qt5base-lts/examples/touch/pinchzoom/graphicsview.cpp

/****************************************************************************
**
** Copyright (C) 2015 The Qt Company Ltd.
** Contact: http://www.qt.io/licensing/
**
** 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 The Qt Company Ltd 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);
}