Qwt - Can we plot an Area chart? - c++

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.