Qwt: Is it possible to perform GUI operations from a separate QProcess?

[d_stranz]

how could I use the signal and slot mechanism to notify when I am finished painting?

You're probably not going to have an actual paintEvent() in your thread, but instead you will have some other method that creates a new QImage with the current data. For whatever class it is that implements this updating, be sure it is derived from QObject (so it can emit signals), and implement a signal with a signature something like:

signals:
 
  void imageUpdated( const QImage & image );

signals:

  void imageUpdated( const QImage & image );

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In the GUI thread, add a slot to whatever QWidget class will display the image, and connect that slot to the thread's signal:

public slots:
  void onImageUpdated( const QImage & image );

public slots:
  void onImageUpdated( const QImage & image );

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In that slot, copy the image, then call QWidget::update() to schedule a paintEvent().

I am not familiar enough with the current state of Qwt to know how you would integrate this QImage-based rendering into a QwtPlot. Perhaps you would need to actually paint the entire QwtPlot into the QImage in your thread, or perhaps Qwt has a spectrogram-like plot where a QImage can be substituted for a calculated spectrogram.