Qt Charts - How to display a specific point value on x and y axis?

Question

I have a chart with QLineSeries and I would like to display x and y value of the point where the mouse is. I think I can handle the problem of retrieving the mouse point but I don't know how to display it with Qt Charts.

I don't see functions to do that in QValueAxis and others.

The point doesn't have to be displayed on axis necessarily, directly under the mouse would be enough as well.

please see http://stackoverflow.com/questions/18140446/display-the-plot-values-on-mouse-over-detect-scatter-points?rq=1 — Vladimir Bershov, Dec 22 '16 at 12:38
this is for QCustomPlot, but if there are no solution with QChart I guess I'll have to go there — Dinendal, Dec 22 '16 at 13:10

Dinendal · Accepted Answer · 2017-01-20T08:51:38.920

I found out a way to do it without too much drawing involved :

void StatisticsChartView::mouseMoveEvent(QMouseEvent * event)
{
    /* Setting the mouse position label on the axis from value to position */
    qreal x = (event->pos()).x();
    qreal y = (event->pos()).y();

    qreal xVal = _chart->mapToValue(event->pos()).x();
    qreal yVal = _chart->mapToValue(event->pos()).y();

    qreal maxX = axisX->max();
    qreal minX = axisX->min();
    qreal maxY = axisY->max();
    qreal minY = axisY->min();

    if (xVal <= maxX && xVal >= minX && yVal <= maxY && yVal >= minY)
    {
        QPointF xPosOnAxis = _chart->mapToPosition(QPointF(x, 0));
        QPointF yPosOnAxis = _chart->mapToPosition(QPointF(0, y));

        /* m_coordX and m_coordY are `QGraphicsSimpleTextItem` */
        m_coordX->setPos(x, xPosOnAxis.y() + 5);
        m_coordY->setPos(yPosOnAxis.x() - 27, y);

        /* Displaying value of the mouse on the label */
        m_coordX->setText(QString("%1").arg(xVal, 4, 'f', 1, '0'));
        m_coordY->setText(QString("%1").arg(yVal, 4, 'f', 1, '0'));
    }

    QGraphicsView::mouseMoveEvent(event);
}

It will display values along both axis

Qt Charts - How to display a specific point value on x and y axis?

1 Answers1