qwt_plot_curve.cpp

/* -*- mode: C++ ; c-file-style: "stroustrup" -*- *****************************
 * Qwt Widget Library
 * Copyright (C) 1997   Josef Wilgen
 * Copyright (C) 2002   Uwe Rathmann
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the Qwt License, Version 1.0
 *****************************************************************************/

#include "qwt_plot_curve.h"
#include "qwt_point_data.h"
#include "qwt_math.h"
#include "qwt_clipper.h"
#include "qwt_painter.h"
#include "qwt_scale_map.h"
#include "qwt_plot.h"
#include "qwt_curve_fitter.h"
#include "qwt_symbol.h"
#include "qwt_point_mapper.h"
#include <qpainter.h>
#include <qpixmap.h>
#include <qalgorithms.h>
#include <qmath.h>

static void qwtUpdateLegendIconSize( QwtPlotCurve *curve )
{
    if ( curve->symbol() && 
        curve->testLegendAttribute( QwtPlotCurve::LegendShowSymbol ) )
    {
        QSize sz = curve->symbol()->boundingRect().size();
        sz += QSize( 2, 2 ); // margin

        if ( curve->testLegendAttribute( QwtPlotCurve::LegendShowLine ) )
        {
            // Avoid, that the line is completely covered by the symbol

            int w = qCeil( 1.5 * sz.width() );
            if ( w % 2 )
                w++;

            sz.setWidth( qMax( 8, w ) );
        }

        curve->setLegendIconSize( sz );
    }
}

static int qwtVerifyRange( int size, int &i1, int &i2 )
{
    if ( size < 1 )
        return 0;

    i1 = qBound( 0, i1, size - 1 );
    i2 = qBound( 0, i2, size - 1 );

    if ( i1 > i2 )
        qSwap( i1, i2 );

    return ( i2 - i1 + 1 );
}

class QwtPlotCurve::PrivateData
{
public:
    PrivateData():
        style( QwtPlotCurve::Lines ),
        baseline( 0.0 ),
        symbol( NULL ),
        attributes( 0 ),
        paintAttributes( 
            QwtPlotCurve::ClipPolygons | QwtPlotCurve::FilterPoints ),
        legendAttributes( 0 )
    {
        pen = QPen( Qt::black );
        curveFitter = new QwtSplineCurveFitter;
    }

    ~PrivateData()
    {
        delete symbol;
        delete curveFitter;
    }

    QwtPlotCurve::CurveStyle style;
    double baseline;

    const QwtSymbol *symbol;
    QwtCurveFitter *curveFitter;

    QPen pen;
    QBrush brush;

    QwtPlotCurve::CurveAttributes attributes;
    QwtPlotCurve::PaintAttributes paintAttributes;

    QwtPlotCurve::LegendAttributes legendAttributes;
};

/*!
  Constructor
  \param title Title of the curve
*/
QwtPlotCurve::QwtPlotCurve( const QwtText &title ):
    QwtPlotSeriesItem( title )
{
    init();
}

/*!
  Constructor
  \param title Title of the curve
*/
QwtPlotCurve::QwtPlotCurve( const QString &title ):
    QwtPlotSeriesItem( QwtText( title ) )
{
    init();
}

//! Destructor
QwtPlotCurve::~QwtPlotCurve()
{
    delete d_data;
}

//! Initialize internal members
void QwtPlotCurve::init()
{
    setItemAttribute( QwtPlotItem::Legend );
    setItemAttribute( QwtPlotItem::AutoScale );

    d_data = new PrivateData;
    setData( new QwtPointSeriesData() );

    setZ( 20.0 );
}

//! \return QwtPlotItem::Rtti_PlotCurve
int QwtPlotCurve::rtti() const
{
    return QwtPlotItem::Rtti_PlotCurve;
}

