Display x and y coordinates on graph in QCustomplot

Question

I want to display the x and y coordinates on mouse move on the graph. I calculated the x and y coordinates but not really sure how to display on the graph near to the point (preferably like (x,y) this

connect(ui->customPlot, SIGNAL(mouseRelease(QMouseEvent*)), this, SLOT(mouseRelease(QMouseEvent*)));
connect(ui->customPlot, SIGNAL(mousePress(QMouseEvent*)), this, SLOT(mousePress(QMouseEvent*)));


float MainWindow::findX(QCustomPlot* customPlot, QCPCursor* cursor1, QMouseEvent* event)
{

    double x = customPlot->xAxis->pixelToCoord(event->pos().x());
    double y = customPlot->yAxis->pixelToCoord(event->pos().y());

    // I think I need to write a function here which will display the text on the graph.
}

void MainWindow::mouseRelease(QMouseEvent* event)
{
    if (event->button() == Qt::LeftButton) {
        static QCPCursor cursor1;
        QCustomPlot* plot = (QCustomPlot*)sender();
        float x = findX(plot, &cursor1, event);
    }
}

void MainWindow::mousePressed(QMouseEvent* event)
{
    if (event->button() == Qt::RightButton) {
        QCustomPlot* plot = (QCustomPlot*)sender();
        plot->setContextMenuPolicy(Qt::CustomContextMenu);
        connect(plot, SIGNAL(customContextMenuRequested(const QPoint&)), this, SLOT(ShowContextMenu(const QPoint&)));
    }
}

eyllanesc · Accepted Answer · 2017-05-31 23:26:19Z

You can create a QCPItemText and place the text and move it to the position you got with pixelToCoord.

*.h

private:
    QCPItemText *textItem;

private slots:
    void onMouseMove(QMouseEvent* event);

*.cpp

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

    textItem = new QCPItemText(ui->customPlot);
    connect(ui->customPlot, &QCustomPlot::mouseMove, this, &MainWindow::onMouseMove);
}


void MainWindow::onMouseMove(QMouseEvent *event)
{
    QCustomPlot* customPlot = qobject_cast<QCustomPlot*>(sender());
    double x = customPlot->xAxis->pixelToCoord(event->pos().x());
    double y = customPlot->yAxis->pixelToCoord(event->pos().y());
    textItem->setText(QString("(%1, %2)").arg(x).arg(2));
    textItem->position->setCoords(QPointF(x, y));
    textItem->setFont(QFont(font().family(), 10));
    customPlot->replot();
}

The following image shows the result but for some reason my capture does not take the image of my pointer.

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Display x and y coordinates on graph in QCustomplot

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