Make QwtPlotRescaler reflect data changes

[hector1984]

I need a plot to maintain a 1:1 aspect ratio, but I'll occasionally change the data. When I try this, the axes don't appear to be altered to fit the new range of the data. For example, when I initially plot a long line (going from (0,0) to (20,20), say), I get the expected behavior; the plot maintains the 1:1 aspect ratio when resizing. But if I then setData() to a shorter line (say, (0,0) to (10,10)), the axes remain the same, and there's a lot of unused space in the plotting area. How do I get the axes to readjust to the new range of the data and keep a 1:1 aspect ratio?

I'm using Qt 4.6.2, Qwt 5.2.1, and GCC 4.5.0 on CentOS 4.

A crude example follows. main.h:

#include <QWidget>
 
 
class QPushButton;
class QHBoxLayout;
class QwtPlot;
class QwtPlotCurve;
class QwtPlotRescaler;
 
 
class Window : public QWidget
{
    Q_OBJECT
 
    public:
        Window( QWidget* parent = 0 );
 
    private:
        QwtPlot* plot;
        QwtPlotCurve* curve;
        QwtPlotRescaler* rescaler;
        QPushButton* switchDataButton;
        QHBoxLayout* layout;
 
    private slots:
        void switchData();
};

#include <QWidget>


class QPushButton;
class QHBoxLayout;
class QwtPlot;
class QwtPlotCurve;
class QwtPlotRescaler;


class Window : public QWidget
{
    Q_OBJECT

    public:
        Window( QWidget* parent = 0 );

    private:
        QwtPlot* plot;
        QwtPlotCurve* curve;
        QwtPlotRescaler* rescaler;
        QPushButton* switchDataButton;
        QHBoxLayout* layout;

    private slots:
        void switchData();
};

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main.cpp:

#include "main.h"
#include "qwt_plot.h"
#include "qwt_plot_curve.h"
#include "qwt_plot_rescaler.h"
#include <QtGui>
 
 
const double HI = 20.0;
const double LO = 10.0;
const int N = 5;
const double DATA_HI[] = { 0.0, 0.25*HI, 0.5*HI, 0.75*HI, HI };
const double DATA_LO[] = { 0.0, 0.25*LO, 0.5*LO, 0.75*LO, LO };
 
 
Window::Window( QWidget* parent ) : QWidget( parent )
{
    resize( 400, 500 );
 
    plot = new QwtPlot( this );
    curve = new QwtPlotCurve;
    curve->setData( DATA_HI, DATA_HI, N );
    curve->attach( plot );
    rescaler = new QwtPlotRescaler( plot->canvas() );
    rescaler->setRescalePolicy( QwtPlotRescaler::Fitting );
 
    switchDataButton = new QPushButton( "Switch data", this );
    connect( switchDataButton, SIGNAL( clicked() ),
             this, SLOT( switchData() ) );
 
    layout = new QHBoxLayout;
    layout->addWidget( plot );
    layout->addWidget( switchDataButton );
    setLayout( layout );
 
    plot->replot();
}
 
 
void Window::switchData()
{
    if ( curve->maxYValue() > LO ) curve->setData( DATA_LO, DATA_LO, N );
    else curve->setData( DATA_HI, DATA_HI, N );
    plot->updateAxes(); // This doesn't make a difference that I can tell
    plot->replot();
    rescaler->rescale();
}
 
 
int main( int argc, char* argv[] )
{
    QApplication app( argc, argv );
 
    Window window;
    window.show();
 
    return app.exec();
}

#include "main.h"
#include "qwt_plot.h"
#include "qwt_plot_curve.h"
#include "qwt_plot_rescaler.h"
#include <QtGui>


const double HI = 20.0;
const double LO = 10.0;
const int N = 5;
const double DATA_HI[] = { 0.0, 0.25*HI, 0.5*HI, 0.75*HI, HI };
const double DATA_LO[] = { 0.0, 0.25*LO, 0.5*LO, 0.75*LO, LO };


Window::Window( QWidget* parent ) : QWidget( parent )
{
    resize( 400, 500 );

    plot = new QwtPlot( this );
    curve = new QwtPlotCurve;
    curve->setData( DATA_HI, DATA_HI, N );
    curve->attach( plot );
    rescaler = new QwtPlotRescaler( plot->canvas() );
    rescaler->setRescalePolicy( QwtPlotRescaler::Fitting );

    switchDataButton = new QPushButton( "Switch data", this );
    connect( switchDataButton, SIGNAL( clicked() ),
             this, SLOT( switchData() ) );

    layout = new QHBoxLayout;
    layout->addWidget( plot );
    layout->addWidget( switchDataButton );
    setLayout( layout );

    plot->replot();
}


void Window::switchData()
{
    if ( curve->maxYValue() > LO ) curve->setData( DATA_LO, DATA_LO, N );
    else curve->setData( DATA_HI, DATA_HI, N );
    plot->updateAxes(); // This doesn't make a difference that I can tell
    plot->replot();
    rescaler->rescale();
}


int main( int argc, char* argv[] )
{
    QApplication app( argc, argv );

    Window window;
    window.show();

    return app.exec();
}

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Thanks!

[Uwe]

The rescaler implicitely calls setAxisScale(), what disables autoscaling. Guess if you reenable autoscaling before calling updateAxes you probably have what you want:

void Window::switchData()
{
    if ( curve->maxYValue() > LO ) curve->setData( DATA_LO, DATA_LO, N );
    else curve->setData( DATA_HI, DATA_HI, N );
 
    for ( int axis = 0; axis < QwtPlot::axisCnt; axis++ )
        plot->setAxisAutoScale(axis);
 
    plot->updateAxes();
    rescaler->rescale();
}

void Window::switchData()
{
    if ( curve->maxYValue() > LO ) curve->setData( DATA_LO, DATA_LO, N );
    else curve->setData( DATA_HI, DATA_HI, N );
   
    for ( int axis = 0; axis < QwtPlot::axisCnt; axis++ )
        plot->setAxisAutoScale(axis);

    plot->updateAxes();
    rescaler->rescale();
}

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HTH,
Uwe