采用Qt绘制多条曲线，跟随鼠标动态显示线上点的值（基于Qt的开源绘图控件QCustomPlot进行二次开发）

QCustomPlot是一个开源的基于Qt的第三方绘图库，能够绘制漂亮的2D图形。
QCustomPlot的官方网址：https://www.qcustomplot.com/
从官网下载QCustomPlot的源文件，包括qcustomplot.h和qcustomplot.cpp。

本程序的源码下载地址： https://github.com/xiongxw/XCustomPlot.git

1. 自定义鼠标显示跟随类XxwTracer和XxwTraceLine：

XxwTracer用于在图表中显示鼠标所在位置的x,y值
XxwTraceLine用于在图中显示水平或垂直的虚线
头文件XxwTracer.h

#ifndef MYTRACER_H
#define MYTRACER_H

#include <QObject>
#include "qcustomplot.h"

///
/// \brief The XxwTracer class:在图表中显示鼠标所在位置的x,y值的追踪显示器
///
class XxwTracer : public QObject
{
Q_OBJECT

public:
enum TracerType
{
        XAxisTracer,//依附在x轴上显示x值
        YAxisTracer,//依附在y轴上显示y值
        DataTracer//在图中显示x,y值
};
    explicit XxwTracer(QCustomPlot *_plot, TracerType _type, QObject *parent = Q_NULLPTR);
    ~XxwTracer();
void setPen(const QPen &pen);
void setBrush(const QBrush &brush);
void setText(const QString &text);
void setLabelPen(const QPen &pen);
void updatePosition(double xValue, double yValue);
    void setVisible(bool m_visible);

protected:
    bool m_visible;//是否可见
    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
};


///
/// \brief The XxwCrossLine class:用于显示鼠标移动过程中的鼠标位置的直线
///
class XxwTraceLine : public QObject
{
public:
    enum LineType
    {
        VerticalLine,//垂直线
        HorizonLine, //水平线
        Both//同时显示水平和垂直线
    };
    explicit XxwTraceLine(QCustomPlot *_plot, LineType _type = VerticalLine, QObject *parent = Q_NULLPTR);
    ~XxwTraceLine();
    void initLine();
    void updatePosition(double xValue, double yValue);

    void setVisible(bool vis)
    {
        if(m_lineV)
            m_lineV->setVisible(vis);
        if(m_lineH)
            m_lineH->setVisible(vis);
    }

protected:
    bool m_visible;//是否可见
    LineType m_type;//类型
    QCustomPlot *m_plot;//图表
    QCPItemStraightLine *m_lineV; //垂直线
    QCPItemStraightLine *m_lineH; //水平线
};

#endif // MYTRACER_H

源文件MyTracer.cpp

#include "MyTracer.h"

XxwTracer::XxwTracer(QCustomPlot *_plot, TracerType _type, QObject *parent)
    : QObject(parent),
      m_plot(_plot),
      m_type(_type)
{
    m_visible = true;
    m_tracer = Q_NULLPTR;// 跟踪的点
    m_label = Q_NULLPTR;// 显示的数值
    m_arrow = Q_NULLPTR;// 箭头
    if (m_plot)
    {
        QColor clrDefault(Qt::red);
        QBrush brushDefault(Qt::NoBrush);
        QPen penDefault(clrDefault);
        //        penDefault.setBrush(brushDefault);
        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("宋体", 8));
        m_label->setFont(QFont("Arial", 8));
        m_label->setColor(clrDefault);
        m_label->setText("");

        m_arrow = new QCPItemLine(m_plot);
        QPen  arrowPen(clrDefault, 1);
        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:
        {
            m_tracer->position->setTypeX(QCPItemPosition::ptPlotCoords);
            m_tracer->position->setTypeY(QCPItemPosition::ptPlotCoords);
            m_tracer->setSize(5);

            m_label->setPositionAlignment(Qt::AlignLeft | Qt::AlignVCenter);

            m_arrow->end->setParentAnchor(m_tracer->position);
            m_arrow->start->setParentAnchor(m_arrow->end);
            m_arrow->start->setCoords(20, 0);
            break;
        }
        default:
            break;
        }
        setVisible(false);
    }
}

