QwtPlotCurve plots quite slowly with 5K points

[sexgirl]

Hi, I am using Qwt5 and Qt4.2.3 to plot curve with 5K points and it may take 20 seconds to plot every time.
I looked up some similar threads in the forum but still have no idea.
My code referred to Qwt Example realtime_plot:

class CustomData
{
public:
    CustomData();
    void append(double *x, double *y, int count);
 
    int count() const;
    int size() const;
    const double *x() const;
    const double *y() const;
private:
    int d_count;
    QwtArray<double> d_x;
    QwtArray<double> d_y;
};
 
//class CustomQwtPlot:public QwtPlot
void CustomQwtPlot::appendDataShow(double *x, double *y, int size, const QPen &curvePen)
{
    ......
 
    if ( d_data == NULL )
        d_data = new CustomData;
    if(cur == NULL)
    {
        cur = new QwtPlotCurve("curve");
        cur->setPaintAttribute(QwtPlotCurve::PaintFiltered);
        cur->setRenderHint(QwtPlotItem::RenderAntialiased);
        d_data->append(x, y, size);
        cur->setRawData(d_data->x(), d_data->y(), d_data->count());
        cur->setPen(curvePen);
        cur->attach(this);
    }
 
   ......
}
 
//CustomQwtPlot *energyplot;
void plot::updateEnergyplot(QList<QStringList> data, QStringList header)
{
    ......
 
    if (energyplot == NULL)
    {
        ......
        energyplot = new CustomQwtPlot;
        double *xData = new double[count];
        double *yData = new double[count];
 
        for (int i = 0; i < count; i++)
        {
            xData[i] = (double)i;
            yData[i] = data.at(0).at(i).toDouble(&ok);
        }
        energyplot->appendDataShow(xData, yData, count, c);
        ......
 
        delete []xData;
        delete []yData;
 
       ......
    }
}

class CustomData
{
public:
    CustomData();
    void append(double *x, double *y, int count);

    int count() const;
    int size() const;
    const double *x() const;
    const double *y() const;
private:
    int d_count;
    QwtArray<double> d_x;
    QwtArray<double> d_y;
};

//class CustomQwtPlot:public QwtPlot
void CustomQwtPlot::appendDataShow(double *x, double *y, int size, const QPen &curvePen)
{
    ......

    if ( d_data == NULL )
        d_data = new CustomData;
    if(cur == NULL)
    {
        cur = new QwtPlotCurve("curve");
        cur->setPaintAttribute(QwtPlotCurve::PaintFiltered);
        cur->setRenderHint(QwtPlotItem::RenderAntialiased);
        d_data->append(x, y, size);
        cur->setRawData(d_data->x(), d_data->y(), d_data->count());
        cur->setPen(curvePen);
        cur->attach(this);
    }

   ......
}

//CustomQwtPlot *energyplot;
void plot::updateEnergyplot(QList<QStringList> data, QStringList header)
{
    ......

    if (energyplot == NULL)
    {
        ......
        energyplot = new CustomQwtPlot;
        double *xData = new double[count];
        double *yData = new double[count];

        for (int i = 0; i < count; i++)
        {
            xData[i] = (double)i;
            yData[i] = data.at(0).at(i).toDouble(&ok);
        }
        energyplot->appendDataShow(xData, yData, count, c);
        ......

        delete []xData;
        delete []yData;

       ......
    }
}

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Hope someone can help me.
Thanks.
Regards,
sexgirl