shape_poly_set.cpp

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/*
 * This program source code file is part of KiCad, a free EDA CAD application.
 *
 * Copyright (C) 2015-2019 CERN
 * Copyright The KiCad Developers, see AUTHORS.txt for contributors.
 *
 * @author Tomasz Wlostowski <[email protected]>
 * @author Alejandro García Montoro <[email protected]>
 *
 * Point in polygon algorithm adapted from Clipper Library (C) Angus Johnson,
 * subject to Clipper library license.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */
 
#include <algorithm>
#include <assert.h>                          // for assert
#include <cmath>                             // for sqrt, cos, hypot, isinf
#include <cstdio>
#include <istream>                           // for operator<<, operator>>
#include <limits>                            // for numeric_limits
#include <map>
#include <memory>
#include <set>
#include <string> // for char_traits, operator!=
#include <unordered_set>
#include <thread>
#include <utility> // for swap, move
#include <vector>
#include <array>
 
#include <clipper2/clipper.h>
#include <geometry/geometry_predicates.h>
#include <geometry/geometry_utils.h>
#include <geometry/polygon_triangulation.h>
#include <geometry/seg.h>                    // for SEG, OPT_VECTOR2I
#include <geometry/shape.h>
#include <geometry/shape_line_chain.h>
#include <geometry/shape_poly_set.h>
#include <geometry/rtree/dynamic_rtree.h>
#include <math/box2.h>                       // for BOX2I
#include <math/util.h>                       // for KiROUND, rescale
#include <math/vector2d.h>                   // for VECTOR2I, VECTOR2D, VECTOR2
#include <hash.h>
#include <mmh3_hash.h>
#include <geometry/shape_segment.h>
#include <geometry/shape_circle.h>
 
#include <wx/log.h>
 
// ADVANCED_CFG::GetCfg() cannot be used on msys2/mingw builds (link failure)
// So we use the ADVANCED_CFG default values
#if defined( __MINGW32__ )
    #define TRIANGULATESIMPLIFICATIONLEVEL 50
    #define ENABLECACHEFRIENDLYFRACTURE true
#else
    #define TRIANGULATESIMPLIFICATIONLEVEL ADVANCED_CFG::GetCfg().m_TriangulateSimplificationLevel
    #define ENABLECACHEFRIENDLYFRACTURE ADVANCED_CFG::GetCfg().m_EnableCacheFriendlyFracture
#endif
 
SHAPE_POLY_SET::SHAPE_POLY_SET() :
    SHAPE( SH_POLY_SET )
{
}
 
 
SHAPE_POLY_SET::SHAPE_POLY_SET( const BOX2D& aRect ) :
    SHAPE( SH_POLY_SET )
{
    NewOutline();
    Append( VECTOR2I( aRect.GetLeft(),  aRect.GetTop() ) );
    Append( VECTOR2I( aRect.GetRight(), aRect.GetTop() ) );
    Append( VECTOR2I( aRect.GetRight(), aRect.GetBottom() ) );
    Append( VECTOR2I( aRect.GetLeft(),  aRect.GetBottom() ) );
    Outline( 0 ).SetClosed( true );
}
 
 
SHAPE_POLY_SET::SHAPE_POLY_SET( const SHAPE_LINE_CHAIN& aOutline ) :
    SHAPE( SH_POLY_SET )
{
    AddOutline( aOutline );
}
 
 
SHAPE_POLY_SET::SHAPE_POLY_SET( const POLYGON& aPolygon ) :
    SHAPE( SH_POLY_SET )
{
    AddPolygon( aPolygon );
}
 
 
SHAPE_POLY_SET::SHAPE_POLY_SET( const SHAPE_POLY_SET& aOther ) :
    SHAPE( aOther ),
    m_polys( aOther.m_polys )
{
    if( aOther.IsTriangulationUpToDate() )
    {
        m_triangulatedPolys.reserve( aOther.TriangulatedPolyCount() );
 
        for( unsigned i = 0; i < aOther.TriangulatedPolyCount(); i++ )
        {
            const TRIANGULATED_POLYGON* poly = aOther.TriangulatedPolygon( i );
            m_triangulatedPolys.push_back( std::make_unique<TRIANGULATED_POLYGON>( *poly ) );
        }
 
        m_hash = aOther.GetHash();
        m_hashValid = true;
        m_triangulationValid = true;
    }
    else
    {
        m_hash.Clear();
        m_hashValid = false;
        m_triangulationValid = false;
    }
 
    m_failedHash = aOther.m_failedHash;
    m_failedHashValid.store( aOther.m_failedHashValid.load() );
}
 
 
SHAPE_POLY_SET::SHAPE_POLY_SET( const SHAPE_POLY_SET& aOther, DROP_TRIANGULATION_FLAG ) :
    SHAPE( aOther ),
    m_polys( aOther.m_polys )
{
    m_hash.Clear();
    m_hashValid = false;
    m_triangulationValid = false;
}
 
 
SHAPE_POLY_SET::~SHAPE_POLY_SET()
{
}
 
 
SHAPE* SHAPE_POLY_SET::Clone() const
{
    return new SHAPE_POLY_SET( *this );
}
 
 
SHAPE_POLY_SET SHAPE_POLY_SET::CloneDropTriangulation() const
{
    return SHAPE_POLY_SET( *this, DROP_TRIANGULATION_FLAG::SINGLETON );
}
 
 
bool SHAPE_POLY_SET::GetRelativeIndices( int aGlobalIdx,
                                         SHAPE_POLY_SET::VERTEX_INDEX* aRelativeIndices ) const
{
    int polygonIdx = 0;
    unsigned int contourIdx = 0;
    int vertexIdx = 0;
 
    int currentGlobalIdx = 0;
 
    for( polygonIdx = 0; polygonIdx < OutlineCount(); polygonIdx++ )
    {
        const POLYGON& currentPolygon = CPolygon( polygonIdx );
 
        for( contourIdx = 0; contourIdx < currentPolygon.size(); contourIdx++ )
        {
            const SHAPE_LINE_CHAIN& currentContour = currentPolygon[contourIdx];
            int totalPoints = currentContour.PointCount();
 
            for( vertexIdx = 0; vertexIdx < totalPoints; vertexIdx++ )
            {
                // Check if the current vertex is the globally indexed as aGlobalIdx
                if( currentGlobalIdx == aGlobalIdx )
                {
                    aRelativeIndices->m_polygon = polygonIdx;
                    aRelativeIndices->m_contour = contourIdx;
                    aRelativeIndices->m_vertex  = vertexIdx;
 
                    return true;
                }
 
                // Advance
                currentGlobalIdx++;
            }
        }
    }
 
    return false;
}
 
 
bool SHAPE_POLY_SET::GetGlobalIndex( SHAPE_POLY_SET::VERTEX_INDEX aRelativeIndices,
                                     int& aGlobalIdx ) const
{
    int          selectedVertex = aRelativeIndices.m_vertex;
    unsigned int selectedContour = aRelativeIndices.m_contour;
    unsigned int selectedPolygon = aRelativeIndices.m_polygon;
 
    // Check whether the vertex indices make sense in this poly set
    if( selectedPolygon < m_polys.size() && selectedContour < m_polys[selectedPolygon].size()
        && selectedVertex < m_polys[selectedPolygon][selectedContour].PointCount() )
    {
        POLYGON currentPolygon;
 
        aGlobalIdx = 0;
 
        for( unsigned int polygonIdx = 0; polygonIdx < selectedPolygon; polygonIdx++ )
        {
            currentPolygon = Polygon( polygonIdx );
 
            for( unsigned int contourIdx = 0; contourIdx < currentPolygon.size(); contourIdx++ )
                aGlobalIdx += currentPolygon[contourIdx].PointCount();
        }
 
        currentPolygon = Polygon( selectedPolygon );
 
        for( unsigned int contourIdx = 0; contourIdx < selectedContour; contourIdx++ )
            aGlobalIdx += currentPolygon[contourIdx].PointCount();
 
        aGlobalIdx += selectedVertex;
 
        return true;
    }
    else
    {
        return false;
    }
}
 
 
int SHAPE_POLY_SET::NewOutline()
{
    SHAPE_LINE_CHAIN empty_path;
    POLYGON          poly;
 
    empty_path.SetClosed( true );
    poly.push_back( empty_path );
    m_polys.push_back( std::move( poly ) );
    return m_polys.size() - 1;
}
 
 
int SHAPE_POLY_SET::NewHole( int aOutline )
{
    SHAPE_LINE_CHAIN empty_path;
 
    empty_path.SetClosed( true );
 
    // Default outline is the last one
    if( aOutline < 0 )
        aOutline += m_polys.size();
 
    // Add hole to the selected outline
    m_polys[aOutline].push_back( empty_path );
 
    return m_polys.back().size() - 2;
}
 
 
int SHAPE_POLY_SET::Append( int x, int y, int aOutline, int aHole, bool aAllowDuplication )
{
    assert( m_polys.size() );
 
    if( aOutline < 0 )
        aOutline += m_polys.size();
 
    int idx;
 
    if( aHole < 0 )
        idx = 0;
    else
        idx = aHole + 1;
 
    assert( aOutline < (int) m_polys.size() );
    assert( idx < (int) m_polys[aOutline].size() );
 
    m_polys[aOutline][idx].Append( x, y, aAllowDuplication );
 
    return m_polys[aOutline][idx].PointCount();
}
 
 
int SHAPE_POLY_SET::Append( const SHAPE_ARC& aArc, int aOutline, int aHole,
                            std::optional<int> aMaxError )
{
    assert( m_polys.size() );
 
    if( aOutline < 0 )
        aOutline += m_polys.size();
 
    int idx;
 
    if( aHole < 0 )
        idx = 0;
    else
        idx = aHole + 1;
 
    assert( aOutline < (int) m_polys.size() );
    assert( idx < (int) m_polys[aOutline].size() );
 
    if( aMaxError.has_value() )
        m_polys[aOutline][idx].Append( aArc, aMaxError.value() );
    else
        m_polys[aOutline][idx].Append( aArc );
 
    return m_polys[aOutline][idx].PointCount();
}
 
 
void SHAPE_POLY_SET::InsertVertex( int aGlobalIndex, const VECTOR2I& aNewVertex )
{
    VERTEX_INDEX index;
 
    if( aGlobalIndex < 0 )
        aGlobalIndex = 0;
 
    if( aGlobalIndex >= TotalVertices() )
    {
        Append( aNewVertex );
    }
    else
    {
        // Assure the position to be inserted exists; throw an exception otherwise
        if( GetRelativeIndices( aGlobalIndex, &index ) )
            m_polys[index.m_polygon][index.m_contour].Insert( index.m_vertex, aNewVertex );
        else
            throw( std::out_of_range( "aGlobalIndex-th vertex does not exist" ) );
    }
}
 
 
int SHAPE_POLY_SET::VertexCount( int aOutline, int aHole  ) const
{
    if( m_polys.size() == 0 ) // Empty poly set
        return 0;
 
    if( aOutline < 0 ) // Use last outline
        aOutline += m_polys.size();
 
    int idx;
 
    if( aHole < 0 )
        idx = 0;
    else
        idx = aHole + 1;
 
    if( aOutline >= (int) m_polys.size() ) // not existing outline
        return 0;
 
    if( idx >= (int) m_polys[aOutline].size() ) // not existing hole
        return 0;
 
    return m_polys[aOutline][idx].PointCount();
}
 
 
int SHAPE_POLY_SET::FullPointCount() const
{
    int full_count = 0;
 
    if( m_polys.size() == 0 ) // Empty poly set
        return full_count;
 
    for( int ii = 0; ii < OutlineCount(); ii++ )
    {
        // the first polygon in m_polys[ii] is the main contour,
        // only others are holes:
        for( int idx = 0; idx <= HoleCount( ii ); idx++ )
        {
            full_count += m_polys[ii][idx].PointCount();
        }
    }
 
    return full_count;
}
 
 
SHAPE_POLY_SET SHAPE_POLY_SET::Subset( int aFirstPolygon, int aLastPolygon )
{
    assert( aFirstPolygon >= 0 && aLastPolygon <= OutlineCount() );
 
    SHAPE_POLY_SET newPolySet;
 
    for( int index = aFirstPolygon; index < aLastPolygon; index++ )
        newPolySet.m_polys.push_back( Polygon( index ) );
 
    return newPolySet;
}
 
 
const VECTOR2I& SHAPE_POLY_SET::CVertex( int aIndex, int aOutline, int aHole ) const
{
    if( aOutline < 0 )
        aOutline += m_polys.size();
 
    int idx;
 
    if( aHole < 0 )
        idx = 0;
    else
        idx = aHole + 1;
 
    assert( aOutline < (int) m_polys.size() );
    assert( idx < (int) m_polys[aOutline].size() );
 
    return m_polys[aOutline][idx].CPoint( aIndex );
}
 
 
const VECTOR2I& SHAPE_POLY_SET::CVertex( int aGlobalIndex ) const
{
    SHAPE_POLY_SET::VERTEX_INDEX index;
 
    // Assure the passed index references a legal position; abort otherwise
    if( !GetRelativeIndices( aGlobalIndex, &index ) )
        throw( std::out_of_range( "aGlobalIndex-th vertex does not exist" ) );
 
    return m_polys[index.m_polygon][index.m_contour].CPoint( index.m_vertex );
}
 
 
const VECTOR2I& SHAPE_POLY_SET::CVertex( SHAPE_POLY_SET::VERTEX_INDEX index ) const
{
    return CVertex( index.m_vertex, index.m_polygon, index.m_contour - 1 );
}
 
 
bool SHAPE_POLY_SET::GetNeighbourIndexes( int aGlobalIndex, int* aPrevious, int* aNext ) const
{
    SHAPE_POLY_SET::VERTEX_INDEX index;
 
    // If the edge does not exist, throw an exception, it is an illegal access memory error
    if( !GetRelativeIndices( aGlobalIndex, &index ) )
        return false;
 
    // Calculate the previous and next index of aGlobalIndex, corresponding to
    // the same contour;
    VERTEX_INDEX inext = index;
    int lastpoint = m_polys[index.m_polygon][index.m_contour].SegmentCount();
 
    if( index.m_vertex == 0 )
    {
        index.m_vertex = lastpoint - 1;
        inext.m_vertex = 1;
    }
    else if( index.m_vertex == lastpoint )
    {
        index.m_vertex--;
        inext.m_vertex = 0;
    }
    else
    {
        inext.m_vertex++;
        index.m_vertex--;
 
        if( inext.m_vertex == lastpoint )
            inext.m_vertex = 0;
    }
 
    if( aPrevious )
    {
        int previous;
        GetGlobalIndex( index, previous );
        *aPrevious = previous;
    }
 
    if( aNext )
    {
        int next;
        GetGlobalIndex( inext, next );
        *aNext = next;
    }
 
    return true;
}
 
 
bool SHAPE_POLY_SET::IsPolygonSelfIntersecting( int aPolygonIndex ) const
{
    std::vector<SEG> segments;
    segments.reserve( FullPointCount() );
 
    for( CONST_SEGMENT_ITERATOR it = CIterateSegmentsWithHoles( aPolygonIndex ); it; it++ )
        segments.emplace_back( *it );
 
    std::sort( segments.begin(), segments.end(), []( const SEG& a, const SEG& b )
            {
                int min_a_x = std::min( a.A.x, a.B.x );
                int min_b_x = std::min( b.A.x, b.B.x );
 
                return min_a_x < min_b_x || ( min_a_x == min_b_x && std::min( a.A.y, a.B.y ) < std::min( b.A.y, b.B.y ) );
            } );
 
    for( auto it = segments.begin(); it != segments.end(); ++it )
    {
        SEG& firstSegment = *it;
 
