4.6/src/gui/kernel/qwidget.cpp:5371
> #31 0xb62aace1 in QWidgetPrivate::paintSiblingsRecursive (this=0x8ebd7e8,
> pdev=0x8f8a7d4, siblings=@0x8ebd7f4, index=0, rgn=@0xbf8eec88,
> offset=@0xbf8eecd4, flags=4, sharedPainter=0x0,
>     backingStore=0x8f8a818) at
> /home/thiago/src/troll/qt-4.6/src/gui/kernel/qwidget.cpp:5435
> #32 0xb62aa8a1 in QWidgetPrivate::drawWidget (this=0x8ebd7e8,
>  pdev=0x8f8a7d4, rgn=@0xbf8eec88, offset=@0xbf8eecd4, flags=4,
>  sharedPainter=0x0,
> backingStore=0x8f8a818)
>     at /home/thiago/src/troll/qt-4.6/src/gui/kernel/qwidget.cpp:5371
> #33 0xb62aace1 in QWidgetPrivate::paintSiblingsRecursive (this=0x8ec20b0,
> pdev=0x8f8a7d4, siblings=@0x8ec20bc, index=0, rgn=@0xbf8eeea8,
> offset=@0xbf8eeef4, flags=4, sharedPainter=0x0,
>     backingStore=0x8f8a818) at
> /home/thiago/src/troll/qt-4.6/src/gui/kernel/qwidget.cpp:5435
> #34 0xb62aa8a1 in QWidgetPrivate::drawWidget (this=0x8ec20b0,
>  pdev=0x8f8a7d4, rgn=@0xbf8eeea8, offset=@0xbf8eeef4, flags=4,
>  sharedPainter=0x0,
> backingStore=0x8f8a818)
>     at /home/thiago/src/troll/qt-4.6/src/gui/kernel/qwidget.cpp:5371
> #35 0xb62aace1 in QWidgetPrivate::paintSiblingsRecursive (this=0x8b90b10,
> pdev=0x8f8a7d4, siblings=@0x8b90b1c, index=48, rgn=@0xbf8ef168,
> offset=@0x8f8a83c, flags=4, sharedPainter=0x0,
>     backingStore=0x8f8a818) at
> /home/thiago/src/troll/qt-4.6/src/gui/kernel/qwidget.cpp:5435
> #36 0xb62aa8a1 in QWidgetPrivate::drawWidget (this=0x8b90b10,
>  pdev=0x8f8a7d4, rgn=@0xbf8ef168, offset=@0x8f8a83c, flags=5,
>  sharedPainter=0x0,
> backingStore=0x8f8a818)
>     at /home/thiago/src/troll/qt-4.6/src/gui/kernel/qwidget.cpp:5371
> #37 0xb64b882c in QWidgetBackingStore::sync (this=0x8f8a818) at
> /home/thiago/src/troll/qt-4.6/src/gui/painting/qbackingstore.cpp:1291
> #38 0xb62a108e in QWidgetPrivate::syncBackingStore (this=0x8b90b10) at
> /home/thiago/src/troll/qt-4.6/src/gui/kernel/qwidget.cpp:1663
> #39 0xb62b208c in QWidget::event (this=0x8b90920, event=0xbf8efab4) at
> /home/thiago/src/troll/qt-4.6/src/gui/kernel/qwidget.cpp:8272
> #40 0xb67553fa in QMainWindow::event (this=0x8b90920, event=0xbf8efab4) at
> /home/thiago/src/troll/qt-4.6/src/gui/widgets/qmainwindow.cpp:1435
> #41 0xb761664c in KMainWindow::event (this=0x8b90920, ev=0xbf8efab4) at
> /home/tmacieir/src/kde4/KDE/kdelibs/kdeui/widgets/kmainwindow.cpp:1103
> #42 0xb7659468 in KXmlGuiWindow::event (this=0x8b90920, ev=0xbf8efab4) at
> /home/tmacieir/src/kde4/KDE/kdelibs/kdeui/xmlgui/kxmlguiwindow.cpp:131
> #43 0xb7ef0060 in KonqMainWindow::event (this=0x8b90920, e=0xbf8efab4) at
> /home/tmacieir/src/kde4/KDE/kdebase/apps/konqueror/src/konqmainwindow.cpp:5
> 639 #44 0xb6245cb2 in QApplicationPrivate::notify_helper (this=0x8aa98b0,
>  receiver=0x8b90920, e=0xbf8efab4) at