/*!
  Specify an attribute how to draw the curve

  \param attribute Paint attribute
  \param on On/Off
  \sa testPaintAttribute()
*/
void QwtPlotCurve::setPaintAttribute( PaintAttribute attribute, bool on )
{
    if ( on )
        d_data->paintAttributes |= attribute;
    else
        d_data->paintAttributes &= ~attribute;
}

/*!
    \return True, when attribute is enabled
    \sa setPaintAttribute()
*/
bool QwtPlotCurve::testPaintAttribute( PaintAttribute attribute ) const
{
    return ( d_data->paintAttributes & attribute );
}

/*!
  Specify an attribute how to draw the legend icon

  \param attribute Attribute
  \param on On/Off
  /sa testLegendAttribute(). legendIcon()
*/
void QwtPlotCurve::setLegendAttribute( LegendAttribute attribute, bool on )
{
    if ( on != testLegendAttribute( attribute ) )
    {
        if ( on )
            d_data->legendAttributes |= attribute;
        else
            d_data->legendAttributes &= ~attribute;

        qwtUpdateLegendIconSize( this );
        legendChanged();
    }
}

/*!
  \return True, when attribute is enabled
  \sa setLegendAttribute()
*/
bool QwtPlotCurve::testLegendAttribute( LegendAttribute attribute ) const
{
    return ( d_data->legendAttributes & attribute );
}

/*!
  Set the curve's drawing style

  \param style Curve style
  \sa style()
*/
void QwtPlotCurve::setStyle( CurveStyle style )
{
    if ( style != d_data->style )
    {
        d_data->style = style;

        legendChanged();
        itemChanged();
    }
}

/*!
  \return Style of the curve
  \sa setStyle()
*/
QwtPlotCurve::CurveStyle QwtPlotCurve::style() const
{
    return d_data->style;
}

/*!
  \brief Assign a symbol

  The curve will take the ownership of the symbol, hence the previously
  set symbol will be delete by setting a new one. If \p symbol is 
  \c NULL no symbol will be drawn.

  \param symbol Symbol
  \sa symbol()
*/
void QwtPlotCurve::setSymbol( QwtSymbol *symbol )
{
    if ( symbol != d_data->symbol )
    {
        delete d_data->symbol;
        d_data->symbol = symbol;

        qwtUpdateLegendIconSize( this );

        legendChanged();
        itemChanged();
    }
}

/*!
  \return Current symbol or NULL, when no symbol has been assigned
  \sa setSymbol()
*/
const QwtSymbol *QwtPlotCurve::symbol() const
{
    return d_data->symbol;
}

/*!
  Build and assign a pen

  In Qt5 the default pen width is 1.0 ( 0.0 in Qt4 ) what makes it
  non cosmetic ( see QPen::isCosmetic() ). This method has been introduced
  to hide this incompatibility.

  \param color Pen color
  \param width Pen width
  \param style Pen style

  \sa pen(), brush()
 */
void QwtPlotCurve::setPen( const QColor &color, qreal width, Qt::PenStyle style )
{
    setPen( QPen( color, width, style ) );
}

/*!
  Assign a pen

  \param pen New pen
  \sa pen(), brush()
*/
void QwtPlotCurve::setPen( const QPen &pen )
{
    if ( pen != d_data->pen )
    {
        d_data->pen = pen;

        legendChanged();
        itemChanged();
    }
}

/*!
  \return Pen used to draw the lines
  \sa setPen(), brush()
*/
const QPen& QwtPlotCurve::pen() const
{
    return d_data->pen;
}

/*!
  \brief Assign a brush.

   In case of brush.style() != QBrush::NoBrush
   and style() != QwtPlotCurve::Sticks
   the area between the curve and the baseline will be filled.

   In case !brush.color().isValid() the area will be filled by
   pen.color(). The fill algorithm simply connects the first and the
   last curve point to the baseline. So the curve data has to be sorted
   (ascending or descending).

