Zooming problem with QwtSymbol::Ellipse

[AnnaP]

Hi!

I can't find a solution to solve one problem.

I draw a plot with a simple curve. What I need is:
1) to mark every point with a circle (QwtSymbol::Ellipse) and
2) to provide zooming

I faced with a problem that after a several zooms I get extra strange points that are not lie on the curve and have unreasonable data.
Here is a code example:

class Plot: public QwtPlot{
 
public:
 
    Plot(QWidget * parent = NULL);
 
    void drawPlot();
 
private:
 
    QwtPlotCurve    _curve;
 
    QwtPlotZoomer   * _zoomer;
};
 
=====================================
Plot::Plot(QWidget *parent) :  QwtPlot (parent)
{
    _curve.setStyle(QwtPlotCurve::Lines);
 
    _curve.setPen(QPen(Qt::black));
 
    QwtSymbol sym;
 
    sym.setStyle(QwtSymbol::Ellipse);
    sym.setPen(QPen(Qt::black));
    QBrush brush(Qt::yellow);
    sym.setBrush(brush);
    sym.setSize(5);
 
    _curve.setSymbol(sym);
 
    _curve.attach(this);
 
    _zoomer = new QwtPlotZoomer (canvas());
 
    _zoomer->setSelectionFlags( QwtPicker::DragSelection | QwtPicker::CornerToCorner );
 
    QwtDoubleRect rect(0, 0, 3000, 3000);
 
    _zoomer->setZoomBase(rect);
 
    drawPlot();
 
}
 
void Plot::drawPlot(){
 
    QVector<double> x(3000);
    QVector<double> y(3000);
 
    for (int i = 0; i < 3000; i++)
    {
        x[i] = i;
        y[i] = i;
    }
 
   _curve.setData(x, y);
 
    replot();
}

class Plot: public QwtPlot{

public:

    Plot(QWidget * parent = NULL);

    void drawPlot();

private:

    QwtPlotCurve    _curve;

    QwtPlotZoomer   * _zoomer;
};

=====================================
Plot::Plot(QWidget *parent) :  QwtPlot (parent)
{
    _curve.setStyle(QwtPlotCurve::Lines);

    _curve.setPen(QPen(Qt::black));

    QwtSymbol sym;

    sym.setStyle(QwtSymbol::Ellipse);
    sym.setPen(QPen(Qt::black));
    QBrush brush(Qt::yellow);
    sym.setBrush(brush);
    sym.setSize(5);

    _curve.setSymbol(sym);

    _curve.attach(this);

    _zoomer = new QwtPlotZoomer (canvas());

    _zoomer->setSelectionFlags( QwtPicker::DragSelection | QwtPicker::CornerToCorner );

    QwtDoubleRect rect(0, 0, 3000, 3000);

    _zoomer->setZoomBase(rect);

    drawPlot();

}

void Plot::drawPlot(){

    QVector<double> x(3000);
    QVector<double> y(3000);

    for (int i = 0; i < 3000; i++)
    {
        x[i] = i;
        y[i] = i;
    }

   _curve.setData(x, y);

    replot();
}

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I get this only with a QwtSymbol::Ellipse but never with Rect, Diamond or Cross.

Thanks for any help!

[AnnaP]

Installation of new qwt software version (qwt-6.0.0-rc5) fixed the problem.

[fatecasino]

Hi,

I have qwt-6.0.0-rc5. The symbols are plotted perfectly fine,
but when I want to zoom I get a segmentation fault.

QwtSymbol sym;
 
          sym.setStyle(QwtSymbol::Ellipse);
          sym.setPen(QPen(Qt::black));
          QBrush brush(Qt::yellow);
          sym.setBrush(brush);
          sym.setSize(1);
 
          continuumCurve->setSymbol(&sym);

QwtSymbol sym;

          sym.setStyle(QwtSymbol::Ellipse);
          sym.setPen(QPen(Qt::black));
          QBrush brush(Qt::yellow);
          sym.setBrush(brush);
          sym.setSize(1);

          continuumCurve->setSymbol(&sym);

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[Uwe]

In Qwt 6.x the symbol needs to be allocated by new. This is something you can expect from all parameters, that are passed as pointer ( in opposite to references ).

Uwe

[fatecasino]

thanks, it worked!

QwtSymbol *sym = new QwtSymbol;

QwtSymbol *sym = new QwtSymbol;

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