        // Iterate through all remaining segments.
        auto innerIterator = it;
        int max_x = std::max( firstSegment.A.x, firstSegment.B.x );
        int max_y = std::max( firstSegment.A.y, firstSegment.B.y );
 
        // Start in the next segment, we don't want to check collision between a segment and itself
        for( innerIterator++; innerIterator != segments.end(); innerIterator++ )
        {
            SEG& secondSegment = *innerIterator;
            int min_x = std::min( secondSegment.A.x, secondSegment.B.x );
            int min_y = std::min( secondSegment.A.y, secondSegment.B.y );
 
            // We are ordered in minimum point order, so checking the static max (first segment) against
            // the ordered min will tell us if any of the following segments are withing the BBox
            if( max_x < min_x || ( max_x == min_x && max_y < min_y ) )
                break;
 
            int index_diff = std::abs( firstSegment.Index() - secondSegment.Index() );
            bool adjacent = ( index_diff == 1) || (index_diff == ((int)segments.size() - 1) );
 
            // Check whether the two segments built collide, only when they are not adjacent.
            if( !adjacent && firstSegment.Collide( secondSegment, 0 ) )
                return true;
        }
    }
 
    return false;
}
 
 
bool SHAPE_POLY_SET::IsSelfIntersecting() const
{
    for( unsigned int polygon = 0; polygon < m_polys.size(); polygon++ )
    {
        if( IsPolygonSelfIntersecting( polygon ) )
            return true;
    }
 
    return false;
}
 
 
int SHAPE_POLY_SET::AddOutline( const SHAPE_LINE_CHAIN& aOutline )
{
    POLYGON poly;
 
    poly.push_back( aOutline );
 
    // This is an assertion because if it's generated by KiCad code, it probably
    // indicates a bug elsewhere that should be fixed, but we also auto-fix it here
    // for SWIG plugins that might mess it up
    wxCHECK2_MSG( aOutline.IsClosed(), poly.back().SetClosed( true ),
                  "Warning: non-closed outline added to SHAPE_POLY_SET" );
 
    m_polys.push_back( std::move( poly ) );
 
    return (int) m_polys.size() - 1;
}
 
 
int SHAPE_POLY_SET::AddHole( const SHAPE_LINE_CHAIN& aHole, int aOutline )
{
    assert( m_polys.size() );
 
    if( aOutline < 0 )
        aOutline += (int) m_polys.size();
 
    assert( aOutline < (int)m_polys.size() );
 
    POLYGON& poly = m_polys[aOutline];
 
    assert( poly.size() );
 
    poly.push_back( aHole );
 
    return (int) poly.size() - 2;
}
 
 
int SHAPE_POLY_SET::AddPolygon( const POLYGON& apolygon )
{
    m_polys.push_back( apolygon );
 
    return m_polys.size() - 1;
}
 
 
double SHAPE_POLY_SET::Area()
{
    double area = 0.0;
 
    for( int i = 0; i < OutlineCount(); i++ )
    {
        area += Outline( i ).Area( true );
 
        for( int j = 0; j < HoleCount( i ); j++ )
            area -= Hole( i, j ).Area( true );
    }
 
    return area;
}
 
 
int SHAPE_POLY_SET::ArcCount() const
{
    int retval = 0;
 
    for( const POLYGON& poly : m_polys )
    {
        for( size_t i = 0; i < poly.size(); i++ )
            retval += poly[i].ArcCount();
    }
 
    return retval;
}
 
 
void SHAPE_POLY_SET::GetArcs( std::vector<SHAPE_ARC>& aArcBuffer ) const
{
    for( const POLYGON& poly : m_polys )
    {
        for( size_t i = 0; i < poly.size(); i++ )
        {
            for( SHAPE_ARC arc : poly[i].m_arcs )
                aArcBuffer.push_back( arc );
        }
    }
}
 
 
void SHAPE_POLY_SET::ClearArcs()
{
    for( POLYGON& poly : m_polys )
    {
        for( size_t i = 0; i < poly.size(); i++ )
            poly[i].ClearArcs();
    }
}
 
 
void SHAPE_POLY_SET::RebuildHolesFromContours()
{
    std::vector<SHAPE_LINE_CHAIN> contours;
 
    for( const POLYGON& poly : m_polys )
        contours.insert( contours.end(), poly.begin(), poly.end() );
 
    std::map<int, std::set<int>> parentToChildren;
    std::map<int, std::set<int>> childToParents;
 
    for( SHAPE_LINE_CHAIN& contour : contours )
        contour.GenerateBBoxCache();
 
    for( size_t i = 0; i < contours.size(); i++ )
    {
        const SHAPE_LINE_CHAIN& outline = contours[i];
 
        for( size_t j = 0; j < contours.size(); j++ )
        {
            if( i == j )
                continue;
 
            const SHAPE_LINE_CHAIN& candidate = contours[j];
            const VECTOR2I&         pt0 = candidate.CPoint( 0 );
 
            if( outline.PointInside( pt0, 0, true ) )
            {
                parentToChildren[i].emplace( j );
                childToParents[j].emplace( i );
            }
        }
    }
 
    std::set<int> topLevelParents;
 
    for( size_t i = 0; i < contours.size(); i++ )
    {
        if( childToParents[i].size() == 0 )
        {
            topLevelParents.emplace( i );
        }
    }
 
    SHAPE_POLY_SET result;
 
    std::function<void( int, int, std::vector<int> )> process;
 
    process =
            [&]( int myId, int parentOutlineId, const std::vector<int>& path )
            {
                std::set<int> relParents = childToParents[myId];
 
                for( int pathId : path )
                {
                    int erased = relParents.erase( pathId );
                    wxASSERT( erased > 0 );
                }
 
                wxASSERT( relParents.size() == 0 );
 
                int myOutline = -1;
 
                bool isOutline = path.size() % 2 == 0;
 
                if( isOutline )
                {
                    int outlineId = result.AddOutline( contours[myId] );
                    myOutline = outlineId;
                }
                else
                {
                    wxASSERT( parentOutlineId != -1 );
                    result.AddHole( contours[myId], parentOutlineId );
                }
 
                auto it = parentToChildren.find( myId );
                if( it != parentToChildren.end() )
                {
                    std::vector<int> thisPath = path;
                    thisPath.emplace_back( myId );
 
                    std::set<int> thisPathSet;
                    thisPathSet.insert( thisPath.begin(), thisPath.end() );
 
                    for( int childId : it->second )
                    {
                        const std::set<int>& childPathSet = childToParents[childId];
 
                        if( thisPathSet != childPathSet )
                            continue; // Only interested in immediate children
 
                        process( childId, myOutline, thisPath );
                    }
                }
            };
 
    for( int topParentId : topLevelParents )
    {
        std::vector<int> path;
        process( topParentId, -1, std::move( path ) );
    }
 
    *this = std::move( result );
}
 
 
void SHAPE_POLY_SET::booleanOp( Clipper2Lib::ClipType aType, const SHAPE_POLY_SET& aOtherShape )
{
    booleanOp( aType, *this, aOtherShape );
}
 
 
void SHAPE_POLY_SET::booleanOp( Clipper2Lib::ClipType aType, const SHAPE_POLY_SET& aShape,
                                const SHAPE_POLY_SET& aOtherShape )
{
    if( ( aShape.OutlineCount() > 1 || aOtherShape.OutlineCount() > 0 )
        && ( aShape.ArcCount() > 0 || aOtherShape.ArcCount() > 0 ) )
    {
        wxFAIL_MSG( wxT( "Boolean ops on curved polygons are not supported. You should call "
                         "ClearArcs() before carrying out the boolean operation." ) );
    }
 
    Clipper2Lib::Clipper64 c;
 
    std::vector<CLIPPER_Z_VALUE> zValues;
    std::vector<SHAPE_ARC> arcBuffer;
    std::map<VECTOR2I, CLIPPER_Z_VALUE> newIntersectPoints;
 
    Clipper2Lib::Paths64 paths;
    Clipper2Lib::Paths64 clips;
 
    for( const POLYGON& poly : aShape.m_polys )
    {
        for( size_t i = 0; i < poly.size(); i++ )
        {
            paths.push_back( poly[i].convertToClipper2( i == 0, zValues, arcBuffer ) );
        }
    }
 
    for( const POLYGON& poly : aOtherShape.m_polys )
    {
        for( size_t i = 0; i < poly.size(); i++ )
        {
            clips.push_back( poly[i].convertToClipper2( i == 0, zValues, arcBuffer ) );
        }
    }
 
    c.AddSubject( paths );
    c.AddClip( clips );
 
    Clipper2Lib::PolyTree64 solution;
 
    Clipper2Lib::ZCallback64 callback =
            [&]( const Clipper2Lib::Point64 & e1bot, const Clipper2Lib::Point64 & e1top,
                 const Clipper2Lib::Point64 & e2bot, const Clipper2Lib::Point64 & e2top,
                 Clipper2Lib::Point64 & pt )
            {
                auto arcIndex =
                    [&]( const ssize_t& aZvalue, const ssize_t& aCompareVal = -1 ) -> ssize_t
                    {
                        ssize_t retval;
 
                        retval = zValues.at( aZvalue ).m_SecondArcIdx;
 
                        if( retval == -1 || ( aCompareVal > 0 && retval != aCompareVal ) )
                            retval = zValues.at( aZvalue ).m_FirstArcIdx;
 
                        return retval;
                    };
 
                auto arcSegment =
                    [&]( const ssize_t& aBottomZ, const ssize_t aTopZ ) -> ssize_t
                    {
                        ssize_t retval = arcIndex( aBottomZ );
 
                        if( retval != -1 )
                        {
                            if( retval != arcIndex( aTopZ, retval ) )
                                retval = -1; // Not an arc segment as the two indices do not match
                        }
 
                        return retval;
                    };
 
                ssize_t e1ArcSegmentIndex = arcSegment( e1bot.z, e1top.z );
                ssize_t e2ArcSegmentIndex = arcSegment( e2bot.z, e2top.z );
 
                CLIPPER_Z_VALUE newZval;
 
                if( e1ArcSegmentIndex != -1 )
                {
                    newZval.m_FirstArcIdx = e1ArcSegmentIndex;
                    newZval.m_SecondArcIdx = e2ArcSegmentIndex;
                }
                else
                {
                    newZval.m_FirstArcIdx = e2ArcSegmentIndex;
                    newZval.m_SecondArcIdx = -1;
                }
 
                size_t z_value_ptr = zValues.size();
                zValues.push_back( newZval );
 
                // Only worry about arc segments for later processing
                if( newZval.m_FirstArcIdx != -1 )
                    newIntersectPoints.insert( { VECTOR2I( pt.x, pt.y ), newZval } );
 
                pt.z = z_value_ptr;
                //@todo amend X,Y values to true intersection between arcs or arc and segment
            };
 
    c.SetZCallback( std::move( callback ) ); // register callback
 
    c.Execute( aType, Clipper2Lib::FillRule::NonZero, solution );
 
    importTree( solution, zValues, arcBuffer );
    solution.Clear(); // Free used memory (not done in dtor)
}
 
 
void SHAPE_POLY_SET::BooleanAdd( const SHAPE_POLY_SET& b )
{
    booleanOp( Clipper2Lib::ClipType::Union, b );
}
 
 
void SHAPE_POLY_SET::BooleanSubtract( const SHAPE_POLY_SET& b )
{
    booleanOp( Clipper2Lib::ClipType::Difference, b );
}
 
 
void SHAPE_POLY_SET::BooleanIntersection( const SHAPE_POLY_SET& b )
{
    booleanOp( Clipper2Lib::ClipType::Intersection, b );
}
 
 
void SHAPE_POLY_SET::BooleanXor( const SHAPE_POLY_SET& b )
{
    booleanOp( Clipper2Lib::ClipType::Xor, b );
}
 
 
void SHAPE_POLY_SET::BooleanAdd( const SHAPE_POLY_SET& a, const SHAPE_POLY_SET& b )
{
    booleanOp( Clipper2Lib::ClipType::Union, a, b );
}
 
 
void SHAPE_POLY_SET::BooleanSubtract( const SHAPE_POLY_SET& a, const SHAPE_POLY_SET& b )
{
    booleanOp( Clipper2Lib::ClipType::Difference, a, b );
}
 
 
void SHAPE_POLY_SET::BooleanIntersection( const SHAPE_POLY_SET& a, const SHAPE_POLY_SET& b )
{
    booleanOp( Clipper2Lib::ClipType::Intersection, a, b );
}
 
 
void SHAPE_POLY_SET::BooleanXor( const SHAPE_POLY_SET& a, const SHAPE_POLY_SET& b )
{
    booleanOp( Clipper2Lib::ClipType::Xor, a, b );
}
 
 
void SHAPE_POLY_SET::InflateWithLinkedHoles( int aFactor, CORNER_STRATEGY aCornerStrategy,
                                             int aMaxError )
{
    Unfracture();
    Inflate( aFactor, aCornerStrategy, aMaxError );
    Fracture();
}
 
 
void SHAPE_POLY_SET::inflate2( int aAmount, int aCircleSegCount, CORNER_STRATEGY aCornerStrategy,
        bool aSimplify )
{
    using namespace Clipper2Lib;
    // A thread-local table to avoid repetitive calculations of the coefficient
    // 1.0 - cos( M_PI / aCircleSegCount )
    // aCircleSegCount is most of time <= 64 and usually 8, 12, 16, 32
    #define SEG_CNT_MAX 64
    static thread_local double arc_tolerance_factor[SEG_CNT_MAX + 1];
 
    ClipperOffset c;
 
    // N.B. see the Clipper documentation for jtSquare/jtMiter/jtRound.  They are poorly named
    // and are not what you'd think they are.
    // http://www.angusj.com/delphi/clipper/documentation/Docs/Units/ClipperLib/Types/JoinType.htm
    JoinType joinType = JoinType::Round;    // The way corners are offsetted
    double   miterLimit = 2.0;      // Smaller value when using jtMiter for joinType
 
    switch( aCornerStrategy )
    {
    case CORNER_STRATEGY::ALLOW_ACUTE_CORNERS:
        joinType = JoinType::Miter;
        miterLimit = 10;        // Allows large spikes
        break;
 
    case CORNER_STRATEGY::CHAMFER_ACUTE_CORNERS: // Acute angles are chamfered
        joinType = JoinType::Miter;
        break;
 
    case CORNER_STRATEGY::ROUND_ACUTE_CORNERS: // Acute angles are rounded
        joinType = JoinType::Miter;
        break;
 
    case CORNER_STRATEGY::CHAMFER_ALL_CORNERS: // All angles are chamfered.
        joinType = JoinType::Square;
        break;
 
    case CORNER_STRATEGY::ROUND_ALL_CORNERS: // All angles are rounded.
        joinType = JoinType::Round;
        break;
    }
 
    std::vector<CLIPPER_Z_VALUE> zValues;
    std::vector<SHAPE_ARC>       arcBuffer;
 
    for( const POLYGON& poly : m_polys )
    {
        Paths64 paths;
 
        for( size_t i = 0; i < poly.size(); i++ )
            paths.push_back( poly[i].convertToClipper2( i == 0, zValues, arcBuffer ) );
 
        c.AddPaths( paths, joinType, EndType::Polygon );
    }
 
    // Calculate the arc tolerance (arc error) from the seg count by circle. The seg count is
    // nn = M_PI / acos(1.0 - c.ArcTolerance / abs(aAmount))
    // http://www.angusj.com/delphi/clipper/documentation/Docs/Units/ClipperLib/Classes/ClipperOffset/Properties/ArcTolerance.htm
 
    if( aCircleSegCount < 6 ) // avoid incorrect aCircleSegCount values
        aCircleSegCount = 6;
 
    double coeff;
 
    if( aCircleSegCount > SEG_CNT_MAX || arc_tolerance_factor[aCircleSegCount] == 0 )
    {
        coeff = 1.0 - cos( M_PI / aCircleSegCount );
 
        if( aCircleSegCount <= SEG_CNT_MAX )
            arc_tolerance_factor[aCircleSegCount] = coeff;
    }
    else
    {
        coeff = arc_tolerance_factor[aCircleSegCount];
    }
 
    c.ArcTolerance( std::abs( aAmount ) * coeff );
    c.MiterLimit( miterLimit );
 
