[Qt-interest] QGraphicsScene and multitouch events

[Devendra Patel]

Hi Sean,

I tried your suggestion but am facing some issues.

Firstly I am interested in raw touch events, not gestures. My goal is to
place two dials in QGraphicsView and rotate them simultaneously using
Multi-touch monitor. I am using Win 7 and Qt 4.7.

I wrote following code to see if I can rotate two dials simultaneously. I
can only rotate one dial simultaneously. I am able to rotate two dials
simultaneously if I place them on QWidget rather than
QGraphicsScene/QGraphicsView.

int main(int argc, char **argv)
{
     QApplication app(argc, argv);
     QCoreApplication::setAttribute(Qt::AA_DontCreateNativeWidgetSiblings);
// just make sure that native widgets are not created
     WCScene scene; //WCScene is derived from QGraphicsScene

     CKnob dial,dial1; //CKnob is derived from QDial
     dial.setGeometry(10,10,200,200);
     dial1.setGeometry(210,10,200,200);

     dial.setObjectName("1");
     dial1.setObjectName("2");
     dial.setAttribute(Qt::WA_AcceptTouchEvents);
     dial1.setAttribute(Qt::WA_AcceptTouchEvents);

     GraphicsView view(&scene); //GraphicsView derived from QGraphicsView
     scene.addWidget(&dial);
     scene.addWidget(&dial1);

     view.setAttribute((Qt::WA_AcceptTouchEvents));
     view.viewport()->setAttribute(Qt::WA_AcceptTouchEvents);
     view.show();
     return app.exec();
}

In all the custom classes I am handling events and print message. Below is
how I handle TouchBegin event in CKnob class.

 switch(e->type())
    {
    case QEvent::TouchBegin:
        qDebug("CKnob  QEvent::TouchBegin");
        return QDial::event(e);
    }

All the Mouse and Touch events are handled similarly in custom classes. In
GraphicsView I am overriding both viewportEvent(QEvent* ) and event(QEvent*)
to print messages.

This is What I see when I try to rotate the dials.

GraphicsView viewportEvent::TouchBegin
SCene QEvent::TouchBegin
GraphicsView QEvent::TouchBegin
GraphicsView viewportEvent::MouseMove
GraphicsView viewportEvent::MouseButtonPress
CKnob  QEvent::MouseButtonPress
GraphicsView viewportEvent::MouseMove
CKnob  QEvent::MouseMove
GraphicsView viewportEvent::MouseMove
CKnob  QEvent::MouseMove
GraphicsView viewportEvent::MouseMove
CKnob  QEvent::MouseMove
GraphicsView viewportEvent::MouseMove
CKnob  QEvent::MouseMove
GraphicsView viewportEvent::MouseMove
CKnob  QEvent::MouseMove
GraphicsView viewportEvent::MouseMove
CKnob  QEvent::MouseMove
GraphicsView viewportEvent::MouseButtonRelease
CKnob  QEvent::MouseButtonRelease

I am puzzled to why I don't receive touchUpdate and touchEnd events at all,
neither in graphicsview, graphicsscene nor in CKnob.
Is there something wrong in my setup?

Thanks,
Devendra


2011/1/5 Sean Hayes <sean.t.hayes at vanderbilt.edu>

> To get gestures to work in a QGraphicsView (in the scene) you have to do
> the following:
>
>    - In the QGraphicsView accept gestures on the viewport (e.g.,
>    viewport()->grabGesture(Qt::PinchGesture);)
>    - In the QGraphicsObjects (and/or the QWidget) accept touch events
>    (i.e., setAcceptTouchEvents(true);), grab the gesture (e.g.,
>    grabGesture(Qt::PinchGesture);).
>    - Finally, in the event function (sceneEvent() for a QGraphicsObject and
>    event() for a QWidget) accept the touch begin events. An example below:
>
> bool QMapTouchItem::sceneEvent(QEvent* pEvent) {
> switch (pEvent->type()) {
>  case QEvent::TouchBegin: // Needed to get around Qt bug
> pEvent->accept();
>  return true;
> case QEvent::Gesture:
>  // handle the gesture
> }
>
> return QMapItem::sceneEvent(pEvent);
> }
>
> You can also check out this forum post.
> http://www.qtcentre.org/threads/31582-Gestures-and-QGraphicsScene?p=172577
> .
>
> On Tue, Jan 4, 2011 at 12:00 AM, Abhishek <abhishekworld at gmail.com> wrote:
>
>> I think you should look at QGraphicsProxyWdiget that makes more sense in
>> your case http://doc.qt.nokia.com/4.7-snapshot/qgraphicsproxywidget.html
>>
>> <http://doc.qt.nokia.com/4.7-snapshot/qgraphicsproxywidget.html>
>>
>>>
>>>    1.
>>>
>>>    	QGraphicsView <http://doc.qt.nokia.com/latest/qgraphicsview.html> view(&scene);
>>>
>>>
>>>    2.
>>>    3.
>>>
>>>            QWidget <http://doc.qt.nokia.com/latest/qwidget.html>* widget=new QWidget <http://doc.qt.nokia.com/latest/qwidget.html>;
>>>
>>>    4.
>>>    5.
>>>
>>>         scene.addWidget(widget);
>>>    6.
>>>
>>>
>>>    7.
>>>
>>>         view.setDragMode(QGraphicsView <http://doc.qt.nokia.com/latest/qgraphicsview.html>::ScrollHandDrag);
>>>
>>>
>>>    8.
>>>    9.
>>>
>>>
>>>
>>
>>
>> --
>> Abhishek Patil
>> http://thezeroth.net
>>
>> _______________________________________________
>> Qt-interest mailing list
>> Qt-interest at qt.nokia.com
>> http://lists.qt.nokia.com/mailman/listinfo/qt-interest
>>
>>
>


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