> /home/thiago/src/troll/qt-4.6/src/gui/kernel/qapplication.cpp:4298
> #45 0xb6245b17 in QApplication::notify (this=0xbf8f0b5c,
>  receiver=0x8b90920, e=0xbf8efab4) at
> /home/thiago/src/troll/qt-4.6/src/gui/kernel/qapplication.cpp:4263
> #46 0xb7521497 in KApplication::notify (this=0xbf8f0b5c,
>  receiver=0x8b90920, event=0xbf8efab4) at
> /home/tmacieir/src/kde4/KDE/kdelibs/kdeui/kernel/kapplication.cpp:302
> #47 0xb6ede741 in QCoreApplication::notifyInternal (this=0xbf8f0b5c,
> receiver=0x8b90920, event=0xbf8efab4) at
> /home/thiago/src/troll/qt-4.6/src/corelib/kernel/qcoreapplication.cpp:704
> #48 0xb6ee2219 in QCoreApplication::sendEvent (receiver=0x8b90920,
> event=0xbf8efab4) at
> ../../include/QtCore/../../../../../src/troll/qt-4.6/src/corelib/kernel/qco
> reapplication.h:215 #49 0xb64b51e7 in sendUpdateRequest (widget=0x8b90920,
>  updateImmediately=true) at
>  /home/thiago/src/troll/qt-4.6/src/gui/painting/qbackingstore.cpp:503 #50
>  0xb64b5cbb in QWidgetBackingStore::markDirty (this=0x8f8a818,
> rect=@0xbf8efbd0, widget=0x94594b0, updateImmediately=true,
> invalidateBuffer=false)
>     at /home/thiago/src/troll/qt-4.6/src/gui/painting/qbackingstore.cpp:641
> #51 0xb62b4c3b in QWidget::repaint (this=0x94594b0, rect=@0xbf8efbd0) at
> /home/thiago/src/troll/qt-4.6/src/gui/kernel/qwidget.cpp:10015
> #52 0xb62b4b0d in QWidget::repaint (this=0x94594b0, x=0, y=0, w=1244,
>  h=649) at /home/thiago/src/troll/qt-4.6/src/gui/kernel/qwidget.cpp:9992
> #53 0xb335c241 in KHTMLView::repaintContents (this=0x94688e0, x=0, y=0,
> w=1244, h=649) at
>  /home/tmacieir/src/kde4/KDE/kdelibs/khtml/khtmlview.cpp:805 #54 0xb335c2b2
>  in KHTMLView::repaintContents (this=0x94688e0, r=@0xbf8efccc) at
>  /home/tmacieir/src/kde4/KDE/kdelibs/khtml/khtmlview.cpp:810
> #55 0xb336f0d5 in KHTMLView::timerEvent (this=0x94688e0, e=0xbf8f0694) at
> /home/tmacieir/src/kde4/KDE/kdelibs/khtml/khtmlview.cpp:4210
> #56 0xb6ef5e26 in QObject::event (this=0x94688e0, e=0xbf8f0694) at
> /home/thiago/src/troll/qt-4.6/src/corelib/kernel/qobject.cpp:1204
> #57 0xb62b27b2 in QWidget::event (this=0x94688e0, event=0xbf8f0694) at
> /home/thiago/src/troll/qt-4.6/src/gui/kernel/qwidget.cpp:8436
> #58 0xb673214c in QFrame::event (this=0x94688e0, e=0xbf8f0694) at
> /home/thiago/src/troll/qt-4.6/src/gui/widgets/qframe.cpp:557
> #59 0xb67dfac2 in QAbstractScrollArea::event (this=0x94688e0, e=0xbf8f0694)
>  at
>  /home/thiago/src/troll/qt-4.6/src/gui/widgets/qabstractscrollarea.cpp:989
>  #60 0xb67e4e5f in QScrollArea::event (this=0x94688e0, e=0xbf8f0694) at
>  /home/thiago/src/troll/qt-4.6/src/gui/widgets/qscrollarea.cpp:314
> #61 0xb335ac61 in KHTMLView::event (this=0x94688e0, e=0xbf8f0694) at
> /home/tmacieir/src/kde4/KDE/kdelibs/khtml/khtmlview.cpp:546
