QwtSyntheticPointData(3) Qwt User's Guide QwtSyntheticPointData(3)

QwtSyntheticPointData - Synthetic point data.

#include <qwt_point_data.h>

Inherits QwtPointSeriesData.

QwtSyntheticPointData (size_t size, const QwtInterval &=QwtInterval())
void setSize (size_t size)
virtual size_t size () const override
void setInterval (const QwtInterval &)
QwtInterval interval () const
virtual QRectF boundingRect () const override
Calculate the bounding rectangle. virtual QPointF sample (size_t index) const override
virtual double y (double x) const =0
virtual double x (uint index) const
virtual void setRectOfInterest (const QRectF &) override
QRectF rectOfInterest () const

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( QwtAxis::XBottom, 0.0, 10.0 );
   plot.setAxisScale( QwtAxis::YLeft, -1.0, 1.0 );
   QwtPlotCurve *curve = new QwtPlotCurve( "y = sin(x)" );
   curve->setData( new SinusData() );
   curve->attach( &plot );
   return a.exec();

Definition at line 157 of file qwt_point_data.h.



size Number of points
interval Bounding interval for the points

See also

setInterval(), setSize()

Definition at line 20 of file qwt_point_data.cpp.

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

Reimplemented from QwtPointSeriesData.

Definition at line 105 of file qwt_point_data.cpp.

QwtInterval QwtSyntheticPointData::interval () const


Bounding interval

See also

setInterval(), size()

Definition at line 62 of file qwt_point_data.cpp.


See also


Definition at line 89 of file qwt_point_data.cpp.

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.

Reimplemented from QwtArraySeriesData< QPointF >.

Definition at line 125 of file qwt_point_data.cpp.

Set the bounding interval


interval Interval

See also

interval(), setSize()

Definition at line 53 of file qwt_point_data.cpp.

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 >.

Definition at line 78 of file qwt_point_data.cpp.

Change the number of points


size Number of points

See also

size(), setInterval()

Definition at line 33 of file qwt_point_data.cpp.


Number of points

See also

setSize(), interval()

Reimplemented from QwtArraySeriesData< QPointF >.

Definition at line 42 of file qwt_point_data.cpp.

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()

Definition at line 148 of file qwt_point_data.cpp.

Calculate a y value for a x value


x x value


Corresponding y value

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Sun Jul 18 2021 Version 6.2.0