Drawing lines on qwtpolarplot

Hi,

I am having some difficulties drawing multiple lines on my polar plot. I can create multiple qwtpolarmarkers on the plot but when I create a line of type qwtpolarcurve and attach it to the polar plot, only the last curve will be displayed.

pseudo code to illustrate:

Code:

---

QwtPolarMarker * polarmarker = new QwtPolarMarker();
polarmarker->setPosition(......);
polarmarker->attach(polarPlot); 
polarPlot->replot(); //1st marker is displayed
 
QwtPolarMarker * polarmarker2 = new QwtPolarMarker();
polarmarker2->setPosition(......);
polarmarker2->attach(polarPlot);
polarPlot->replot(); //2nd marker is displayed
 
QwtPolarCurve * curve = new QwtPolarCurve();
curve->setData(......);
curve->attach(polarPlot); 
polarPlot->replot(); // 1st line is displayed
 
QwtPolarCurve * curve2 = new QwtPolarCurve();
curve2->setData(......);
curve2->attach(polarPlot); 
polarPlot->replot(); // 2nd line is displayed, 1st line disappears

---

I stepped through the codes and I can see that the 1st curve is plotted before disappearing on the last replot call. Any ideas on what I might be missing?

Pseudo code is o.k. and of course it is possible to have more than one curve: see the examples.

Uwe

Hi Uwe,

I realized that by calling replot on the polar plot anywhere in my program will cause any drawn qwtpolarcurve to disappear as well.

Could it be the way I do setdata?

Heres the code i used to pass into setdata:

Code:

---

class PolarData: public QwtSeriesData<QwtPointPolar>
{
public:
    PolarData (const double* x, const double* y, size_t size) :
        d_x (x),
        d_y (y),
        d_size (size) {}
 
    virtual QRectF boundingRect() const {
        if (d_boundingRect.width() < 0) {
            d_boundingRect = qwtBoundingRect (*this);
        }
        return d_boundingRect;
    }
 
    virtual size_t size() const {
        return d_size;
    }
    virtual QwtPointPolar sample (size_t i) const {
        return QwtPointPolar (d_x[int (i)], d_y[int (i)]);
    }
 
private:
    const double* d_x;
    const double* d_y;
    size_t d_size;
};

---

Depends on what happens to the memory d_x, d_y are pointing to.

Uwe