    PolyTree64 tree;
 
    if( aSimplify )
    {
        Paths64 paths;
        c.Execute( aAmount, paths );
 
        Clipper2Lib::SimplifyPaths( paths, std::abs( aAmount ) * coeff, true );
 
        Clipper64 c2;
        c2.PreserveCollinear( false );
        c2.ReverseSolution( false );
        c2.AddSubject( paths );
        c2.Execute(ClipType::Union, FillRule::Positive, tree);
    }
    else
    {
        c.Execute( aAmount, tree );
    }
 
    importTree( tree, zValues, arcBuffer );
    tree.Clear();
}
 
 
void SHAPE_POLY_SET::inflateLine2( const SHAPE_LINE_CHAIN& aLine, int aAmount, int aCircleSegCount,
                                   CORNER_STRATEGY aCornerStrategy, bool aSimplify )
{
    using namespace Clipper2Lib;
    // A thread-local table to avoid repetitive calculations of the coefficient
    // 1.0 - cos( M_PI / aCircleSegCount )
    // aCircleSegCount is most of time <= 64 and usually 8, 12, 16, 32
    #define SEG_CNT_MAX 64
    static thread_local double arc_tolerance_factor[SEG_CNT_MAX + 1];
 
    ClipperOffset c;
 
    // N.B. see the Clipper documentation for jtSquare/jtMiter/jtRound.  They are poorly named
    // and are not what you'd think they are.
    // http://www.angusj.com/delphi/clipper/documentation/Docs/Units/ClipperLib/Types/JoinType.htm
    JoinType joinType = JoinType::Round; // The way corners are offsetted
    double   miterLimit = 2.0;           // Smaller value when using jtMiter for joinType
 
    switch( aCornerStrategy )
    {
    case CORNER_STRATEGY::ALLOW_ACUTE_CORNERS:
        joinType = JoinType::Miter;
        miterLimit = 10; // Allows large spikes
        break;
 
    case CORNER_STRATEGY::CHAMFER_ACUTE_CORNERS: // Acute angles are chamfered
        joinType = JoinType::Miter;
        break;
 
    case CORNER_STRATEGY::ROUND_ACUTE_CORNERS: // Acute angles are rounded
        joinType = JoinType::Miter;
        break;
 
    case CORNER_STRATEGY::CHAMFER_ALL_CORNERS: // All angles are chamfered.
        joinType = JoinType::Square;
        break;
 
    case CORNER_STRATEGY::ROUND_ALL_CORNERS: // All angles are rounded.
        joinType = JoinType::Round;
        break;
    }
 
    std::vector<CLIPPER_Z_VALUE> zValues;
    std::vector<SHAPE_ARC>       arcBuffer;
 
    Path64 path = aLine.convertToClipper2( true, zValues, arcBuffer );
    c.AddPath( path, joinType, EndType::Butt );
 
    // Calculate the arc tolerance (arc error) from the seg count by circle. The seg count is
    // nn = M_PI / acos(1.0 - c.ArcTolerance / abs(aAmount))
    // http://www.angusj.com/delphi/clipper/documentation/Docs/Units/ClipperLib/Classes/ClipperOffset/Properties/ArcTolerance.htm
 
    if( aCircleSegCount < 6 ) // avoid incorrect aCircleSegCount values
        aCircleSegCount = 6;
 
    double coeff;
 
    if( aCircleSegCount > SEG_CNT_MAX || arc_tolerance_factor[aCircleSegCount] == 0 )
    {
        coeff = 1.0 - cos( M_PI / aCircleSegCount );
 
        if( aCircleSegCount <= SEG_CNT_MAX )
            arc_tolerance_factor[aCircleSegCount] = coeff;
    }
    else
    {
        coeff = arc_tolerance_factor[aCircleSegCount];
    }
 
    c.ArcTolerance( std::abs( aAmount ) * coeff );
    c.MiterLimit( miterLimit );
 
    PolyTree64 tree;
 
    if( aSimplify )
    {
        Paths64 paths2;
        c.Execute( aAmount, paths2 );
 
        Clipper2Lib::SimplifyPaths( paths2, std::abs( aAmount ) * coeff, false );
 
        Clipper64 c2;
        c2.PreserveCollinear( false );
        c2.ReverseSolution( false );
        c2.AddSubject( paths2 );
        c2.Execute( ClipType::Union, FillRule::Positive, tree );
    }
    else
    {
        c.Execute( aAmount, tree );
    }
 
    importTree( tree, zValues, arcBuffer );
    tree.Clear();
}
 
 
void SHAPE_POLY_SET::Inflate( int aAmount, CORNER_STRATEGY aCornerStrategy, int aMaxError,
                              bool aSimplify )
{
    int segCount = GetArcToSegmentCount( std::abs( aAmount ), aMaxError, FULL_CIRCLE );
 
    inflate2( aAmount, segCount, aCornerStrategy, aSimplify );
}
 
 
void SHAPE_POLY_SET::OffsetLineChain( const SHAPE_LINE_CHAIN& aLine, int aAmount,
                                  CORNER_STRATEGY aCornerStrategy, int aMaxError, bool aSimplify )
{
    int segCount = GetArcToSegmentCount( std::abs( aAmount ), aMaxError, FULL_CIRCLE );
 
    inflateLine2( aLine, aAmount, segCount, aCornerStrategy, aSimplify );
}
 
 
void SHAPE_POLY_SET::importPolyPath( const std::unique_ptr<Clipper2Lib::PolyPath64>& aPolyPath,
                                     const std::vector<CLIPPER_Z_VALUE>&             aZValueBuffer,
                                     const std::vector<SHAPE_ARC>&                   aArcBuffer )
{
    if( !aPolyPath->IsHole() )
    {
        POLYGON paths;
        paths.reserve( aPolyPath->Count() + 1 );
        paths.emplace_back( aPolyPath->Polygon(), aZValueBuffer, aArcBuffer );
 
        for( const std::unique_ptr<Clipper2Lib::PolyPath64>& child : *aPolyPath )
        {
            paths.emplace_back( child->Polygon(), aZValueBuffer, aArcBuffer );
 
            for( const std::unique_ptr<Clipper2Lib::PolyPath64>& grandchild : *child )
                importPolyPath( grandchild, aZValueBuffer, aArcBuffer );
        }
 
        m_polys.emplace_back( std::move( paths ) );
    }
}
 
 
void SHAPE_POLY_SET::importTree( Clipper2Lib::PolyTree64&            tree,
                                 const std::vector<CLIPPER_Z_VALUE>& aZValueBuffer,
                                 const std::vector<SHAPE_ARC>&       aArcBuffer )
{
    m_polys.clear();
 
    for( const std::unique_ptr<Clipper2Lib::PolyPath64>& n : tree )
        importPolyPath( n, aZValueBuffer, aArcBuffer );
}
 
 
void SHAPE_POLY_SET::importPaths( Clipper2Lib::Paths64&              aPath,
                                 const std::vector<CLIPPER_Z_VALUE>& aZValueBuffer,
                                 const std::vector<SHAPE_ARC>&       aArcBuffer )
{
    m_polys.clear();
    POLYGON path;
 
    for( const Clipper2Lib::Path64& n : aPath )
    {
        if( Clipper2Lib::Area( n ) > 0 )
        {
            if( !path.empty() )
                m_polys.emplace_back( path );
 
            path.clear();
        }
        else
        {
            wxCHECK2_MSG( !path.empty(), continue, wxT( "Cannot add a hole before an outline" ) );
        }
 
        path.emplace_back( n, aZValueBuffer, aArcBuffer );
    }
 
    if( !path.empty() )
        m_polys.emplace_back( std::move( path ) );
}
 
 
struct FractureEdge
{
    using Index = int;
 
    FractureEdge() = default;
 
    FractureEdge( const VECTOR2I& p1, const VECTOR2I& p2, Index next ) :
            m_p1( p1 ),
            m_p2( p2 ),
            m_next( next )
    {
    }
 
    bool matches( int y ) const
    {
        return ( y >= m_p1.y || y >= m_p2.y ) && ( y <= m_p1.y || y <= m_p2.y );
    }
 
    VECTOR2I m_p1;
    VECTOR2I m_p2;
    Index    m_next;
};
 
 
typedef std::vector<FractureEdge> FractureEdgeSet;
 
 
static FractureEdge* processHole( FractureEdgeSet& edges, FractureEdge::Index provokingIndex,
                                  FractureEdge::Index edgeIndex, FractureEdge::Index bridgeIndex )
{
    FractureEdge& edge = edges[edgeIndex];
    int           x = edge.m_p1.x;
    int           y = edge.m_p1.y;
    int           min_dist = std::numeric_limits<int>::max();
    int           x_nearest = 0;
 
    FractureEdge* e_nearest = nullptr;
 
    // Since this function is run for all holes left to right, no need to
    // check for any edge beyond the provoking one because they will always be
    // further to the right, and unconnected to the outline anyway.
    for( FractureEdge::Index i = 0; i < provokingIndex; i++ )
    {
        FractureEdge& e = edges[i];
        // Don't consider this edge if it can't be bridged to, or faces left.
        if( !e.matches( y ) )
            continue;
 
        int x_intersect;
 
        if( e.m_p1.y == e.m_p2.y ) // horizontal edge
        {
            x_intersect = std::max( e.m_p1.x, e.m_p2.x );
        }
        else
        {
            x_intersect =
                    e.m_p1.x + rescale( e.m_p2.x - e.m_p1.x, y - e.m_p1.y, e.m_p2.y - e.m_p1.y );
        }
 
        int dist = ( x - x_intersect );
 
        if( dist >= 0 && dist < min_dist )
        {
            min_dist = dist;
            x_nearest = x_intersect;
            e_nearest = &e;
        }
    }
 
    if( e_nearest )
    {
        const FractureEdge::Index outline2hole_index = bridgeIndex;
        const FractureEdge::Index hole2outline_index = bridgeIndex + 1;
        const FractureEdge::Index split_index = bridgeIndex + 2;
        // Make an edge between the split outline edge and the hole...
        edges[outline2hole_index] = FractureEdge( VECTOR2I( x_nearest, y ), edge.m_p1, edgeIndex );
        // ...between the hole and the edge...
        edges[hole2outline_index] =
                FractureEdge( edge.m_p1, VECTOR2I( x_nearest, y ), split_index );
        // ...and between the split outline edge and the rest.
        edges[split_index] =
                FractureEdge( VECTOR2I( x_nearest, y ), e_nearest->m_p2, e_nearest->m_next );
 
        // Perform the actual outline edge split
        e_nearest->m_p2 = VECTOR2I( x_nearest, y );
        e_nearest->m_next = outline2hole_index;
 
        FractureEdge* last = &edge;
        for( ; last->m_next != edgeIndex; last = &edges[last->m_next] )
            ;
        last->m_next = hole2outline_index;
    }
 
    return e_nearest;
}
 
 
static void fractureSingleCacheFriendly( SHAPE_POLY_SET::POLYGON& paths )
{
    FractureEdgeSet edges;
    bool            outline = true;
 
    if( paths.size() == 1 )
        return;
 
    size_t total_point_count = 0;
 
    for( const SHAPE_LINE_CHAIN& path : paths )
    {
        total_point_count += path.PointCount();
    }
 
    if( total_point_count > (size_t) std::numeric_limits<FractureEdge::Index>::max() )
    {
        wxLogWarning( wxT( "Polygon has more points than int limit" ) );
        return;
    }
 
    // Reserve space in the edge set so pointers don't get invalidated during
    // the whole fracture process; one for each original edge, plus 3 per
    // path to join it to the outline.
    edges.reserve( total_point_count + paths.size() * 3 );
 
    // Sort the paths by their lowest X bound before processing them.
    // This ensures the processing order for processEdge() is correct.
    struct PathInfo
    {
        int                 path_or_provoking_index;
        FractureEdge::Index leftmost;
        int                 x;
        int                 y_or_bridge;
    };
    std::vector<PathInfo> sorted_paths;
    const int             paths_count = static_cast<int>( paths.size() );
    sorted_paths.reserve( paths_count );
 
    for( int path_index = 0; path_index < paths_count; path_index++ )
    {
        const SHAPE_LINE_CHAIN&      path = paths[path_index];
        const std::vector<VECTOR2I>& points = path.CPoints();
        const int                    point_count = static_cast<int>( points.size() );
        int                          x_min = std::numeric_limits<int>::max();
        int                          y_min = std::numeric_limits<int>::max();
        int                          leftmost = -1;
 
        for( int point_index = 0; point_index < point_count; point_index++ )
        {
            const VECTOR2I& point = points[point_index];
            if( point.x < x_min )
            {
                x_min = point.x;
                leftmost = point_index;
            }
            if( point.y < y_min )
                y_min = point.y;
        }
 
        sorted_paths.emplace_back( PathInfo{ path_index, leftmost, x_min, y_min } );
    }
 
    std::sort( sorted_paths.begin() + 1, sorted_paths.end(),
               []( const PathInfo& a, const PathInfo& b )
               {
                   if( a.x == b.x )
                       return a.y_or_bridge < b.y_or_bridge;
                   return a.x < b.x;
               } );
 
    FractureEdge::Index edge_index = 0;
 
    for( PathInfo& path_info : sorted_paths )
    {
        const SHAPE_LINE_CHAIN&      path = paths[path_info.path_or_provoking_index];
        const std::vector<VECTOR2I>& points = path.CPoints();
        const size_t                 point_count = points.size();
 
        // Index of the provoking (first) edge for this path
        const FractureEdge::Index provoking_edge = edge_index;
 
        for( size_t i = 0; i < point_count - 1; i++ )
        {
            edges.emplace_back( points[i], points[i + 1], edge_index + 1 );
            edge_index++;
        }
 
        // Create last edge looping back to the provoking one.
        edges.emplace_back( points[point_count - 1], points[0], provoking_edge );
        edge_index++;
 
        if( !outline )
        {
            // Repurpose the path sorting data structure to schedule the leftmost edge
            // for merging to the outline, which will in turn merge the rest of the path.
            path_info.path_or_provoking_index = provoking_edge;
            path_info.y_or_bridge = edge_index;
 
            // Reserve 3 additional edges to bridge with the outline.
            edge_index += 3;
            edges.resize( edge_index );
        }
 
        outline = false; // first path is always the outline
    }
 
    for( auto it = sorted_paths.begin() + 1; it != sorted_paths.end(); it++ )
    {
        auto edge = processHole( edges, it->path_or_provoking_index,
                                 it->path_or_provoking_index + it->leftmost, it->y_or_bridge );
 
        // If we can't handle the hole, the zone is broken (maybe)
        if( !edge )
        {
            wxLogWarning( wxT( "Broken polygon, dropping path" ) );
 
            return;
        }
    }
 
    paths.resize( 1 );
    SHAPE_LINE_CHAIN& newPath = paths[0];
 
    newPath.Clear();
    newPath.SetClosed( true );
 
    // Root edge is always at index 0
    FractureEdge* e = &edges[0];
 
    for( ; e->m_next != 0; e = &edges[e->m_next] )
        newPath.Append( e->m_p1 );
 
    newPath.Append( e->m_p1 );
}
 
 
struct FractureEdgeSlow
{
    FractureEdgeSlow( int y = 0 ) : m_connected( false ), m_next( nullptr ) { m_p1.x = m_p2.y = y; }
 
