qt-everywhere-src-5.15.1/qtcharts/examples/charts/zoomlinechart/chart.cpp

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#include "chart.h"
#include <QtWidgets/QGesture>
#include <QtWidgets/QGraphicsScene>
#include <QtWidgets/QGraphicsView>

Chart::Chart(QGraphicsItem *parent, Qt::WindowFlags wFlags)
    : QChart(QChart::ChartTypeCartesian, parent, wFlags)
{
    // Seems that QGraphicsView (QChartView) does not grab gestures.
    // They can only be grabbed here in the QGraphicsWidget (QChart).
    grabGesture(Qt::PanGesture);
    grabGesture(Qt::PinchGesture);
}

Chart::~Chart()
{

}

//![1]
bool Chart::sceneEvent(QEvent *event)
{
    if (event->type() == QEvent::Gesture)
        return gestureEvent(static_cast<QGestureEvent *>(event));
    return QChart::event(event);
}

bool Chart::gestureEvent(QGestureEvent *event)
{
    if (QGesture *gesture = event->gesture(Qt::PanGesture)) {
        QPanGesture *pan = static_cast<QPanGesture *>(gesture);
        QChart::scroll(-(pan->delta().x()), pan->delta().y());
    }

    if (QGesture *gesture = event->gesture(Qt::PinchGesture)) {
        QPinchGesture *pinch = static_cast<QPinchGesture *>(gesture);
        if (pinch->changeFlags() & QPinchGesture::ScaleFactorChanged)
            QChart::zoom(pinch->scaleFactor());
    }

    return true;
}
//![1]