shifting curve up or down

[oliver_mpt]

Hi,

I have plotted several curves (qwtPlotCurve) in the same plot (qwtPlot), and as they overlap a lot, I would like to shift some using a qwtCounter to increase an offset value that I would use to shift a selected curve up or down.
I was wondering what was the best way of doing it - is there any simple or build-in way to add a constant double to all the y values of my curve data ?

regards

Oliver

[Uwe]

Assuming that your points are stored in a QPolygonF:


class YourData: public QwtPointSeriesData
{
public:
YourData( const QVector<QPointF> &samples ):
QwtPointSeriesData( samples ):
m_offset( 0.0 )
{
}

void setOffset( double off )
{
m_offset = offset;
}

virtual QPointF sample( size_t index ) const
{
QPointF point = QwtPointSeriesData::sample( index );
return QPointF( point.x(), point.y() + m_offset );
}

virtual QRectF boundingRect() const
{
return QwtPointSeriesData::boundingRect().translated( 0.0, m_offset );
}
private:
double m_offset;
};

and:


curve->setData( new YourData( points ) );

Of course you have to replace QwtPointSeriesData by the type of series data object you were using so far ( QwtPlotCurve::setSamples does nothing else than creating such an data object internally - check the implementation ).

When you have many points it might be a good idea to use a different implementation for YourData::sample() that directly accesses your point container instead of calling the base class.

HTH,
Uwe



}

[oliver_mpt]

Hi Uwe,

Thanks for the detailed answer. I will experiment this approach today and report the results on the forum.

best regards

Oliver

[oliver_mpt]

Hello Uwe,

I pasted your code with almost no changes and it worled perfectly at once !

Thanks a lot for your support.

Oliver