[Qt-interest] QGraphicsView performance issue

[Alexis Ménard]

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.
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...

> 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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