QwtSyntheticPointData man page

QwtSyntheticPointData —

Synthetic point data.


#include <qwt_point_data.h>

Inherits QwtSeriesData< QPointF >.

Public Member Functions

QwtSyntheticPointData (size_t size, const QwtInterval &=QwtInterval())

void setSize (size_t size)

virtual size_t size () const

void setInterval (const QwtInterval &)

QwtInterval interval () const

virtual QRectF boundingRect () const
Calculate the bounding rectangle.
virtual QPointF sample (size_t i) const

virtual double y (double x) const =0

virtual double x (uint index) const

virtual void setRectOfInterest (const QRectF &)

QRectF rectOfInterest () const

Additional Inherited Members

Detailed Description

Synthetic point data.

QwtSyntheticPointData provides a fixed number of points for an interval. The points are calculated in equidistant steps in x-direction.

If the interval is invalid, the points are calculated for the 'rectangle of interest', what normally is the displayed area on the plot canvas. In this mode you get different levels of detail, when zooming in/out.


The following example shows how to implement a sinus curve.

#include <cmath>
#include <qwt_series_data.h>
#include <qwt_plot_curve.h>
#include <qwt_plot.h>
#include <qapplication.h>

class SinusData: public QwtSyntheticPointData
        QwtSyntheticPointData( 100 )

    virtual double y( double x ) const
        return qSin( x );

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

    QwtPlot plot;
    plot.setAxisScale( QwtPlot::xBottom, 0.0, 10.0 );
    plot.setAxisScale( QwtPlot::yLeft, -1.0, 1.0 );

    QwtPlotCurve *curve = new QwtPlotCurve( "y = sin(x)" );
    curve->setData( new SinusData() );
    curve->attach( &plot );

    return a.exec();

Constructor & Destructor Documentation

QwtSyntheticPointData::QwtSyntheticPointData (size_tsize, const QwtInterval &interval = QwtInterval())



size Number of points
interval Bounding interval for the points

See Also:

setInterval(), setSize()

Member Function Documentation

QRectF QwtSyntheticPointData::boundingRect () const [virtual]

Calculate the bounding rectangle. This implementation iterates over all points, what could often be implemented much faster using the characteristics of the series. When there are many points it is recommended to overload and reimplement this method using the characteristics of the series ( if possible ).


Bounding rectangle

Implements QwtSeriesData< QPointF >.

QwtInterval QwtSyntheticPointData::interval () const


Bounding interval

See Also:

setInterval(), size()

QRectF QwtSyntheticPointData::rectOfInterest () const


'rectangle of interest'

See Also:


QPointF QwtSyntheticPointData::sample (size_tindex) const [virtual]

Calculate the point from an index


index Index


QPointF(x(index), y(x(index)));


For invalid indices ( index < 0 || index >= size() ) (0, 0) is returned.

Implements QwtSeriesData< QPointF >.

void QwtSyntheticPointData::setInterval (const QwtInterval &interval)

Set the bounding interval


interval Interval

See Also:

interval(), setSize()

void QwtSyntheticPointData::setRectOfInterest (const QRectF &rect) [virtual]

Set a the 'rectangle of interest'

QwtPlotSeriesItem defines the current area of the plot canvas as 'rect of interest' ( QwtPlotSeriesItem::updateScaleDiv() ).

If interval().isValid() == false the x values are calculated in the interval rect.left() -> rect.right().

See Also:


Reimplemented from QwtSeriesData< QPointF >.

void QwtSyntheticPointData::setSize (size_tsize)

Change the number of points


size Number of points

See Also:

size(), setInterval()

size_t QwtSyntheticPointData::size () const [virtual]


Number of points

See Also:

setSize(), interval()

Implements QwtSeriesData< QPointF >.

double QwtSyntheticPointData::x (uintindex) const [virtual]

Calculate a x-value from an index

x values are calculated by dividing an interval into equidistant steps. If !interval().isValid() the interval is calculated from the 'rectangle of interest'.


index Index of the requested point


Calculated x coordinate

See Also:

interval(), rectOfInterest(), y()

virtual double QwtSyntheticPointData::y (doublex) const [pure virtual]

Calculate a y value for a x value


x x value


Corresponding y value


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Qwt User's Guide Version 6.1.2 Thu Dec 11 2014