PyQt, Qwt: Add a horizontal line (y=value)

[Lykanthropie]

Hi,

I am trying to plot a simple horizontal line in my QwtPlot. I have a plot with DateTimeScaleEngine (X-Axis) and a 'normal' y-axis with values 0-255.
How can I draw a horizontal line into this plot? This const. line will represent the mean value.

I don't want to fill the curve, just a line.

I tried f.e. this:

self.meanline = QwtPlotCurve()
self.meanline.setPen(QPen(Qt.green,2))
self.meanline.setStyle(QwtPlotCurve.NoCurve) 
self.meanline.setCurveType(QwtPlotCurve.Yfx)
self.meanline.attach(self.qwtPlot)

self.meanline = QwtPlotCurve()
self.meanline.setPen(QPen(Qt.green,2))
self.meanline.setStyle(QwtPlotCurve.NoCurve) 
self.meanline.setCurveType(QwtPlotCurve.Yfx)
self.meanline.attach(self.qwtPlot)

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All my tests failed!

Thanks!