  \param brush New brush
  \sa brush(), setBaseline(), baseline()
*/
void QwtPlotCurve::setBrush( const QBrush &brush )
{
    if ( brush != d_data->brush )
    {
        d_data->brush = brush;

        legendChanged();
        itemChanged();
    }
}

/*!
  \return Brush used to fill the area between lines and the baseline
  \sa setBrush(), setBaseline(), baseline()
*/
const QBrush& QwtPlotCurve::brush() const
{
    return d_data->brush;
}

/*!
  Draw an interval of the curve

  \param painter Painter
  \param xMap Maps x-values into pixel coordinates.
  \param yMap Maps y-values into pixel coordinates.
  \param canvasRect Contents rectangle of the canvas
  \param from Index of the first point to be painted
  \param to Index of the last point to be painted. If to < 0 the
         curve will be painted to its last point.

  \sa drawCurve(), drawSymbols(),
*/
void QwtPlotCurve::drawSeries( QPainter *painter,
    const QwtScaleMap &xMap, const QwtScaleMap &yMap,
    const QRectF &canvasRect, int from, int to ) const
{
    const size_t numSamples = dataSize();

    if ( !painter || numSamples <= 0 )
        return;

    if ( to < 0 )
        to = numSamples - 1;

    if ( qwtVerifyRange( numSamples, from, to ) > 0 )
    {
        painter->save();
        painter->setPen( d_data->pen );

        /*
          Qt 4.0.0 is slow when drawing lines, but it's even
          slower when the painter has a brush. So we don't
          set the brush before we really need it.
         */

        drawCurve( painter, d_data->style, xMap, yMap, canvasRect, from, to );
        painter->restore();

        if ( d_data->symbol &&
            ( d_data->symbol->style() != QwtSymbol::NoSymbol ) )
        {
            painter->save();
            drawSymbols( painter, *d_data->symbol,
                xMap, yMap, canvasRect, from, to );
            painter->restore();
        }
    }
}

/*!
  \brief Draw the line part (without symbols) of a curve interval.
  \param painter Painter
  \param style curve style, see QwtPlotCurve::CurveStyle
  \param xMap x map
  \param yMap y map
  \param canvasRect Contents rectangle of the canvas
  \param from index of the first point to be painted
  \param to index of the last point to be painted
  \sa draw(), drawDots(), drawLines(), drawSteps(), drawSticks()
*/
void QwtPlotCurve::drawCurve( QPainter *painter, int style,
    const QwtScaleMap &xMap, const QwtScaleMap &yMap,
    const QRectF &canvasRect, int from, int to ) const
{
    switch ( style )
    {
        case Lines:
            if ( testCurveAttribute( Fitted ) )
            {
                // we always need the complete
                // curve for fitting
                from = 0;
                to = dataSize() - 1;
            }
            drawLines( painter, xMap, yMap, canvasRect, from, to );
            break;
        case Sticks:
            drawSticks( painter, xMap, yMap, canvasRect, from, to );
            break;
        case Steps:
            drawSteps( painter, xMap, yMap, canvasRect, from, to );
            break;
        case Dots:
            drawDots( painter, xMap, yMap, canvasRect, from, to );
            break;
        case NoCurve:
        default:
            break;
    }
}

/*!
  \brief Draw lines

  If the CurveAttribute Fitted is enabled a QwtCurveFitter tries
  to interpolate/smooth the curve, before it is painted.

  \param painter Painter
  \param xMap x map
  \param yMap y map
  \param canvasRect Contents rectangle of the canvas
  \param from index of the first point to be painted
  \param to index of the last point to be painted

  \sa setCurveAttribute(), setCurveFitter(), draw(),
      drawLines(), drawDots(), drawSteps(), drawSticks()
*/
void QwtPlotCurve::drawLines( QPainter *painter,
    const QwtScaleMap &xMap, const QwtScaleMap &yMap,
    const QRectF &canvasRect, int from, int to ) const
{
    if ( from > to )
        return;

    const bool doAlign = QwtPainter::roundingAlignment( painter );
    const bool doFit = ( d_data->attributes & Fitted ) && d_data->curveFitter;
    const bool doFill = ( d_data->brush.style() != Qt::NoBrush )
            && ( d_data->brush.color().alpha() > 0 );