XxwTracer::~XxwTracer()
{
    if(m_plot)
    {
        if (m_tracer)
            m_plot->removeItem(m_tracer);
        if (m_label)
            m_plot->removeItem(m_label);
        if (m_arrow)
            m_plot->removeItem(m_arrow);
    }
}

void XxwTracer::setPen(const QPen &pen)
{
    if(m_tracer)
        m_tracer->setPen(pen);
    if(m_arrow)
        m_arrow->setPen(pen);
}

void XxwTracer::setBrush(const QBrush &brush)
{
    if(m_tracer)
        m_tracer->setBrush(brush);
}

void XxwTracer::setLabelPen(const QPen &pen)
{
    if(m_label)
    {
        m_label->setPen(pen);
        m_label->setBrush(Qt::NoBrush);
        m_label->setColor(pen.color());
    }
}

void XxwTracer::setText(const QString &text)
{
    if(m_label)
        m_label->setText(text);
}

void XxwTracer::setVisible(bool vis)
{
    m_visible = vis;
    if(m_tracer)
        m_tracer->setVisible(m_visible);
    if(m_label)
        m_label->setVisible(m_visible);
    if(m_arrow)
        m_arrow->setVisible(m_visible);
}

void XxwTracer::updatePosition(double xValue, double yValue)
{
    if (!m_visible)
    {
        setVisible(true);
        m_visible = true;
    }

    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);
        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);
        setText(QString::number(yValue));
        break;
    }
    case DataTracer:
    {
        m_tracer->position->setCoords(xValue, yValue);
        m_label->position->setCoords(20, 0);
        setText(QString("x:%1,y:%2").arg(xValue).arg(yValue));
        break;
    }
    default:
        break;
    }
}

XxwTraceLine::XxwTraceLine(QCustomPlot *_plot, LineType _type, QObject *parent)
    : QObject(parent),
      m_type(_type),
      m_plot(_plot)
{
    m_lineV = Q_NULLPTR;
    m_lineH = Q_NULLPTR;
    initLine();
}

XxwTraceLine::~XxwTraceLine()
{
    if(m_plot)
    {
        if (m_lineV)
            m_plot->removeItem(m_lineV);
        if (m_lineH)
            m_plot->removeItem(m_lineH);
    }
}

void XxwTraceLine::initLine()
{
    if(m_plot)
    {
        QPen linesPen(Qt::red, 1, Qt::DashLine);

        if(VerticalLine == m_type || Both == m_type)
        {
            m_lineV = new QCPItemStraightLine(m_plot);//垂直线
            m_lineV->setLayer("overlay");
            m_lineV->setPen(linesPen);
            m_lineV->setClipToAxisRect(true);
            m_lineV->point1->setCoords(0, 0);
            m_lineV->point2->setCoords(0, 0);
        }

        if(HorizonLine == m_type || Both == m_type)
        {
            m_lineH = new QCPItemStraightLine(m_plot);//水平线
            m_lineH->setLayer("overlay");
            m_lineH->setPen(linesPen);
            m_lineH->setClipToAxisRect(true);
            m_lineH->point1->setCoords(0, 0);
            m_lineH->point2->setCoords(0, 0);
        }
    }
}

void XxwTraceLine::updatePosition(double xValue, double yValue)
{
    if(VerticalLine == m_type || Both == m_type)
    {
        if(m_lineV)
        {
            m_lineV->point1->setCoords(xValue, m_plot->yAxis->range().lower);
            m_lineV->point2->setCoords(xValue, m_plot->yAxis->range().upper);
        }
    }

    if(HorizonLine == m_type || Both == m_type)
    {
        if(m_lineH)
        {
            m_lineH->point1->setCoords(m_plot->xAxis->range().lower, yValue);
            m_lineH->point2->setCoords(m_plot->xAxis->range().upper, yValue);
        }
    }
}