    FractureEdgeSlow( bool connected, const VECTOR2I& p1, const VECTOR2I& p2 ) :
            m_connected( connected ), m_p1( p1 ), m_p2( p2 ), m_next( nullptr )
    {
    }
 
    bool matches( int y ) const
    {
        return ( y >= m_p1.y || y >= m_p2.y ) && ( y <= m_p1.y || y <= m_p2.y );
    }
 
    bool              m_connected;
    VECTOR2I          m_p1;
    VECTOR2I          m_p2;
    FractureEdgeSlow* m_next;
};
 
 
typedef std::vector<FractureEdgeSlow*> FractureEdgeSetSlow;
 
 
static int processEdge( FractureEdgeSetSlow& edges, FractureEdgeSlow* edge )
{
    int x = edge->m_p1.x;
    int y = edge->m_p1.y;
    int min_dist = std::numeric_limits<int>::max();
    int x_nearest = 0;
 
    FractureEdgeSlow* e_nearest = nullptr;
 
    for( FractureEdgeSlow* e : edges )
    {
        if( !e->matches( y ) )
            continue;
 
        int x_intersect;
 
        if( e->m_p1.y == e->m_p2.y ) // horizontal edge
        {
            x_intersect = std::max( e->m_p1.x, e->m_p2.x );
        }
        else
        {
            x_intersect = e->m_p1.x
                          + rescale( e->m_p2.x - e->m_p1.x, y - e->m_p1.y, e->m_p2.y - e->m_p1.y );
        }
 
        int dist = ( x - x_intersect );
 
        if( dist >= 0 && dist < min_dist && e->m_connected )
        {
            min_dist = dist;
            x_nearest = x_intersect;
            e_nearest = e;
        }
    }
 
    if( e_nearest && e_nearest->m_connected )
    {
        int count = 0;
 
        FractureEdgeSlow* lead1 =
                new FractureEdgeSlow( true, VECTOR2I( x_nearest, y ), VECTOR2I( x, y ) );
        FractureEdgeSlow* lead2 =
                new FractureEdgeSlow( true, VECTOR2I( x, y ), VECTOR2I( x_nearest, y ) );
        FractureEdgeSlow* split_2 =
                new FractureEdgeSlow( true, VECTOR2I( x_nearest, y ), e_nearest->m_p2 );
 
        edges.push_back( split_2 );
        edges.push_back( lead1 );
        edges.push_back( lead2 );
 
        FractureEdgeSlow* link = e_nearest->m_next;
 
        e_nearest->m_p2 = VECTOR2I( x_nearest, y );
        e_nearest->m_next = lead1;
        lead1->m_next = edge;
 
        FractureEdgeSlow* last;
 
        for( last = edge; last->m_next != edge; last = last->m_next )
        {
            last->m_connected = true;
            count++;
        }
 
        last->m_connected = true;
        last->m_next = lead2;
        lead2->m_next = split_2;
        split_2->m_next = link;
 
        return count + 1;
    }
 
    return 0;
}
 
 
static void fractureSingleSlow( SHAPE_POLY_SET::POLYGON& paths )
{
    FractureEdgeSetSlow edges;
    FractureEdgeSetSlow border_edges;
    FractureEdgeSlow*   root = nullptr;
 
    bool first = true;
 
    if( paths.size() == 1 )
        return;
 
    int num_unconnected = 0;
 
    for( const SHAPE_LINE_CHAIN& path : paths )
    {
        const std::vector<VECTOR2I>& points = path.CPoints();
        int                          pointCount = points.size();
 
        FractureEdgeSlow *prev = nullptr, *first_edge = nullptr;
 
        int x_min = std::numeric_limits<int>::max();
 
        for( int i = 0; i < pointCount; i++ )
        {
            if( points[i].x < x_min )
                x_min = points[i].x;
 
            // Do not use path.CPoint() here; open-coding it using the local variables "points"
            // and "pointCount" gives a non-trivial performance boost to zone fill times.
            FractureEdgeSlow* fe = new FractureEdgeSlow( first, points[i],
                                                         points[i + 1 == pointCount ? 0 : i + 1] );
 
            if( !root )
                root = fe;
 
            if( !first_edge )
                first_edge = fe;
 
            if( prev )
                prev->m_next = fe;
 
            if( i == pointCount - 1 )
                fe->m_next = first_edge;
 
            prev = fe;
            edges.push_back( fe );
 
            if( !first )
            {
                if( fe->m_p1.x == x_min )
                    border_edges.push_back( fe );
            }
 
            if( !fe->m_connected )
                num_unconnected++;
        }
 
        first = false; // first path is always the outline
    }
 
    // keep connecting holes to the main outline, until there's no holes left...
    while( num_unconnected > 0 )
    {
        int  x_min = std::numeric_limits<int>::max();
        auto it = border_edges.begin();
 
        FractureEdgeSlow* smallestX = nullptr;
 
        // find the left-most hole edge and merge with the outline
        for( ; it != border_edges.end(); ++it )
        {
            FractureEdgeSlow* border_edge = *it;
            int               xt = border_edge->m_p1.x;
 
            if( ( xt <= x_min ) && !border_edge->m_connected )
            {
                x_min = xt;
                smallestX = border_edge;
            }
        }
 
        int num_processed = processEdge( edges, smallestX );
 
        // If we can't handle the edge, the zone is broken (maybe)
        if( !num_processed )
        {
            wxLogWarning( wxT( "Broken polygon, dropping path" ) );
 
            for( FractureEdgeSlow* edge : edges )
                delete edge;
 
            return;
        }
 
        num_unconnected -= num_processed;
    }
 
    paths.clear();
    SHAPE_LINE_CHAIN newPath;
 
    newPath.SetClosed( true );
 
    FractureEdgeSlow* e;
 
    for( e = root; e->m_next != root; e = e->m_next )
        newPath.Append( e->m_p1 );
 
    newPath.Append( e->m_p1 );
 
    for( FractureEdgeSlow* edge : edges )
        delete edge;
 
    paths.push_back( std::move( newPath ) );
}
 
 
void SHAPE_POLY_SET::fractureSingle( POLYGON& paths )
{
    if( ENABLECACHEFRIENDLYFRACTURE )
        return fractureSingleCacheFriendly( paths );
    fractureSingleSlow( paths );
}
 
 
void SHAPE_POLY_SET::Fracture( bool aSimplify )
{
    if( aSimplify )
        Simplify();    // remove overlapping holes/degeneracy
 
    for( POLYGON& paths : m_polys )
        fractureSingle( paths );
}
 
 
void SHAPE_POLY_SET::unfractureSingle( SHAPE_POLY_SET::POLYGON& aPoly )
{
    assert( aPoly.size() == 1 );
 
    struct EDGE
    {
        int m_index = 0;
        SHAPE_LINE_CHAIN* m_poly = nullptr;
        bool m_duplicate = false;
 
        EDGE( SHAPE_LINE_CHAIN* aPolygon, int aIndex ) :
            m_index( aIndex ),
            m_poly( aPolygon )
        {}
 
        bool compareSegs( const SEG& s1, const SEG& s2 ) const
        {
            return (s1.A == s2.B && s1.B == s2.A);
        }
 
        bool operator==( const EDGE& aOther ) const
        {
            return compareSegs( m_poly->CSegment( m_index ),
                                aOther.m_poly->CSegment( aOther.m_index ) );
        }
 
        bool operator!=( const EDGE& aOther ) const
        {
            return !compareSegs( m_poly->CSegment( m_index ),
                                 aOther.m_poly->CSegment( aOther.m_index ) );
        }
 
        struct HASH
        {
            std::size_t operator()(  const EDGE& aEdge ) const
            {
                const SEG& a = aEdge.m_poly->CSegment( aEdge.m_index );
                std::size_t seed = 0xa82de1c0;
                hash_combine( seed, a.A.x, a.B.x, a.A.y, a.B.y );
                return seed;
            }
        };
    };
 
    struct EDGE_LIST_ENTRY
    {
        int              index;
        EDGE_LIST_ENTRY* next;
    };
 
    std::unordered_set<EDGE, EDGE::HASH> uniqueEdges;
 
    SHAPE_LINE_CHAIN lc = aPoly[0];
    lc.Simplify();
 
    auto edgeList = std::make_unique<EDGE_LIST_ENTRY[]>( lc.SegmentCount() );
 
    for( int i = 0; i < lc.SegmentCount(); i++ )
    {
        edgeList[i].index   = i;
        edgeList[i].next    = &edgeList[ (i != lc.SegmentCount() - 1) ? i + 1 : 0 ];
    }
 
    std::unordered_set<EDGE_LIST_ENTRY*> queue;
 
    for( int i = 0; i < lc.SegmentCount(); i++ )
    {
        EDGE e( &lc, i );
        uniqueEdges.insert( e );
    }
 
    for( int i = 0; i < lc.SegmentCount(); i++ )
    {
        EDGE    e( &lc, i );
        auto    it = uniqueEdges.find( e );
 
        if( it != uniqueEdges.end() && it->m_index != i )
        {
            int e1  = it->m_index;
            int e2  = i;
 
            if( e1 > e2 )
                std::swap( e1, e2 );
 
            int e1_prev = e1 - 1;
 
            if( e1_prev < 0 )
                e1_prev = lc.SegmentCount() - 1;
 
            int e2_prev = e2 - 1;
 
            if( e2_prev < 0 )
                e2_prev = lc.SegmentCount() - 1;
 
            int e1_next = e1 + 1;
 
            if( e1_next == lc.SegmentCount() )
                e1_next = 0;
 
            int e2_next = e2 + 1;
 
            if( e2_next == lc.SegmentCount() )
                e2_next = 0;
 
            edgeList[e1_prev].next  = &edgeList[ e2_next ];
            edgeList[e2_prev].next  = &edgeList[ e1_next ];
            edgeList[i].next = nullptr;
            edgeList[it->m_index].next = nullptr;
        }
    }
 
    for( int i = 0; i < lc.SegmentCount(); i++ )
    {
        if( edgeList[i].next )
            queue.insert( &edgeList[i] );
    }
 
    auto edgeBuf = std::make_unique<EDGE_LIST_ENTRY* []>( lc.SegmentCount() );
 
    int n = 0;
    int outline = -1;
 
    POLYGON result;
    double max_poly = 0.0;
 
    while( queue.size() )
    {
        EDGE_LIST_ENTRY* e_first = *queue.begin();
        EDGE_LIST_ENTRY* e = e_first;
        int              cnt = 0;
 
        do
        {
            edgeBuf[cnt++] = e;
            e = e->next;
        } while( e && e != e_first );
 
        SHAPE_LINE_CHAIN outl;
 
        for( int i = 0; i < cnt; i++ )
        {
            VECTOR2I p = lc.CPoint( edgeBuf[i]->index );
            outl.Append( p );
            queue.erase( edgeBuf[i] );
        }
 
        outl.SetClosed( true );
 
        double area = std::fabs( outl.Area() );
 
        if( area > max_poly )
        {
            outline = n;
            max_poly = area;
        }
 
        result.push_back( outl );
        n++;
    }
 
    if( outline > 0 )
        std::swap( result[0], result[outline] );
 
    aPoly = std::move( result );
}
 
 
bool SHAPE_POLY_SET::HasHoles() const
{
    // Iterate through all the polygons on the set
    for( const POLYGON& paths : m_polys )
    {
        // If any of them has more than one contour, it is a hole.
        if( paths.size() > 1 )
            return true;
    }
 
    // Return false if and only if every polygon has just one outline, without holes.
    return false;
}
 
 
void SHAPE_POLY_SET::Unfracture()
{
    for( POLYGON& path : m_polys )
        unfractureSingle( path );
 
    Simplify();    // remove overlapping holes/degeneracy
}
 
 
bool SHAPE_POLY_SET::isExteriorWaist( const SEG& aSegA, const SEG& aSegB ) const
{
    const VECTOR2I da = aSegA.B - aSegA.A;
 
    int axis = std::abs( da.x ) >= std::abs( da.y ) ? 0 : 1;
 
    std::array<VECTOR2I,4> pts = { aSegA.A, aSegA.B, aSegB.A, aSegB.B };
 
    std::sort( pts.begin(), pts.end(), [axis]( const VECTOR2I& p, const VECTOR2I& q )
    {
        if( axis == 0 )
            return p.x < q.x || ( p.x == q.x && p.y < q.y );
        else
            return p.y < q.y || ( p.y == q.y && p.x < q.x );
    } );
 
    VECTOR2I s = pts[1];
    VECTOR2I e = pts[2];
 
    // Check if there is polygon material on either side of the overlapping segments
    // Get the midpoint between s and e for testing
    VECTOR2I midpoint = ( s + e ) / 2;
 
    // Create perpendicular offset vector to check both sides
    VECTOR2I segDir = e - s;
 
    if( segDir.EuclideanNorm() > 25 )
    {
        VECTOR2I perp = segDir.Perpendicular().Resize( 10 );
 
        // Both sides must be outside for this to be an exterior waist. Short-circuit if
        // either side is inside the polygon to avoid the second O(N) point-in-polygon test.
        if( !PointInside( midpoint + perp ) && !PointInside( midpoint - perp ) )
        {
            wxLogTrace( wxT( "collinear" ), wxT( "Found exterior waist between (%d,%d)-(%d,%d) and (%d,%d)-(%d,%d)" ),
                        aSegA.A.x, aSegA.A.y, aSegA.B.x, aSegA.B.y,
                        aSegB.A.x, aSegB.A.y, aSegB.B.x, aSegB.B.y );
            return true;
        }
    }
 
    return false;
}
 
 
void SHAPE_POLY_SET::splitCollinearOutlines()
{
    for( size_t polyIdx = 0; polyIdx < m_polys.size(); ++polyIdx )
    {
        bool changed = true;
 
        while( changed )
        {
            changed = false;
 
            SHAPE_LINE_CHAIN& outline = m_polys[polyIdx][0];
            intptr_t count = outline.PointCount();
 
            KIRTREE::DYNAMIC_RTREE<intptr_t, intptr_t, 2> rtree;
 
            for( intptr_t i = 0; i < count; ++i )
            {
                const VECTOR2I& a = outline.CPoint( i );
                const VECTOR2I& b = outline.CPoint( ( i + 1 ) % count );
                intptr_t min[2] = { std::min( a.x, b.x ), std::min( a.y, b.y ) };
                intptr_t max[2] = { std::max( a.x, b.x ), std::max( a.y, b.y ) };
                rtree.Insert( min, max, i );
            }
 
            bool found = false;
            int segA = -1;
            int segB = -1;
 
            for( intptr_t i = 0; i < count && !found; ++i )
            {
                const VECTOR2I& a = outline.CPoint( i );
                const VECTOR2I& b = outline.CPoint( ( i + 1 ) % count );
                SEG seg( a, b );
                intptr_t min[2] = { std::min( a.x, b.x ), std::min( a.y, b.y ) };
                intptr_t max[2] = { std::max( a.x, b.x ), std::max( a.y, b.y ) };
 
                auto visitor =
                        [&]( const intptr_t& j ) -> bool
                        {
                            if( j == i || j == ( ( i + 1 ) % count ) || j == ( ( i + count - 1 ) % count ) )
                                return true;
 
                            VECTOR2I oa = outline.CPoint( j );
                            VECTOR2I ob = outline.CPoint( ( j + 1 ) % count );
                            SEG other( oa, ob );
 
                            // Skip segments that share start/end points.  This is the case for
                            // fractured segments
                            if( oa == a && ob == b )
                                return true;
 
                            if( oa == b && ob == a )
                                return true;
 
                            if( seg.ApproxCollinear( other, 10 ) && isExteriorWaist( seg, other ) )
                            {
                                segA = i;
                                segB = j;
                                found = true;
                                return false;
                            }
 
