QGIS/external/qwt-6.3.0/qwt_weeding_curve_fitter.cpp

/******************************************************************************
 * 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_weeding_curve_fitter.h"
#include "qwt_math.h"

#include <qpainterpath.h>
#include <qpolygon.h>
#include <qstack.h>
#include <qvector.h>

class QwtWeedingCurveFitter::PrivateData
{
  public:
    PrivateData()
        : tolerance( 1.0 )
        , chunkSize( 0 )
    {
    }

    double tolerance;
    uint chunkSize;
};

class QwtWeedingCurveFitter::Line
{
  public:
    Line( int i1 = 0, int i2 = 0 )
        : from( i1 )
        , to( i2 )
    {
    }

    int from;
    int to;
};

/*!
   Constructor

   \param tolerance Tolerance
   \sa setTolerance(), tolerance()
 */
QwtWeedingCurveFitter::QwtWeedingCurveFitter( double tolerance )
    : QwtCurveFitter( QwtCurveFitter::Polygon )
{
    m_data = new PrivateData;
    setTolerance( tolerance );
}

//! Destructor
QwtWeedingCurveFitter::~QwtWeedingCurveFitter()
{
    delete m_data;
}

/*!
   Assign the tolerance

   The tolerance is the maximum distance, that is acceptable
   between the original curve and the smoothed curve.

   Increasing the tolerance will reduce the number of the
   resulting points.

   \param tolerance Tolerance

   \sa tolerance()
 */
void QwtWeedingCurveFitter::setTolerance( double tolerance )
{
    m_data->tolerance = qwtMaxF( tolerance, 0.0 );
}

/*!
   \return Tolerance
   \sa setTolerance()
 */
double QwtWeedingCurveFitter::tolerance() const
{
    return m_data->tolerance;
}

/*!
   Limit the number of points passed to a run of the algorithm

   The runtime of the Douglas Peucker algorithm increases non linear
   with the number of points. For a chunk size > 0 the polygon
   is split into pieces passed to the algorithm one by one.

   \param numPoints Maximum for the number of points passed to the algorithm

   \sa chunkSize()
 */
void QwtWeedingCurveFitter::setChunkSize( uint numPoints )
{
    if ( numPoints > 0 )
        numPoints = qMax( numPoints, 3U );

    m_data->chunkSize = numPoints;
}

/*!
   \return Maximum for the number of points passed to a run
          of the algorithm - or 0, when unlimited
   \sa setChunkSize()
 */
uint QwtWeedingCurveFitter::chunkSize() const
{
    return m_data->chunkSize;
}

/*!
   \param points Series of data points
   \return Curve points
   \sa fitCurvePath()
 */
QPolygonF QwtWeedingCurveFitter::fitCurve( const QPolygonF& points ) const
{
    if ( points.isEmpty() )
        return points;

    QPolygonF fittedPoints;
    if ( m_data->chunkSize == 0 )
    {
        fittedPoints = simplify( points );
    }
    else
    {
        for ( int i = 0; i < points.size(); i += m_data->chunkSize )
        {
            const QPolygonF p = points.mid( i, m_data->chunkSize );
            fittedPoints += simplify( p );
        }
    }

    return fittedPoints;
}

/*!
   \param points Series of data points
   \return Curve path
   \sa fitCurve()
 */
QPainterPath QwtWeedingCurveFitter::fitCurvePath( const QPolygonF& points ) const
{
    QPainterPath path;
    path.addPolygon( fitCurve( points ) );
    return path;
}

QPolygonF QwtWeedingCurveFitter::simplify( const QPolygonF& points ) const
{
    const double toleranceSqr = m_data->tolerance * m_data->tolerance;

    QStack< Line > stack;
    stack.reserve( 500 );

    const QPointF* p = points.data();
    const int nPoints = points.size();

    QVector< bool > usePoint( nPoints, false );

    stack.push( Line( 0, nPoints - 1 ) );

    while ( !stack.isEmpty() )
    {
        const Line r = stack.pop();

        // initialize line segment
        const double vecX = p[r.to].x() - p[r.from].x();
        const double vecY = p[r.to].y() - p[r.from].y();

        const double vecLength = std::sqrt( vecX * vecX + vecY * vecY );

        const double unitVecX = ( vecLength != 0.0 ) ? vecX / vecLength : 0.0;
        const double unitVecY = ( vecLength != 0.0 ) ? vecY / vecLength : 0.0;

        double maxDistSqr = 0.0;
        int nVertexIndexMaxDistance = r.from + 1;
        for ( int i = r.from + 1; i < r.to; i++ )
        {
            //compare to anchor
            const double fromVecX = p[i].x() - p[r.from].x();
            const double fromVecY = p[i].y() - p[r.from].y();

            double distToSegmentSqr;
            if ( fromVecX * unitVecX + fromVecY * unitVecY < 0.0 )
            {
                distToSegmentSqr = fromVecX * fromVecX + fromVecY * fromVecY;
            }
            else
            {
                const double toVecX = p[i].x() - p[r.to].x();
                const double toVecY = p[i].y() - p[r.to].y();
                const double toVecLength = toVecX * toVecX + toVecY * toVecY;

                const double s = toVecX * ( -unitVecX ) + toVecY * ( -unitVecY );
                if ( s < 0.0 )
                {
                    distToSegmentSqr = toVecLength;
                }
                else
                {
                    distToSegmentSqr = std::fabs( toVecLength - s * s );
                }
            }

            if ( maxDistSqr < distToSegmentSqr )
            {
                maxDistSqr = distToSegmentSqr;
                nVertexIndexMaxDistance = i;
            }
        }
        if ( maxDistSqr <= toleranceSqr )
        {
            usePoint[r.from] = true;
            usePoint[r.to] = true;
        }
        else
        {
            stack.push( Line( r.from, nVertexIndexMaxDistance ) );
            stack.push( Line( nVertexIndexMaxDistance, r.to ) );
        }
    }

    QPolygonF stripped;
    for ( int i = 0; i < nPoints; i++ )
    {
        if ( usePoint[i] )
            stripped += p[i];
    }

    return stripped;
}