QwtSpline - how to use it with QGraphicsView ?

[mih90]

Hi,

I want to display interpolated smooth line between set of points in QGraphicsView, the example from Qwt site doesn't seem to work for me, can I get some help on how to use QwtSpline ?
Here is the code i'm using right now :

QPolygonF points;
 
        ...
 
        int numPoints = points.size();
        QwtSpline spline;
        spline.setSplineType(QwtSpline::Natural);
        if(!spline.setPoints(points));
            qDebug() << "error setting points for spline";
        QPolygonF interpolatedPoints(numPoints);
        const double delta = (points[numPoints - 1].x() - points[0].x()) / (points.size() - 1);
        for(int i = 0; i < points.size(); i++)
        {
            const double x = points[i].x(); + i * delta;
            interpolatedPoints[i].setX(x);
            interpolatedPoints[i].setY(spline.value(x));
        }
 
        p.addPolygon(interpolatedPoints);

QPolygonF points;

        ...

        int numPoints = points.size();
        QwtSpline spline;
        spline.setSplineType(QwtSpline::Natural);
        if(!spline.setPoints(points));
            qDebug() << "error setting points for spline";
        QPolygonF interpolatedPoints(numPoints);
        const double delta = (points[numPoints - 1].x() - points[0].x()) / (points.size() - 1);
        for(int i = 0; i < points.size(); i++)
        {
            const double x = points[i].x(); + i * delta;
            interpolatedPoints[i].setX(x);
            interpolatedPoints[i].setY(spline.value(x));
        }

        p.addPolygon(interpolatedPoints);

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Will the effect be any different from QPainterPath.cubicTo() function ?