#nullable enable
using System;
using System.Collections;
using System.Collections.Generic;
using System.Runtime.CompilerServices;

namespace Clipper2Lib
{
    [Flags]
    public enum PointInPolygonResult
    {
        IsOn = 0,
        IsInside = 1,
        IsOutside = 2
    };

    [Flags]
    internal enum VertexFlags
    {
        None = 0,
        OpenStart = 1,
        OpenEnd = 2,
        LocalMax = 4,
        LocalMin = 8
    };

    internal class Vertex
    {
        public readonly Point64 pt;
        public Vertex? next;
        public Vertex? prev;
        public VertexFlags flags;

        public Vertex(Point64 pt, VertexFlags flags, Vertex? prev)
        {
            this.pt = pt;
            this.flags = flags;
            next = null;
            this.prev = prev;
        }
    };

    internal readonly struct LocalMinima
    {
        public readonly Vertex vertex;
        public readonly PathType polytype;
        public readonly bool isOpen;

        public LocalMinima(Vertex vertex, PathType polytype, bool isOpen = false)
        {
            this.vertex = vertex;
            this.polytype = polytype;
            this.isOpen = isOpen;
        }

        public static bool operator ==(LocalMinima lm1, LocalMinima lm2)
        {
            return ReferenceEquals(lm1.vertex, lm2.vertex);
        }

        public static bool operator !=(LocalMinima lm1, LocalMinima lm2)
        {
            return !(lm1 == lm2);
        }

        public override bool Equals(object? obj)
        {
            return obj is LocalMinima minima && this == minima;
        }

        public override int GetHashCode()
        {
            return vertex.GetHashCode();
        }

    };

    // IntersectNode: a structure representing 2 intersecting edges.
    // Intersections must be sorted so they are processed from the largest
    // Y coordinates to the smallest while keeping edges adjacent.
    internal struct IntersectNode
    {
        public readonly Point64 pt;
        public readonly Active edge1;
        public readonly Active edge2;

        public IntersectNode(Point64 pt, Active edge1, Active edge2)
        {
            this.pt = pt;
            this.edge1 = edge1;
            this.edge2 = edge2;
        }
    };

    internal struct LocMinSorter : IComparer<LocalMinima>
    {
        public int Compare(LocalMinima locMin1, LocalMinima locMin2)
        {
            return locMin2.vertex.pt.Y.CompareTo(locMin1.vertex.pt.Y);
        }
    }

    // OutPt: vertex data structure for clipping solutions
    internal class OutPt
    {
        public Point64 pt;
        public OutPt? next;
        public OutPt prev;
        public OutRec outrec;
        public Joiner? joiner;

        public OutPt(Point64 pt, OutRec outrec)
        {
            this.pt = pt;
            this.outrec = outrec;
            next = this;
            prev = this;
            joiner = null;
        }
    };

    // OutRec: path data structure for clipping solutions
    internal class OutRec
    {
        public int idx;
        public OutRec? owner;
        public List<OutRec>? splits;
        public Active? frontEdge;
        public Active? backEdge;
        public OutPt? pts;
        public PolyPathNode? polypath;
        public Rect64 bounds;
        public Path64 path;
        public bool isOpen;
        public OutRec()
        {
            bounds = new Rect64();
            path = new Path64();
        }
    };

    // Joiner: structure used in merging "touching" solution polygons
    internal class Joiner
    {
        public int idx;
        public OutPt op1;
        public OutPt? op2;
        public Joiner? next1;
        public Joiner? next2;
        public Joiner? nextH;

        public Joiner(OutPt op1, OutPt? op2, Joiner? nextH)
        {
            idx = -1;
            this.nextH = nextH;
            this.op1 = op1;
            this.op2 = op2;
            next1 = op1.joiner;
            op1.joiner = this;

            if (op2 != null)
            {
                next2 = op2.joiner;
                op2.joiner = this;
            }
            else
                next2 = null;
        }
    }

    ///////////////////////////////////////////////////////////////////
    // Important: UP and DOWN here are premised on Y-axis positive down
    // displays, which is the orientation used in Clipper's development.
    ///////////////////////////////////////////////////////////////////

    internal class Active
    {
        public Point64 bot;
        public Point64 top;
        public long curX; // current (updated at every new scanline)
        public double dx;
        public int windDx; // 1 or -1 depending on winding direction
        public int windCount;
        public int windCount2; // winding count of the opposite polytype
        public OutRec? outrec;

        // AEL: 'active edge list' (Vatti's AET - active edge table)
        //     a linked list of all edges (from left to right) that are present
        //     (or 'active') within the current scanbeam (a horizontal 'beam' that
        //     sweeps from bottom to top over the paths in the clipping operation).
        public Active? prevInAEL;
        public Active? nextInAEL;

        // SEL: 'sorted edge list' (Vatti's ST - sorted table)
        //     linked list used when sorting edges into their new positions at the
        //     top of scanbeams, but also (re)used to process horizontals.
        public Active? prevInSEL;
        public Active? nextInSEL;
        public Active? jump;
        public Vertex? vertexTop;
        public LocalMinima localMin; // the bottom of an edge 'bound' (also Vatti)
        internal bool isLeftBound;
    };

    public class ClipperBase
    {
        private ClipType _cliptype;
        private FillRule _fillrule;
        private Active? _actives;
        private Active? _sel;
        private Joiner? _horzJoiners;
        private readonly List<LocalMinima> _minimaList;
        private readonly List<IntersectNode> _intersectList;
        private readonly List<Vertex> _vertexList;
        private readonly List<OutRec> _outrecList;
        private readonly List<Joiner?> _joinerList;
        private readonly List<long> _scanlineList;
        private int _currentLocMin;
        private long _currentBotY;
        private bool _isSortedMinimaList;
        private bool _hasOpenPaths;
        internal bool _using_polytree;
        internal bool _succeeded;
        public bool PreserveCollinear { get; set; }
        public bool ReverseSolution { get; set; }

