基于QCustomPlot绘图，鼠标跟随动态显示曲线上的点的值

1 自定义鼠标显示跟随类XxwTracer和XxwTraceLine：
XxwTracer.h

ifndef MYTRACER_H

define MYTRACER_H

include

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

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.h

ifndef XCUSTOMPLOT_H

define XCUSTOMPLOT_H

include "qcustomplot.h"

include "MyTracer.h"

include

include

class XCustomPlot:public QCustomPlot
{
Q_OBJECT

public:
XCustomPlot(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

XCustomPlot.h

include "XCustomPlot.h"

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

void XCustomPlot::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);//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

XCustomPlot *customPlot = new XCustomPlot();
customPlot->showTracer(true);

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

customPlot->legend->setVisible(true);
QFont legendFont = font(); // start out with MainWindow's font..
legendFont.setPointSize(9); // and make a bit smaller for legend
customPlot->legend->setFont(legendFont);
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:
customPlot->axisRect()->insetLayout()->setInsetAlignment(0, Qt::AlignTop|Qt::AlignCenter);

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

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

// generate some data:
int nCount = 100;
QVector

4 效果图