2. 自定义的图表类XCustomPlot

XCustomPlot是基于QCustomPlot二次开发的图表类，在鼠标移动过程中动态显示曲线上点的值。
头文件XCustomPlot.h

#ifndef XCUSTOMPLOT_H
#define XCUSTOMPLOT_H

#include "XxwTracer.h"
#include "qcustomplot.h"
#include <QObject>
#include <QList>

class XxwCustomPlot:public QCustomPlot
{
    Q_OBJECT

public:
    XxwCustomPlot(QWidget *parent = 0);

protected:
    virtual void mouseMoveEvent(QMouseEvent *event);

public:
    ///
    /// \brief 设置是否显示鼠标追踪器
    /// \param show:是否显示
    ///
    void showTracer(bool show)
    {
        m_isShowTracer = show;
        if(m_xTracer)
            m_xTracer->setVisible(m_isShowTracer);
        foreach (XxwTracer *tracer, m_dataTracers)
        {
            if(tracer)
                tracer->setVisible(m_isShowTracer);
        }
        if(m_lineTracer)
            m_lineTracer->setVisible(m_isShowTracer);
    }

    ///
    /// \brief 是否显示鼠标追踪器
    /// \return
    ///
    bool isShowTracer(){return m_isShowTracer;};

private:
    bool m_isShowTracer;//是否显示追踪器（鼠标在图中移动，显示对应的值）
    XxwTracer *m_xTracer;//x轴
    XxwTracer *m_yTracer;//y轴
    QList<XxwTracer *> m_dataTracers;//
    XxwTraceLine  *m_lineTracer;//直线
};

#endif // XCUSTOMPLOT_H
源文件XCustomPlot.h

#include "XxwCustomPlot.h"

XxwCustomPlot::XxwCustomPlot(QWidget *parent)
    :QCustomPlot(parent)
    ,m_isShowTracer(false)
    ,m_xTracer(Q_NULLPTR)
    ,m_yTracer(Q_NULLPTR)
    ,m_dataTracers(QList<XxwTracer *>())
    ,m_lineTracer(Q_NULLPTR)
{
}

void XxwCustomPlot::mouseMoveEvent(QMouseEvent *event)
{
    QCustomPlot::mouseMoveEvent(event);

    if(m_isShowTracer)
    {
        //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
        float x_val = this->xAxis->pixelToCoord(x_pos);
        float y_val = this->yAxis->pixelToCoord(y_pos);

        if(Q_NULLPTR == m_xTracer)
            m_xTracer = new XxwTracer(this, XxwTracer::XAxisTracer);//x轴
        m_xTracer->updatePosition(x_val, y_val);

        if(Q_NULLPTR == m_yTracer)
            m_yTracer = new XxwTracer(this, XxwTracer::YAxisTracer);//y轴
        m_yTracer->updatePosition(x_val, y_val);

        int nTracerCount = m_dataTracers.count();
        int nGraphCount = graphCount();
        if(nTracerCount < nGraphCount)
        {
            for(int i = nTracerCount; i < nGraphCount; ++i)
            {
                XxwTracer *tracer = new XxwTracer(this, XxwTracer::DataTracer);
                m_dataTracers.append(tracer);
            }
        }
        else if(nTracerCount > nGraphCount)
        {
            for(int i = nGraphCount; i < nTracerCount; ++i)
            {
                XxwTracer *tracer = m_dataTracers[i];
                if(tracer)
                {
                    tracer->setVisible(false);
                }
            }
        }
        for (int i = 0; i < nGraphCount; ++i)
        {
            XxwTracer *tracer = m_dataTracers[i];
            if(!tracer)
                tracer = new XxwTracer(this, XxwTracer::DataTracer);
            tracer->setVisible(true);
            tracer->setPen(this->graph(i)->pen());
            tracer->setBrush(Qt::NoBrush);
            tracer->setLabelPen(this->graph(i)->pen());
            auto iter = this->graph(i)->data()->findBegin(x_val);
            double value = iter->mainValue();
//            double value = this->graph(i)->data()->findBegin(x_val)->value;
            tracer->updatePosition(x_val, value);
        }

