Looking for advices to do a ruler plus other questions

[raphael.lencrerot]

Hi,
It is my very first post in the Qt center I'll try to be clear.
I have 3 questions.

First question:
My plot represents a sky view of a map XY. I would like to create a ruler to compute distance between to points a(x1,y1) and b(x2,y2).
And I need also a way to draw one line from point a to point b when the ruler is activated.
I was hesitating between 2 possibilities:
- First way: use a QwtPlotPicker in polygon state machine. But I couldn't find a good example of how to manage the appended and selected signals. And in my case I don't really need several lines but just ONE line.
- Second way: Create my own QwtPlotItem that use a QwtPlotPicker with click machine and manage first and second click to compute distances and draw the line.

If their is a smarter way to do this I would like to know.
Hoping a ruler tool could be provided by default in qwt library.


Second question:
Is there a way to change the mouse shape or color? I would like to make it a little bit transparent.


Last question:
This is a general question since I'm new in Qt.
When we do something like:
setStateMachine(new QwtPickerTrackerMachine());
or
setSymbol(ptr_symbol);
or
setValidator(new QDoubleValidator()); (for a QLineEdit)

who is in charge of deleting the pointers?
Thanks by advance.

[Uwe]

class PickerDragLineMachine: public QwtPickerMachine
{
public:
    PickerDragLineMachine():
        QwtPickerMachine( PolygonSelection )
    {
    }
 
    virtual QList<Command> transition(
        const QwtEventPattern &eventPattern, const QEvent *event )
    {
        QList<QwtPickerMachine::Command> cmdList;
 
        if ( event->type() == QEvent::MouseButtonPress )
        {
            if ( eventPattern.mouseMatch( QwtEventPattern::MouseSelect1,
                static_cast<const QMouseEvent *>( event ) ) )
            {
                if ( state() == 0 )
                {
                    cmdList += Begin;
                    cmdList += Append;
                    cmdList += Append;
                    setState( 1 );
                }
            }
        }
        else if ( event->type() == QEvent::MouseMove )
        {
            if ( state() != 0 )
                cmdList += Move;
        }
        else if ( event->type() == QEvent::MouseButtonRelease )
        {
            if ( state() != 0 )
            {
                cmdList += End;
                setState( 0 );
            }
        }
 
        return cmdList;
    }
};

class PickerDragLineMachine: public QwtPickerMachine
{
public:
    PickerDragLineMachine():
        QwtPickerMachine( PolygonSelection )
    {
    }

    virtual QList<Command> transition(
        const QwtEventPattern &eventPattern, const QEvent *event )
    {
        QList<QwtPickerMachine::Command> cmdList;

        if ( event->type() == QEvent::MouseButtonPress )
        {
            if ( eventPattern.mouseMatch( QwtEventPattern::MouseSelect1,
                static_cast<const QMouseEvent *>( event ) ) )
            {
                if ( state() == 0 )
                {
                    cmdList += Begin;
                    cmdList += Append;
                    cmdList += Append;
                    setState( 1 );
                }
            }
        }
        else if ( event->type() == QEvent::MouseMove )
        {
            if ( state() != 0 )
                cmdList += Move;
        }
        else if ( event->type() == QEvent::MouseButtonRelease )
        {
            if ( state() != 0 )
            {
                cmdList += End;
                setState( 0 );
            }
        }

        return cmdList;
    }
};

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class DistancePicker: public QwtPlotPicker
{
public:
    DistancePicker( QWidget *canvas ):
        QwtPlotPicker( canvas )
    {
        setTrackerMode( QwtPicker::ActiveOnly );
        setStateMachine( new PickerDragLineMachine() );
        setMousePattern( QwtEventPattern::MouseSelect1, Qt::LeftButton );
        setRubberBand( QwtPlotPicker::PolygonRubberBand );
    }
 
    virtual QwtText trackerTextF( const QPointF &pos ) const
    {
        QwtText text;
 
        const QPolygon points = selection();
        if ( !points.isEmpty() )
        {
            QString num;
            num.setNum( QLineF( pos, invTransform( points[0] ) ).length() );
 
            QColor bg( Qt::white );
            bg.setAlpha( 200 );
 
            text.setBackgroundBrush( QBrush( bg ) );
            text.setText( num );
        }
        return text;
    }
};

class DistancePicker: public QwtPlotPicker
{
public:
    DistancePicker( QWidget *canvas ):
        QwtPlotPicker( canvas )
    {
        setTrackerMode( QwtPicker::ActiveOnly );
        setStateMachine( new PickerDragLineMachine() );
        setMousePattern( QwtEventPattern::MouseSelect1, Qt::LeftButton );
        setRubberBand( QwtPlotPicker::PolygonRubberBand );
    }

    virtual QwtText trackerTextF( const QPointF &pos ) const
    {
        QwtText text;

        const QPolygon points = selection();
        if ( !points.isEmpty() )
        {
            QString num;
            num.setNum( QLineF( pos, invTransform( points[0] ) ).length() );

            QColor bg( Qt::white );
            bg.setAlpha( 200 );

            text.setBackgroundBrush( QBrush( bg ) );
            text.setText( num );
        }
        return text;
    }
};

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HTH,
Uwe

[raphael.lencrerot]

Thank you so much for this.
Is It possible to put these lines in further examples provided by the library in such a way that users can see how we can easily implement our own pickermachine then our own pickeritem.

Just one question, why their is 2 times append in cmdlist?

Thanks again uwe.

[Uwe]

Is It possible to put these lines in further examples provided by the library in such a way that users can see how we can easily implement our own pickermachine then our own pickeritem.

This example doesn't contain more information than what you have had when looking at the implementation of any picker machine. In fact I did nothing else than copying the transition method from 2 existing machines.

Just one question, why their is 2 times append in cmdlist?

Because a line consists of 2 points - the second one gets moved by mouse move events.

Uwe

[raphael.lencrerot]

Ok,
thanks again.

[Uwe]

I have added QwtPickerDragLineMachine to SVN trunk - the scatterplot example shows an implementation of a picker for distance measurements using it.

Uwe

[raphael.lencrerot]

Nice !
My plotting software is almost finished. I'll will then integrate this change ASAP to reduce lines code.

Thanks again for your hard work.

[jesse_mark]

@Uwe
Would you please, set what are the includes we have to used to get the code posted to compile ? and would you add some expmle to show how to use??

thanks.

I have added these #includes:

#include <QtCore>
#include <qwt_picker_machine.h>
#include <qevent.h>

still getting this error
PickerDragLineMachin.cpp:24: error: invalid use of incomplete type 'const struct QwtEventPattern'

---

Added after 1 22 minutes:

Thanks It was clear, I was just blinded i guess.

add :
#include <QtCore>
#include <qwt_picker_machine.h>
#include <qevent.h>
#include <qwt_event_pattern.h>

in PickerDragLineMachin
and
#include <QtCore>
#include <qwt_text.h>
#include <qwt_plot_picker.h>
#include "PickerDragLineMachin.h"

now its working great.

Thank you so much for you code and your effort, It is a real help.
best regards,

Jesse.