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# flickable.cpp Example File

demos/embedded/flickable/flickable.cpp

     /****************************************************************************
     **
     ** Copyright (C) 2015 The Qt Company Ltd.
     ** Contact: http://www.qt.io/licensing/
     **
     ** This file is part of the demonstration applications of the Qt Toolkit.
     **
     ** $QT_BEGIN_LICENSE:LGPL$
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     ** GNU Lesser General Public License Usage
     ** Alternatively, this file may be used under the terms of the GNU Lesser
     ** General Public License version 2.1 or version 3 as published by the Free
     ** Software Foundation and appearing in the file LICENSE.LGPLv21 and
     ** LICENSE.LGPLv3 included in the packaging of this file. Please review the
     ** following information to ensure the GNU Lesser General Public License
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     ** rights. These rights are described in The Qt Company LGPL Exception
     ** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
     **
     ** GNU General Public License Usage
     ** Alternatively, this file may be used under the terms of the GNU
     ** General Public License version 3.0 as published by the Free Software
     ** Foundation and appearing in the file LICENSE.GPL included in the
     ** packaging of this file.  Please review the following information to
     ** ensure the GNU General Public License version 3.0 requirements will be
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     ** $QT_END_LICENSE$
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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();
         }
     }