Incremental Spectrogram...

[Uwe]

All right. this is possible with a "normal" QwtPlotCurve. There I can draw() data from and to. But how to do this with a spectrogram?

Derive from QwtPlotSpectrogram and introduce a QImage, where you collect your increasing values. Whenever you want to add new values call QwtPlotSpectrogram::renderImage with a painter initialized with your image and for the new area only.

Then overload YourPlotSpectrogram::renderImage returning parts of your image instead of rendering it ( don't call this one for the image composition above ).

When you want to paint new parts of your spectrogram on screen do something like this:

QRectF newArea = ...; // 
QRectF rect = QwtScaleMap::transform( 
    spectrogram->canvasMap( QwtPlot::xBottom), 
    spectrogram->canvasMap( QwtPlot::yLeft ), 
    newArea );
plot->canvas()->repaint( rect );

QRectF newArea = ...; // 
QRectF rect = QwtScaleMap::transform( 
    spectrogram->canvasMap( QwtPlot::xBottom), 
    spectrogram->canvasMap( QwtPlot::yLeft ), 
    newArea );
plot->canvas()->repaint( rect );

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When will the qwt6 be finished? Or is the rc5 stable enough?

Use SVN trunk - this is planned to be the final version of Qwt 6.

Uwe

[AndiTheCoder]

Hello Uwe,

good news! I have separated sampling (with threading!) from refreshing the plot(s) and it runs very good!

I have not to draw only parts of a curve because the sampling data are saved in the yData of the QwtPlotCurve directly. So every replot() (by now only with 25Hz) all sampled data will be displayed at once. So there is also enough time to update the (whole) spectrogram with 25Hz.

The step updating to Qwt6 is not easy for me. Many functions I use aren't available any more (e. g. QwtPlot:rint(); also the QwtPlotSpectrogram class has changed).

But thank you very much for helping me! And if I will have another problem I will post it in this forum.

Thanks and Servus

Andreas