graphicsview.cpp Example File

 /****************************************************************************
 **
 ** Copyright (C) 2013 Digia Plc and/or its subsidiary(-ies).
 ** Contact: http://www.qt-project.org/legal
 **
 ** This file is part of the examples of the Qt Toolkit.
 **
 ** $QT_BEGIN_LICENSE:BSD$
 ** You may use this file under the terms of the BSD license as follows:
 **
 ** "Redistribution and use in source and binary forms, with or without
 ** modification, are permitted provided that the following conditions are
 ** met:
 **   * Redistributions of source code must retain the above copyright
 **     notice, this list of conditions and the following disclaimer.
 **   * Redistributions in binary form must reproduce the above copyright
 **     notice, this list of conditions and the following disclaimer in
 **     the documentation and/or other materials provided with the
 **     distribution.
 **   * Neither the name of Digia Plc and its Subsidiary(-ies) nor the names
 **     of its contributors may be used to endorse or promote products derived
 **     from this software without specific prior written permission.
 **
 **
 ** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 ** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 ** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 ** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 ** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 ** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 ** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 ** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 ** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 ** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 ** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
 **
 ** $QT_END_LICENSE$
 **
 ****************************************************************************/

 #include "graphicsview.h"

 #include <QScrollBar>
 #include <QTouchEvent>

 GraphicsView::GraphicsView(QGraphicsScene *scene, QWidget *parent)
     : QGraphicsView(scene, parent), totalScaleFactor(1)
 {
     viewport()->setAttribute(Qt::WA_AcceptTouchEvents);
     setDragMode(ScrollHandDrag);
 }

 bool GraphicsView::viewportEvent(QEvent *event)
 {
     switch (event->type()) {
     case QEvent::TouchBegin:
     case QEvent::TouchUpdate:
     case QEvent::TouchEnd:
     {
         QTouchEvent *touchEvent = static_cast<QTouchEvent *>(event);
         QList<QTouchEvent::TouchPoint> touchPoints = touchEvent->touchPoints();
         if (touchPoints.count() == 2) {
             // determine scale factor
             const QTouchEvent::TouchPoint &touchPoint0 = touchPoints.first();
             const QTouchEvent::TouchPoint &touchPoint1 = touchPoints.last();
             qreal currentScaleFactor =
                     QLineF(touchPoint0.pos(), touchPoint1.pos()).length()
                     / QLineF(touchPoint0.startPos(), touchPoint1.startPos()).length();
             if (touchEvent->touchPointStates() & Qt::TouchPointReleased) {
                 // if one of the fingers is released, remember the current scale
                 // factor so that adding another finger later will continue zooming
                 // by adding new scale factor to the existing remembered value.
                 totalScaleFactor *= currentScaleFactor;
                 currentScaleFactor = 1;
             }
             setTransform(QTransform().scale(totalScaleFactor * currentScaleFactor,
                                             totalScaleFactor * currentScaleFactor));
         }
         return true;
     }
     default:
         break;
     }
     return QGraphicsView::viewportEvent(event);
 }