QwtPlotPicker Subclass Segfaults

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I am trying to subclass QwtPlotPicker to change the default value for the displayed text, and everything I am doing causes segfaults. I have spent a couple hours at this with no avail. I am using latest Qwt from SVN (6.x series).

My QwtPlotPicker subclass .h:

Code:

class FreqdBmPicker : public QwtPlotPicker {
public:
	FreqdBmPicker( QWidget *canvas );
private:
	virtual QwtText trackerTextF( const QPointF &pos ) const;
};

My QwtPlotPicker subclass .cpp:

Code:

FreqdBmPicker::FreqdBmPicker( QWidget *canvas ): QwtPlotPicker( canvas ) {
  setTrackerMode( QwtPicker::AlwaysOn );
  setRubberBand( QwtPlotPicker::CrossRubberBand );
  setStateMachine( new QwtPickerTrackerMachine() );
  setTrackerPen(QColor(Qt::cyan));
  setRubberBandPen(QColor(Qt::cyan));
}
QwtText FreqdBmPicker::trackerTextF( const QPointF &pos ) const {
  QString rtn;
  switch ( (int) std::log10(pos.x())) {
    case 9: rtn = QString("(%1GHz, %2dBm)").arg(pos.x()/1e9, 0, 'f', 2).arg(pos.y(), 0, 'f', 1); break;
    case 8:
    case 7:
    case 6: rtn = QString("(%1MHz, %2dBm)").arg(pos.x()/1e6, 0, 'f', 2).arg(pos.y(), 0, 'f', 1); break;
    case 5:
    case 4:
    case 3: rtn = QString("(%1kHz, %2dBm)").arg(pos.x()/1e3, 0, 'f', 2).arg(pos.y(), 0, 'f', 1); break;
    case 2:
    case 1:
    case 0: rtn = QString("(%1Hz, %2dBm)").arg(pos.x(), 0, 'f', 2).arg(pos.y(), 0, 'f', 1); break;
  }
  return QwtText(rtn);
}

In the calling *.cpp class:

Code:

canvas = new QwtPlotCanvas();
canvas->setPalette( Qt::black );
canvas->setBorderRadius(0);
plot->setCanvas(canvas);
TimeFreqPicker *pkr = new TimeFreqPicker(plot->canvas());

It appears to run, but the minute I click anywhere on the plot, it immediately segfaults. gdb backtrace:

Code:

#0  0x00007ffff6ffe26c in QwtPicker::adjustedPoints(QPolygon const&) const () from /home/nickp/code/SpectralSignalHound-Viewer/qwt/lib/libqwt.so.6
#1  0x00007ffff6fffb20 in QwtPicker::updateDisplay() () from /home/nickp/code/SpectralSignalHound-Viewer/qwt/lib/libqwt.so.6
#2  0x00007ffff6ffec76 in QwtPicker::eventFilter(QObject*, QEvent*) () from /home/nickp/code/SpectralSignalHound-Viewer/qwt/lib/libqwt.so.6
#3  0x00007ffff754a9e5 in QCoreApplicationPrivate::sendThroughObjectEventFilters(QObject*, QEvent*) () from /usr/lib64/libQt5Core.so.5
#4  0x00007ffff78e843c in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib64/libQt5Widgets.so.5
#5  0x00007ffff78ed470 in QApplication::notify(QObject*, QEvent*) () from /usr/lib64/libQt5Widgets.so.5
#6  0x00007ffff754a7a5 in QCoreApplication::notifyInternal(QObject*, QEvent*) () from /usr/lib64/libQt5Core.so.5
#7  0x00007ffff7920295 in QWidgetPrivate::setGeometry_sys(int, int, int, int, bool) () from /usr/lib64/libQt5Widgets.so.5
#8  0x00007ffff7920f89 in QWidget::setGeometry(QRect const&) () from /usr/lib64/libQt5Widgets.so.5
#9  0x00007ffff7031334 in QwtPlot::updateLayout() () from /home/nickp/code/SpectralSignalHound-Viewer/qwt/lib/libqwt.so.6
#10 0x00007ffff7034491 in QwtPlot::event(QEvent*) () from /home/nickp/code/SpectralSignalHound-Viewer/qwt/lib/libqwt.so.6
#11 0x00007ffff78e845c in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib64/libQt5Widgets.so.5
#12 0x00007ffff78ed470 in QApplication::notify(QObject*, QEvent*)  () from /usr/lib64/libQt5Widgets.so.5
#13 0x00007ffff754a7a5 in QCoreApplication::notifyInternal(QObject*, QEvent*)  () from /usr/lib64/libQt5Core.so.5
#14 0x00007ffff754c63f in QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) () from /usr/lib64/libQt5Core.so.5
#15 0x00007ffff7031d02 in QwtPlot::replot() ()  from /home/nickp/code/SpectralSignalHound-Viewer/qwt/lib/libqwt.so.6
#16 0x00007ffff7065fd1 in QwtPlotZoomer::zoom(QRectF const&) () from /home/nickp/code/SpectralSignalHound-Viewer/qwt/lib/libqwt.so.6
#17 0x00007ffff7066581 in QwtPlotZoomer::end(bool) () from /home/nickp/code/SpectralSignalHound-Viewer/qwt/lib/libqwt.so.6
#18 0x00007ffff700128a in QwtPicker::transition(QEvent const*) () from /home/nickp/code/SpectralSignalHound-Viewer/qwt/lib/libqwt.so.6
#19 0x00007ffff6ffec01 in QwtPicker::eventFilter(QObject*, QEvent*) () from /home/nickp/code/SpectralSignalHound-Viewer/qwt/lib/libqwt.so.6
#20 0x00007ffff754a9e5 in QCoreApplicationPrivate::sendThroughObjectEventFilters(QObject*, QEvent*) () from /usr/lib64/libQt5Core.so.5
#21 0x00007ffff78e843c in QApplicationPrivate::notify_helper(QObject*, QEvent*)  () from /usr/lib64/libQt5Widgets.so.5
#22 0x00007ffff78edda6 in QApplication::notify(QObject*, QEvent*) ()  from /usr/lib64/libQt5Widgets.so.5
....

