[Qt-interest] QGraphicsView performance issue

[Alexis Ménard]

On Monday 11 May 2009 16:10:04 Santhosh Y wrote:
> Please read my comments below
>
> Alexis Ménard wrote:
> > On Monday 11 May 2009 15:01:52 Santhosh Y wrote:
> >> Santhosh Y wrote:
> >>> Hi,
> >
> > Hi,
> >
> >>> I added  30,000 items to the scene.
> >>> While updating the scene, the response from the view is very slow.
> >>>
> >>> Among these 30,000 items only 3,000 items have the distinctive
> >>> locations and the rest of 27,000 items have the same location of those
> >>> 3,000 items.
> >>>
> >>> In such a scenario to improve the performance, what flags
> >>> I should use on the scene to improve the performance.
> >
> > If the painting (paint method) is slow on items, you can use the cache
> > mode, itemCoordinateCache if you have no transformations otherwise
> > DeviceCoordinateCache.
>
> I am not able to find the above flag for setting cache mode.
> I am using 4.3.3 version of Qt.
> I can use only cacheNone or cacheBackGround.

OoOooOOooooOOo. Then i fully encourage you to upgrade to 4.5. Lot of 
performance improvements has been made since 4.3.3 and those repaint bugs has 
been
probably fixed. And you have more features.

