qcustomplot鼠标点击后在坐标轴显示值

版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/leijia_xing/article/details/79865822

首先上图看下要实现的效果：

即图中有两条曲线，鼠标点击后显示横坐标的值，以及与两条曲线交点的纵坐标的值。注意：本例只是实现了坐标值的显示，所以显示的值和曲线值不符，鼠标点击的事件可以自行实现。

参照网址：http://www.qcustomplot.com/index.php/tutorials/specialcases/axistags 的方法，稍加改编实现。

主要步骤：

1.在qt中添加类TagAxis，内容如下

tagaxis.h

#ifndef TAGAXIS_H

#define TAGAXIS_H

#include <QObject>

#include "qcustomplot.h"

class TagAxis : public QObject

{

    Q_OBJECT

public:

    explicit TagAxis(QCPAxis *parentAxis);

    virtual ~TagAxis();

    // setters:

    void setPen(const QPen &pen);

    void setBrush(const QBrush &brush);

    void setTextY1(const QString &text);

    void setTextY2(const QString &text);

    void setTextX(const QString &text);

    void updatePosition(double valueY1,double valueY2,double valueX);

signals:

public slots:

protected:

    QCPAxis *mAxis;

    int yAxisCount;

    QPointer<QCPItemTracer> mDummyTracerY1;

    QPointer<QCPItemText> mLabelY1;

    QPointer<QCPItemTracer> mDummyTracerY2;

    QPointer<QCPItemText> mLabelY2;

    QPointer<QCPItemTracer> mDummyTracerX;

    QPointer<QCPItemText> mLabelX;

};

#endif // TAGAXIS_H

tagaxis.cpp

#include "tagaxis.h"

TagAxis::TagAxis(QCPAxis *parentAxis) : QObject(parentAxis),

    mAxis(parentAxis)

{

    mDummyTracerY1 = new QCPItemTracer(mAxis->parentPlot());

    mDummyTracerY1->setVisible(true);

    mDummyTracerY1->position->setTypeX(QCPItemPosition::ptAxisRectRatio);//QCPItemPosition::ptPlotCoords

    mDummyTracerY1->position->setTypeY(QCPItemPosition::ptPlotCoords);

    mDummyTracerY1->position->setAxisRect(mAxis->axisRect());

    mDummyTracerY1->position->setAxes(0, mAxis);

    mLabelY1 = new QCPItemText(mAxis->parentPlot());

    mLabelY1->setLayer("overlay");

    mLabelY1->setClipToAxisRect(false);

    mLabelY1->setPadding(QMargins(3, 0, 3, 0));

    mLabelY1->setBrush(QBrush(Qt::white));

    mLabelY1->setPen(QPen(Qt::blue));

    mLabelY1->setPositionAlignment(Qt::AlignRight|Qt::AlignVCenter);

    mLabelY1->position->setTypeX(QCPItemPosition::ptAxisRectRatio);//QCPItemPosition::ptPlotCoords

    mLabelY1->position->setTypeY(QCPItemPosition::ptPlotCoords);

    mDummyTracerY2 = new QCPItemTracer(mAxis->parentPlot());

    mDummyTracerY2->setVisible(true);

    mDummyTracerY2->position->setTypeX(QCPItemPosition::ptAxisRectRatio);//QCPItemPosition::ptPlotCoords

    mDummyTracerY2->position->setTypeY(QCPItemPosition::ptPlotCoords);

   // mDummyTracerY1->position->setAxisRect(mAxis->axisRect());

   // mDummyTracerY1->position->setAxes(0, mAxis);

    mLabelY2 = new QCPItemText(mAxis->parentPlot());

    mLabelY2->setLayer("overlay");

    mLabelY2->setClipToAxisRect(false);

    mLabelY2->setPadding(QMargins(3, 0, 3, 0));

    mLabelY2->setBrush(QBrush(Qt::white));

    mLabelY2->setPen(QPen(Qt::blue));

    mLabelY2->setPositionAlignment(Qt::AlignRight|Qt::AlignVCenter);

    mLabelY2->position->setTypeX(QCPItemPosition::ptAxisRectRatio);//QCPItemPosition::ptPlotCoords

    mLabelY2->position->setTypeY(QCPItemPosition::ptPlotCoords);

    mDummyTracerX = new QCPItemTracer(mAxis->parentPlot());

    mDummyTracerX->setVisible(true);

    mDummyTracerX->position->setTypeX(QCPItemPosition::ptPlotCoords);//QCPItemPosition::ptPlotCoords

    mDummyTracerX->position->setTypeY(QCPItemPosition::ptAxisRectRatio);

//    mDummyTracerX->position->setAxisRect(mAxis->axisRect());

//    mDummyTracerX->position->setAxes(0, mAxis);

    mLabelX = new QCPItemText(mAxis->parentPlot());

    mLabelX->setLayer("overlay");

    mLabelX->setClipToAxisRect(false);

    mLabelX->setPadding(QMargins(3, 0, 3, 0));

    mLabelX->setBrush(QBrush(Qt::white));

    mLabelX->setPen(QPen(Qt::blue));

    mLabelX->setPositionAlignment(Qt::AlignTop|Qt::AlignHCenter);

    mLabelX->position->setTypeX(QCPItemPosition::ptPlotCoords);//QCPItemPosition::ptPlotCoords

    mLabelX->position->setTypeY(QCPItemPosition::ptAxisRectRatio);

}

TagAxis::~TagAxis()