        if(Q_NULLPTR == m_lineTracer)
            m_lineTracer = new XxwTraceLine(this,XxwTraceLine::Both);//直线
        m_lineTracer->updatePosition(x_val, y_val);

        this->replot();//曲线重绘
    }
}

3. 使用自定义图表类XCustomPlot

在需要绘图的地方使用，代码如下：

  m_customPlot = new XxwCustomPlot();
    m_customPlot->showTracer(true);

    // add title layout element:
    m_customPlot->plotLayout()->insertRow(0);
    m_customPlot->plotLayout()->addElement(0, 0, new QCPTextElement(m_customPlot, "标题", QFont("黑体", 12, QFont::Bold)));

    m_customPlot->legend->setVisible(true);
    QFont legendFont = font();  // start out with MainWindow's font..
    legendFont.setPointSize(9); // and make a bit smaller for legend
    m_customPlot->legend->setFont(legendFont);
    m_customPlot->legend->setBrush(QBrush(QColor(255,255,255,230)));
    // by default, the legend is in the inset layout of the main axis rect. So this is how we access it to change legend placement:
    m_customPlot->axisRect()->insetLayout()->setInsetAlignment(0, Qt::AlignTop|Qt::AlignCenter);

    // make left and bottom axes always transfer their ranges to right and top axes:
    connect(m_customPlot->xAxis, SIGNAL(rangeChanged(QCPRange)), m_customPlot->xAxis2, SLOT(setRange(QCPRange)));
    connect(m_customPlot->yAxis, SIGNAL(rangeChanged(QCPRange)), m_customPlot->yAxis2, SLOT(setRange(QCPRange)));

    // Allow user to drag axis ranges with mouse, zoom with mouse wheel and select graphs by clicking:
    m_customPlot->setInteractions(QCP::iRangeDrag | QCP::iRangeZoom | QCP::iSelectPlottables);

    // generate some data:
    int nCount = 100;
    QVector<double> x(nCount), y0(nCount), y1(nCount); // initialize with entries 0..100
    for (int i = 0; i < nCount; ++i)
    {
        x[i] = i; // x goes from -1 to 1
        y0[i] = qSin(i * 10.0f / nCount); //sin
        y1[i] = qCos(i * 10.0f / nCount); //cos
    }
    // create graph and assign data to it:
    QPen pen;
    int i = 1;
    QCPGraph *pGraph = m_customPlot->addGraph();
    //        m_customPlot->graph(0)->setData(x, y0);
    pGraph->setName("sin曲线");
    pGraph->setData(x,y0);
    pGraph->setPen(QPen(Qt::blue));

    pGraph = m_customPlot->addGraph();
    //        m_customPlot->graph(0)->setData(x, y0);
    pGraph->setName("cos曲线");
    pGraph->setData(x,y1);
    pGraph->setPen(QPen(Qt::darkYellow));

    // give the axes some labels:
    m_customPlot->xAxis->setLabel("x");
    m_customPlot->yAxis->setLabel("y");

    // set axes ranges, so we see all data:
//    m_customPlot->xAxis->setRange(-1, 1);
//    m_customPlot->yAxis->setRange(0, 1);
    m_customPlot->rescaleAxes(true);

    m_customPlot->replot();

4. 效果图

效果图

本程序的源码下载地址： https://github.com/xiongxw/XCustomPlot.git

参考：https://blog.csdn.net/sunnyloves/article/details/82344815