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