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.

Answer 1

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