QwtPicker with QwtHistogram

[Uwe]

QwtPlot is a composite widget, that consists of widgets for title, legend, 4 scales and the canvas. The canvas is the widget in the center, where all plot items ( f.e your histogram ) are painted to. With a picker you can select a polygon a rectangle or a position on the canvas.

So what you need to do then is to translate the selected coordinate into something that has to do with your data ( this is what you have passed to the histogram item ). F.e iterate over your samples and check if the bounding rectangle of one of your sample contains the clicked coordinate. Then you have the selected bar ( = visual representation of your sample )

Uwe

[cptpingu]

It's much much clearer for me now. Thanks for the explanation.

Using the "event_filter" example I found in the Qwt source, I tried to implement the move event, but it don't works. The "selected" works fine.

Can I have some help on this piece of code ?

HistogramPlot.hh

#ifndef HISTOGRAMPLOT_HH_
# define HISTOGRAMPLOT_HH_
 
# include <qwt_plot.h>
# include <qwt_picker.h>
# include <qwt_plot_picker.h>
 
class HistogramPlot : public QwtPlot
{
  Q_OBJECT
public:
  HistogramPlot(QWidget* = 0);
 
private:
  void populate();
 
private Q_SLOTS:
  void showItem(QwtPlotItem*, bool on);
  void moved(const QPoint& pos);
  void selected(const QPointF& pos);
 
protected:
  QwtScaleDiv fixedNumberScaleDiv() const;
  QwtPlotPicker* picker_;
};
 
#endif /* !HISTOGRAMPLOT_HH_ */

#ifndef HISTOGRAMPLOT_HH_
# define HISTOGRAMPLOT_HH_

# include <qwt_plot.h>
# include <qwt_picker.h>
# include <qwt_plot_picker.h>

class HistogramPlot : public QwtPlot
{
  Q_OBJECT
public:
  HistogramPlot(QWidget* = 0);

private:
  void populate();

private Q_SLOTS:
  void showItem(QwtPlotItem*, bool on);
  void moved(const QPoint& pos);
  void selected(const QPointF& pos);

protected:
  QwtScaleDiv fixedNumberScaleDiv() const;
  QwtPlotPicker* picker_;
};

#endif /* !HISTOGRAMPLOT_HH_ */

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HistogramPlot.cc

HistogramPlot::HistogramPlot(QWidget* parent)
  : QwtPlot(parent)
{
  [...]
 
  picker_ = new QwtPlotPicker(this->canvas());
  picker_->setStateMachine(new QwtPickerClickPointMachine);
  connect(picker_, SIGNAL(moved(const QPoint&)),
          SLOT(moved(const QPoint&)));
  connect(picker_, SIGNAL(selected(const QPointF&)),
          SLOT(selected(const QPointF&)));
}
 
void HistogramPlot::moved(const QPoint& pos)
{
    QString info;
    info.sprintf("Freq=%g, Ampl=%g, Phase=%g",
        invTransform(QwtPlot::xBottom, pos.x()),
        invTransform(QwtPlot::yLeft, pos.y()),
        invTransform(QwtPlot::yRight, pos.y())
    );
    qDebug() << info;
}
 
void HistogramPlot::selected(const QPointF& pos)
{
  QString info;
  info.sprintf("Freq=%g, Ampl=%g, Phase=%g",
      invTransform(QwtPlot::xBottom, pos.x()),
      invTransform(QwtPlot::yLeft, pos.y()),
      invTransform(QwtPlot::yRight, pos.y())
  );
  qDebug() << info;
}

HistogramPlot::HistogramPlot(QWidget* parent)
  : QwtPlot(parent)
{
  [...]

  picker_ = new QwtPlotPicker(this->canvas());
  picker_->setStateMachine(new QwtPickerClickPointMachine);
  connect(picker_, SIGNAL(moved(const QPoint&)),
          SLOT(moved(const QPoint&)));
  connect(picker_, SIGNAL(selected(const QPointF&)),
          SLOT(selected(const QPointF&)));
}

void HistogramPlot::moved(const QPoint& pos)
{
    QString info;
    info.sprintf("Freq=%g, Ampl=%g, Phase=%g",
        invTransform(QwtPlot::xBottom, pos.x()),
        invTransform(QwtPlot::yLeft, pos.y()),
        invTransform(QwtPlot::yRight, pos.y())
    );
    qDebug() << info;
}

void HistogramPlot::selected(const QPointF& pos)
{
  QString info;
  info.sprintf("Freq=%g, Ampl=%g, Phase=%g",
      invTransform(QwtPlot::xBottom, pos.x()),
      invTransform(QwtPlot::yLeft, pos.y()),
      invTransform(QwtPlot::yRight, pos.y())
  );
  qDebug() << info;
}

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Edit: I just understand that "moved" is use when you drag something, not when you move the mouse. I don't found a signal/slot which deal with mouse move. How can I implement that ?

[Uwe]

Maybe QwtPickerTrackerMachine is what you are looking for.

Uwe

[cptpingu]

I understand. Problem solved

Thanks a lot.