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#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);

}