Qwt PlotCurve does not apply as "Line"

[Flung Dung]

Hello human,

I try to create a simple sinus Line with qwt into a QwtPlot.

My problem is, that I don't get the line out of the samples I save in my QwtPlotCurve. As far as I understand the documentation I have to call setStyle(QwtPlotCurve::Lines) to connect the samples to a curve but it doesn't work for me.

I am new in c++ and qt so maybe anyone can answer this. probably something simple but I couldn't find out for hours....

Here's the relevant code. before I call replot() at the end I check for the style and its ture...!

   xData = new double[(int)plot_r->axisScaleDiv(2).upperBound()];
    yData = new double[(int)plot_r->axisScaleDiv(2).upperBound()];
    curve_rotor = new QwtPlotCurve("Rotor");
    curve_rotor->setStyle(QwtPlotCurve::Lines);


    QwtSymbol *sym=new QwtSymbol(QwtSymbol::Ellipse,QBrush(Qt::white),QPen(Qt::white),QSize(1,1));

    curve_rotor->setRenderHint( QwtPlotItem::RenderAntialiased, true );
    curve_rotor->setSymbol(sym);

    
    for(int i = 0; i < (int)plot_r->axisScaleDiv(2).upperBound(); i++)
    {
        xData[i] = i;
        yData[i] = 400 * sin(2*M_PI*50*i*0.001);
    }
    curve_rotor->setSamples(xData, yData, (int)plot_r->axisScaleDiv(2).upperBound());

    curve_rotor->attach(plot_r);


    if(curve_rotor->style() == QwtPlotCurve::Lines)
    {
        std::cout <<" Yes it is" << std::endl;
    }
    plot_r->replot();

How it looks at the moment:

[SGaist]

Hi,

Can you provide a complete minimal buildable example ?
That will make things easier for people to help you.

[uwer]

The default curve line pen is black - guess you simply don't see the lines because you don't see black lines on a black canvas.