Gestures and QGraphicsScene

[stretchtiberius]

By the way - on a slightly different topic, "Gesture Pan Events swallowed" - does the example work for you on Windows 7: http://bugreports.qt.nokia.com/secur...iewGesture.zip

That code works under Windows 7 if one bug is fixed. Change the gestureEvent() function to match the following code.

bool GestureGraphicsScene::gestureEvent(const QGestureEvent *event)
{
    bool result = false;
    if (QGesture *pan = event->gesture(Qt::PanGesture)) {
        result = panTriggered(static_cast<QPanGesture *>(pan));
    }
    if (QGesture *pinch = event->gesture(Qt::PinchGesture)) {
        result = pinchTriggered(static_cast<QPinchGesture *>(pinch));
    }
 
    return result;
}

bool GestureGraphicsScene::gestureEvent(const QGestureEvent *event)
{
    bool result = false;
    if (QGesture *pan = event->gesture(Qt::PanGesture)) {
        result = panTriggered(static_cast<QPanGesture *>(pan));
    }
    if (QGesture *pinch = event->gesture(Qt::PinchGesture)) {
        result = pinchTriggered(static_cast<QPinchGesture *>(pinch));
    }

    return result;
}

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For an explanation, take a look at this: http://doc.qt.nokia.com/4.7/gestures...andling-events.

From the documentation:

As one target object can subscribe to more than one gesture type, the QGestureEvent can contain more than one QGesture, indicating several possible gestures are active at the same time. It is then up to the widget to determine how to handle those multiple gestures and choose if some should be canceled in favor of others.

[Oliver Knoll]

Thanks, I will stich your example together and try it out on Mac OS X and post my results here.

Unfortunatelly it really seems that on Mac (MacBook Pro with touchpad, Mac OS 10.6.6) the QGraphicsObject based items do not receive Gesture events

I took your example and adapted it slightly:

- use qDebug instead of stdout, so I actually see the debug statements also in Qt Creator
- explicitly also grab gestures for the viewport! You mentioned that in your posts, but I don't see that in your actual example code (probably it is there in your real code, as you say "Within the GraphicsView", and in the example code there is no derived class of QGraphicsView)

Anyway, just for the record:

TouchObject.h:

#ifndef ___TOUCHOBJECT___
#define ___TOUCHOBJECT___
 
#include <QtGui>
#include <QGesture>
#include <iostream>
 
class TouchObject : public QGraphicsObject {
    Q_OBJECT
public:
    TouchObject(QGraphicsItem* pParent = NULL) : QGraphicsObject(pParent) {
 
        grabGesture(Qt::PinchGesture);
        setAcceptTouchEvents(true);
    }
 
    QRectF boundingRect() const {
        return QRectF(-WIDTH / 2, -HEIGHT / 2, WIDTH, HEIGHT);
    }
 
    QPainterPath shape() const {
        QPainterPath path;
        path.addEllipse(boundingRect());
        return path;
    }
 
    void paint(QPainter *painter, const QStyleOptionGraphicsItem *pOption, QWidget *pWidget) {
        Q_UNUSED(pOption)
        Q_UNUSED(pWidget)
        painter->setBrush(Qt::blue);
        painter->drawEllipse(boundingRect());
    }
 
 
    bool sceneEvent(QEvent* pEvent) {
        QGestureEvent* pGestureEvent ;
        switch (pEvent->type()) {
        case QEvent::TouchBegin:
            pEvent->accept();
            qDebug("Touch Event Received from sceneEvent()");
            return true;
        case QEvent::Gesture:
            qDebug("Gesture Event Received from sceneEvent()");
            pGestureEvent = static_cast<QGestureEvent*>(pEvent);
            if(QGesture *pinch = pGestureEvent->gesture(Qt::PinchGesture)) {
                qDebug(" Pinch Gesture: state: %d",  pinch->state());
            }
            else {
                qDebug(" not a pinch gesture.");
            }
            break;
                        default:
            break;
 
        }
 
        return QGraphicsObject::sceneEvent(pEvent);
    }
 
private:
    static const int WIDTH = 160;
    static const int HEIGHT = 160;
};
 