    QRectF clipRect;
    if ( d_data->paintAttributes & ClipPolygons )
    {
        qreal pw = qMax( qreal( 1.0 ), painter->pen().widthF());
        clipRect = canvasRect.adjusted(-pw, -pw, pw, pw);
    }

    bool doIntegers = false;

#if QT_VERSION < 0x040800

    // For Qt <= 4.7 the raster paint engine is significantly faster
    // for rendering QPolygon than for QPolygonF. So let's
    // see if we can use it.

    if ( painter->paintEngine()->type() == QPaintEngine::Raster )
    {
        // In case of filling or fitting performance doesn't count
        // because both operations are much more expensive
        // then drawing the polyline itself

        if ( !doFit && !doFill )
            doIntegers = true; 
    }
#endif

    const bool noDuplicates = d_data->paintAttributes & FilterPoints;

    QwtPointMapper mapper;
    mapper.setFlag( QwtPointMapper::RoundPoints, doAlign );
    mapper.setFlag( QwtPointMapper::WeedOutPoints, noDuplicates );
    mapper.setBoundingRect( canvasRect );

    if ( doIntegers )
    {
        const QPolygon polyline = mapper.toPolygon( 
            xMap, yMap, data(), from, to );

        if ( d_data->paintAttributes & ClipPolygons )
        {
            const QPolygon clipped = QwtClipper::clipPolygon( 
                clipRect.toAlignedRect(), polyline, false );

            QwtPainter::drawPolyline( painter, clipped );
        }
        else
        {
            QwtPainter::drawPolyline( painter, polyline );
        }
    }
    else
    {
        QPolygonF polyline = mapper.toPolygonF( xMap, yMap,
            data(), from, to );

        if ( doFit )
            polyline = d_data->curveFitter->fitCurve( polyline );

        if ( d_data->paintAttributes & ClipPolygons )
        {
            const QPolygonF clipped = QwtClipper::clipPolygonF( 
                clipRect, polyline, false );

            QwtPainter::drawPolyline( painter, clipped );
        }
        else
        {
            QwtPainter::drawPolyline( painter, polyline );
        }

        if ( doFill )
        {
            fillCurve( painter, xMap, yMap, canvasRect, polyline );
        }
    }
}

/*!
  Draw sticks

  \param painter Painter
  \param xMap x map
  \param yMap y map
  \param canvasRect Contents rectangle of the canvas
  \param from index of the first point to be painted
  \param to index of the last point to be painted

  \sa draw(), drawCurve(), drawDots(), drawLines(), drawSteps()
*/
void QwtPlotCurve::drawSticks( QPainter *painter,
    const QwtScaleMap &xMap, const QwtScaleMap &yMap,
    const QRectF &, int from, int to ) const
{
    painter->save();
    painter->setRenderHint( QPainter::Antialiasing, false );

    const bool doAlign = QwtPainter::roundingAlignment( painter );

    double x0 = xMap.transform( d_data->baseline );
    double y0 = yMap.transform( d_data->baseline );
    if ( doAlign )
    {
        x0 = qRound( x0 );
        y0 = qRound( y0 );
    }

    const Qt::Orientation o = orientation();

    const QwtSeriesData<QPointF> *series = data();

    for ( int i = from; i <= to; i++ )
    {
        const QPointF sample = series->sample( i );
        double xi = xMap.transform( sample.x() );
        double yi = yMap.transform( sample.y() );
        if ( doAlign )
        {
            xi = qRound( xi );
            yi = qRound( yi );
        }

        if ( o == Qt::Horizontal )
            QwtPainter::drawLine( painter, x0, yi, xi, yi );
        else
            QwtPainter::drawLine( painter, xi, y0, xi, yi );
    }

    painter->restore();
}

/*!
  Draw dots

  \param painter Painter
  \param xMap x map
  \param yMap y map
  \param canvasRect Contents rectangle of the canvas
  \param from index of the first point to be painted
  \param to index of the last point to be painted