                            return true;
                        };
 
                rtree.Search( min, max, visitor );
            }
 
            if( !found )
                break;
 
            int a0 = segA;
            int a1 = ( segA + 1 ) % outline.PointCount();
            int b0 = segB;
            int b1 = ( segB + 1 ) % outline.PointCount();
 
            SHAPE_LINE_CHAIN lc1;
            int idx = a1;
            lc1.Append( outline.CPoint( idx ) );
 
            while( idx != b0 )
            {
                idx = ( idx + 1 ) % outline.PointCount();
                lc1.Append( outline.CPoint( idx ) );
            }
 
            lc1.SetClosed( true );
 
            SHAPE_LINE_CHAIN lc2;
            idx = b1;
            lc2.Append( outline.CPoint( idx ) );
 
            while( idx != a0 )
            {
                idx = ( idx + 1 ) % outline.PointCount();
                lc2.Append( outline.CPoint( idx ) );
            }
 
            lc2.SetClosed( true );
 
            m_polys[polyIdx][0] = std::move( lc1 );
 
            POLYGON np;
            np.push_back( std::move( lc2 ) );
            m_polys.push_back( std::move( np ) );
 
            changed = true;
        }
    }
}
 
 
void SHAPE_POLY_SET::splitSelfTouchingOutlines()
{
    for( size_t polyIdx = 0; polyIdx < m_polys.size(); ++polyIdx )
    {
        bool changed = true;
 
        while( changed )
        {
            changed = false;
 
            SHAPE_LINE_CHAIN& outline = m_polys[polyIdx][0];
            const int count = outline.PointCount();
 
            if( count < 4 )
                break;
 
            int insertSegIdx = -1;
            int insertVertIdx = -1;
 
            // For small polygons, direct O(n²) search is faster than R-tree overhead
            constexpr int RTREE_THRESHOLD = 32;
 
            if( count < RTREE_THRESHOLD )
            {
                for( int vertIdx = 0; vertIdx < count && insertSegIdx < 0; ++vertIdx )
                {
                    const VECTOR2I& pt = outline.CPoint( vertIdx );
                    const int prevSeg = ( vertIdx + count - 1 ) % count;
 
                    for( int segIdx = 0; segIdx < count; ++segIdx )
                    {
                        // Skip adjacent segments
                        if( segIdx == prevSeg || segIdx == vertIdx )
                            continue;
 
                        const VECTOR2I& a = outline.CPoint( segIdx );
                        const VECTOR2I& b = outline.CPoint( ( segIdx + 1 ) % count );
 
                        // SquaredDistance returns 0 only when pt lies exactly on the
                        // segment.  Clipper2 rounds corridor-cut vertices to integer
                        // coordinates; they can land within 1nm of an endpoint but are
                        // not true pinch points.
                        if( pt != a && pt != b && SEG( a, b ).SquaredDistance( pt ) == 0 )
                        {
                            insertSegIdx = segIdx;
                            insertVertIdx = vertIdx;
                            break;
                        }
                    }
                }
            }
            else
            {
                KIRTREE::DYNAMIC_RTREE<intptr_t, int, 2> rtree;
 
                for( int i = 0; i < count; ++i )
                {
                    const VECTOR2I& a = outline.CPoint( i );
                    const VECTOR2I& b = outline.CPoint( ( i + 1 ) % count );
                    int bmin[2] = { std::min( a.x, b.x ), std::min( a.y, b.y ) };
                    int bmax[2] = { std::max( a.x, b.x ), std::max( a.y, b.y ) };
                    rtree.Insert( bmin, bmax, i );
                }
 
                for( int vertIdx = 0; vertIdx < count && insertSegIdx < 0; ++vertIdx )
                {
                    const VECTOR2I& pt = outline.CPoint( vertIdx );
                    const int prevSeg = ( vertIdx + count - 1 ) % count;
                    int bmin[2] = { pt.x, pt.y };
                    int bmax[2] = { pt.x, pt.y };
 
                    auto pinchVisitor =
                            [&]( const intptr_t& segIdx ) -> bool
                            {
                                if( segIdx == prevSeg || segIdx == vertIdx )
                                    return true;
 
                                const VECTOR2I& a = outline.CPoint( segIdx );
                                const VECTOR2I& b = outline.CPoint( ( segIdx + 1 ) % count );
 
                                // SquaredDistance returns 0 only when pt lies exactly on the
                                // segment.  Clipper2 rounds corridor-cut vertices to integer
                                // coordinates; they can land within 1nm of an endpoint but
                                // are not true pinch points.
                                if( pt != a && pt != b && SEG( a, b ).SquaredDistance( pt ) == 0 )
                                {
                                    insertSegIdx = segIdx;
                                    insertVertIdx = vertIdx;
                                    return false;
                                }
 
                                return true;
                            };
 
                    rtree.Search( bmin, bmax, pinchVisitor );
                }
            }
 
            if( insertSegIdx < 0 )
                break;
 
            // Split the polygon at the pinch point into two separate polygons.
            // Polygon 1: vertices from (insertSegIdx+1) to insertVertIdx
            // Polygon 2: vertices from insertVertIdx to insertSegIdx
 
            const int splitStart1 = ( insertSegIdx + 1 ) % count;
 
            // Calculate sizes for each polygon
            int size1, size2;
 
            if( insertVertIdx >= splitStart1 )
                size1 = insertVertIdx - splitStart1 + 1;
            else
                size1 = count - splitStart1 + insertVertIdx + 1;
 
            if( insertSegIdx >= insertVertIdx )
                size2 = insertSegIdx - insertVertIdx + 1;
            else
                size2 = count - insertVertIdx + insertSegIdx + 1;
 
            if( size1 < 3 || size2 < 3 )
                break;
 
            SHAPE_LINE_CHAIN poly1;
            SHAPE_LINE_CHAIN poly2;
            poly1.ReservePoints( size1 );
            poly2.ReservePoints( size2 );
 
            int idx = splitStart1;
 
            for( int i = 0; i < size1; ++i )
            {
                poly1.Append( outline.CPoint( idx ) );
                idx = ( idx + 1 ) % count;
            }
 
            poly1.SetClosed( true );
 
            idx = insertVertIdx;
 
            for( int i = 0; i < size2; ++i )
            {
                poly2.Append( outline.CPoint( idx ) );
                idx = ( idx + 1 ) % count;
            }
 
            poly2.SetClosed( true );
 
            m_polys[polyIdx][0] = std::move( poly1 );
 
            POLYGON np;
            np.push_back( std::move( poly2 ) );
            m_polys.push_back( std::move( np ) );
 
            changed = true;
        }
    }
}
 
 
void SHAPE_POLY_SET::Simplify()
{
    splitCollinearOutlines();
 
    SHAPE_POLY_SET empty;
 
    booleanOp( Clipper2Lib::ClipType::Union, empty );
}
 
 
void SHAPE_POLY_SET::SimplifyOutlines( int aTolerance )
{
    for( POLYGON& paths : m_polys )
    {
        for( SHAPE_LINE_CHAIN& path : paths )
        {
            path.Simplify( aTolerance );
        }
    }
}
 
 
int SHAPE_POLY_SET::NormalizeAreaOutlines()
{
    // We are expecting only one main outline, but this main outline can have holes
    // if holes: combine holes and remove them from the main outline.
    // Note also we are usingin polygon
    // calculations, but it is not mandatory. It is used mainly
    // because there is usually only very few vertices in area outlines
    SHAPE_POLY_SET::POLYGON& outline = Polygon( 0 );
    SHAPE_POLY_SET holesBuffer;
 
    // Move holes stored in outline to holesBuffer:
    // The first SHAPE_LINE_CHAIN is the main outline, others are holes
    while( outline.size() > 1 )
    {
        holesBuffer.AddOutline( outline.back() );
        outline.pop_back();
    }
 
    Simplify();
 
    // If any hole, subtract it to main outline
    if( holesBuffer.OutlineCount() )
    {
        holesBuffer.Simplify();
        BooleanSubtract( holesBuffer );
    }
 
    // In degenerate cases, simplify might return no outlines
    if( OutlineCount() > 0 )
        RemoveNullSegments();
 
    return OutlineCount();
}
 
 
const std::string SHAPE_POLY_SET::Format( bool aCplusPlus ) const
{
    std::stringstream ss;
 
    ss << "SHAPE_LINE_CHAIN poly; \n";
 
    for( unsigned i = 0; i < m_polys.size(); i++ )
    {
        for( unsigned j = 0; j < m_polys[i].size(); j++ )
        {
 
            ss << "{ auto tmp = " << m_polys[i][j].Format() << ";\n";
 
            SHAPE_POLY_SET poly;
 
            if( j == 0 )
            {
                ss << " poly.AddOutline(tmp); } \n";
            }
            else
            {
                ss << " poly.AddHole(tmp); } \n";
            }
 
        }
    }
 
    return ss.str();
}
 
 
bool SHAPE_POLY_SET::Parse( std::stringstream& aStream )
{
    std::string tmp;
 
    aStream >> tmp;
 
    if( tmp != "polyset" )
        return false;
 
    aStream >> tmp;
 
    int n_polys = atoi( tmp.c_str() );
 
    if( n_polys < 0 )
        return false;
 
    for( int i = 0; i < n_polys; i++ )
    {
        POLYGON paths;
 
        aStream >> tmp;
 
        if( tmp != "poly" )
            return false;
 
        aStream >> tmp;
        int n_outlines = atoi( tmp.c_str() );
 
        if( n_outlines < 0 )
            return false;
 
        for( int j = 0; j < n_outlines; j++ )
        {
            SHAPE_LINE_CHAIN outline;
 
            outline.SetClosed( true );
 
            aStream >> tmp;
            int n_vertices = atoi( tmp.c_str() );
 
            for( int v = 0; v < n_vertices; v++ )
            {
                VECTOR2I p;
 
                aStream >> tmp; p.x = atoi( tmp.c_str() );
                aStream >> tmp; p.y = atoi( tmp.c_str() );
                outline.Append( p );
            }
 
            paths.push_back( std::move( outline ) );
        }
 
        m_polys.push_back( std::move( paths ) );
    }
 
    return true;
}
 
 
const BOX2I SHAPE_POLY_SET::BBox( int aClearance ) const
{
    BOX2I bb;
 
    for( unsigned i = 0; i < m_polys.size(); i++ )
    {
        if( i == 0 )
            bb = m_polys[i][0].BBox();
        else
            bb.Merge( m_polys[i][0].BBox() );
    }
 
    bb.Inflate( aClearance );
    return bb;
}
 
 
const BOX2I SHAPE_POLY_SET::BBoxFromCaches() const
{
    BOX2I bb;
 
    for( unsigned i = 0; i < m_polys.size(); i++ )
    {
        if( i == 0 )
            bb = *m_polys[i][0].GetCachedBBox();
        else
            bb.Merge( *m_polys[i][0].GetCachedBBox() );
    }
 
    return bb;
}
 
 
bool SHAPE_POLY_SET::PointOnEdge( const VECTOR2I& aP, int aAccuracy ) const
{
    // Iterate through all the polygons in the set
    for( const POLYGON& polygon : m_polys )
    {
        // Iterate through all the line chains in the polygon
        for( const SHAPE_LINE_CHAIN& lineChain : polygon )
        {
            if( lineChain.PointOnEdge( aP, aAccuracy ) )
                return true;
        }
    }
 
    return false;
}
 
 
bool SHAPE_POLY_SET::Collide( const SEG& aSeg, int aClearance, int* aActual,
                              VECTOR2I* aLocation ) const
{
    VECTOR2I nearest;
    ecoord dist_sq = SquaredDistanceToSeg( aSeg, aLocation ? &nearest : nullptr );
 
    if( dist_sq == 0 || dist_sq < SEG::Square( aClearance ) )
    {
        if( aLocation )
            *aLocation = nearest;
 
        if( aActual )
            *aActual = sqrt( dist_sq );
 
        return true;
    }
 
    return false;
}
 
 
bool SHAPE_POLY_SET::Collide( const VECTOR2I& aP, int aClearance, int* aActual,
                              VECTOR2I* aLocation ) const
{
    if( IsEmpty() || VertexCount() == 0 )
        return false;
 
    VECTOR2I nearest;
    ecoord dist_sq = SquaredDistance( aP, false, aLocation ? &nearest : nullptr );
 
    if( dist_sq == 0 || dist_sq < SEG::Square( aClearance ) )
    {
        if( aLocation )
            *aLocation = nearest;
 
        if( aActual )
            *aActual = sqrt( dist_sq );
 
        return true;
    }
 
    return false;
}
 
 
bool SHAPE_POLY_SET::Collide( const SHAPE* aShape, int aClearance, int* aActual,
                              VECTOR2I* aLocation ) const
{
    // A couple of simple cases are worth trying before we fall back on triangulation.
 
    if( aShape->Type() == SH_SEGMENT )
    {
        const SHAPE_SEGMENT* segment = static_cast<const SHAPE_SEGMENT*>( aShape );
        int                  extra = segment->GetWidth() / 2;
 
        if( Collide( segment->GetSeg(), aClearance + extra, aActual, aLocation ) )
        {
            if( aActual )
                *aActual = std::max( 0, *aActual - extra );
 
            return true;
        }
 
        return false;
    }
 
    if( aShape->Type() == SH_CIRCLE )
    {
        const SHAPE_CIRCLE* circle = static_cast<const SHAPE_CIRCLE*>( aShape );
        int                 extra = circle->GetRadius();
 
        if( Collide( circle->GetCenter(), aClearance + extra, aActual, aLocation ) )
        {
            if( aActual )
                *aActual = std::max( 0, *aActual - extra );
 
            return true;
        }
 
        return false;
    }
 
    const_cast<SHAPE_POLY_SET*>( this )->CacheTriangulation();
 
    int      actual = INT_MAX;
    VECTOR2I location;
 
    for( const std::unique_ptr<TRIANGULATED_POLYGON>& tpoly : m_triangulatedPolys )
    {
        for( const TRIANGULATED_POLYGON::TRI& tri : tpoly->Triangles() )
        {
            if( aActual || aLocation )
            {
                int      triActual;
                VECTOR2I triLocation;
 
                if( aShape->Collide( &tri, aClearance, &triActual, &triLocation ) )
                {
                    if( triActual < actual )
                    {
                        actual = triActual;
                        location = triLocation;
                    }
                }
            }
            else    // A much faster version of above
            {
                if( aShape->Collide( &tri, aClearance ) )
                    return true;
            }
        }
    }
 
    if( actual < INT_MAX )
    {
        if( aActual )
            *aActual = std::max( 0, actual );
 
        if( aLocation )
            *aLocation = location;
 
        return true;
    }
 
    return false;
}
 
 
void SHAPE_POLY_SET::RemoveAllContours()
{
    m_polys.clear();
    m_triangulatedPolys.clear();
    m_triangulationValid = false;
}
 
 
void SHAPE_POLY_SET::RemoveContour( int aContourIdx, int aPolygonIdx )
{
    // Default polygon is the last one
    if( aPolygonIdx < 0 )
        aPolygonIdx += m_polys.size();
 
    m_polys[aPolygonIdx].erase( m_polys[aPolygonIdx].begin() + aContourIdx );
}
 
 
void SHAPE_POLY_SET::RemoveOutline( int aOutlineIdx )
{
    m_polys.erase( m_polys.begin() + aOutlineIdx );
}
 
 
int SHAPE_POLY_SET::RemoveNullSegments()
{
    int removed = 0;
 
    ITERATOR iterator = IterateWithHoles();
 
    VECTOR2I    contourStart = *iterator;
    VECTOR2I    segmentStart, segmentEnd;
 