{

    if (mDummyTracerY1)

        mDummyTracerY1->parentPlot()->removeItem(mDummyTracerY1);

    if (mLabelY1)

        mLabelY1->parentPlot()->removeItem(mLabelY1);

    if (mDummyTracerY2)

        mDummyTracerY2->parentPlot()->removeItem(mDummyTracerY2);

    if (mLabelY2)

        mLabelY2->parentPlot()->removeItem(mLabelY2);

    if (mDummyTracerX)

        mDummyTracerX->parentPlot()->removeItem(mDummyTracerX);

    if (mLabelX)

        mLabelX->parentPlot()->removeItem(mLabelX);

}

void TagAxis::setPen(const QPen &pen)

{

  mLabelY1->setPen(pen);

  mLabelY2->setPen(pen);

  mLabelX->setPen(pen);

}

void TagAxis::setBrush(const QBrush &brush)

{

  mLabelY1->setBrush(brush);

  mLabelY2->setBrush(brush);

  mLabelX->setBrush(brush);

}

void TagAxis::setTextY1(const QString &text)

{

  mLabelY1->setText(text);

}

void TagAxis::setTextY2(const QString &text)

{

  mLabelY2->setText(text);

}

void TagAxis::setTextX(const QString &text)

{

  mLabelX->setText(text);

}

void TagAxis::updatePosition(double valueY1,double valueY2,double valueX)

{

    mDummyTracerY1->position->setCoords(0, valueY1);

    mLabelY1->position->setCoords(0,valueY1);

    mDummyTracerY2->position->setCoords(0, valueY2);

    mLabelY2->position->setCoords(0,valueY2);

    mDummyTracerX->position->setCoords(valueX,1);

    mLabelX->position->setCoords(valueX,1);

}

2.在主文件中引用

#ifndef MAINWINDOW_H

#define MAINWINDOW_H

#include <QMainWindow>

#include "qcustomplot.h"

#include "axistag.h"

#include "tagaxis.h"

namespace Ui {

class MainWindow;

}

class MainWindow : public QMainWindow

{

    Q_OBJECT

public:

    explicit MainWindow(QWidget *parent = 0);

    ~MainWindow();

private slots:

  void timerSlot();

private:

    Ui::MainWindow *ui;

    QCustomPlot *mPlot;

    QPointer<QCPGraph> mGraph1;

    QPointer<QCPGraph> mGraph2;

//    AxisTag *mTag1;

//    AxisTag *mTag2;

    TagAxis *tagAxis;

    QTimer mDataTimer;

};

#endif // MAINWINDOW_H

mainwindow.cpp中实现：

    ui->setupUi(this);

    mPlot = new QCustomPlot(this);

    setCentralWidget(mPlot);

    connect(mPlot->yAxis2, SIGNAL(rangeChanged(QCPRange)), mPlot->yAxis, SLOT(setRange(QCPRange))); 

    connect(mPlot->yAxis2, SIGNAL(rangeChanged(QCPRange)), mPlot->yAxis2, SLOT(setRange(QCPRange)));

    mPlot->yAxis2->setVisible(true);

    mPlot->addGraph();

    mPlot->graph(0)->setPen(QPen(Qt::blue)); // line color blue for first graph

    mPlot->graph(0)->setBrush(QBrush(QColor(0, 0, 255, 20))); // first graph will be filled with translucent blue

    mPlot->addGraph();

    mPlot->graph(1)->setPen(QPen(Qt::red)); // line color red for second graph

    tagAxis = new TagAxis(mPlot->graph(0)->valueAxis());

    tagAxis->setPen(mPlot->graph(0)->pen());

    QVector<double> x(251), y0(251), y1(251);

    for (int i=0; i<251; ++i)

    {

        x[i] = i;

        y0[i] = qExp(-i/150.0)*qCos(i/10.0); // exponentially decaying cosine

        y1[i] = qExp(-i/150.0);              // exponential envelope

    }

    mPlot->xAxis2->setVisible(true);

    mPlot->xAxis2->setTickLabels(false);

    mPlot->yAxis2->setVisible(true);

    mPlot->yAxis2->setTickLabels(false);

    // make left and bottom axes always transfer their ranges to right and top axes:

    connect(mPlot->xAxis, SIGNAL(rangeChanged(QCPRange)), mPlot->xAxis2, SLOT(setRange(QCPRange)));

    connect(mPlot->yAxis, SIGNAL(rangeChanged(QCPRange)), mPlot->yAxis2, SLOT(setRange(QCPRange)));

    // pass data points to graphs:

    mPlot->graph(0)->setData(x, y0);

    mPlot->graph(1)->setData(x, y1);

    // let the ranges scale themselves so graph 0 fits perfectly in the visible area:

    mPlot->graph(0)->rescaleAxes();

    // same thing for graph 1, but only enlarge ranges (in case graph 1 is smaller than graph 0):

    mPlot->graph(1)->rescaleAxes(true);

    // Note: we could have also just called customPlot->rescaleAxes(); instead

    // Allow user to drag axis ranges with mouse, zoom with mouse wheel and select graphs by clicking:

    mPlot->setInteractions(QCP::iRangeDrag | QCP::iRangeZoom | QCP::iSelectPlottables);

    tagAxis->setTextY1("-0.3");

    tagAxis->setTextY2("0.6");

    tagAxis->setTextX("125");

    tagAxis->updatePosition(-0.3,0.6,125);

    mPlot->replot();

完毕！

完整工程代码github地址：https://github.com/cloudsmile/axisTest