How to make replot qicker with curves and marker in a plot ?

[Uwe]

If one curve's about 300,000 samples, with 3,4 curves in a plot ...

There are several ways how to improve the performance for drawing of a curve, but before going into details you should have an idea about what is consuming the time in your plot. So try the following:

class YourCurve: public QwtPlotCurve
{
    ....
 
    virtual void drawSeries( QPainter *painter,
        const QwtScaleMap &xMap, const QwtScaleMap &yMap,
        const QRectF &canvasRect, int from, int to ) const
    {
        QElapsedTimer timer;
        timer.start();
 
        QwtPlotCurve::drawSeries( painter, xMap, yMap, canvasRect, from, to );
 
        qDebug() << "Elapsed: #" << to - from << timer.elapsed();
    }
};

class YourCurve: public QwtPlotCurve
{
    ....

    virtual void drawSeries( QPainter *painter,
        const QwtScaleMap &xMap, const QwtScaleMap &yMap,
        const QRectF &canvasRect, int from, int to ) const
    {
        QElapsedTimer timer;
        timer.start();

        QwtPlotCurve::drawSeries( painter, xMap, yMap, canvasRect, from, to );

        qDebug() << "Elapsed: #" << to - from << timer.elapsed();
    }
};

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Then:

• disable antialiasing
• set "no symbols"
• use a curve line width of 0

Now you will know if rendering of the curves is the main factor of the time used in a replot cycle.

Uwe