Qwt - Can we plot an Area chart?

Question

Does anyone know if we can plot an area chart using the Qwt library on Qt creator ? If yes, could someone help me with a sample program ?

Answer 1

Based on the screenshots and the listing of examples, I would look at the source for cpuplot.

./qwt-6.1.2/examples>ls

animation  curvdemo1     examples.pro  radio        simpleplot   sysinfo
barchart   dials         friedberg     rasterview   sinusplot    tvplot
bode       distrowatch   itemeditor    realtime     spectrogram
controls   event_filter  legends       refreshtest  stockchart
cpuplot    examples.pri  oscilloscope  scatterplot  stylesheets

./qwt-6.1.2/examples/cpuplot>ls

cpupiemarker.cpp  cpuplot.cpp  cpuplot.pro  cpustat.h
cpupiemarker.h    cpuplot.h    cpustat.cpp

And

cpuplot.cpp

#include <qapplication.h>
#include <qlayout.h>
#include <qlabel.h>
#include <qpainter.h>
#include <qwt_plot_layout.h>
#include <qwt_plot_curve.h>
#include <qwt_scale_draw.h>
#include <qwt_scale_widget.h>
#include <qwt_legend.h>
#include <qwt_legend_label.h>
#include <qwt_plot_canvas.h>
#include "cpupiemarker.h"
#include "cpuplot.h"

class TimeScaleDraw: public QwtScaleDraw
{
public:
    TimeScaleDraw( const QTime &base ):
        baseTime( base )
    {
    }
    virtual QwtText label( double v ) const
    {
        QTime upTime = baseTime.addSecs( static_cast<int>( v ) );
        return upTime.toString();
    }
private:
    QTime baseTime;
};

class Background: public QwtPlotItem
{
public:
    Background()
    {
        setZ( 0.0 );
    }

    virtual int rtti() const
    {
        return QwtPlotItem::Rtti_PlotUserItem;
    }

    virtual void draw( QPainter *painter,
        const QwtScaleMap &, const QwtScaleMap &yMap,
        const QRectF &canvasRect ) const
    {
        QColor c( Qt::white );
        QRectF r = canvasRect;

        for ( int i = 100; i > 0; i -= 10 )
        {
            r.setBottom( yMap.transform( i - 10 ) );
            r.setTop( yMap.transform( i ) );
            painter->fillRect( r, c );

            c = c.dark( 110 );
        }
    }
};

class CpuCurve: public QwtPlotCurve
{
public:
    CpuCurve( const QString &title ):
        QwtPlotCurve( title )
    {
        setRenderHint( QwtPlotItem::RenderAntialiased );
    }

    void setColor( const QColor &color )
    {
        QColor c = color;
        c.setAlpha( 150 );

        setPen( QPen( Qt::NoPen ) );
        setBrush( c );
    }
};

CpuPlot::CpuPlot( QWidget *parent ):
    QwtPlot( parent ),
    dataCount( 0 )
{
    setAutoReplot( false );

    QwtPlotCanvas *canvas = new QwtPlotCanvas();
    canvas->setBorderRadius( 10 );

    setCanvas( canvas );

    plotLayout()->setAlignCanvasToScales( true );

    QwtLegend *legend = new QwtLegend;
    legend->setDefaultItemMode( QwtLegendData::Checkable );
    insertLegend( legend, QwtPlot::RightLegend );

    setAxisTitle( QwtPlot::xBottom, " System Uptime [h:m:s]" );
    setAxisScaleDraw( QwtPlot::xBottom,
        new TimeScaleDraw( cpuStat.upTime() ) );
    setAxisScale( QwtPlot::xBottom, 0, HISTORY );
    setAxisLabelRotation( QwtPlot::xBottom, -50.0 );
    setAxisLabelAlignment( QwtPlot::xBottom, Qt::AlignLeft | Qt::AlignBottom );

    /*
     In situations, when there is a label at the most right position of the
     scale, additional space is needed to display the overlapping part
     of the label would be taken by reducing the width of scale and canvas.
     To avoid this "jumping canvas" effect, we add a permanent margin.
     We don't need to do the same for the left border, because there
     is enough space for the overlapping label below the left scale.
     */

