use factor for displaying y values

[phenoboy]

Is it possible to use or define a factor that would be used to determine sample array points y-coordinate ?

For example I am now using this code to modify each points Y value accordint to a factor.

void CustomQwtCurve::setYFactor(const qreal &value)
{    
    if (value==0) return;
    qDebug() << " current factor: " << y_factor;
    qreal newfactor=value/y_factor;
    y_factor=value;
    qDebug() << " factor to multiply current points: " << newfactor;
    qDebug() << " new y_factor: " << y_factor;
 
    for (int i=0; i<points_x.count(); i++) {
        qreal px=points_x.at(i);
        qreal py=points_y.at(i);
        py=py * newfactor;
        points_y[i]=py;
    }
}

void CustomQwtCurve::setYFactor(const qreal &value)
{    
    if (value==0) return;
    qDebug() << " current factor: " << y_factor;
    qreal newfactor=value/y_factor;
    y_factor=value;
    qDebug() << " factor to multiply current points: " << newfactor;
    qDebug() << " new y_factor: " << y_factor;

    for (int i=0; i<points_x.count(); i++) {
        qreal px=points_x.at(i);
        qreal py=points_y.at(i);
        py=py * newfactor;
        points_y[i]=py;
    }
}

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Problem is this is very slow approach as I might have 100 000 or even more samples in an array.

Would it be possible to define a factor (where ?) that would be used only when drawing points so that I would not have to modify the array every time ?


For drawing I use:

QwtPlotDirectPainter->drawSeries( curve, curve->getLastX()-2, curve->pointsCount() - 1 );

'curve' is own class derived from QwtPlotCurve

[phenoboy]

Also I can't override drawSeries in my own curve class

void QwtPlotCurve::drawSeries( QPainter *painter,
    const QwtScaleMap &xMap, const QwtScaleMap &yMap,
    const QRectF &canvasRect, int from, int to ) const

void QwtPlotCurve::drawSeries( QPainter *painter,
    const QwtScaleMap &xMap, const QwtScaleMap &yMap,
    const QRectF &canvasRect, int from, int to ) const

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because that function accesses private data variable: d_data

---

Added after 20 minutes:

Ok, I can override QwtPlotCurve::drawCurve function.

I can see that it uses QwtScaleMap. I would guess by using this class I can set my own factor for sample point's y-coordinate value. But the problem is I don't know how to use it.

There is QwtScaleMap::updateFactor which calculates conversionfactor: d_cnv.

Help is appreciated.

[Uwe]

Curve and points are connected by a class derived from QwtSeriesData<QPointF>.
You can simply overload the sample() ( and depending on your code the boundingRect() ) method including the factor there.

By the way: I'm working on an aggressive point weeding filter for curves lines ( FilterPointsAggressive ), that significantly improves the performance in situations, where you throw trillions of points to a curve. Unfortunately there is a nasty bug in the raster paint engine of Qt in all versions since Qt 4.8, that becomes very dominant in this mode. Hope I have a workaround soon.

Uwe

[phenoboy]

Thanks!

It seems 'sample' does not get called with the following code.

I have now this:

.h

class CustomQwtCurve : public QwtPlotCurve
{
 
public:
 
    CustomQwtCurve();
    void appendPoint(qreal x, qreal y);
    virtual QPointF sample(int) const;
...
}

class CustomQwtCurve : public QwtPlotCurve
{

public:

    CustomQwtCurve();
    void appendPoint(qreal x, qreal y);
    virtual QPointF sample(int) const;
...
}

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.cpp:

QPointF CustomQwtCurve::sample(int index) const
{
    QPointF p=QwtSeriesStore<QPointF>::sample(index);
    qDebug() << "sample: x:" << p.x() << ",y:" << p.y();
    p.setY(factorYj*p.y());
    return p;
}

QPointF CustomQwtCurve::sample(int index) const
{
    QPointF p=QwtSeriesStore<QPointF>::sample(index);
    qDebug() << "sample: x:" << p.x() << ",y:" << p.y();
    p.setY(factorYj*p.y());
    return p;
}

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I need to take a look why.. does the code above look ok ?

---

Added after 1 12 minutes:

Ah, it seems QwtSeriesStore<QPointF>::sample is called when drawing and not QwtPlotCurve->sample. Looks like I need to provide derived class from QwtSeriesStore<QPointF> and take that into use in QwtPlotCurve. Need to figure out how to do that because QwtSeriesStore is inherited in QwtPlotCurve class.

