QwtPlotSpectrogram contour lines not visible (qwt 6.0.1)

[okachobi]

I have a plot working now with QwtPlotSpectrogram using my own data class for continuous interpolated values.

The documentation on QwtPlotSpectrogram is fairly brief, so I've been following the example/Spectrogram. I decided to try turning on contour lines and added initialization of the contour levels using setContourLevels with code similar to this...

QList<double> contourLevels;
    for ( double level = 0.5; level < 110.0; level += 15.0 )
        contourLevels += level;
    spectrogram->setContourLevels( contourLevels );
 
    spectrogram->setDefaultContourPen( QPen() );
    spectrogram->setDisplayMode(QwtPlotSpectrogram::ContourMode, true);

QList<double> contourLevels;
    for ( double level = 0.5; level < 110.0; level += 15.0 )
        contourLevels += level;
    spectrogram->setContourLevels( contourLevels );

    spectrogram->setDefaultContourPen( QPen() );
    spectrogram->setDisplayMode(QwtPlotSpectrogram::ContourMode, true);

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This follows the example code pretty closely. I use a QwtPlotGrid as well.

I don't see the lines drawn over my spectrogram plot, so I tried disabling ImageMode and only enabling the ContourMode, but this produced nothing.

I'm sure I'm missing something simple. I'm not subclassing QwtPlotSpectrogram- only the data class. Everything is working with the ImageMode and my spectrogram plot, except the countour lines.

thanks in advance...