DOKK / manpages / debian 10 / libqwt-doc / QwtSyntheticPointData.3.en
QwtSyntheticPointData(3) Qwt User's Guide QwtSyntheticPointData(3)

QwtSyntheticPointData - Synthetic point data.

#include <qwt_point_data.h>

Inherits QwtSeriesData< QPointF >.


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 index) const
virtual double y (double x) const =0
virtual double x (uint index) const
virtual void setRectOfInterest (const QRectF &)
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.

Example

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
{
public:


    SinusData():


        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 );


    plot.show();


    return a.exec();
}

Constructor

Parameters:

size Number of points
interval Bounding interval for the points

See also:

setInterval(), setSize()

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 ).

Returns:

Bounding rectangle

Implements QwtSeriesData< QPointF >.

QwtInterval QwtSyntheticPointData::interval () const

Returns:

Bounding interval

See also:

setInterval(), size()

Returns:

See also:

setRectOfInterest()

Calculate the point from an index

Parameters:

index Index

Returns:

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

Warning:

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

Implements QwtSeriesData< QPointF >.

Set the bounding interval

Parameters:

interval Interval

See also:

interval(), setSize()

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:

rectOfInterest()

Reimplemented from QwtSeriesData< QPointF >.

Change the number of points

Parameters:

size Number of points

See also:

size(), setInterval()

Returns:

Number of points

See also:

setSize(), interval()

Implements QwtSeriesData< QPointF >.

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'.

Parameters:

index Index of the requested point

Returns:

Calculated x coordinate

See also:

interval(), rectOfInterest(), y()

Calculate a y value for a x value

Parameters:

x x value

Returns:

Corresponding y value

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Wed Jan 2 2019 Version 6.1.4