  \sa draw(), drawCurve(), drawSticks(), drawLines(), drawSteps()
*/
void QwtPlotCurve::drawDots( QPainter *painter,
    const QwtScaleMap &xMap, const QwtScaleMap &yMap,
    const QRectF &canvasRect, int from, int to ) const
{
    const QColor color = painter->pen().color();

    if ( painter->pen().style() == Qt::NoPen || color.alpha() == 0 )
    {
        return;
    }

    const bool doFill = ( d_data->brush.style() != Qt::NoBrush )
            && ( d_data->brush.color().alpha() > 0 );
    const bool doAlign = QwtPainter::roundingAlignment( painter );

    QwtPointMapper mapper;
    mapper.setBoundingRect( canvasRect );
    mapper.setFlag( QwtPointMapper::RoundPoints, doAlign );

    if ( d_data->paintAttributes & FilterPoints )
    {
        if ( ( color.alpha() == 255 )
            && !( painter->renderHints() & QPainter::Antialiasing ) )
        {
            mapper.setFlag( QwtPointMapper::WeedOutPoints, true );
        }
    }

    if ( doFill )
    {
        mapper.setFlag( QwtPointMapper::WeedOutPoints, false );

        QPolygonF points = mapper.toPointsF( 
            xMap, yMap, data(), from, to );

        QwtPainter::drawPoints( painter, points );
        fillCurve( painter, xMap, yMap, canvasRect, points );
    }
    else if ( d_data->paintAttributes & ImageBuffer )
    {
        const QImage image = mapper.toImage( xMap, yMap,
            data(), from, to, d_data->pen, 
            painter->testRenderHint( QPainter::Antialiasing ),
            renderThreadCount() );

        painter->drawImage( canvasRect.toAlignedRect(), image );
    }
    else if ( d_data->paintAttributes & MinimizeMemory )
    {
        const QwtSeriesData<QPointF> *series = data();

        for ( int i = from; i <= to; i++ )
        {
            const QPointF sample = series->sample( i );

            double xi = xMap.transform( sample.x() );
            double yi = yMap.transform( sample.y() );

            if ( doAlign )
            {
                xi = qRound( xi );
                yi = qRound( yi );
            }

            QwtPainter::drawPoint( painter, QPointF( xi, yi ) );
        }
    }
    else
    {
        if ( doAlign )
        {
            const QPolygon points = mapper.toPoints(
                xMap, yMap, data(), from, to ); 

            QwtPainter::drawPoints( painter, points );
        }
        else
        {
            const QPolygonF points = mapper.toPointsF( 
                xMap, yMap, data(), from, to );

            QwtPainter::drawPoints( painter, points );
        }
    }
}

/*!
  Draw step function

  The direction of the steps depends on Inverted attribute.

  \param painter Painter
  \param xMap x map
  \param yMap y map
  \param canvasRect Contents rectangle of the canvas
  \param from index of the first point to be painted
  \param to index of the last point to be painted

  \sa CurveAttribute, setCurveAttribute(),
      draw(), drawCurve(), drawDots(), drawLines(), drawSticks()
*/
void QwtPlotCurve::drawSteps( QPainter *painter,
    const QwtScaleMap &xMap, const QwtScaleMap &yMap,
    const QRectF &canvasRect, int from, int to ) const
{
    const bool doAlign = QwtPainter::roundingAlignment( painter );

