is it possible to make spectrogram's Y axis labels "fall" over time (waterfall case)

[embeddedmz]

Hi,

I wrote a class "Waterfallplot" that uses QwtPlotSpectrogram to show a "Waterfall", this last has an history (the number of horizontal layers in it, 64 layers => y range : 0 - 64 excluded) and each history corresponds to a number of points (let's call this last layerPoints).

I also wrote a subclass of "QwtMatrixRasterData" named "WaterfallData" to store spectrogram's data (fixed 2D buffer - size = waterfall history) and that is shifted to the left by "layerPoints when data (1-D) is appended.

In "WaterfallData", I also keep track of the insert times of layers (data) so I can show them in the Y axis.

The problem is, unlike the "cpluplot" example, the Y axis labels doesn't seem "to fall" over time. I think it's nice to have this fall over time effect but I failed to achieve it. Instead, I have something similar to this video https://youtu.be/Ma_fNlouBGk?t=310 whereas, I'm wondering if it's possible to have something like this one : https://youtu.be/ZHvraLfV5kU?t=30

Below, the QwtScaleDraw subclass to generate Y labels strings with some comments :

class WaterfallTimeScaleDraw: public QwtScaleDraw
{
   const Waterfallplot& m_waterfallPlot;
   mutable QDateTime m_dateTime;
 
public:
    WaterfallTimeScaleDraw(const Waterfallplot& waterfall) :
        m_waterfallPlot(waterfall)
    {
    }
 
    // When I add data, I need to invalidate y axis cache, so I need to make invalidateCache public !
    // and use : static_cast<WaterfallTimeScaleDraw*>(m_plot->axisScaleDraw(QwtPlot::yLeft))->invalidateCache();
    using QwtScaleDraw::invalidateCache;
 
    // I noticed that for a waterfall having 64 layers (history), v is called with 0, 10, 20, 30, 40, 50 and 60
    // Thus, it's clear that we can't have a "fall" effect with such values
    virtual QwtText label(double v) const
    {
        time_t ret = m_waterfallPlot.getLayerDate(v);
        if (ret > 0)
        {
            m_dateTime.setTime_t(ret);
            //return m_dateTime.toString("hh:mm:ss:zzz"); // change time_t => zzz
            return m_dateTime.toString("hh:mm:ss");
        }
        return QwtText(); // this is only executed when the waterfall is not completely filled
    }
};

class WaterfallTimeScaleDraw: public QwtScaleDraw
{
   const Waterfallplot& m_waterfallPlot;
   mutable QDateTime m_dateTime;

public:
    WaterfallTimeScaleDraw(const Waterfallplot& waterfall) :
        m_waterfallPlot(waterfall)
    {
    }

    // When I add data, I need to invalidate y axis cache, so I need to make invalidateCache public !
    // and use : static_cast<WaterfallTimeScaleDraw*>(m_plot->axisScaleDraw(QwtPlot::yLeft))->invalidateCache();
    using QwtScaleDraw::invalidateCache;

    // I noticed that for a waterfall having 64 layers (history), v is called with 0, 10, 20, 30, 40, 50 and 60
    // Thus, it's clear that we can't have a "fall" effect with such values
    virtual QwtText label(double v) const
    {
        time_t ret = m_waterfallPlot.getLayerDate(v);
        if (ret > 0)
        {
            m_dateTime.setTime_t(ret);
            //return m_dateTime.toString("hh:mm:ss:zzz"); // change time_t => zzz
            return m_dateTime.toString("hh:mm:ss");
        }
        return QwtText(); // this is only executed when the waterfall is not completely filled
    }
};

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If someone is interested in such project (Waterfall view based on Qwt), let me know so I will share my current source code with you on github.

Thanks.