QwtCurve with multiple colors

[hassinoss]

Hi everybody,

I want to know if there is a possibility to draw one qwtCurve with different colors ? if yes how ?

Thank you.

[Uwe]

You have to overload one of the draw methods of QwtPlotCurve. For instance if your curve is a line plot and you want to have segments with different line pens:

YourCurve::drawLines(QPainter *painter, const QwtScaleMap &xMap, const QwtScaleMap &yMap,
    const QRectF &canvasRect, int from, int to ) const
{
    for ( int i = 0; i < numSegments; i++ )
    {
        ....
 
       painter->setPen( segmentPen[i] );
       QwtPlotCurve::drawLines(painter ,xMap, yMap, canvasRect, 
            segmentStart[i], segmentStart[i+1] );
}

YourCurve::drawLines(QPainter *painter, const QwtScaleMap &xMap, const QwtScaleMap &yMap,
    const QRectF &canvasRect, int from, int to ) const
{
    for ( int i = 0; i < numSegments; i++ )
    {
        ....

       painter->setPen( segmentPen[i] );
       QwtPlotCurve::drawLines(painter ,xMap, yMap, canvasRect, 
            segmentStart[i], segmentStart[i+1] );
}

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When you are not using QwtPlotDirectPainter from/to should always be for the complete curve.

Uwe

[hassinoss]

Can you give me please un exemple how i can call the method drawLines? i don't know what is QwtScaleMap ? also what do you want to say by segmentPen[]

Thank you in advance

[Cah]

i don't know what is QwtScaleMap

The doc says..

QwtScaleMap offers transformations from the coordinate system of a scale into the linear coordinate system of a paint device and vice versa.

also what do you want to say by segmentPen[]

The colors effectively divide the curve into segments ...
Thus, if you have 3 colors in the curve, you have 3 segments

Thus, numSegments == 3
int segmentPen[numSegments] ... initialize the array with the pen you want

I believe thats it

[hassinoss]

hi,

This my code ;
class CCurvePlot :
public QwtPlotCurve
{
public:
CCurvePlot(const QwtText &title);
CCurvePlot(const QString &title = QString::null );
~CCurvePlot(void);
protected:
virtual void drawLines( QPainter *painter, const QwtScaleMap &xMap, const QwtScaleMap &yMap, const QRectF &canvasRect, int from, int to ) const;
};


void CCurvePlot::drawLines( QPainter *painter, const QwtScaleMap &xMap, const QwtScaleMap &yMap, const QRectF &canvasRect, int from, int to ) const
{
for ( int i = 1; i < 20; i++ )
{
if(0 < i && i < 5 )
painter->setPen(Qt::red );
if(5 < i && i < 10 )
painter->setPen(Qt::blue );
if(10 < i && i < 15 )
painter->setPen(Qt::green );
if(15 < i && i < 20 )
painter->setPen(Qt::yellow );

drawLines(painter ,xMap, yMap, canvasRect, i *10, (i+1) *10 );
}
}

i call this in other classe

CCurvePlot* pCurve = new CCurvePlot();
pCurve->setSamples( samples );// sample is a vector of QPointF

But it doesn't work.

[Cah]

#ifndef CUSTOMCURVE_H
#define CUSTOMCURVE_H
 
#include <qwt_plot_curve.h>
 
/*
 *QVector<QPointF> samplesVec()
{
    QVector<QPointF> result;
    for(int i=0; i<=300; ++i)
        result << QPointF(i, 8+i*i); //y=8+x^2
    return result;
}
*/
 
class CustomCurve : public QwtPlotCurve
{
public:
    explicit CustomCurve(const QString &title=QString::null):QwtPlotCurve (title)
    {
 
    }
 
    virtual void  drawLines (QPainter *p, const QwtScaleMap &xMap,
                             const QwtScaleMap &yMap, const QRectF &canvasRect, int from, int to) const
    {
 
        const int numOfSegments = m_segColor.size();
        if(numOfSegments)
        {
            p->save();
            for(int i=0; i<numOfSegments; ++i)
            {
                p->setPen(m_segColor[i]);
                QwtPlotCurve::drawLines (p, xMap, yMap, canvasRect, m_segStart[i], m_segFinish[i]);
            }
            p->restore();
        }
        else
            QwtPlotCurve::drawLines (p, xMap, yMap, canvasRect, from, to);
 
    }
 
    void setSegmentInfo(int segmentStartIndex, int segmentFinisIndex, const QColor & color)
    {
        m_segColor.push_back(color);
        m_segStart.push_back(segmentStartIndex);
        m_segFinish.push_back(segmentFinisIndex);
 
    }
 
private:
    QList<QColor>   m_segColor;
    QList<int>      m_segStart;
    QList<int>      m_segFinish;
 
 
 
};
 
#endif // CUSTOMCURVE_H

#ifndef CUSTOMCURVE_H
#define CUSTOMCURVE_H

#include <qwt_plot_curve.h>

/*
 *QVector<QPointF> samplesVec()
{
    QVector<QPointF> result;
    for(int i=0; i<=300; ++i)
        result << QPointF(i, 8+i*i); //y=8+x^2
    return result;
}
*/

class CustomCurve : public QwtPlotCurve
{
public:
    explicit CustomCurve(const QString &title=QString::null):QwtPlotCurve (title)
    {

    }

    virtual void  drawLines (QPainter *p, const QwtScaleMap &xMap,
                             const QwtScaleMap &yMap, const QRectF &canvasRect, int from, int to) const
    {

        const int numOfSegments = m_segColor.size();
        if(numOfSegments)
        {
            p->save();
            for(int i=0; i<numOfSegments; ++i)
            {
                p->setPen(m_segColor[i]);
                QwtPlotCurve::drawLines (p, xMap, yMap, canvasRect, m_segStart[i], m_segFinish[i]);
            }
            p->restore();
        }
        else
            QwtPlotCurve::drawLines (p, xMap, yMap, canvasRect, from, to);

    }

    void setSegmentInfo(int segmentStartIndex, int segmentFinisIndex, const QColor & color)
    {
        m_segColor.push_back(color);
        m_segStart.push_back(segmentStartIndex);
        m_segFinish.push_back(segmentFinisIndex);

    }

private:
    QList<QColor>   m_segColor;
    QList<int>      m_segStart;
    QList<int>      m_segFinish;



};

#endif // CUSTOMCURVE_H

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If you have 300 points in a samples vec..

....
 
    curve->setSegmentInfo(0, 100, QColor("red"));
    curve->setSegmentInfo(100, 200, QColor("green"));
    curve->setSegmentInfo(200, 300, QColor("blue"));
...

....

    curve->setSegmentInfo(0, 100, QColor("red"));
    curve->setSegmentInfo(100, 200, QColor("green"));
    curve->setSegmentInfo(200, 300, QColor("blue"));
...

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Then the above calls to setSegmentInfo() by a client of a CustomCurve instance
will draw the curve in three colors..

[hassinoss]

Thank you it work now