    QPolygonF polygon( 2 * ( to - from ) + 1 );
    QPointF *points = polygon.data();

    bool inverted = orientation() == Qt::Vertical;
    if ( d_data->attributes & Inverted )
        inverted = !inverted;

    const QwtSeriesData<QPointF> *series = data();

    int i, ip;
    for ( i = from, ip = 0; i <= to; i++, ip += 2 )
    {
        const QPointF sample = series->sample( i );
        double xi = xMap.transform( sample.x() );
        double yi = yMap.transform( sample.y() );
        if ( doAlign )
        {
            xi = qRound( xi );
            yi = qRound( yi );
        }

        if ( ip > 0 )
        {
            const QPointF &p0 = points[ip - 2];
            QPointF &p = points[ip - 1];

            if ( inverted )
            {
                p.rx() = p0.x();
                p.ry() = yi;
            }
            else
            {
                p.rx() = xi;
                p.ry() = p0.y();
            }
        }

        points[ip].rx() = xi;
        points[ip].ry() = yi;
    }

    if ( d_data->paintAttributes & ClipPolygons )
    {
        const QPolygonF clipped = QwtClipper::clipPolygonF( 
            canvasRect, polygon, false );

        QwtPainter::drawPolyline( painter, clipped );
    }
    else
    {
        QwtPainter::drawPolyline( painter, polygon );
    }

    if ( d_data->brush.style() != Qt::NoBrush )
        fillCurve( painter, xMap, yMap, canvasRect, polygon );
}


/*!
  Specify an attribute for drawing the curve

  \param attribute Curve attribute
  \param on On/Off

  /sa testCurveAttribute(), setCurveFitter()
*/
void QwtPlotCurve::setCurveAttribute( CurveAttribute attribute, bool on )
{
    if ( bool( d_data->attributes & attribute ) == on )
        return;

    if ( on )
        d_data->attributes |= attribute;
    else
        d_data->attributes &= ~attribute;

    itemChanged();
}

/*!
    \return true, if attribute is enabled
    \sa setCurveAttribute()
*/
bool QwtPlotCurve::testCurveAttribute( CurveAttribute attribute ) const
{
    return d_data->attributes & attribute;
}

/*!
  Assign a curve fitter

  The curve fitter "smooths" the curve points, when the Fitted
  CurveAttribute is set. setCurveFitter(NULL) also disables curve fitting.

  The curve fitter operates on the translated points ( = widget coordinates)
  to be functional for logarithmic scales. Obviously this is less performant
  for fitting algorithms, that reduce the number of points.

  For situations, where curve fitting is used to improve the performance
  of painting huge series of points it might be better to execute the fitter
  on the curve points once and to cache the result in the QwtSeriesData object.

  \param curveFitter() Curve fitter
  \sa Fitted
*/
void QwtPlotCurve::setCurveFitter( QwtCurveFitter *curveFitter )
{
    delete d_data->curveFitter;
    d_data->curveFitter = curveFitter;

    itemChanged();
}

/*!
  Get the curve fitter. If curve fitting is disabled NULL is returned.

  \return Curve fitter
  \sa setCurveFitter(), Fitted
*/
QwtCurveFitter *QwtPlotCurve::curveFitter() const
{
    return d_data->curveFitter;
}

/*!
  Fill the area between the curve and the baseline with
  the curve brush

  \param painter Painter
  \param xMap x map
  \param yMap y map
  \param canvasRect Contents rectangle of the canvas
  \param polygon Polygon - will be modified !

  \sa setBrush(), setBaseline(), setStyle()
*/
void QwtPlotCurve::fillCurve( QPainter *painter,
    const QwtScaleMap &xMap, const QwtScaleMap &yMap,
    const QRectF &canvasRect, QPolygonF &polygon ) const
{
    if ( d_data->brush.style() == Qt::NoBrush )
        return;

    closePolyline( painter, xMap, yMap, polygon );
    if ( polygon.count() <= 2 ) // a line can't be filled
        return;

    QBrush brush = d_data->brush;
    if ( !brush.color().isValid() )
        brush.setColor( d_data->pen.color() );

    if ( d_data->paintAttributes & ClipPolygons )
        polygon = QwtClipper::clipPolygonF( canvasRect, polygon, true );

    painter->save();

    painter->setPen( Qt::NoPen );
    painter->setBrush( brush );

    QwtPainter::drawPolygon( painter, polygon );

    painter->restore();
}

/*!
  \brief Complete a polygon to be a closed polygon including the 
         area between the original polygon and the baseline.