    VERTEX_INDEX indexStart;
    std::vector<VERTEX_INDEX> indices_to_remove;
 
    while( iterator )
    {
        // Obtain first point and its index
        segmentStart = *iterator;
        indexStart = iterator.GetIndex();
 
        // Obtain last point
        if( iterator.IsEndContour() )
        {
            segmentEnd = contourStart;
 
            // Advance
            iterator++;
 
            // If we have rolled into the next contour, remember its position
            // segmentStart and segmentEnd remain valid for comparison here
            if( iterator )
                contourStart = *iterator;
        }
        else
        {
            // Advance
            iterator++;
 
            // If we have reached the end of the SHAPE_POLY_SET, something is broken here
            wxCHECK_MSG( iterator, removed, wxT( "Invalid polygon.  Reached end without noticing.  Please report this error" ) );
 
            segmentEnd = *iterator;
        }
 
        // Remove segment start if both points are equal
        if( segmentStart == segmentEnd )
        {
            indices_to_remove.push_back( indexStart );
            removed++;
        }
    }
 
    // Proceed in reverse direction to remove the vertices because they are stored as absolute indices in a vector
    // Removing in reverse order preserves the remaining index values
    for( auto it = indices_to_remove.rbegin(); it != indices_to_remove.rend(); ++it )
        RemoveVertex( *it );
 
    return removed;
}
 
 
void SHAPE_POLY_SET::DeletePolygon( int aIdx )
{
    m_polys.erase( m_polys.begin() + aIdx );
}
 
 
void SHAPE_POLY_SET::DeletePolygonAndTriangulationData( int aIdx, bool aUpdateHash )
{
    m_polys.erase( m_polys.begin() + aIdx );
 
    if( m_triangulationValid )
    {
        for( int ii = m_triangulatedPolys.size() - 1; ii >= 0; --ii )
        {
            std::unique_ptr<TRIANGULATED_POLYGON>& triangleSet = m_triangulatedPolys[ii];
 
            if( triangleSet->GetSourceOutlineIndex() == aIdx )
                m_triangulatedPolys.erase( m_triangulatedPolys.begin() + ii );
            else if( triangleSet->GetSourceOutlineIndex() > aIdx )
                triangleSet->SetSourceOutlineIndex( triangleSet->GetSourceOutlineIndex() - 1 );
        }
 
        if( aUpdateHash )
        {
            m_hash = checksum();
            m_hashValid = true;
        }
    }
}
 
 
void SHAPE_POLY_SET::UpdateTriangulationDataHash()
{
    m_hash = checksum();
    m_hashValid = true;
}
 
 
void SHAPE_POLY_SET::Append( const SHAPE_POLY_SET& aSet )
{
    m_polys.insert( m_polys.end(), aSet.m_polys.begin(), aSet.m_polys.end() );
}
 
 
void SHAPE_POLY_SET::Append( const VECTOR2I& aP, int aOutline, int aHole )
{
    Append( aP.x, aP.y, aOutline, aHole );
}
 
 
bool SHAPE_POLY_SET::CollideVertex( const VECTOR2I& aPoint,
                                    SHAPE_POLY_SET::VERTEX_INDEX* aClosestVertex,
                                    int aClearance ) const
{
    // Shows whether there was a collision
    bool collision = false;
 
    // Difference vector between each vertex and aPoint.
    VECTOR2D    delta;
    ecoord      distance_squared;
    ecoord      clearance_squared = SEG::Square( aClearance );
 
    for( CONST_ITERATOR iterator = CIterateWithHoles(); iterator; iterator++ )
    {
        // Get the difference vector between current vertex and aPoint
        delta = *iterator - aPoint;
 
        // Compute distance
        distance_squared = delta.SquaredEuclideanNorm();
 
        // Check for collisions
        if( distance_squared <= clearance_squared )
        {
            if( !aClosestVertex )
                return true;
 
            collision = true;
 
            // Update clearance to look for closer vertices
            clearance_squared = distance_squared;
 
            // Store the indices that identify the vertex
            *aClosestVertex = iterator.GetIndex();
        }
    }
 
    return collision;
}
 
 
bool SHAPE_POLY_SET::CollideEdge( const VECTOR2I& aPoint,
                                  SHAPE_POLY_SET::VERTEX_INDEX* aClosestVertex,
                                  int aClearance ) const
{
    // Shows whether there was a collision
    bool   collision = false;
    ecoord clearance_squared = SEG::Square( aClearance );
 
    for( CONST_SEGMENT_ITERATOR iterator = CIterateSegmentsWithHoles(); iterator; iterator++ )
    {
        const SEG currentSegment = *iterator;
        ecoord    distance_squared = currentSegment.SquaredDistance( aPoint );
 
        // Check for collisions
        if( distance_squared <= clearance_squared )
        {
            if( !aClosestVertex )
                return true;
 
            collision = true;
 
            // Update clearance to look for closer edges
            clearance_squared = distance_squared;
 
            // Store the indices that identify the vertex
            *aClosestVertex = iterator.GetIndex();
        }
    }
 
    return collision;
}
 
 
void SHAPE_POLY_SET::BuildBBoxCaches() const
{
    for( int polygonIdx = 0; polygonIdx < OutlineCount(); polygonIdx++ )
    {
        COutline( polygonIdx ).GenerateBBoxCache();
 
        for( int holeIdx = 0; holeIdx < HoleCount( polygonIdx ); holeIdx++ )
            CHole( polygonIdx, holeIdx ).GenerateBBoxCache();
    }
}
 
 
bool SHAPE_POLY_SET::Contains( const VECTOR2I& aP, int aSubpolyIndex, int aAccuracy,
                               bool aUseBBoxCaches ) const
{
    if( m_polys.empty() )
        return false;
 
    // If there is a polygon specified, check the condition against that polygon
    if( aSubpolyIndex >= 0 )
        return containsSingle( aP, aSubpolyIndex, aAccuracy, aUseBBoxCaches );
 
    // In any other case, check it against all polygons in the set
    for( int polygonIdx = 0; polygonIdx < OutlineCount(); polygonIdx++ )
    {
        if( containsSingle( aP, polygonIdx, aAccuracy, aUseBBoxCaches ) )
            return true;
    }
 
    return false;
}
 
 
void SHAPE_POLY_SET::RemoveVertex( int aGlobalIndex )
{
    VERTEX_INDEX index;
 
    // Assure the to be removed vertex exists, abort otherwise
    if( GetRelativeIndices( aGlobalIndex, &index ) )
        RemoveVertex( index );
    else
        throw( std::out_of_range( "aGlobalIndex-th vertex does not exist" ) );
}
 
 
void SHAPE_POLY_SET::RemoveVertex( VERTEX_INDEX aIndex )
{
    m_polys[aIndex.m_polygon][aIndex.m_contour].Remove( aIndex.m_vertex );
}
 
 
void SHAPE_POLY_SET::SetVertex( int aGlobalIndex, const VECTOR2I& aPos )
{
    VERTEX_INDEX index;
 
    if( GetRelativeIndices( aGlobalIndex, &index ) )
        SetVertex( index, aPos );
    else
        throw( std::out_of_range( "aGlobalIndex-th vertex does not exist" ) );
}
 
 
void SHAPE_POLY_SET::SetVertex( const VERTEX_INDEX& aIndex, const VECTOR2I& aPos )
{
    m_polys[aIndex.m_polygon][aIndex.m_contour].SetPoint( aIndex.m_vertex, aPos );
}
 
 
bool SHAPE_POLY_SET::containsSingle( const VECTOR2I& aP, int aSubpolyIndex, int aAccuracy,
                                     bool aUseBBoxCaches ) const
{
    // Check that the point is inside the outline
    if( m_polys[aSubpolyIndex][0].PointInside( aP, aAccuracy ) )
    {
        // Check that the point is not in any of the holes
        for( int holeIdx = 0; holeIdx < HoleCount( aSubpolyIndex ); holeIdx++ )
        {
            const SHAPE_LINE_CHAIN& hole = CHole( aSubpolyIndex, holeIdx );
 
            // If the point is inside a hole it is outside of the polygon.  Do not use aAccuracy
            // here as it's meaning would be inverted.
            if( hole.PointInside( aP, 1, aUseBBoxCaches ) )
                return false;
        }
 
        return true;
    }
 
    return false;
}
 
 
void SHAPE_POLY_SET::Move( const VECTOR2I& aVector )
{
    for( POLYGON& poly : m_polys )
    {
        for( SHAPE_LINE_CHAIN& path : poly )
            path.Move( aVector );
    }
 
    for( std::unique_ptr<TRIANGULATED_POLYGON>& tri : m_triangulatedPolys )
        tri->Move( aVector );
 
    m_hash = checksum();
    m_hashValid = true;
}
 
 
void SHAPE_POLY_SET::Mirror( const VECTOR2I& aRef, FLIP_DIRECTION aFlipDirection )
{
    for( POLYGON& poly : m_polys )
    {
        for( SHAPE_LINE_CHAIN& path : poly )
            path.Mirror( aRef, aFlipDirection );
    }
 
    if( m_triangulationValid )
        CacheTriangulation();
}
 
 
void SHAPE_POLY_SET::Rotate( const EDA_ANGLE& aAngle, const VECTOR2I& aCenter )
{
    for( POLYGON& poly : m_polys )
    {
        for( SHAPE_LINE_CHAIN& path : poly )
            path.Rotate( aAngle, aCenter );
    }
 
    // Don't re-cache if the triangulation is already invalid
    if( m_triangulationValid )
        CacheTriangulation();
}
 
 
int SHAPE_POLY_SET::TotalVertices() const
{
    int c = 0;
 
    for( const POLYGON& poly : m_polys )
    {
        for( const SHAPE_LINE_CHAIN& path : poly )
            c += path.PointCount();
    }
 
    return c;
}
 
 
SHAPE_POLY_SET::POLYGON SHAPE_POLY_SET::ChamferPolygon( unsigned int aDistance, int aIndex )
{
    return chamferFilletPolygon( CHAMFERED, aDistance, aIndex, 0 );
}
 
 
SHAPE_POLY_SET::POLYGON SHAPE_POLY_SET::FilletPolygon( unsigned int aRadius, int aErrorMax,
                                                       int aIndex )
{
    return chamferFilletPolygon( FILLETED, aRadius, aIndex, aErrorMax );
}
 
 
SEG::ecoord SHAPE_POLY_SET::SquaredDistanceToPolygon( VECTOR2I aPoint, int aPolygonIndex,
                                                      VECTOR2I* aNearest ) const
{
    // We calculate the min dist between the segment and each outline segment.  However, if the
    // segment to test is inside the outline, and does not cross any edge, it can be seen outside
    // the polygon.  Therefore test if a segment end is inside (testing only one end is enough).
    // Use an accuracy of "1" to say that we don't care if it's exactly on the edge or not.
    if( containsSingle( aPoint, aPolygonIndex, 1 ) )
    {
        if( aNearest )
            *aNearest = aPoint;
 
        return 0;
    }
 
    CONST_SEGMENT_ITERATOR iterator = CIterateSegmentsWithHoles( aPolygonIndex );
 
    SEG::ecoord minDistance = (*iterator).SquaredDistance( aPoint );
 
    if( aNearest )
        *aNearest = ( *iterator ).NearestPoint( aPoint );
 
    for( iterator++; iterator && minDistance > 0; iterator++ )
    {
        SEG::ecoord currentDistance = (*iterator).SquaredDistance( aPoint );
 
        if( currentDistance < minDistance )
        {
            if( aNearest )
                *aNearest = (*iterator).NearestPoint( aPoint );
 
            minDistance = currentDistance;
        }
    }
 
    return minDistance;
}
 
 
SEG::ecoord SHAPE_POLY_SET::SquaredDistanceToPolygon( const SEG& aSegment, int aPolygonIndex,
                                                      VECTOR2I* aNearest ) const
{
    // Check if the segment is fully-contained.  If so, its midpoint is a good-enough nearest point.
    if( containsSingle( aSegment.A, aPolygonIndex, 1 ) &&
        containsSingle( aSegment.B, aPolygonIndex, 1 ) )
    {
        if( aNearest )
            *aNearest = ( aSegment.A + aSegment.B ) / 2;
 
        return 0;
    }
 
    CONST_SEGMENT_ITERATOR iterator = CIterateSegmentsWithHoles( aPolygonIndex );
    SEG::ecoord            minDistance = (*iterator).SquaredDistance( aSegment );
 
    if( aNearest )
        *aNearest = ( *iterator ).NearestPoint( aSegment );
 
    for( iterator++; iterator && minDistance > 0; iterator++ )
    {
        SEG::ecoord currentDistance = (*iterator).SquaredDistance( aSegment );
 
        if( currentDistance < minDistance )
        {
            if( aNearest )
                *aNearest = (*iterator).NearestPoint( aSegment );
 
            minDistance = currentDistance;
        }
    }
 
    // Return the maximum of minDistance and zero
    return minDistance < 0 ? 0 : minDistance;
}
 
 
SEG::ecoord SHAPE_POLY_SET::SquaredDistance( const VECTOR2I& aPoint, bool aOutlineOnly,
                                             VECTOR2I* aNearest ) const
{
    wxASSERT_MSG( !aOutlineOnly, wxT( "Warning: SHAPE_POLY_SET::SquaredDistance does not yet "
                                      "support aOutlineOnly==true" ) );
 
    SEG::ecoord currentDistance_sq;
    SEG::ecoord minDistance_sq = VECTOR2I::ECOORD_MAX;
    VECTOR2I    nearest;
 
    // Iterate through all the polygons and get the minimum distance.
    for( unsigned int polygonIdx = 0; polygonIdx < m_polys.size(); polygonIdx++ )
    {
        currentDistance_sq = SquaredDistanceToPolygon( aPoint, polygonIdx,
                                                       aNearest ? &nearest : nullptr );
 
        if( currentDistance_sq < minDistance_sq )
        {
            if( aNearest )
                *aNearest = nearest;
 
            minDistance_sq = currentDistance_sq;
        }
    }
 
    return minDistance_sq;
}
 
 
SEG::ecoord SHAPE_POLY_SET::SquaredDistanceToSeg( const SEG& aSegment, VECTOR2I* aNearest ) const
{
    SEG::ecoord currentDistance_sq;
    SEG::ecoord minDistance_sq = VECTOR2I::ECOORD_MAX;
    VECTOR2I    nearest;
 
    // Iterate through all the polygons and get the minimum distance.
    for( unsigned int polygonIdx = 0; polygonIdx < m_polys.size(); polygonIdx++ )
    {
        currentDistance_sq = SquaredDistanceToPolygon( aSegment, polygonIdx,
                                                       aNearest ? &nearest : nullptr );
 
        if( currentDistance_sq < minDistance_sq )
        {
            if( aNearest )
                *aNearest = nearest;
 
            minDistance_sq = currentDistance_sq;
        }
    }
 
    return minDistance_sq;
}
 
 
bool SHAPE_POLY_SET::IsVertexInHole( int aGlobalIdx )
{
    VERTEX_INDEX index;
 
    // Get the polygon and contour where the vertex is. If the vertex does not exist, return false
    if( !GetRelativeIndices( aGlobalIdx, &index ) )
        return false;
 
    // The contour is a hole if its index is greater than zero
    return index.m_contour > 0;
}
 