#endif

#ifndef ___TOUCHOBJECT___
#define ___TOUCHOBJECT___

#include <QtGui>
#include <QGesture>
#include <iostream>

class TouchObject : public QGraphicsObject {
    Q_OBJECT
public:
    TouchObject(QGraphicsItem* pParent = NULL) : QGraphicsObject(pParent) {

        grabGesture(Qt::PinchGesture);
        setAcceptTouchEvents(true);
    }

    QRectF boundingRect() const {
        return QRectF(-WIDTH / 2, -HEIGHT / 2, WIDTH, HEIGHT);
    }

    QPainterPath shape() const {
        QPainterPath path;
        path.addEllipse(boundingRect());
        return path;
    }

    void paint(QPainter *painter, const QStyleOptionGraphicsItem *pOption, QWidget *pWidget) {
        Q_UNUSED(pOption)
        Q_UNUSED(pWidget)
        painter->setBrush(Qt::blue);
        painter->drawEllipse(boundingRect());
    }


    bool sceneEvent(QEvent* pEvent) {
        QGestureEvent* pGestureEvent ;
        switch (pEvent->type()) {
        case QEvent::TouchBegin:
            pEvent->accept();
            qDebug("Touch Event Received from sceneEvent()");
            return true;
        case QEvent::Gesture:
            qDebug("Gesture Event Received from sceneEvent()");
            pGestureEvent = static_cast<QGestureEvent*>(pEvent);
            if(QGesture *pinch = pGestureEvent->gesture(Qt::PinchGesture)) {
                qDebug(" Pinch Gesture: state: %d",  pinch->state());
            }
            else {
                qDebug(" not a pinch gesture.");
            }
            break;
                        default:
            break;

        }

        return QGraphicsObject::sceneEvent(pEvent);
    }

private:
    static const int WIDTH = 160;
    static const int HEIGHT = 160;
};

#endif

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main.cpp:

#include <QApplication>
#include <QGraphicsView>
#include <QGraphicsScene>
#include "TouchObject.h"
 
int main(int argc, char* argv[]){
 
    QApplication app(argc, argv);
    QGraphicsScene* pScene = new QGraphicsScene();
    pScene->setSceneRect(-300, -300, 600, 600);
    pScene->addItem(new TouchObject());
    QGraphicsView view(pScene);
    view.viewport()->grabGesture(Qt::PinchGesture);
    view.show();
 
    return app.exec();
}

#include <QApplication>
#include <QGraphicsView>
#include <QGraphicsScene>
#include "TouchObject.h"

int main(int argc, char* argv[]){

    QApplication app(argc, argv);
    QGraphicsScene* pScene = new QGraphicsScene();
    pScene->setSceneRect(-300, -300, 600, 600);
    pScene->addItem(new TouchObject());
    QGraphicsView view(pScene);
    view.viewport()->grabGesture(Qt::PinchGesture);
    view.show();

    return app.exec();
}

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GraphicsObjectGesture.pro:

TEMPLATE   = app
CONFIG	  += qt warn_on no_keywords
QT        +=
TARGET     = GraphicsObjectGestures
SOURCES	   = main.cpp
HEADERS	   = TouchObject.h
LIBS      +=
CONFIG    += console
 
# Treat warnings as errors
win32:QMAKE_CXXFLAGS += /WX

TEMPLATE   = app
CONFIG	  += qt warn_on no_keywords
QT        +=
TARGET     = GraphicsObjectGestures
SOURCES	   = main.cpp
HEADERS	   = TouchObject.h
LIBS      +=
CONFIG    += console

# Treat warnings as errors
win32:QMAKE_CXXFLAGS += /WX

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The only event I really receive is the QEvent::TouchBegin (so yes, the QGraphicsObject seems to receive touch events) - but never a QEvent::Gesture event, as it seems...

I will open a Qt issue for that and post my own example code there as well...

Cheers, Oliver

---

Added after 24 minutes:

I created an issue for that: http://bugreports.qt.nokia.com/browse/QTBUG-16618