[Uwe]

The only way to connect data with a curve is:

QwtPlotCurve::setData( QwtSeriesData<QPointF> *series );

QwtPlotCurve::setData( QwtSeriesData<QPointF> *series );

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All other APIs are convenience only and sooner or later end in calling setData().

So all you need to do is to derive from QwtSeriesData<QPointF> ( or one of its descendents ).

Uwe

[phenoboy]

Perfect! Thanks for great support!

[phenoboy]

Here's the code if someone else is interested also. If there's better/more efficient way, let me know !!

header:

#include <qwt_plot_curve.h>
 
class CustomQwtCurveData: public QwtSeriesData<QPointF>
{
public:
    CustomQwtCurveData();
    QPointF realSample( size_t index ) const;
    virtual QPointF sample( size_t index ) const;
    virtual size_t size() const;
    virtual QRectF boundingRect() const;
 
    void appendPoint(qreal x, qreal y);
    quint64 pointsCount();
 
    quint64 getLastX() const;
    void setLastX(const quint64 &value);
 
    qreal getFactorY() const;
    void setFactorY(const qreal &value);
 
    qreal getMaxYValue() const;
    void setMaxYValue(const qreal &value);
 
    qreal getMinYValue() const;
    void setMinYValue(const qreal &value);
 
    void clear();
 
    QVector<double>& pointsX();
    QVector<double>& pointsY();
    QRectF _boundingRect;
 
 
 
protected:
    QVector<double> points_x;
    QVector<double> points_y;
    qreal factorY;
    qreal maxYValue;
    qreal minYValue;
    quint64 lastX;
};

#include <qwt_plot_curve.h>

class CustomQwtCurveData: public QwtSeriesData<QPointF>
{
public:
    CustomQwtCurveData();
    QPointF realSample( size_t index ) const;
    virtual QPointF sample( size_t index ) const;
    virtual size_t size() const;
    virtual QRectF boundingRect() const;

    void appendPoint(qreal x, qreal y);
    quint64 pointsCount();

    quint64 getLastX() const;
    void setLastX(const quint64 &value);

    qreal getFactorY() const;
    void setFactorY(const qreal &value);

    qreal getMaxYValue() const;
    void setMaxYValue(const qreal &value);

    qreal getMinYValue() const;
    void setMinYValue(const qreal &value);

    void clear();

    QVector<double>& pointsX();
    QVector<double>& pointsY();
    QRectF _boundingRect;



protected:
    QVector<double> points_x;
    QVector<double> points_y;
    qreal factorY;
    qreal maxYValue;
    qreal minYValue;
    quint64 lastX;
};

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cpp:

#include "customqwtcurve.h"
#include <qwt_scale_map.h>
#include <qwt_point_data.h>
 
 
qreal CustomQwtCurveData::getMaxYValue() const
{
    return maxYValue;
}
 
void CustomQwtCurveData::setMaxYValue(const qreal &value)
{
    maxYValue = value;
}
 
QPointF CustomQwtCurveData::realSample(size_t index) const
{
    QPointF p(points_x.value(index), points_y.value(index));
    return p;
}
 
QPointF CustomQwtCurveData::sample(size_t index) const
{
    QPointF p(points_x.value(index), points_y.value(index));
    p.setY(factorY*p.y());
    return p;
}
 
size_t CustomQwtCurveData::size() const
{
    return points_x.size();
}
 
QRectF CustomQwtCurveData::boundingRect() const
{
    // adjust the bounding rectangle
 
    return _boundingRect;
}
 
qreal CustomQwtCurveData::getFactorY() const
{
    return factorY;
}
 
void CustomQwtCurveData::setFactorY(const qreal &value)
{
    factorY = value;
}
 
 
void CustomQwtCurveData::appendPoint(qreal x, qreal y)
{
    if (y>maxYValue) {
        maxYValue=y;
    }
 
    if (y<minYValue) {
        minYValue=y;
    }
 
    points_x.append(x);
    points_y.append(y);
 
    QPointF sample=QPointF(x,y);
 
    if ( _boundingRect.width() < 0 || _boundingRect.height() < 0 )
    {
        _boundingRect.setRect( sample.x(), sample.y(), 0.0, 0.0 );
    }
    else
    {
        _boundingRect.setRight( sample.x() );
 
        if ( sample.y() > _boundingRect.bottom() )
            _boundingRect.setBottom( sample.y() );
 
        qreal top=_boundingRect.top();
        qreal bottom=_boundingRect.bottom();
        if ( sample.y() < _boundingRect.top() )
            _boundingRect.setTop( sample.y() );
    }
}
 
 
quint64 CustomQwtCurveData::pointsCount() {
    return points_x.size();
}
 
void CustomQwtCurveData::clear() {
    points_x.clear();
    points_y.clear();
}
 
QVector<double> &CustomQwtCurveData::pointsX()
{
    return points_x;
}
 
QVector<double> &CustomQwtCurveData::pointsY()
{
    return points_y;
}
qreal CustomQwtCurveData::getMinYValue() const
{
    return minYValue;
}
 
void CustomQwtCurveData::setMinYValue(const qreal &value)
{
    minYValue = value;
}
 
