Hello!

After I changed the display to the one with higher resolution (1920 Ñ… 1080) the spectrogram slowed down.

So now I'd like to return to the approach you suggesed erlier "Incremental image composition". Do I understand it right that it is possible to plot only part of the spectrogram OR to add data to the spectrogram?

I looked at the topic "Incremental Spectrogram".
I do not understand how to properly reimplement method QwtPlotSpectrogram::renderImage.

For example, I have a spectrogram, filling from left to right by columns. I want to render only new part of the picture (Today for display I use overloading method QwtRasterData::value and replot all picture).
1. What triggers the method QwtPlotSpectrogram::renderImage? Repaint, replot etc.? Or do I need to call it myself?
2. How to set the return value in an overloaded method?
3. Do I need an analog for method QwtRasterData::value,that i used when call replot?
4. Can you provide a brief description of how to make incremental spectrogram data plotting?

Thank you in advance.