What am I doing wrong?

6th December 2014, 10:27
Uwe

Re: QwtPlotPicker Subclass Segfaults

The stack indicates a crash starting with a QwtPlotZoomer - how the code you have shown related to this ?

Uwe

Re: QwtPlotPicker Subclass Segfaults

Hm.. That is a bit wierd. Ok, not sure why I missed that earlier. I removed all the zoomer code, it no longer sefgaults, but now there are NO markers. I am expecting a horizontal and vertical bars to follow the mouse around on the screen with some custom text. Again:

QwtPlotPicker .cpp and .h

Code:

class FreqdBmPicker : public QwtPlotPicker {
public:
	FreqdBmPicker( QWidget *canvas );
	FreqdBmPicker(int xAxis, int yAxis, RubberBand rubberBand, DisplayMode trackerMode, QWidget* canvas);
	virtual QwtText trackerTextF( const QPointF & ) const;
};

Code:

QwtText TimeScaleDraw::label(double v) const { //Convert Double date to a string
  return QwtText(QDateTime::fromMSecsSinceEpoch((qint64) (v*1000)).toString("yyyy-MM-dd\nHH:mm:ss.zzz"));
}
 
FreqdBmPicker::FreqdBmPicker(int x, int y, RubberBand rb, DisplayMode dm, QWidget* w): QwtPlotPicker(x, y, rb, dm, w) {
  setTrackerMode( dm );
  setRubberBand( rb );
  setStateMachine( new QwtPickerTrackerMachine() );
  setTrackerPen(QColor(Qt::cyan));
  setRubberBandPen(QColor(Qt::cyan));
  qDebug() << isEnabled();
  setEnabled(true);
}
FreqdBmPicker::FreqdBmPicker( QWidget *canvas ): QwtPlotPicker( canvas ) {
  setTrackerMode( QwtPicker::AlwaysOn );
  setRubberBand( QwtPlotPicker::CrossRubberBand );
  setStateMachine( new QwtPickerTrackerMachine() );
  setTrackerPen(QColor(Qt::cyan));
  setRubberBandPen(QColor(Qt::cyan));
  qDebug() << isEnabled();
  setEnabled(true);
}
QwtText FreqdBmPicker::trackerTextF( const QPointF &pos ) const {
  QString rtn;
  switch ( (int) std::log10(pos.x())) {
    case 9: rtn = QString("(%1GHz, %2dBm)").arg(pos.x()/1e9, 0, 'f', 2); break;
    case 8:
    case 7:
    case 6: rtn = QString("(%1MHz, %2dBm)").arg(pos.x()/1e6, 0, 'f', 2); break;
    case 5:
    case 4:
    case 3: rtn = QString("(%1kHz, %2dBm)").arg(pos.x()/1e3, 0, 'f', 2); break;
    case 2:
    case 1:
    case 0:
    default: rtn = QString("(%1Hz, %2dBm)").arg(pos.x(), 0, 'f', 2); break;
  }
  rtn = rtn.arg(pos.y(), 0, 'f', 1);
  return QwtText(rtn);
}