CustomQwtCurveData::CustomQwtCurveData()
{
    factorY=1;
    maxYValue=0;
    minYValue=0;
    points_x.reserve(5000);
    points_y.reserve(5000);
}
 
quint64 CustomQwtCurveData::getLastX() const
{
    return lastX;
}
 
void CustomQwtCurveData::setLastX(const quint64 &value)
{
    lastX = value;
}

#include "customqwtcurve.h"
#include <qwt_scale_map.h>
#include <qwt_point_data.h>


qreal CustomQwtCurveData::getMaxYValue() const
{
    return maxYValue;
}

void CustomQwtCurveData::setMaxYValue(const qreal &value)
{
    maxYValue = value;
}

QPointF CustomQwtCurveData::realSample(size_t index) const
{
    QPointF p(points_x.value(index), points_y.value(index));
    return p;
}

QPointF CustomQwtCurveData::sample(size_t index) const
{
    QPointF p(points_x.value(index), points_y.value(index));
    p.setY(factorY*p.y());
    return p;
}

size_t CustomQwtCurveData::size() const
{
    return points_x.size();
}

QRectF CustomQwtCurveData::boundingRect() const
{
    // adjust the bounding rectangle

    return _boundingRect;
}

qreal CustomQwtCurveData::getFactorY() const
{
    return factorY;
}

void CustomQwtCurveData::setFactorY(const qreal &value)
{
    factorY = value;
}


void CustomQwtCurveData::appendPoint(qreal x, qreal y)
{
    if (y>maxYValue) {
        maxYValue=y;
    }

    if (y<minYValue) {
        minYValue=y;
    }

    points_x.append(x);
    points_y.append(y);

    QPointF sample=QPointF(x,y);

    if ( _boundingRect.width() < 0 || _boundingRect.height() < 0 )
    {
        _boundingRect.setRect( sample.x(), sample.y(), 0.0, 0.0 );
    }
    else
    {
        _boundingRect.setRight( sample.x() );

        if ( sample.y() > _boundingRect.bottom() )
            _boundingRect.setBottom( sample.y() );

        qreal top=_boundingRect.top();
        qreal bottom=_boundingRect.bottom();
        if ( sample.y() < _boundingRect.top() )
            _boundingRect.setTop( sample.y() );
    }
}


quint64 CustomQwtCurveData::pointsCount() {
    return points_x.size();
}

void CustomQwtCurveData::clear() {
    points_x.clear();
    points_y.clear();
}

QVector<double> &CustomQwtCurveData::pointsX()
{
    return points_x;
}

QVector<double> &CustomQwtCurveData::pointsY()
{
    return points_y;
}
qreal CustomQwtCurveData::getMinYValue() const
{
    return minYValue;
}

void CustomQwtCurveData::setMinYValue(const qreal &value)
{
    minYValue = value;
}

CustomQwtCurveData::CustomQwtCurveData()
{
    factorY=1;
    maxYValue=0;
    minYValue=0;
    points_x.reserve(5000);
    points_y.reserve(5000);
}

quint64 CustomQwtCurveData::getLastX() const
{
    return lastX;
}

void CustomQwtCurveData::setLastX(const quint64 &value)
{
    lastX = value;
}

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[HappyCoder]

Hello phenoboy,

many thanks for your mail and support. With that i was able to create a subclass that
is very similar to your CustomQwtCurveData.

How did you use it?
I guess you create an object in header file from your CustomQwtCurveData and use
CustomQwtCurveData::appendPoint(qreal x, qreal y) to add a single value (x,y) and
QwtPlotCurve::setSamples(CustomQwtCurveData *). Is that right?

Thx
Stefan

[phenoboy]

Hello phenoboy,

many thanks for your mail and support. With that i was able to create a subclass that
is very similar to your CustomQwtCurveData.

How did you use it?
I guess you create an object in header file from your CustomQwtCurveData and use
CustomQwtCurveData::appendPoint(qreal x, qreal y) to add a single value (x,y) and
QwtPlotCurve::setSamples(CustomQwtCurveData *). Is that right?

Thx
Stefan

Sorry for late answer. Yes, you're correct. That is how I use it.