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#include <QtGui>

#include "mousepangesturerecognizer.h"

class ScrollArea : public QScrollArea

{

    Q_OBJECT

public:

    ScrollArea(QWidget *parent = 0)

        : QScrollArea(parent), outside(false)

    {

        viewport()->grabGesture(Qt::PanGesture, Qt::ReceivePartialGestures);

    }

protected:

    bool viewportEvent(QEvent *event)

    {

        if (event->type() == QEvent::Gesture) {

            gestureEvent(static_cast<QGestureEvent *>(event));

            return true;

        } else if (event->type() == QEvent::GestureOverride) {

            QGestureEvent *ge = static_cast<QGestureEvent *>(event);

            if (QPanGesture *pan = static_cast<QPanGesture *>(ge->gesture(Qt::PanGesture)))

                if (pan->state() == Qt::GestureStarted) {

                    outside = false;

                }

        }

        return QScrollArea::viewportEvent(event);

    }

    void gestureEvent(QGestureEvent *event)

    {

        QPanGesture *pan = static_cast<QPanGesture *>(event->gesture(Qt::PanGesture));

        if (pan) {

            switch(pan->state()) {

            case Qt::GestureStarted: qDebug() << this << "Pan: started"; break;

            case Qt::GestureFinished: qDebug() << this << "Pan: finished"; break;

            case Qt::GestureCanceled: qDebug() << this << "Pan: canceled"; break;

            case Qt::GestureUpdated: break;

            default: qDebug() << this << "Pan: <unknown state>"; break;

            }

            if (pan->state() == Qt::GestureStarted)

                outside = false;

            event->ignore();

            event->ignore(pan);

            if (outside)

                return;

            const QPointF delta = pan->delta();

            const QPointF totalOffset = pan->offset();

            QScrollBar *vbar = verticalScrollBar();

            QScrollBar *hbar = horizontalScrollBar();

            if ((vbar->value() == vbar->minimum() && totalOffset.y() > 10) ||

                (vbar->value() == vbar->maximum() && totalOffset.y() < -10)) {

                outside = true;

                return;

            }

            if ((hbar->value() == hbar->minimum() && totalOffset.x() > 10) ||

                (hbar->value() == hbar->maximum() && totalOffset.x() < -10)) {

                outside = true;

                return;

            }

            vbar->setValue(vbar->value() - delta.y());

            hbar->setValue(hbar->value() - delta.x());

            event->accept(pan);

        }

    }

private:

    bool outside;

};

class Slider : public QSlider

{

public:

    Slider(Qt::Orientation orientation, QWidget *parent = 0)

        : QSlider(orientation, parent)

    {

        grabGesture(Qt::PanGesture);

    }

protected:

    bool event(QEvent *event)

    {

        if (event->type() == QEvent::Gesture) {

            gestureEvent(static_cast<QGestureEvent *>(event));

            return true;

        }

        return QSlider::event(event);

    }

    void gestureEvent(QGestureEvent *event)

    {

        QPanGesture *pan = static_cast<QPanGesture *>(event->gesture(Qt::PanGesture));

        if (pan) {

            switch (pan->state()) {

            case Qt::GestureStarted: qDebug() << this << "Pan: started"; break;

            case Qt::GestureFinished: qDebug() << this << "Pan: finished"; break;

            case Qt::GestureCanceled: qDebug() << this << "Pan: canceled"; break;

            case Qt::GestureUpdated: break;

            default: qDebug() << this << "Pan: <unknown state>"; break;

            }

            if (pan->state() == Qt::GestureStarted)

                outside = false;

            event->ignore();

            event->ignore(pan);

            if (outside)

                return;

            const QPointF delta = pan->delta();

            const QPointF totalOffset = pan->offset();

            if (orientation() == Qt::Horizontal) {

                if ((value() == minimum() && totalOffset.x() < -10) ||

                    (value() == maximum() && totalOffset.x() > 10)) {

                    outside = true;

                    return;

                }

                if (totalOffset.y() < 40 && totalOffset.y() > -40) {

                    setValue(value() + delta.x());

                    event->accept(pan);

                } else {

                    outside = true;

                }

            } else if (orientation() == Qt::Vertical) {

                if ((value() == maximum() && totalOffset.y() < -10) ||

                    (value() == minimum() && totalOffset.y() > 10)) {

                    outside = true;

                    return;

                }

                if (totalOffset.x() < 40 && totalOffset.x() > -40) {

                    setValue(value() - delta.y());

                    event->accept(pan);

                } else {

                    outside = true;

                }

            }

        }

    }

private:

    bool outside;

};

class MainWindow : public QMainWindow

{

public:

    MainWindow()

    {

        rootScrollArea = new ScrollArea;

        rootScrollArea->setObjectName(QLatin1String("rootScrollArea"));

        setCentralWidget(rootScrollArea);

        QWidget *root = new QWidget;

        root->setFixedSize(3000, 3000);

        rootScrollArea->setWidget(root);

        Slider *verticalSlider = new Slider(Qt::Vertical, root);

        verticalSlider->setObjectName(QLatin1String("verticalSlider"));

        verticalSlider ->move(650, 1100);

        Slider *horizontalSlider = new Slider(Qt::Horizontal, root);

        horizontalSlider->setObjectName(QLatin1String("horizontalSlider"));

        horizontalSlider ->move(600, 1000);

        childScrollArea = new ScrollArea(root);

        childScrollArea->setObjectName(QLatin1String("childScrollArea"));

        childScrollArea->move(500, 500);

        QWidget *w = new QWidget;

        w->setMinimumWidth(700);

        QVBoxLayout *l = new QVBoxLayout(w);

        l->setMargin(20);

        for (int i = 0; i < 100; ++i) {

            QWidget *w = new QWidget;

            QHBoxLayout *ll = new QHBoxLayout(w);

            ll->addWidget(new QLabel(QString("Label %1").arg(i)));

            ll->addWidget(new QPushButton(QString("Button %1").arg(i)));

            l->addWidget(w);

        }

        childScrollArea->setWidget(w);

#if defined(Q_OS_WIN)

        // Windows can force Qt to create a native window handle for an

        // intermediate widget and that will block gesture to get touch events.

        // So this hack to make sure gestures get all touch events they need.

        foreach (QObject *w, children())

            if (w->isWidgetType())

                static_cast<QWidget *>(w)->setAttribute(Qt::WA_AcceptTouchEvents);

#endif

    }

private:

    ScrollArea *rootScrollArea;

    ScrollArea *childScrollArea;

};

int main(int argc, char **argv)

{

    QApplication app(argc, argv);

    QGestureRecognizer::registerRecognizer(new MousePanGestureRecognizer);

    MainWindow w;

    w.show();

    return app.exec();

}

#include "main.moc"