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:
Qt Code: 
  1. class Plot: public QwtPlot{
  2.  
  3. public:
  4.  
  5.     Plot(QWidget * parent = NULL);
  6.  
  7.     void drawPlot();
  8.  
  9. private:
  10.  
  11.     QwtPlotCurve    _curve;
  12.  
  13.     QwtPlotZoomer   * _zoomer;
  14. };
  15.  
  16. =====================================
  17. Plot::Plot(QWidget *parent) :  QwtPlot (parent)
  18. {
  19.     _curve.setStyle(QwtPlotCurve::Lines);
  20.  
  21.     _curve.setPen(QPen(Qt::black));
  22.  
  23.     QwtSymbol sym;
  24.  
  25.     sym.setStyle(QwtSymbol::Ellipse);
  26.     sym.setPen(QPen(Qt::black));
  27.     QBrush brush(Qt::yellow);
  28.     sym.setBrush(brush);
  29.     sym.setSize(5);
  30.  
  31.     _curve.setSymbol(sym);
  32.  
  33.     _curve.attach(this);
  34.  
  35.     _zoomer = new QwtPlotZoomer (canvas());
  36.  
  37.     _zoomer->setSelectionFlags( QwtPicker::DragSelection | QwtPicker::CornerToCorner );
  38.  
  39.     QwtDoubleRect rect(0, 0, 3000, 3000);
  40.  
  41.     _zoomer->setZoomBase(rect);
  42.  
  43.     drawPlot();
  44.  
  45. }
  46.  
  47. void Plot::drawPlot(){
  48.  
  49.     QVector<double> x(3000);
  50.     QVector<double> y(3000);
  51.  
  52.     for (int i = 0; i < 3000; i++)
  53.     {
  54.         x[i] = i;
  55.         y[i] = i;
  56.     }
  57.  
  58.    _curve.setData(x, y);
  59.  
  60.     replot();
  61. }
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I get this only with a QwtSymbol::Ellipse but never with Rect, Diamond or Cross.

Thanks for any help!