Initialization and calling code. loadSweep() is called multiple times over the lifetime of the application

Code:

SweepInspector::SweepInspector(QWidget *parent) : QWidget(parent), data(NULL), d_curve(NULL), picker(NULL) {
  setupUi(this);
  plot->setObjectName( "SweepData" );
  plot->setTitle( "RF Sweep" );
  plot->setAxisTitle( QwtPlot::xBottom, "Frequency");
  plot->setAxisTitle( QwtPlot::yLeft, QString( "Power Level (dBm)"));
  plot->setAutoReplot(true);
 
  plot->enableAxis(QwtPlot::xBottom, true);
  plot->enableAxis(QwtPlot::yLeft, true);
  plot->enableAxis(QwtPlot::xTop, false);
  plot->enableAxis(QwtPlot::yRight, false);
 
  canvas = new QwtPlotCanvas();
  canvas->setPalette( Qt::black );
  canvas->setBorderRadius(0);
  plot->setCanvas(canvas);
 
  //Allow zooming / panning
  // zoomer = new QwtPlotZoomer( canvas );
  // zoomer->setRubberBandPen( QColor( Qt::white ) );
  // zoomer->setTrackerPen( QColor( Qt::white ) );
  panner = new QwtPlotPanner( canvas );
  panner->setMouseButton( Qt::MidButton );
 
  picker = new FreqdBmPicker(QwtPlot::xBottom, QwtPlot::yLeft, QwtPlotPicker::CrossRubberBand, QwtPicker::AlwaysOn, canvas);
 
 
  //Setup grid
  grid = new QwtPlotGrid();
  grid->enableXMin( true );
  grid->enableYMin( true );
  QColor color(Qt::gray); color.setAlpha(128);
  grid->setMajorPen( color, 1, Qt::DotLine );
  grid->setMinorPen( color, 1, Qt::DotLine );
  grid->attach( plot );
 
  //format in kHz, MHz, GHz, not raw values
  plot->setAxisScaleDraw(QwtPlot::xBottom, new FreqScaleDraw);
 
  //connects
  connect(timeIndex, SIGNAL(valueChanged(int)), this, SLOT(loadSweep(int)));
  connect(timeIndex, SIGNAL(sliderMoved(int)), this, SLOT(sliderMoved(int)));
}
 
void SweepInspector::loadSweep(int index) {
  //load in new sweep values from data
  if (data == NULL) return;
 
  //remove old data and get new
  if (d_curve) d_curve->attach(NULL);
  plot->detachItems();
  fsweep sweep = data->getSweep(index);
 
  d_curve = new QwtPlotCurve( timestamp->text() ); //Qwt will delete() this when its done with it
  d_curve->setRenderHint( QwtPlotItem::RenderAntialiased );
  d_curve->setStyle( QwtPlotCurve::Lines );
  d_curve->setPen( QColor( Qt::yellow ), 2, Qt::SolidLine );
  d_curve->setSamples( sweep );
  d_curve->attach(plot);
 
  delete(picker);
  picker = new FreqdBmPicker(QwtPlot::xBottom, QwtPlot::yLeft, QwtPlotPicker::CrossRubberBand, QwtPicker::AlwaysOn, canvas);
  connect(picker, SIGNAL(selected(QPointF)), this, SLOT(moved(QPointF)));
 
  QwtInterval frange = data->limits(FREQ);
  plot->setAxisScale(QwtPlot::xBottom, frange.minValue(), frange.maxValue(), (frange.maxValue() - frange.minValue())/ 5.0);
  plot->setAxisScale(QwtPlot::yLeft, -135, 20, 10.0);
  plot->setTitle( QString("RF Sweep @ %1").arg(timestamp->text()) );
  //set maximum zoom out
  // zoomer->setZoomBase(QRectF(QPointF(frange.minValue(), 20), QPointF(frange.maxValue(), -135)));
  // zoomer->zoomBase();
  plot->replot();
  plot->repaint();
}

7th December 2014, 09:28
Uwe

Re: QwtPlotPicker Subclass Segfaults

A lot of code, but what is your question ?

Uwe
7th December 2014, 16:59
npotts

Re: QwtPlotPicker Subclass Segfaults

Haha, trees from the Forrest....

Essentially, my QwtPlotPickers are not appearing on the plots, and the format functions are never called.