 
SHAPE_POLY_SET SHAPE_POLY_SET::Chamfer( int aDistance )
{
    SHAPE_POLY_SET chamfered;
 
    for( unsigned int idx = 0; idx < m_polys.size(); idx++ )
        chamfered.m_polys.push_back( ChamferPolygon( aDistance, idx ) );
 
    return chamfered;
}
 
 
SHAPE_POLY_SET SHAPE_POLY_SET::Fillet( int aRadius, int aErrorMax )
{
    SHAPE_POLY_SET filleted;
 
    for( size_t idx = 0; idx < m_polys.size(); idx++ )
        filleted.m_polys.push_back( FilletPolygon( aRadius, aErrorMax, idx ) );
 
    return filleted;
}
 
 
SHAPE_POLY_SET &SHAPE_POLY_SET::operator=( const SHAPE_POLY_SET& aOther )
{
    SHAPE::operator=( aOther );
    m_polys = aOther.m_polys;
 
    m_triangulatedPolys.clear();
 
    if( aOther.IsTriangulationUpToDate() )
    {
        m_triangulatedPolys.reserve( aOther.TriangulatedPolyCount() );
 
        for( unsigned i = 0; i < aOther.TriangulatedPolyCount(); i++ )
        {
            const TRIANGULATED_POLYGON* poly = aOther.TriangulatedPolygon( i );
            m_triangulatedPolys.push_back( std::make_unique<TRIANGULATED_POLYGON>( *poly ) );
        }
 
        m_hash = aOther.m_hash;
        m_hashValid.store( aOther.m_hashValid.load() );
        m_triangulationValid = aOther.m_triangulationValid.load();
    }
    else
    {
        m_hash.Clear();
        m_hashValid = false;
        m_triangulationValid = false;
    }
 
    m_failedHash = aOther.m_failedHash;
    m_failedHashValid.store( aOther.m_failedHashValid.load() );
 
    return *this;
}
 
 
HASH_128 SHAPE_POLY_SET::GetHash() const
{
    if( !m_hashValid )
        return checksum();
 
    return m_hash;
}
 
 
bool SHAPE_POLY_SET::IsTriangulationUpToDate() const
{
    if( !m_triangulationValid )
        return false;
 
    if( !m_hashValid )
        return false;
 
    HASH_128 hash = checksum();
 
    return hash == m_hash;
}
 
 
void SHAPE_POLY_SET::cacheTriangulation( bool aSimplify,
                                         std::vector<std::unique_ptr<TRIANGULATED_POLYGON>>* aHintData,
                                         const TASK_SUBMITTER& aSubmitter )
{
    // if( m_triangulationValid && m_hashValid && m_hash == checksum() )
    //     return;
    // if( m_failedHashValid && m_failedHash == checksum() )
    //     return;
 
    std::unique_lock<std::mutex> lock( m_triangulationMutex );
 
    if( m_triangulationValid && m_hashValid && m_hash == checksum() )
        return;
    if( m_failedHashValid && m_failedHash == checksum() )
        return;
 
    // Invalidate, in case anything goes wrong below
    m_triangulationValid = false;
    m_hashValid = false;
    m_failedHashValid = false;
 
    auto triangulate =
            []( SHAPE_POLY_SET& polySet, int forOutline,
                std::vector<std::unique_ptr<TRIANGULATED_POLYGON>>& dest,
                std::vector<std::unique_ptr<TRIANGULATED_POLYGON>>* hintData,
                const TASK_SUBMITTER& taskSubmitter )
            {
                bool triangulationValid = false;
                int pass = 0;
                int index = 0;
 
                if( hintData && hintData->size() != (unsigned) polySet.OutlineCount() )
                    hintData = nullptr;
 
                while( polySet.OutlineCount() > 0 )
                {
                    if( !dest.empty() && dest.back()->GetTriangleCount() == 0 )
                        dest.erase( dest.end() - 1 );
 
                    {
                        const SHAPE_LINE_CHAIN& outline = polySet.Polygon( 0 ).front();
                        TRIANGULATED_POLYGON    partitionScratch( forOutline );
                        POLYGON_TRIANGULATION   partitioner( partitionScratch );
                        size_t                  partitionLeaves = partitioner.suggestedPartitionLeafCount( outline );
 
                        if( partitionLeaves > 1 )
                        {
                            std::vector<SHAPE_LINE_CHAIN> partitions =
                                    partitioner.partitionPolygonBalanced( outline, partitionLeaves );
 
                            if( partitions.size() > 1 )
                            {
                                polySet.DeletePolygon( 0 );
 
                                if( taskSubmitter && partitions.size() > 2 )
                                {
                                    size_t leafCount = partitions.size();
 
                                    struct WorkStealState
                                    {
                                        std::unique_ptr<std::atomic<bool>[]> claimed;
                                        std::unique_ptr<std::atomic<bool>[]> done;
                                        std::unique_ptr<std::atomic<bool>[]> ok;
 
                                        explicit WorkStealState( size_t n ) :
                                                claimed( new std::atomic<bool>[n] ),
                                                done( new std::atomic<bool>[n] ),
                                                ok( new std::atomic<bool>[n] )
                                        {
                                            for( size_t i = 0; i < n; ++i )
                                            {
                                                claimed[i].store( false );
                                                done[i].store( false );
                                                ok[i].store( false );
                                            }
                                        }
                                    };
 
                                    auto state = std::make_shared<WorkStealState>( leafCount );
 
                                    std::vector<std::unique_ptr<TRIANGULATED_POLYGON>> results( leafCount );
 
                                    for( size_t i = 0; i < leafCount; ++i )
                                    {
                                        results[i] = std::make_unique<TRIANGULATED_POLYGON>( forOutline );
                                    }
 
                                    for( size_t i = 0; i < leafCount; ++i )
                                    {
                                        auto* triPoly = results[i].get();
                                        auto* leaf = &partitions[i];
 
                                        taskSubmitter( [state, i, triPoly, leaf]()
                                            {
                                                if( state->claimed[i].exchange( true ) )
                                                    return;
 
                                                POLYGON_TRIANGULATION tess( *triPoly );
                                                state->ok[i].store( tess.TesselatePolygon( *leaf, nullptr ) );
                                                state->done[i].store( true, std::memory_order_release );
                                            } );
                                    }
 
                                    for( size_t i = 0; i < leafCount; ++i )
                                    {
                                        if( state->claimed[i].exchange( true ) )
                                            continue;
 
                                        POLYGON_TRIANGULATION tess( *results[i] );
                                        state->ok[i].store( tess.TesselatePolygon( partitions[i], nullptr ) );
                                        state->done[i].store( true, std::memory_order_release );
                                    }
 
                                    for( size_t i = 0; i < leafCount; ++i )
                                    {
                                        while( !state->done[i].load( std::memory_order_acquire ) )
                                        {
                                            std::this_thread::yield();
                                        }
                                    }
 
                                    bool allOk = true;
 
                                    for( size_t i = 0; i < leafCount; ++i )
                                        allOk = allOk && state->ok[i].load();
 
                                    if( allOk )
                                    {
                                        for( auto& r : results )
                                        {
                                            if( r->GetTriangleCount() > 0 )
                                                dest.push_back( std::move( r ) );
                                        }
 
                                        triangulationValid = true;
                                        hintData = nullptr;
                                        continue;
                                    }
 
                                }
 
                                for( auto it = partitions.rbegin(); it != partitions.rend(); ++it )
                                    polySet.AddOutline( *it );
 
                                hintData = nullptr;
                                continue;
                            }
                        }
                    }
 
                    dest.push_back( std::make_unique<TRIANGULATED_POLYGON>( forOutline ) );
                    POLYGON_TRIANGULATION tess( *dest.back() );
 
                    // If the tessellation fails, we re-fracture the polygon, which will
                    // first simplify the system before fracturing and removing the holes
                    // This may result in multiple, disjoint polygons.
                    if( !tess.TesselatePolygon( polySet.Polygon( 0 ).front(),
                                                hintData ? hintData->at( index ).get() : nullptr ) )
                    {
                        ++pass;
 
                        if( pass == 1 )
                        {
                            polySet.SimplifyOutlines( TRIANGULATESIMPLIFICATIONLEVEL );
                        }
                        // In Clipper2, there is only one type of simplification
                        else
                        {
                            break;
                        }
 
                        triangulationValid = false;
                        hintData = nullptr;
                        continue;
                    }
 
                    polySet.DeletePolygon( 0 );
                    index++;
                    triangulationValid = true;
                }
 
                return triangulationValid;
            };
 
    m_triangulatedPolys.clear();
 
    const SHAPE_POLY_SET* srcSet = this;
    SHAPE_POLY_SET        tmpSet;
 
    if( ArcCount() > 0 || aSimplify )
    {
        tmpSet = SHAPE_POLY_SET( *this );
        tmpSet.ClearArcs();
 
        if( aSimplify )
            tmpSet.Simplify();
 
        srcSet = &tmpSet;
    }
 
    bool directOk = true;
 
    for( int ii = 0; ii < srcSet->OutlineCount() && directOk; ++ii )
    {
        const POLYGON& poly = srcSet->CPolygon( ii );
        size_t         prevCount = m_triangulatedPolys.size();
 
        if( poly.size() > 1 )
        {
            m_triangulatedPolys.push_back( std::make_unique<TRIANGULATED_POLYGON>( ii ) );
            POLYGON_TRIANGULATION tess( *m_triangulatedPolys.back() );
 
            if( tess.TesselatePolygon( poly, nullptr ) )
                continue;
 
            // Hole bridging failed; fracture to merge holes into the outline
            m_triangulatedPolys.resize( prevCount );
 
            SHAPE_POLY_SET flatSet( poly.front() );
 
            for( size_t jj = 1; jj < poly.size(); ++jj )
                flatSet.AddHole( poly[jj] );
 
            flatSet.Fracture();
            flatSet.splitSelfTouchingOutlines();
 
            if( triangulate( flatSet, ii, m_triangulatedPolys, nullptr, aSubmitter ) )
                continue;
 
            m_triangulatedPolys.resize( prevCount );
            directOk = false;
            continue;
        }
 
        {
            TRIANGULATED_POLYGON  partScratch( -1 );
            POLYGON_TRIANGULATION partChecker( partScratch );
 
            if( partChecker.suggestedPartitionLeafCount( poly.front() ) > 1 )
            {
                SHAPE_POLY_SET partSet;
                partSet.AddOutline( poly.front() );
 
                if( triangulate( partSet, ii, m_triangulatedPolys, nullptr, aSubmitter ) )
                {
                    continue;
                }
 
                m_triangulatedPolys.resize( prevCount );
            }
        }
 
        m_triangulatedPolys.push_back( std::make_unique<TRIANGULATED_POLYGON>( ii ) );
        POLYGON_TRIANGULATION tess( *m_triangulatedPolys.back() );
 
        bool ok = tess.TesselatePolygon( poly.front(), nullptr );
 
        // Self-touching outlines produce overlapping triangles; detect via area coverage
        if( ok )
        {
            double originalArea = std::abs( poly.front().Area() );
 
            if( originalArea > 0.0 )
            {
                double triArea = 0.0;
 
                for( const auto& tri : m_triangulatedPolys.back()->Triangles() )
                    triArea += std::abs( tri.Area() );
 
                double coverage = triArea / originalArea;
 
                if( coverage > 1.01 || coverage < 0.99 )
                    ok = false;
            }
        }
 
        if( !ok )
        {
            m_triangulatedPolys.resize( prevCount );
 
            SHAPE_POLY_SET splitSet;
            splitSet.AddOutline( poly[0] );
            splitSet.splitSelfTouchingOutlines();
 
            bool splitOk = true;
 
            for( int jj = 0; jj < splitSet.OutlineCount() && splitOk; ++jj )
            {
                m_triangulatedPolys.push_back( std::make_unique<TRIANGULATED_POLYGON>( ii ) );
                POLYGON_TRIANGULATION splitTess( *m_triangulatedPolys.back() );
                splitOk = splitTess.TesselatePolygon( splitSet.CPolygon( jj ).front(), nullptr );
            }
 
            if( !splitOk )
                directOk = false;
        }
    }
 
    if( !m_triangulatedPolys.empty() && m_triangulatedPolys.back()->GetTriangleCount() == 0 )
        m_triangulatedPolys.pop_back();
 
    if( directOk && !m_triangulatedPolys.empty() )
    {
        m_hash = checksum();
        m_hashValid = true;
        m_triangulationValid = true;
    }
    else
    {
        // Fracture each outline individually to preserve source outline indices
        m_triangulatedPolys.clear();
        bool fallbackOk = true;
 
        for( int ii = 0; ii < srcSet->OutlineCount() && fallbackOk; ++ii )
        {
            const POLYGON& poly = srcSet->CPolygon( ii );
            SHAPE_POLY_SET flatSet( poly.front() );
 
            for( size_t jj = 1; jj < poly.size(); ++jj )
                flatSet.AddHole( poly[jj] );
 
            flatSet.ClearArcs();
            flatSet.Fracture();
            flatSet.splitSelfTouchingOutlines();
 
            if( !triangulate( flatSet, ii, m_triangulatedPolys, nullptr, aSubmitter ) )
                fallbackOk = false;
        }
 
        if( !fallbackOk )
        {
            // Last resort: flatten everything together (loses outline indices)
            m_triangulatedPolys.clear();
            SHAPE_POLY_SET fallbackSet( *this );
            fallbackSet.ClearArcs();
            fallbackSet.Fracture();
            fallbackSet.splitSelfTouchingOutlines();
 
            if( !triangulate( fallbackSet, -1, m_triangulatedPolys, aHintData, aSubmitter ) )
            {
                wxLogTrace( TRIANGULATE_TRACE, "Failed to triangulate polygon" );
            }
            else
            {
                m_triangulationValid = true;
            }
        }
        else
        {
            m_triangulationValid = true;
        }
 
        if( m_triangulationValid )
        {
            m_hash = checksum();
            m_hashValid = true;
        }
        else
        {
            m_failedHash = checksum();
            m_failedHashValid = true;
        }
    }
}
 
 
 
HASH_128 SHAPE_POLY_SET::checksum() const
{
    MMH3_HASH hash( 0x68AF835D ); // Arbitrary seed
 
    hash.add( m_polys.size() );
 
    for( const POLYGON& outline : m_polys )
    {
        hash.add( outline.size() );
 
        for( const SHAPE_LINE_CHAIN& lc : outline )
        {
            hash.add( lc.PointCount() );
 
            for( int i = 0; i < lc.PointCount(); i++ )
            {
                VECTOR2I pt = lc.CPoint( i );
 
                hash.add( pt.x );
                hash.add( pt.y );
            }
        }
    }
 
    return hash.digest();
}
 
 
bool SHAPE_POLY_SET::HasTouchingHoles() const
{
    for( int i = 0; i < OutlineCount(); i++ )
    {
        if( hasTouchingHoles( CPolygon( i ) ) )
            return true;
    }
 
    return false;
}
 
 
bool SHAPE_POLY_SET::hasTouchingHoles( const POLYGON& aPoly ) const
{
    std::set<long long> ptHashes;
 
    for( const SHAPE_LINE_CHAIN& lc : aPoly )
    {
        for( const VECTOR2I& pt : lc.CPoints() )
        {
            const long long ptHash = (long long) pt.x << 32 | pt.y;
 
            if( ptHashes.count( ptHash ) > 0 )
                return true;
 
            ptHashes.insert( ptHash );
        }
    }
 
    return false;
}
 
 
bool SHAPE_POLY_SET::HasIndexableSubshapes() const
{
    return IsTriangulationUpToDate();
}
 
 
size_t SHAPE_POLY_SET::GetIndexableSubshapeCount() const
{
    size_t n = 0;
 
    for( const std::unique_ptr<TRIANGULATED_POLYGON>& t : m_triangulatedPolys )
        n += t->GetTriangleCount();
 
    return n;
}
 
 
void SHAPE_POLY_SET::GetIndexableSubshapes( std::vector<const SHAPE*>& aSubshapes ) const
{
    aSubshapes.reserve( GetIndexableSubshapeCount() );
 
    for( const std::unique_ptr<TRIANGULATED_POLYGON>& tpoly : m_triangulatedPolys )
    {
        for( const TRIANGULATED_POLYGON::TRI& tri : tpoly->Triangles() )
            aSubshapes.push_back( &tri );
    }
}
 
 
const BOX2I SHAPE_POLY_SET::TRIANGULATED_POLYGON::TRI::BBox( int aClearance ) const
{
    BOX2I bbox( parent->m_vertices[a] );
    bbox.Merge( parent->m_vertices[b] );
    bbox.Merge( parent->m_vertices[c] );
 
    if( aClearance != 0 )
        bbox.Inflate( aClearance );
 
    return bbox;
}
 
 
void SHAPE_POLY_SET::TRIANGULATED_POLYGON::AddTriangle( int a, int b, int c )
{
    m_triangles.emplace_back( a, b, c, this );
}
 
