QCustomPlot坐标轴游标(显示当前x、y坐标值)

注：在坐标轴添加游标时，单独x轴或单独y轴应用游标无异常，当双轴均显示游标时会出现卡顿情况，需要在.pro中添加如下OpenGL的应用即可解决。

LIBS+=-lopengl32 -lglu32
DEFINES += QCUSTOMPLOT_USE_OPENGL

1、与鼠标跟随一样，建立游标类如下

#ifndef AXISTRACER_H
#define AXISTRACER_H

#include <QObject>
#include "qcustomplot.h"
enum TracerType
{
    XAxisTracer=0,//依附在x轴上显示x值
    YAxisTracer=1,//依附在y轴上显示y值
    DataTracer=2,//在图中显示x,y值
    MouseMarker=3//固定游标
};

class AxisTracer : public QObject
{
    Q_OBJECT
public:
    explicit AxisTracer(QCustomPlot *_plot, TracerType _type, QObject *parent = nullptr);

    void updatePosition(double xValue, double yValue);

protected:
    TracerType m_type;//类型
    QCustomPlot *m_plot;//图表
    QCPItemTracer *m_tracer;//跟踪的点
    QCPItemText *m_label;//显示的数值
    QCPItemLine *m_arrow;//箭头

signals:

public slots:
};

#endif // AXISTRACER_H


#include "axistracer.h"

AxisTracer::AxisTracer(QCustomPlot *_plot, TracerType _type, QObject *parent) : QObject(parent),
    m_type(_type),
    m_plot(_plot)
{
    if(m_plot)
    {
        QColor clrDefault(Qt::red);
        QBrush brushDefault(Qt::NoBrush);
        QPen penDefault(clrDefault);
        penDefault.setWidthF(0.5);

        m_tracer = new QCPItemTracer(m_plot);
        m_tracer->setStyle(QCPItemTracer::tsCircle);
        m_tracer->setPen(penDefault);
        m_tracer->setBrush(brushDefault);

        m_label = new QCPItemText(m_plot);
        m_label->setLayer("overlay");
        m_label->setClipToAxisRect(false);
        m_label->setPadding(QMargins(5, 5, 5, 5));
        m_label->setBrush(brushDefault);
        m_label->setPen(penDefault);
        m_label->position->setParentAnchor(m_tracer->position);
        m_label->setFont(QFont("Arial", 8));
        m_label->setColor(clrDefault);
        m_label->setText("");

        m_arrow = new QCPItemLine(m_plot);
        m_arrow->setPen(penDefault);
        m_arrow->setLayer("overlay");
        m_arrow->setClipToAxisRect(false);
        m_arrow->setHead(QCPLineEnding::esSpikeArrow);//设置头部为箭头形状

        switch(m_type)
        {
        case XAxisTracer:
        {
            m_tracer->position->setTypeX(QCPItemPosition::ptPlotCoords);
            m_tracer->position->setTypeY(QCPItemPosition::ptAxisRectRatio);
            m_tracer->setSize(7);
            m_label->setPositionAlignment(Qt::AlignTop | Qt::AlignHCenter);

            m_arrow->end->setParentAnchor(m_tracer->position);
            m_arrow->start->setParentAnchor(m_arrow->end);
            m_arrow->start->setCoords(0, 20);//偏移量
        }
            break;
        case YAxisTracer:
        {
            m_tracer->position->setTypeX(QCPItemPosition::ptAxisRectRatio);
            m_tracer->position->setTypeY(QCPItemPosition::ptPlotCoords);
            m_tracer->setSize(7);
            m_label->setPositionAlignment(Qt::AlignRight | Qt::AlignHCenter);

            m_arrow->end->setParentAnchor(m_tracer->position);
            m_arrow->start->setParentAnchor(m_label->position);
            m_arrow->start->setCoords(-20, 0);//偏移量
        }
            break;
        case DataTracer:
            break;
        case MouseMarker:
            break;
        }
    }
}

void AxisTracer::updatePosition(double xValue, double yValue)
{
    if (yValue > m_plot->yAxis->range().upper)
        yValue = m_plot->yAxis->range().upper;

    switch (m_type)
    {
    case XAxisTracer:
    {
        m_tracer->position->setCoords(xValue, 1);
        m_label->position->setCoords(0, 15);
        m_arrow->start->setCoords(0, 15);
        m_arrow->end->setCoords(0, 0);
        m_label->setText(QString::number(xValue));
        break;
    }
    case YAxisTracer:
    {
        m_tracer->position->setCoords(0, yValue);
        m_label->position->setCoords(-20, 0);
        m_arrow->start->setCoords(-20, 0);
        m_arrow->end->setCoords(0, 0);
        m_label->setText(QString::number(yValue));
        break;
    }
    case DataTracer:
    {
        break;
    }
    case MouseMarker:
        break;
    }
}

2、QCustomPlot重写进行游标功能呈现

#ifndef QCUSTOMPLOTEX_H
#define QCUSTOMPLOTEX_H

#include "qcustomplot.h"
#include "mousetraceline.h"
#include "axistracer.h"
class QCustomPlotEx : public QCustomPlot
{
    Q_OBJECT
public:
    QCustomPlotEx();

protected:
    virtual void mouseMoveEvent(QMouseEvent *event);

private:
    MouseTraceLine  *m_lineTracer;//鼠标跟随线

    AxisTracer *m_xTracer;//x轴游标
    AxisTracer *m_yTracer;//y轴游标
};

#endif // QCUSTOMPLOTEX_H


#include "qcustomplotex.h"

QCustomPlotEx::QCustomPlotEx()
{
    m_lineTracer = new MouseTraceLine(this,LineType::Both);
    m_xTracer = new AxisTracer(this, TracerType::XAxisTracer);//x轴
    m_yTracer = new AxisTracer(this, TracerType::YAxisTracer);//y轴
}

void QCustomPlotEx::mouseMoveEvent(QMouseEvent *event)
{
    QCustomPlot::mouseMoveEvent(event);
    //当前鼠标位置（像素坐标）
    int x_pos = event->pos().x();
    int y_pos = event->pos().y();

    //像素坐标转成实际的x,y轴的坐标
    double x_val = this->xAxis->pixelToCoord(x_pos);
    double y_val = this->yAxis->pixelToCoord(y_pos);
    m_lineTracer->updatePosition(x_val, y_val);

    m_xTracer->updatePosition(x_val, y_val);
    m_yTracer->updatePosition(x_val, y_val);
    this->replot();
}