  \param painter Painter
  \param xMap X map
  \param yMap Y map
  \param polygon Polygon to be completed
*/
void QwtPlotCurve::closePolyline( QPainter *painter,
    const QwtScaleMap &xMap, const QwtScaleMap &yMap,
    QPolygonF &polygon ) const
{
    if ( polygon.size() < 2 )
        return;

    const bool doAlign = QwtPainter::roundingAlignment( painter );

    double baseline = d_data->baseline;
    
    if ( orientation() == Qt::Vertical )
    {
        if ( yMap.transformation() )
            baseline = yMap.transformation()->bounded( baseline );

        double refY = yMap.transform( baseline );
        if ( doAlign )
            refY = qRound( refY );

        polygon += QPointF( polygon.last().x(), refY );
        polygon += QPointF( polygon.first().x(), refY );
    }
    else
    {
        if ( xMap.transformation() )
            baseline = xMap.transformation()->bounded( baseline );

        double refX = xMap.transform( baseline );
        if ( doAlign )
            refX = qRound( refX );

        polygon += QPointF( refX, polygon.last().y() );
        polygon += QPointF( refX, polygon.first().y() );
    }
}

/*!
  Draw symbols

  \param painter Painter
  \param symbol Curve symbol
  \param xMap x map
  \param yMap y map
  \param canvasRect Contents rectangle of the canvas
  \param from Index of the first point to be painted
  \param to Index of the last point to be painted

  \sa setSymbol(), drawSeries(), drawCurve()
*/
void QwtPlotCurve::drawSymbols( QPainter *painter, const QwtSymbol &symbol,
    const QwtScaleMap &xMap, const QwtScaleMap &yMap,
    const QRectF &canvasRect, int from, int to ) const
{
    QwtPointMapper mapper;
    mapper.setFlag( QwtPointMapper::RoundPoints, 
        QwtPainter::roundingAlignment( painter ) );
    mapper.setFlag( QwtPointMapper::WeedOutPoints, 
        testPaintAttribute( QwtPlotCurve::FilterPoints ) );
    mapper.setBoundingRect( canvasRect );

    const int chunkSize = 500;

    for ( int i = from; i <= to; i += chunkSize )
    {
        const int n = qMin( chunkSize, to - i + 1 );

        const QPolygonF points = mapper.toPointsF( xMap, yMap,
            data(), i, i + n - 1 );

        if ( points.size() > 0 )
            symbol.drawSymbols( painter, points );
    }
}

/*!
  \brief Set the value of the baseline

  The baseline is needed for filling the curve with a brush or
  the Sticks drawing style.

  The interpretation of the baseline depends on the orientation().
  With Qt::Horizontal, the baseline is interpreted as a horizontal line
  at y = baseline(), with Qt::Vertical, it is interpreted as a vertical
  line at x = baseline().

  The default value is 0.0.

  \param value Value of the baseline
  \sa baseline(), setBrush(), setStyle(), QwtPlotAbstractSeriesItem::orientation()
*/
void QwtPlotCurve::setBaseline( double value )
{
    if ( d_data->baseline != value )
    {
        d_data->baseline = value;
        itemChanged();
    }
}

/*!
  \return Value of the baseline
  \sa setBaseline()
*/
double QwtPlotCurve::baseline() const
{
    return d_data->baseline;
}

/*!
  Find the closest curve point for a specific position

  \param pos Position, where to look for the closest curve point
  \param dist If dist != NULL, closestPoint() returns the distance between
              the position and the closest curve point
  \return Index of the closest curve point, or -1 if none can be found
          ( f.e when the curve has no points )
  \note closestPoint() implements a dumb algorithm, that iterates
        over all points
*/
int QwtPlotCurve::closestPoint( const QPoint &pos, double *dist ) const
{
    const size_t numSamples = dataSize();