QCustomPlot绘图并设置游标，双游标

最终实现功能：

1.鼠标单击生成游标（两个游标在一起），并随着鼠标移动而移动。

2.鼠标双击固定第一个游标，第二个游标仍可随着鼠标移动而移动。

3.鼠标再次双击固定第二个游标。

4.起始，结束编辑框分别显示第一个游标和第二个游标的位置信息。

头文件添加两个游标对象，画图函数和三个鼠标点击，双击，移动槽函数如下：

class CursorDialog : public QDialog
{
    Q_OBJECT

public:
    explicit CursorDialog(QWidget *parent = nullptr);
    ~CursorDialog();

    void PlotWaterfall(QCustomPlot* customPlot);

    QCustomPlot* customPlot;
    QCPColorMap* cpColorMap;

    QCPItemTracer* tracer1;
    QCPItemTracer* tracer2;
    bool    bTracer1;
    bool    bTracer2;

private slots:
    void mousePress(QMouseEvent* e);
    void mouseDoubleClick(QMouseEvent* e);
    void mouseMove(QMouseEvent *e);

private:
    Ui::CursorDialog *ui;
};

CursorDialog::CursorDialog(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::CursorDialog)
{
    ui->setupUi(this);

    ui->lineEditStart->setText("0");
    ui->lineEditEnd->setText("0");

    customPlot = ui->widget;
    PlotWaterfall(customPlot);

    bTracer1 = false;
    bTracer2 = false;

    //信号连接槽函数
    connect(customPlot, SIGNAL(mousePress(QMouseEvent*)), this, SLOT(mousePress(QMouseEvent*)));
    connect(customPlot, SIGNAL(mouseDoubleClick(QMouseEvent*)), this, SLOT(mouseDoubleClick(QMouseEvent*)));
    connect(customPlot, SIGNAL(mouseMove(QMouseEvent*)), this, SLOT(mouseMove(QMouseEvent*)));

}

画图函数PlotWaterfall(QCustomPlot* customPlot)中初始化两个游标

   //构造游标1
    tracer1 = new QCPItemTracer(customPlot);
    tracer1->setPen(QPen(Qt::SolidLine)); //实线游标
    tracer1->setStyle(QCPItemTracer::tsCrosshair);//十字星线
    tracer1->setSize(2.0);
    tracer1->setVisible(false);

    //构建游标2
    tracer2 = new QCPItemTracer(customPlot);
    tracer2->setPen(QPen(Qt::SolidLine)); //实线游标
    tracer2->setStyle(QCPItemTracer::tsCrosshair);//十字星线
    tracer2->setSize(2.0);
    tracer2->setVisible(false);
    

/**
 * @brief 鼠标点击事件
 * @param e
 */
int clickNum = 0; //用于判断是偶数双击还是单数双击
void CursorDialog::mousePress(QMouseEvent* e)
{
    QCustomPlot *curCustomPlot = qobject_cast<QCustomPlot *>(sender());
    if(curCustomPlot == customPlot)
    {
        if(e->button() == Qt::LeftButton)
        {
            bTracer1 = true;
            tracer1->setVisible(true);

            bTracer2 = true;
            tracer2->setVisible(true);
        }
        if(e->button() == Qt::RightButton)
        {
            bTracer1 = false;
            tracer1->setVisible(false);

            bTracer2 = false;
            tracer2->setVisible(false);

            clickNum = 0;
        }

        curCustomPlot->replot();
    }
}

/**
 * @brief 鼠标双击事件
 * @param e
 */
void CursorDialog::mouseDoubleClick(QMouseEvent* e)
{
    QCustomPlot *curCustomPlot = qobject_cast<QCustomPlot *>(sender());
    if(curCustomPlot == customPlot)
    {
        if(clickNum%2 == 0)
        {
            bTracer1 = false;
            tracer1->setVisible(true);
        }
        else
        {
            bTracer2 = false;
            tracer2->setVisible(true);
            bTracer1 = false; //双击时会先触发单击事件，单击时会把bTracer1置为true，所以这里重新设置为false
        }
        clickNum++;
    }
}

/**
 * @brief 鼠标移动事件
 * @param e
 */
void CursorDialog::mouseMove(QMouseEvent *e)
{
    QCustomPlot *curCustomPlot = qobject_cast<QCustomPlot *>(sender());
    if(curCustomPlot == customPlot)
    {
        if(bTracer1)
        {
            int x = curCustomPlot->xAxis->pixelToCoord(e->pos().x());
            int pos = x;
            if(pos < 0)
            {
                return ;
            }
            qDebug() << "POS:" << pos;

            tracer1->position->setCoords(pos, 0);
            tracer1->setVisible(true);
            curCustomPlot->replot();
            ui->lineEditStart->setText(QString("%1").arg(x));
        }

        if(bTracer2)
        {
            int x = curCustomPlot->xAxis->pixelToCoord(e->pos().x());
            int pos = x;
            if(pos < 0)
            {
                return ;
            }

            tracer2->position->setCoords(pos, 0);
            tracer2->setVisible(true);
            curCustomPlot->replot();
            ui->lineEditEnd->setText(QString("%1").arg(x));
        }
    }
}