Hey.

I've a plot with a curve and a bunch of markers on it.
When zooming in sometimes I get some random markers apearing.
ufos.jpg

Points with text are added by me, all other points appear from somewhere.

I have no idea why it's happening. Maybe I'm missing some zoomer setting?

Anyway, I've created simple example app to demonstrate the issue:
Qt Code: 
  1. //mainwindow.h
  2. #ifndef MAINWINDOW_H
  3. #define MAINWINDOW_H
  4.  
  5. #include <QtGui/QMainWindow>
  6.  
  7. class QwtPlot;
  9.  
  10. class MainWindow : public QMainWindow
  11. {
  12.     Q_OBJECT
  13.  
  14. public:
  15.     MainWindow(QWidget *parent = 0);
  16.     ~MainWindow();
  17.  
  18. private:
  19.     void addCurve( void );
  20.     void addMarkers( void );
  21.  
  22.     QwtPlot* plot;
  23.     QwtPlotZoomer* zoomer;
  24.  
  25.     QVector<double> x;
  26.     QVector<double> y;
  27. };
  28.  
  29. #endif // MAINWINDOW_H
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Qt Code: 
  1. // mainwindow.cpp
  2. #include "mainwindow.h"
  3.  
  4. #include <qwt_plot.h>
  5. #include <qwt_plot_curve.h>
  6. #include <qwt_plot_marker.h>
  7. #include <qwt_symbol.h>
  8. #include <qwt_plot_zoomer.h>
  9.  
  10. MainWindow::MainWindow(QWidget *parent)
  11.     : QMainWindow(parent)
  12. {
  13.     this->plot = new QwtPlot(this);
  14.     this->zoomer = new QwtPlotZoomer(this->plot->canvas());
  15.  
  16.     this->addCurve();
  17.     this->addMarkers();
  18.  
  19.     this->zoomer->setZoomBase();;
  20.     this->setCentralWidget(this->plot);
  21. }
  22.  
  23. MainWindow::~MainWindow()
  24. {
  25.  
  26. }
  27.  
  28. void MainWindow::addCurve( void )
  29. {
  30.     int count = 20000;
  31.  
  32.     for(int i = 0; i < count; ++i)
  33.     {
  34.         this->x.append(i);
  35.         this->y.append(i);
  36.     }
  37.  
  38.     QwtPlotCurve* curve = new QwtPlotCurve();
  39.     curve->setRawData(this->x.constBegin(), this->y.constBegin(), this->x.size());
  40.     curve->attach(this->plot);
  41. }
  42.  
  43. void MainWindow::addMarkers( void )
  44. {
  45.     int count = 5000;
  46.     int step = this->x.size()/count;
  47.  
  48.     for(int i = 0; i < count; ++i)
  49.     {
  50.         int x = i*step;
  51.         int y = this->y[x];
  52.  
  54.         m->setSymbol(QwtSymbol(QwtSymbol::Ellipse, QBrush(Qt::red), QPen(Qt::red), QSize(5,5)));
  55.         m->setValue(x, y);
  56.         m->setLabel(QString("%1x%2").arg(x).arg(y));
  57.  
  58.         m->attach(this->plot);
  59.     }
  60. }
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Any suggestions how to get rid of that UFOs are welcome.

PS: I'm running w7 64 bit with qt 4.6.3 and qwt 5.2.0.