qt-everywhere-src-5.14.1/qtcharts/examples/charts/chartinteractions/chart.cpp

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#include "chart.h"
#include <QtCharts/QValueAxis>
#include <QtCharts/QAbstractAxis>
#include <QtCore/QtMath>

Chart::Chart(QGraphicsItem *parent, Qt::WindowFlags wFlags, QLineSeries *series)
    : QChart(QChart::ChartTypeCartesian, parent, wFlags), m_series(series)
{
    m_clicked = false;
}

Chart::~Chart()
{
}

void Chart::clickPoint(const QPointF &point)
{
    // Find the closest data point
    m_movingPoint = QPoint();
    m_clicked = false;
    const auto points = m_series->points();
    for (QPointF p : points) {
        if (distance(p, point) < distance(m_movingPoint, point)) {
            m_movingPoint = p;
            m_clicked = true;
        }
    }
}

qreal Chart::distance(const QPointF &p1, const QPointF &p2)
{
    return qSqrt((p1.x() - p2.x()) * (p1.x() - p2.x())
                + (p1.y() - p2.y()) * (p1.y() - p2.y()));
}

void Chart::setPointClicked(bool clicked)
{
    m_clicked = clicked;
}

void Chart::handlePointMove(const QPoint &point)
{
    if (m_clicked) {
        //Map the point clicked from the ChartView
        //to the area occupied by the chart.
        QPoint mappedPoint = point;
        mappedPoint.setX(point.x() - this->plotArea().x());
        mappedPoint.setY(point.y() - this->plotArea().y());

        //Get the x- and y axis to be able to convert the mapped
        //coordinate point to the charts scale.
        QAbstractAxis *axisx = axes(Qt::Horizontal).first();
        QValueAxis *haxis = 0;
        if (axisx->type() == QAbstractAxis::AxisTypeValue)
            haxis = qobject_cast<QValueAxis *>(axisx);

        QAbstractAxis *axisy = axes(Qt::Vertical).first();
        QValueAxis *vaxis = 0;
        if (axisy->type() == QAbstractAxis::AxisTypeValue)
            vaxis = qobject_cast<QValueAxis *>(axisy);

        if (haxis && vaxis) {
            //Calculate the "unit" between points on the x
            //y axis.
            double xUnit = this->plotArea().width() / haxis->max();
            double yUnit = this->plotArea().height() / vaxis->max();

            //Convert the mappedPoint to the actual chart scale.
            double x = mappedPoint.x() / xUnit;
            double y = vaxis->max() - mappedPoint.y() / yUnit;

            //Replace the old point with the new one.
            m_series->replace(m_movingPoint, QPointF(x, y));

            //Update the m_movingPoint so we are able to
            //do the replace also during mousemoveEvent.
            m_movingPoint.setX(x);
            m_movingPoint.setY(y);
        }
    }
}