Offsetting Qwt Plot Markers and adding symbols to Qwt Legend

[Uwe]

Is there a method of partially raising a marker, so that it can reveal a marker beneath it?

If you want to modify the position of the marker text in widget coordinates:

class YourMarker: public QwtPlotMarker
{
    virtual void drawLabel( QPainter *painter,
        const QRectF &canvasRect, const QPointF &pos ) const
    {
         const QPointF &translatedPos = ...;
         QwtPlotMarker::drawLabel( painter, canvasRect, translatedPos );
};

class YourMarker: public QwtPlotMarker
{
    virtual void drawLabel( QPainter *painter,
        const QRectF &canvasRect, const QPointF &pos ) const
    {
         const QPointF &translatedPos = ...;
         QwtPlotMarker::drawLabel( painter, canvasRect, translatedPos );
};

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Secondly, I have a set of symbols to denote different phases on the plot. I would like to include them in the legend even when they are absent from the graph.

legend and plot are synchronized by QwtPlot::legendDataChanged() and QwtAbstractLegend::updateLegend(). The second is virtual and would be a candidate for appending extra entries.

But there is also nothing wrong with inserting a dummy item. But if you don't want to insert real markers you can create a dummy QwtPlotItem, where you set the QwtPlotItem::Legend flag and overload QwtPlotItem::legendData(). Note that an item can have more than one entry ( f.e QwtPlotMultiBarChart ).

Uwe