Sharing on QwtPlotPicker showing values of dual Y axes

[Uwe]

For the implementation of trackerText(), all I need is to return a text with both Y axes value but the problem is how.

You can use the canvas maps:

virtual QwtText YourPicker::trackerText(const QwtDoublePoint &pos) const
{
    QPointF p = transform(pos);
 
    int axis = (yAxis() == QwtPlot::yRight) ? QwtPlot::yLeft : QwtPlot::yRight:
    double y2 = plot()->canvasMap(axis).invTransform(p.y());
 
    ...
}

virtual QwtText YourPicker::trackerText(const QwtDoublePoint &pos) const
{
    QPointF p = transform(pos);

    int axis = (yAxis() == QwtPlot::yRight) ? QwtPlot::yLeft : QwtPlot::yRight:
    double y2 = plot()->canvasMap(axis).invTransform(p.y());

    ...
}

To copy to clipboard, switch view to plain text mode 

In your special situation, where you simple append the second y value to the text you could also do the following:

virtual QwtText YourPicker::trackerText(const QPoint &pos) const
{
    int axis = (yAxis() == QwtPlot::yRight) ? QwtPlot::yLeft : QwtPlot::yRight:
    double y2 = plot()->canvasMap(axis).transform(p.y());
 
    QwtText text = QwtPlotPicker::trackerText(pos);
    text += ...
    return text:
}

virtual QwtText YourPicker::trackerText(const QPoint &pos) const
{
    int axis = (yAxis() == QwtPlot::yRight) ? QwtPlot::yLeft : QwtPlot::yRight:
    double y2 = plot()->canvasMap(axis).transform(p.y());

    QwtText text = QwtPlotPicker::trackerText(pos);
    text += ...
    return text:
}

To copy to clipboard, switch view to plain text mode 

Uwe