QwtPlotLegend only uses one column

[orignihn]

Hello,

I'm trying to include a legend with multiple columns on top of my plot, but only one ever appears.

Here's the code for adding a new data set (part of a member function of a class that inherits QwtPlot):

QwtPlotCurve* curve = new QwtPlotCurve(var->get_name());
curve->attach(this);
plotLayout()->setLegendPosition(QwtPlot::TopLegend);

QwtPlotCurve* curve = new QwtPlotCurve(var->get_name());
curve->attach(this);
plotLayout()->setLegendPosition(QwtPlot::TopLegend);

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but every time I add a curve, the legend gets a new item directly underneath the old one. I have no other legend-related code anywhere, and there is plenty of space for 2-3 more legend items before adding another row. I'm using Qwt-5.2.1.

How do I get legend items to appear in multiple columns above my plot?

Thanks,
Tom