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#include "flickable.h"

#include <QtCore>

#include <QtGui>

class FlickableTicker: QObject

{

public:

    FlickableTicker(Flickable *scroller) {

        m_scroller = scroller;

    }

    void start(int interval) {

        if (!m_timer.isActive())

            m_timer.start(interval, this);

    }

    void stop() {

        m_timer.stop();

    }

protected:

    void timerEvent(QTimerEvent *event) {

        Q_UNUSED(event);

        m_scroller->tick();

    }

private:

    Flickable *m_scroller;

    QBasicTimer m_timer;

};

class FlickablePrivate

{

public:

    typedef enum {

        Steady,

        Pressed,

        ManualScroll,

        AutoScroll,

        Stop

    } State;

    State state;

    int threshold;

    QPoint pressPos;

    QPoint offset;

    QPoint delta;

    QPoint speed;

    FlickableTicker *ticker;

    QTime timeStamp;

    QWidget *target;

    QList<QEvent*> ignoreList;

};

Flickable::Flickable()

{

    d = new FlickablePrivate;

    d->state = FlickablePrivate::Steady;

    d->threshold = 10;

    d->ticker = new FlickableTicker(this);

    d->timeStamp = QTime::currentTime();

    d->target = 0;

}

Flickable::~Flickable()

{

    delete d;

}

void Flickable::setThreshold(int th)

{

    if (th >= 0)

        d->threshold = th;

}

int Flickable::threshold() const

{

    return d->threshold;

}

void Flickable::setAcceptMouseClick(QWidget *target)

{

    d->target = target;

}

static QPoint deaccelerate(const QPoint &speed, int a = 1, int max = 64)

{

    int x = qBound(-max, speed.x(), max);

    int y = qBound(-max, speed.y(), max);

    x = (x == 0) ? x : (x > 0) ? qMax(0, x - a) : qMin(0, x + a);

    y = (y == 0) ? y : (y > 0) ? qMax(0, y - a) : qMin(0, y + a);

    return QPoint(x, y);

}

void Flickable::handleMousePress(QMouseEvent *event)

{

    event->ignore();

    if (event->button() != Qt::LeftButton)

        return;

    if (d->ignoreList.removeAll(event))

        return;

    switch (d->state) {

    case FlickablePrivate::Steady:

        event->accept();

        d->state = FlickablePrivate::Pressed;

        d->pressPos = event->pos();

        break;

    case FlickablePrivate::AutoScroll:

        event->accept();

        d->state = FlickablePrivate::Stop;

        d->speed = QPoint(0, 0);

        d->pressPos = event->pos();

        d->offset = scrollOffset();

        d->ticker->stop();

        break;

    default:

        break;

    }

}

void Flickable::handleMouseRelease(QMouseEvent *event)

{

    event->ignore();

    if (event->button() != Qt::LeftButton)

        return;

    if (d->ignoreList.removeAll(event))

        return;

    QPoint delta;

    switch (d->state) {

    case FlickablePrivate::Pressed:

        event->accept();

        d->state = FlickablePrivate::Steady;

        if (d->target) {

            QMouseEvent *event1 = new QMouseEvent(QEvent::MouseButtonPress,

                                                  d->pressPos, Qt::LeftButton,

                                                  Qt::LeftButton, Qt::NoModifier);

            QMouseEvent *event2 = new QMouseEvent(*event);

            d->ignoreList << event1;

            d->ignoreList << event2;

            QApplication::postEvent(d->target, event1);

            QApplication::postEvent(d->target, event2);

        }

        break;

    case FlickablePrivate::ManualScroll:

        event->accept();

        delta = event->pos() - d->pressPos;

        if (d->timeStamp.elapsed() > 100) {

            d->timeStamp = QTime::currentTime();

            d->speed = delta - d->delta;

            d->delta = delta;

        }

        d->offset = scrollOffset();

        d->pressPos = event->pos();

        if (d->speed == QPoint(0, 0)) {

            d->state = FlickablePrivate::Steady;

        } else {

            d->speed /= 4;

            d->state = FlickablePrivate::AutoScroll;

            d->ticker->start(20);

        }

        break;

    case FlickablePrivate::Stop:

        event->accept();

        d->state = FlickablePrivate::Steady;

        d->offset = scrollOffset();

        break;

    default:

        break;

    }

}

void Flickable::handleMouseMove(QMouseEvent *event)

{

    event->ignore();

    if (!(event->buttons() & Qt::LeftButton))

        return;

    if (d->ignoreList.removeAll(event))

        return;

    QPoint delta;

    switch (d->state) {

    case FlickablePrivate::Pressed:

    case FlickablePrivate::Stop:

        delta = event->pos() - d->pressPos;

        if (delta.x() > d->threshold || delta.x() < -d->threshold ||

                delta.y() > d->threshold || delta.y() < -d->threshold) {

            d->timeStamp = QTime::currentTime();

            d->state = FlickablePrivate::ManualScroll;

            d->delta = QPoint(0, 0);

            d->pressPos = event->pos();

            event->accept();

        }

        break;

    case FlickablePrivate::ManualScroll:

        event->accept();

        delta = event->pos() - d->pressPos;

        setScrollOffset(d->offset - delta);

        if (d->timeStamp.elapsed() > 100) {

            d->timeStamp = QTime::currentTime();

            d->speed = delta - d->delta;

            d->delta = delta;

        }

        break;

    default:

        break;

    }

}

void Flickable::tick()

{

    if (d->state == FlickablePrivate:: AutoScroll) {

        d->speed = deaccelerate(d->speed);

        setScrollOffset(d->offset - d->speed);

        d->offset = scrollOffset();

        if (d->speed == QPoint(0, 0)) {

            d->state = FlickablePrivate::Steady;

            d->ticker->stop();

        }

    } else {

        d->ticker->stop();

    }

}