> #62 0xb6245cb2 in QApplicationPrivate::notify_helper (this=0x8aa98b0,
> receiver=0x94688e0, e=0xbf8f0694) at
> /home/thiago/src/troll/qt-4.6/src/gui/kernel/qapplication.cpp:4298
> #63 0xb6245b17 in QApplication::notify (this=0xbf8f0b5c,
>  receiver=0x94688e0, e=0xbf8f0694) at
> /home/thiago/src/troll/qt-4.6/src/gui/kernel/qapplication.cpp:4263
> #64 0xb7521497 in KApplication::notify (this=0xbf8f0b5c,
>  receiver=0x94688e0, event=0xbf8f0694) at
> /home/tmacieir/src/kde4/KDE/kdelibs/kdeui/kernel/kapplication.cpp:302
> #65 0xb6ede741 in QCoreApplication::notifyInternal (this=0xbf8f0b5c,
> receiver=0x94688e0, event=0xbf8f0694) at
> /home/thiago/src/troll/qt-4.6/src/corelib/kernel/qcoreapplication.cpp:704
> #66 0xb6ee2219 in QCoreApplication::sendEvent (receiver=0x94688e0,
> event=0xbf8f0694) at
> ../../include/QtCore/../../../../../src/troll/qt-4.6/src/corelib/kernel/qco
> reapplication.h:215 #67 0xb6f1908a in QTimerInfoList::activateTimers
>  (this=0x8aac6a4) at
>  /home/thiago/src/troll/qt-4.6/src/corelib/kernel/qeventdispatcher_unix.cpp
> :603 #68 0xb6f14f70 in timerSourceDispatch (source=0x8aac670) at
> /home/thiago/src/troll/qt-4.6/src/corelib/kernel/qeventdispatcher_glib.cpp:
> 184 #69 0xb6f15029 in idleTimerSourceDispatch (source=0x8aacb00) at
> /home/thiago/src/troll/qt-4.6/src/corelib/kernel/qeventdispatcher_glib.cpp:
> 231 #70 0xb5b1db92 in g_main_context_dispatch () from
>  /usr/lib/libglib-2.0.so.0 #71 0xb5b21468 in ?? () from
>  /usr/lib/libglib-2.0.so.0
> #72 0xb5b2158e in g_main_context_iteration () from
>  /usr/lib/libglib-2.0.so.0 #73 0xb6f1611c in
>  QEventDispatcherGlib::processEvents (this=0x8aa9870, flags={i = 36}) at
> /home/thiago/src/troll/qt-4.6/src/corelib/kernel/qeventdispatcher_glib.cpp:
> 412 #74 0xb631ac46 in QGuiEventDispatcherGlib::processEvents
>  (this=0x8aa9870, flags={i = 36}) at
> /home/thiago/src/troll/qt-4.6/src/gui/kernel/qguieventdispatcher_glib.cpp:2
> 04 #75 0xb6edbb1b in QEventLoop::processEvents (this=0xbf8f095c, flags={i =
>  36}) at
>  /home/thiago/src/troll/qt-4.6/src/corelib/kernel/qeventloop.cpp:149 #76
>  0xb6edbc60 in QEventLoop::exec (this=0xbf8f095c, flags={i = 0}) at
>  /home/thiago/src/troll/qt-4.6/src/corelib/kernel/qeventloop.cpp:201 #77
>  0xb6edee1d in QCoreApplication::exec () at
> /home/thiago/src/troll/qt-4.6/src/corelib/kernel/qcoreapplication.cpp:981
> #78 0xb6243002 in QApplication::exec () at
> /home/thiago/src/troll/qt-4.6/src/gui/kernel/qapplication.cpp:3577
> #79 0xb7f3fd33 in kdemain (argc=1, argv=0xbf8f0e84) at
> /home/tmacieir/src/kde4/KDE/kdebase/apps/konqueror/src/konqmain.cpp:257
> #80 0x080485db in main (argc=1, argv=0xbf8f0e84) at
> /home/tmacieir/obj/kde4/KDE/kdebase/apps/konqueror/src/konqueror_dummy.cpp:
> 3
>