 
SHAPE_POLY_SET::TRIANGULATED_POLYGON::TRIANGULATED_POLYGON( const TRIANGULATED_POLYGON& aOther )
{
    m_sourceOutline = aOther.m_sourceOutline;
    m_vertices = aOther.m_vertices;
    m_triangles = aOther.m_triangles;
 
    for( TRI& tri : m_triangles )
        tri.parent = this;
}
 
 
SHAPE_POLY_SET::TRIANGULATED_POLYGON& SHAPE_POLY_SET::TRIANGULATED_POLYGON::operator=( const TRIANGULATED_POLYGON& aOther )
{
    m_sourceOutline = aOther.m_sourceOutline;
    m_vertices = aOther.m_vertices;
    m_triangles = aOther.m_triangles;
 
    for( TRI& tri : m_triangles )
        tri.parent = this;
 
    return *this;
}
 
 
void SHAPE_POLY_SET::TRIANGULATED_POLYGON::Refine()
{
    const size_t triCount = m_triangles.size();
 
    // Indices are int; skip an implausibly huge mesh rather than overflow.
    if( triCount < 2 || triCount > static_cast<size_t>( std::numeric_limits<int>::max() ) / 6 )
        return;
 
    const int halfEdgeCount = static_cast<int>( 3 * triCount );
 
    // heVertex[3k+j] is vertex j of triangle k.
    std::vector<int> heVertex( halfEdgeCount );
 
    for( size_t k = 0; k < triCount; k++ )
    {
        heVertex[3 * k + 0] = m_triangles[k].a;
        heVertex[3 * k + 1] = m_triangles[k].b;
        heVertex[3 * k + 2] = m_triangles[k].c;
    }
 
    auto nextInTriangle = []( int aEdge ) { return aEdge - aEdge % 3 + ( aEdge + 1 ) % 3; };
 
    // An untwinned edge is a polygon boundary and must never flip. Slots are never tombstoned so
    // probe chains stay intact.
    std::vector<int> twin( halfEdgeCount, -1 );
 
    int tableSize = 1;
 
    while( tableSize < halfEdgeCount * 2 )
        tableSize <<= 1;
 
    const uint32_t    tableMask = static_cast<uint32_t>( tableSize - 1 );
    std::vector<int>  slotEdge( tableSize, -1 );
 
    // A non-manifold edge (three or more triangles, e.g. a hole-bridge pinch) is retired so no
    // triangle straddling it can flip.
    std::vector<char> retired( tableSize, 0 );
    std::vector<int>  toVisit;
    std::vector<char> queued( halfEdgeCount, 0 );
 
    for( int edge = 0; edge < halfEdgeCount; edge++ )
    {
        int      from    = heVertex[edge];
        int      to      = heVertex[nextInTriangle( edge )];
        uint32_t keyLow  = static_cast<uint32_t>( from < to ? from : to );
        uint32_t keyHigh = static_cast<uint32_t>( from < to ? to : from );
        uint32_t slot    = ( ( keyLow * 0x9e3779b1u ) ^ ( keyHigh * 0x85ebca6bu ) ) & tableMask;
        bool     handled = false;
 
        while( slotEdge[slot] != -1 )
        {
            int      other     = slotEdge[slot];
            int      otherFrom = heVertex[other];
            int      otherTo   = heVertex[nextInTriangle( other )];
            uint32_t otherLow  = static_cast<uint32_t>( otherFrom < otherTo ? otherFrom : otherTo );
            uint32_t otherHigh = static_cast<uint32_t>( otherFrom < otherTo ? otherTo : otherFrom );
 
            if( otherLow == keyLow && otherHigh == keyHigh )
            {
                if( retired[slot] )
                {
                    // Non-manifold; stays a boundary.
                }
                else if( twin[other] == -1 )
                {
                    twin[edge]    = other;
                    twin[other]   = edge;
                    queued[other] = 1;
                    toVisit.push_back( other );
                }
                else
                {
                    // Third half-edge here: retire the edge and unlink the pair already formed.
                    int mate      = twin[other];
                    twin[other]   = -1;
                    twin[mate]    = -1;
                    retired[slot] = 1;
                }
 
                handled = true;
                break;
            }
 
            slot = ( slot + 1 ) & tableMask;
        }
 
        if( !handled )
            slotEdge[slot] = edge;
    }
 
    while( !toVisit.empty() )
    {
        int edge = toVisit.back();
        toVisit.pop_back();
        queued[edge] = 0;
 
        int twinEdge = twin[edge];
 
        if( twinEdge == -1 )
            continue;
 
        int tri     = edge - edge % 3;
        int twinTri = twinEdge - twinEdge % 3;
 
        int apexAEdge      = tri + ( edge + 2 ) % 3;
        int sharedEndEdge  = tri + ( edge + 1 ) % 3;
        int apexBEdge      = twinTri + ( twinEdge + 2 ) % 3;
        int twinSharedEdge = twinTri + ( twinEdge + 1 ) % 3;
 
        int apexA      = heVertex[apexAEdge];
        int sharedFrom = heVertex[edge];
        int sharedTo   = heVertex[sharedEndEdge];
        int apexB      = heVertex[apexBEdge];
 
        const VECTOR2I& apexAPt      = m_vertices[apexA];
        const VECTOR2I& sharedFromPt = m_vertices[sharedFrom];
        const VECTOR2I& sharedToPt   = m_vertices[sharedTo];
        const VECTOR2I& apexBPt      = m_vertices[apexB];
 
        // A non-convex quad would flip a triangle outside the polygon.
        if( KIGEOM::OrientationSign( apexAPt, sharedFromPt, apexBPt ) <= 0 )
            continue;
 
        if( KIGEOM::OrientationSign( apexAPt, apexBPt, sharedToPt ) <= 0 )
            continue;
 
        // Prefer the diagonal with fewer slivers, Delaunay breaks ties. Each flip lowers
        // (slivers, then -min-angle) lexicographically, so the loop terminates.
        bool legal = KIGEOM::InCircleDelaunayLegal( apexAPt, sharedFromPt, sharedToPt, apexBPt );
 
        int curSlivers = KIGEOM::IsSliverTriangle( apexAPt, sharedFromPt, sharedToPt )
                         + KIGEOM::IsSliverTriangle( apexBPt, sharedToPt, sharedFromPt );
 
        // Nothing to gain when already Delaunay and neither triangle is a sliver.
        if( legal && curSlivers == 0 )
            continue;
 
        int flipSlivers = KIGEOM::IsSliverTriangle( apexAPt, sharedFromPt, apexBPt )
                          + KIGEOM::IsSliverTriangle( apexAPt, apexBPt, sharedToPt );
 
        bool doFlip = ( flipSlivers != curSlivers ) ? ( flipSlivers < curSlivers ) : !legal;
 
        if( !doFlip )
            continue;
 
        heVertex[edge]     = apexB;
        heVertex[twinEdge] = apexA;
 
        int apexBOuterTwin = twin[apexBEdge];
        int apexAOuterTwin = twin[apexAEdge];
 
        twin[edge] = apexBOuterTwin;
 
        if( apexBOuterTwin != -1 )
            twin[apexBOuterTwin] = edge;
 
        twin[twinEdge] = apexAOuterTwin;
 
        if( apexAOuterTwin != -1 )
            twin[apexAOuterTwin] = twinEdge;
 
        twin[apexAEdge] = apexBEdge;
        twin[apexBEdge] = apexAEdge;
 
        // The flip may have made the quad's four outer edges illegal.
        for( int outer : { edge, twinEdge, sharedEndEdge, twinSharedEdge } )
        {
            if( twin[outer] != -1 && !queued[outer] )
            {
                queued[outer] = 1;
                toVisit.push_back( outer );
            }
        }
    }
 
    std::deque<TRI> refined;
 
    for( size_t i = 0; i < triCount; i++ )
        refined.emplace_back( heVertex[3 * i + 0], heVertex[3 * i + 1], heVertex[3 * i + 2], this );
 
    m_triangles = std::move( refined );
}
 
 
SHAPE_POLY_SET::TRIANGULATED_POLYGON::TRIANGULATED_POLYGON( int aSourceOutline ) :
        m_sourceOutline( aSourceOutline )
{
}
 
 
SHAPE_POLY_SET::TRIANGULATED_POLYGON::~TRIANGULATED_POLYGON()
{
}
 
 
void SHAPE_POLY_SET::Scale( double aScaleFactorX, double aScaleFactorY, const VECTOR2I& aCenter )
{
    for( POLYGON& poly : m_polys )
    {
        for( SHAPE_LINE_CHAIN& path : poly )
        {
            for( int i = 0; i < path.PointCount(); i++ )
            {
                VECTOR2I pt = path.CPoint( i );
                VECTOR2D vec;
                vec.x = ( pt.x - aCenter.x ) * aScaleFactorX;
                vec.y = ( pt.y - aCenter.y ) * aScaleFactorY;
                pt.x = KiROUND<double, int>( aCenter.x + vec.x );
                pt.y = KiROUND<double, int>( aCenter.y + vec.y );
                path.SetPoint( i, pt );
            }
        }
    }
 
    if( m_triangulationValid )
        CacheTriangulation();
}
 
 
void
SHAPE_POLY_SET::BuildPolysetFromOrientedPaths( const std::vector<SHAPE_LINE_CHAIN>& aPaths,
                                               bool                                 aEvenOdd )
{
    Clipper2Lib::Clipper64 clipper;
    Clipper2Lib::PolyTree64 tree;
    Clipper2Lib::Paths64 paths;
 
    for( const SHAPE_LINE_CHAIN& path : aPaths )
    {
        Clipper2Lib::Path64 lc;
        lc.reserve( path.PointCount() );
 
        for( int i = 0; i < path.PointCount(); i++ )
            lc.emplace_back( path.CPoint( i ).x, path.CPoint( i ).y );
 
        paths.push_back( std::move( lc ) );
    }
 
    clipper.AddSubject( paths );
    clipper.Execute( Clipper2Lib::ClipType::Union, aEvenOdd ? Clipper2Lib::FillRule::EvenOdd
                                                            : Clipper2Lib::FillRule::NonZero, tree );
 
    std::vector<CLIPPER_Z_VALUE> zValues;
    std::vector<SHAPE_ARC> arcBuffer;
 
    importTree( tree, zValues, arcBuffer );
    tree.Clear(); // Free used memory (not done in dtor)
}
 
 
bool SHAPE_POLY_SET::PointInside( const VECTOR2I& aPt, int aAccuracy, bool aUseBBoxCache ) const
{
    for( int idx = 0; idx < OutlineCount(); idx++ )
    {
        if( COutline( idx ).PointInside( aPt, aAccuracy, aUseBBoxCache ) )
            return true;
    }
 
    return false;
}
 
 
const std::vector<SEG> SHAPE_POLY_SET::GenerateHatchLines( const std::vector<double>& aSlopes,
                                                           int aSpacing, int aLineLength ) const
{
    std::vector<SEG> hatchLines;
 
    if( OutlineCount() == 0 || TotalVertices() == 0 )
        return hatchLines;
 
    // define range for hatch lines
    int min_x = CVertex( 0 ).x;
    int max_x = CVertex( 0 ).x;
    int min_y = CVertex( 0 ).y;
    int max_y = CVertex( 0 ).y;
 
    for( auto iterator = CIterateWithHoles(); iterator; iterator++ )
    {
        if( iterator->x < min_x )
            min_x = iterator->x;
 
        if( iterator->x > max_x )
            max_x = iterator->x;
 
        if( iterator->y < min_y )
            min_y = iterator->y;
 
        if( iterator->y > max_y )
            max_y = iterator->y;
    }
 
    auto sortEndsByDescendingX =
            []( const VECTOR2I& ref, const VECTOR2I& tst )
            {
                return tst.x < ref.x;
            };
 
    for( double slope : aSlopes )
    {
        int64_t max_a, min_a;
 
        if( slope > 0 )
        {
            max_a = KiROUND<double, int64_t>( max_y - slope * min_x );
            min_a = KiROUND<double, int64_t>( min_y - slope * max_x );
        }
        else
        {
            max_a = KiROUND<double, int64_t>( max_y - slope * max_x );
            min_a = KiROUND<double, int64_t>( min_y - slope * min_x );
        }
 
        min_a = ( min_a / aSpacing ) * aSpacing;
 
        // loop through hatch lines
        std::vector<VECTOR2I> pointbuffer;
        pointbuffer.reserve( 256 );
 
        for( int64_t a = min_a; a < max_a; a += aSpacing )
        {
            pointbuffer.clear();
 
            // Iterate through all vertices
            for( auto iterator = CIterateSegmentsWithHoles(); iterator; iterator++ )
            {
                const SEG seg = *iterator;
                VECTOR2I  pt;
 
                if( seg.IntersectsLine( slope, a, pt ) )
                {
                    // If the intersection point is outside the polygon, skip it
                    if( pt.x < min_x || pt.x > max_x || pt.y < min_y || pt.y > max_y )
                        continue;
 
                    // Add the intersection point to the buffer
                    pointbuffer.emplace_back( KiROUND( pt.x ), KiROUND( pt.y ) );
                }
            }
 
            // sort points in order of descending x (if more than 2) to
            // ensure the starting point and the ending point of the same segment
            // are stored one just after the other.
            if( pointbuffer.size() > 2 )
                sort( pointbuffer.begin(), pointbuffer.end(), sortEndsByDescendingX );
 
            // creates lines or short segments inside the complex polygon
            for( size_t ip = 0; ip + 1 < pointbuffer.size(); ip++ )
            {
                const VECTOR2I& p1 = pointbuffer[ip];
                const VECTOR2I& p2 = pointbuffer[ip + 1];
 
                // Avoid duplicated intersections or segments
                if( p1 == p2 )
                    continue;
 
                SEG candidate( p1, p2 );
 
                VECTOR2I mid( ( candidate.A.x + candidate.B.x ) / 2, ( candidate.A.y + candidate.B.y ) / 2 );
 
                // Check if segment is inside the polygon by checking its middle point
                if( Contains( mid, -1, 1, true ) )
                {
                    int dx = p2.x - p1.x;
 
                    // Push only one line for diagonal hatch or for small lines < twice
                    // the line length; else push 2 small lines
                    if( aLineLength == -1 || std::abs( dx ) < 2 * aLineLength )
                    {
                        hatchLines.emplace_back( candidate );
                    }
                    else
                    {
                        double dy = p2.y - p1.y;
                        slope = dy / dx;
 
                        if( dx > 0 )
                            dx = aLineLength;
                        else
                            dx = -aLineLength;
 
                        int x1 = KiROUND( p1.x + dx );
                        int x2 = KiROUND( p2.x - dx );
                        int y1 = KiROUND( p1.y + dx * slope );
                        int y2 = KiROUND( p2.y - dx * slope );
 
                        hatchLines.emplace_back( SEG( p1.x, p1.y, x1, y1 ) );
 
                        hatchLines.emplace_back( SEG( p2.x, p2.y, x2, y2 ) );
                    }
                }
            }
        }
    }
 
    return hatchLines;
}