setting one value transparent in QwtPlotSpectrogram

[qt_gotcha]

thanks for helping. it doesn't work yet. I can make certain ranges (semi) transparent but I don't see a the previous plot that is in the same widget, but the background color value, i.e. color1 of the linearcolormap(color1, color2). I'll continue looking

[Uwe]

In SVN trunk I have added a slider to the spectrogram example, where you can see how to use the alpha value.

Uwe