QwtPlotSpectrogram, don't draw from scratch!

k_kaz

I want to draw a spectrogram periodically, which means that data come over time, and i want to just add columns to the previous graph.

What i did is to declare a QwtPlotSpectrogram * spectrogram instance, and i use the setData() function where i pass a SpectrogramData instance:

class SpectrogramData : public QwtRasterData {

private:
    std::vector<std::vector<double>> data;

public:
    SpectrogramData(int height, int width);

    ~SpectrogramData();

    virtual double value(double x, double y) const;
};

spectrogram->setData(spectrogram_data);

When new data come, i add them to the data structure, and call replot() in the QwtPlot instance that the QwtSpectrogram is attached to.

Because the spectrogram will ultimately have about 700*22000 size, i don't know what does replot() do. Is there a way to tell qwt to only plot a certain column of data or region or rectangular or something?

SGaist

Hi,

That's a question you should ask to the Qwt authors.