    QwtScaleWidget *scaleWidget = axisWidget( QwtPlot::xBottom );
    const int fmh = QFontMetrics( scaleWidget->font() ).height();
    scaleWidget->setMinBorderDist( 0, fmh / 2 );

    setAxisTitle( QwtPlot::yLeft, "Cpu Usage [%]" );
    setAxisScale( QwtPlot::yLeft, 0, 100 );

    Background *bg = new Background();
    bg->attach( this );

    CpuPieMarker *pie = new CpuPieMarker();
    pie->attach( this );

    CpuCurve *curve;

    curve = new CpuCurve( "System" );
    curve->setColor( Qt::red );
    curve->attach( this );
    data[System].curve = curve;

    curve = new CpuCurve( "User" );
    curve->setColor( Qt::blue );
    curve->setZ( curve->z() - 1 );
    curve->attach( this );
    data[User].curve = curve;

    curve = new CpuCurve( "Total" );
    curve->setColor( Qt::black );
    curve->setZ( curve->z() - 2 );
    curve->attach( this );
    data[Total].curve = curve;

    curve = new CpuCurve( "Idle" );
    curve->setColor( Qt::darkCyan );
    curve->setZ( curve->z() - 3 );
    curve->attach( this );
    data[Idle].curve = curve;

    showCurve( data[System].curve, true );
    showCurve( data[User].curve, true );
    showCurve( data[Total].curve, false );
    showCurve( data[Idle].curve, false );

    for ( int i = 0; i < HISTORY; i++ )
        timeData[HISTORY - 1 - i] = i;

    ( void )startTimer( 1000 ); // 1 second

    connect( legend, SIGNAL( checked( const QVariant &, bool, int ) ),
        SLOT( legendChecked( const QVariant &, bool ) ) );
}

void CpuPlot::timerEvent( QTimerEvent * )
{
    for ( int i = dataCount; i > 0; i-- )
    {
        for ( int c = 0; c < NCpuData; c++ )
        {
            if ( i < HISTORY )
                data[c].data[i] = data[c].data[i-1];
        }
    }

    cpuStat.statistic( data[User].data[0], data[System].data[0] );

    data[Total].data[0] = data[User].data[0] + data[System].data[0];
    data[Idle].data[0] = 100.0 - data[Total].data[0];

    if ( dataCount < HISTORY )
        dataCount++;

    for ( int j = 0; j < HISTORY; j++ )
        timeData[j]++;

    setAxisScale( QwtPlot::xBottom,
        timeData[HISTORY - 1], timeData[0] );

    for ( int c = 0; c < NCpuData; c++ )
    {
        data[c].curve->setRawSamples(
            timeData, data[c].data, dataCount );
    }

    replot();
}

void CpuPlot::legendChecked( const QVariant &itemInfo, bool on )
{
    QwtPlotItem *plotItem = infoToItem( itemInfo );
    if ( plotItem )
        showCurve( plotItem, on );
}

void CpuPlot::showCurve( QwtPlotItem *item, bool on )
{
    item->setVisible( on );

    QwtLegend *lgd = qobject_cast<QwtLegend *>( legend() );

    QList<QWidget *> legendWidgets = 
        lgd->legendWidgets( itemToInfo( item ) );

    if ( legendWidgets.size() == 1 )
    {
        QwtLegendLabel *legendLabel =
            qobject_cast<QwtLegendLabel *>( legendWidgets[0] );

        if ( legendLabel )
            legendLabel->setChecked( on );
    }

    replot();
}

int main( int argc, char **argv )
{
    QApplication a( argc, argv );

    QWidget vBox;
    vBox.setWindowTitle( "Cpu Plot" );

    CpuPlot *plot = new CpuPlot( &vBox );
    plot->setTitle( "History" );

    const int margin = 5;
    plot->setContentsMargins( margin, margin, margin, margin );

    QString info( "Press the legend to en/disable a curve" );

    QLabel *label = new QLabel( info, &vBox );

    QVBoxLayout *layout = new QVBoxLayout( &vBox );
    layout->addWidget( plot );
    layout->addWidget( label );

    vBox.resize( 600, 400 );
    vBox.show();

    return a.exec();
}

Hope that helps.