>
> > If you trigger full updates on the scene, then you need to set the
> > viewportUpdate to fullviewport update because sometimes it is slower to
> > caculate the exact dirty area than repainting the all scene (aka OpenGL).
> >
> >> To add to the above issue, what I have observed is that, paintEvent() on
> >> QGraphicsview is being called multiple times
> >> which is taking around 3 sec for each call to pick the items from the
> >> visible region for sending to
> >
> > That why we are working on an API to allow you to create your custom
> > indexing where you can skip some parts of the scene or skipping items
> > that you don't need.
> >
> >> QGraphicsScene::drawItems(QPainter* p, int numItems, QGraphicsItem**
> >> items, const QStyleOptionGraphicsItem* options )
> >>  function dispatch.
> >>
> >> Can anybody tell me how to track from where this paintEvent call is
> >> dispatched so many times.
> >
> > recalculateContentSize can be the source of those calls because you query
> > a full update (see below).
> >
> >> I have no QGraphicsView::update() calls in my code, but I have the
> >> QGraphicsScene::update() calls.
> >
> > Calling update on the scene is not a good idea unless you give a
> > rectangle to update(). Without parameter it will redraw everything... Why
> > do you need to update the whole scene? Updating the content should
> > triggers updates on items for you...
>
> I removed all the QGraphicsScene::update () calls. Still the performance
> have not improved.
>
> >> But none of the QGraphicsScene::update () call is immediately resulting
> >> a QGraphicsView::paintEvent(QPaintEvent*)
> >>
> >> My observation is that all the mutliple calls on
> >> QGraphicsView::paintEvent(QPaintEvent*) are resulting from the following
> >> stack.
> >> ------------------------------------------------------------------------
> >>--- --------------------------- QGraphicsView::paintEvent(QPaintEvent *
> >> e=0x0012b550)  Line 1282    C++ QtGuid4.dll!QWidget::event(QEvent *
> >> event=0x0012b550)  Line 6256    C++ QtGuid4.dll!QFrame::event(QEvent *
> >> e=0x0012b550)  Line 641    C++
> >> QtGuid4.dll!QAbstractScrollArea::viewportEvent(QEvent *
> >> e=0x0012b550)  Line 909 + 0xc bytes    C++
> >>      QtGuid4.dll!QGraphicsView::viewportEvent(QEvent *
> >> event=0x0012b550)  Line 2324    C++
> >>      QtGuid4.dll!QAbstractScrollAreaPrivate::viewportEvent(QEvent *
> >> event=0x0012b550)  Line 78 + 0x28 bytes    C++
> >>      QtGuid4.dll!QAbstractScrollAreaFilter::eventFilter(QObject *
> >> o=0x08705aa0, QEvent * e=0x0012b550)  Line 89 + 0x29 bytes    C++
> >>      QtGuid4.dll!QApplicationPrivate::notify_helper(QObject *
> >> receiver=0x08705aa0, QEvent * e=0x0012b550)  Line 3533 + 0x1b bytes   
> >> C++ QtGuid4.dll!QApplication::notify(QObject * receiver=0x08705aa0,
> >> QEvent * e=0x0012b550)  Line 3482 + 0x10 bytes    C++
> >>      QtCored4.dll!QCoreApplication::notifyInternal(QObject *
> >> receiver=0x08705aa0, QEvent * event=0x0012b550)  Line 516    C++
> >>      QtCored4.dll!QCoreApplication::sendSpontaneousEvent(QObject *
> >> receiver=0x08705aa0, QEvent * event=0x0012b550)  Line 188 + 0x38
> >> bytes    C++
> >>      QtGuid4.dll!qt_sendSpontaneousEvent(QObject * receiver=0x08705aa0,
> >> QEvent * event=0x0012b550)  Line 1182 + 0xe bytes    C++
> >>      QtGuid4.dll!QWidgetPrivate::drawWidget(QPaintDevice *
> >> pdev=0x02a0a878, const QRegion & rgn={...}, const QPoint & offset={...},
> >> int flags=4)  Line 1195 + 0xd bytes    C++
> >>
> >> QtGuid4.dll!QWidgetBackingStore::paintSiblingsRecursive(QPaintDevice *
> >> pdev=0x02a0a878, const QList<QObject *> & siblings={...}, int index=0,
> >> const QRegion & rgn={...}, const QPoint & offset={...}, int flags=4)
> >> Line 1099    C++
> >>      QtGuid4.dll!QWidgetPrivate::drawWidget(QPaintDevice *
> >> pdev=0x02a0a878, const QRegion & rgn={...}, const QPoint & offset={...},
> >> int flags=4)  Line 1231 + 0x2e bytes    C++
> >>
> >> QtGuid4.dll!QWidgetBackingStore::paintSiblingsRecursive(QPaintDevice *
> >> pdev=0x02a0a878, const QList<QObject *> & siblings={...}, int index=2,
> >> const QRegion & rgn={...}, const QPoint & offset={...}, int flags=4)
> >> Line 1099    C++
> >>
> >> QtGuid4.dll!QWidgetBackingStore::paintSiblingsRecursive(QPaintDevice *
> >> pdev=0x02a0a878, const QList<QObject *> & siblings={...}, int index=3,
> >> const QRegion & rgn={...}, const QPoint & offset={...}, int flags=4)
> >> Line 1089 + 0x20 bytes    C++
> >>
> >> QtGuid4.dll!QWidgetBackingStore::paintSiblingsRecursive(QPaintDevice *
> >> pdev=0x02a0a878, const QList<QObject *> & siblings={...}, int index=4,
> >> const QRegion & rgn={...}, const QPoint & offset={...}, int flags=4)
> >> Line 1089 + 0x20 bytes    C++
> >>      QtGuid4.dll!QWidgetPrivate::drawWidget(QPaintDevice *
> >> pdev=0x02a0a878, const QRegion & rgn={...}, const QPoint & offset={...},
> >> int flags=4)  Line 1231 + 0x2e bytes    C++
> >>
> >> QtGuid4.dll!QWidgetBackingStore::paintSiblingsRecursive(QPaintDevice *
> >> pdev=0x02a0a878, const QList<QObject *> & siblings={...}, int index=13,
> >> const QRegion & rgn={...}, const QPoint & offset={...}, int flags=4)
> >> Line 1099    C++
> >>      QtGuid4.dll!QWidgetPrivate::drawWidget(QPaintDevice *
> >> pdev=0x02a0a878, const QRegion & rgn={...}, const QPoint & offset={...},
> >> int flags=4)  Line 1231 + 0x2e bytes    C++
> >>
> >> QtGuid4.dll!QWidgetBackingStore::paintSiblingsRecursive(QPaintDevice *
> >> pdev=0x02a0a878, const QList<QObject *> & siblings={...}, int index=5,
> >> const QRegion & rgn={...}, const QPoint & offset={...}, int flags=4)
> >> Line 1099    C++
> >>      QtGuid4.dll!QWidgetPrivate::drawWidget(QPaintDevice *
> >> pdev=0x02a0a878, const QRegion & rgn={...}, const QPoint & offset={...},
> >> int flags=4)  Line 1231 + 0x2e bytes    C++
> >>
> >> QtGuid4.dll!QWidgetBackingStore::paintSiblingsRecursive(QPaintDevice *
> >> pdev=0x02a0a878, const QList<QObject *> & siblings={...}, int index=40,
> >> const QRegion & rgn={...}, const QPoint & offset={...}, int flags=4)
> >> Line 1099    C++
> >>
> >> QtGuid4.dll!QWidgetBackingStore::paintSiblingsRecursive(QPaintDevice *
> >> pdev=0x02a0a878, const QList<QObject *> & siblings={...}, int index=41,
> >> const QRegion & rgn={...}, const QPoint & offset={...}, int flags=4)
> >> Line 1089 + 0x20 bytes    C++
> >>
> >> QtGuid4.dll!QWidgetBackingStore::paintSiblingsRecursive(QPaintDevice *
> >> pdev=0x02a0a878, const QList<QObject *> & siblings={...}, int index=42,
> >> const QRegion & rgn={...}, const QPoint & offset={...}, int flags=4)
> >> Line 1089 + 0x20 bytes    C++
> >>      QtGuid4.dll!QWidgetPrivate::drawWidget(QPaintDevice *
> >> pdev=0x02a0a878, const QRegion & rgn={...}, const QPoint & offset={...},
> >> int flags=5)  Line 1231 + 0x2e bytes    C++
> >>      QtGuid4.dll!QWidgetBackingStore::cleanRegion(const QRegion &
> >> rgn={...}, QWidget * widget=0x0012fd58, bool
> >> recursiveCopyToScreen=false)  Line 1000    C++
> >>      QtGuid4.dll!qt_syncBackingStore(QRegion rgn={...}, QWidget *
> >> widget=0x0012fd58, bool recursive=false)  Line 230    C++
> >>      QtGuid4.dll!QETWidget::translatePaintEvent(const tagMSG &
> >> msg={...})  Line 3094 + 0x2b bytes    C++
> >>      QtGuid4.dll!QtWndProc(HWND__ * hwnd=0x000a1118, unsigned int
> >> message=15, unsigned int wParam=0, long lParam=0)  Line 1680 + 0xc
> >> bytes    C++
> >> ------------------------------------------------------------------------
> >>--- ---------------------------
> >>
> >> Please tell me how to track the event call of paint over QGraphicsView.

-- 

Alexis Ménard
Software Engineer, Widgets Team 1
Qt Software, Nokia Norge AS, Sandakerveien 116, 0484 Oslo, Norway
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