#if USINGZ
    public delegate void ZCallback64(Point64 bot1, Point64 top1,
        Point64 bot2, Point64 top2, ref Point64 intersectPt);

    public long DefaultZ { get; set; }
    protected ZCallback64? _zCallback;
#endif
        public ClipperBase()
        {
            _minimaList = new List<LocalMinima>();
            _intersectList = new List<IntersectNode>();
            _vertexList = new List<Vertex>();
            _outrecList = new List<OutRec>();
            _joinerList = new List<Joiner?>();
            _scanlineList = new List<long>();
            PreserveCollinear = true;
        }

#if USINGZ
    private bool XYCoordsEqual(Point64 pt1, Point64 pt2)
    {
      return (pt1.X == pt2.X && pt1.Y == pt2.Y);
    }
    
    private void SetZ(Active e1, Active e2, ref Point64 intersectPt)
    {
      if (_zCallback == null) return;

      // prioritize subject vertices over clip vertices
      // and pass the subject vertices before clip vertices in the callback
      if (GetPolyType(e1) == PathType.Subject)
      {
        if (XYCoordsEqual(intersectPt, e1.bot))
          intersectPt = new Point64(intersectPt.X, intersectPt.Y, e1.bot.Z);
        else if (XYCoordsEqual(intersectPt, e1.top))
          intersectPt = new Point64(intersectPt.X, intersectPt.Y, e1.top.Z);
        else if (XYCoordsEqual(intersectPt, e2.bot))
          intersectPt = new Point64(intersectPt.X, intersectPt.Y, e2.bot.Z);
        else if (XYCoordsEqual(intersectPt, e2.top))
          intersectPt = new Point64(intersectPt.X, intersectPt.Y, e2.top.Z);
        else
          intersectPt = new Point64(intersectPt.X, intersectPt.Y, DefaultZ);
        _zCallback(e1.bot, e1.top, e2.bot, e2.top, ref intersectPt);
      }
      else
      {
        if (XYCoordsEqual(intersectPt, e2.bot))
          intersectPt = new Point64(intersectPt.X, intersectPt.Y, e2.bot.Z);
        else if (XYCoordsEqual(intersectPt, e2.top))
          intersectPt = new Point64(intersectPt.X, intersectPt.Y, e2.top.Z);
        else if (XYCoordsEqual(intersectPt, e1.bot))
          intersectPt = new Point64(intersectPt.X, intersectPt.Y, e1.bot.Z);
        else if (XYCoordsEqual(intersectPt, e1.top))
          intersectPt = new Point64(intersectPt.X, intersectPt.Y, e1.top.Z);
        else
          intersectPt = new Point64(intersectPt.X, intersectPt.Y, DefaultZ);
        _zCallback(e2.bot, e2.top, e1.bot, e1.top, ref intersectPt);
      }
    }
#endif

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static bool IsOdd(int val)
        {
            return ((val & 1) != 0);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static bool IsHotEdge(Active ae)
        {
            return ae.outrec != null;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static bool IsOpen(Active ae)
        {
            return ae.localMin.isOpen;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static bool IsOpenEnd(Active ae)
        {
            return ae.localMin.isOpen && IsOpenEnd(ae.vertexTop!);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static bool IsOpenEnd(Vertex v)
        {
            return (v.flags & (VertexFlags.OpenStart | VertexFlags.OpenEnd)) != VertexFlags.None;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static Active? GetPrevHotEdge(Active ae)
        {
            Active? prev = ae.prevInAEL;
            while (prev != null && (IsOpen(prev) || !IsHotEdge(prev)))
                prev = prev.prevInAEL;
            return prev;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static bool IsFront(Active ae)
        {
            return (ae == ae.outrec!.frontEdge);
        }

        /*******************************************************************************
        *  Dx:                             0(90deg)                                    *
        *                                  |                                           *
        *               +inf (180deg) <--- o --. -inf (0deg)                          *
        *******************************************************************************/

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static double GetDx(Point64 pt1, Point64 pt2)
        {
            double dy = pt2.Y - pt1.Y;
            if (dy != 0)
                return (pt2.X - pt1.X) / dy;
            if (pt2.X > pt1.X)
                return double.NegativeInfinity;
            return double.PositiveInfinity;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static long TopX(Active ae, long currentY)
        {
            if ((currentY == ae.top.Y) || (ae.top.X == ae.bot.X)) return ae.top.X;
            if (currentY == ae.bot.Y) return ae.bot.X;
            return ae.bot.X + (long)Math.Round(ae.dx * (currentY - ae.bot.Y));
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static bool IsHorizontal(Active ae)
        {
            return (ae.top.Y == ae.bot.Y);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static bool IsHeadingRightHorz(Active ae)
        {
            return (double.IsNegativeInfinity(ae.dx));
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static bool IsHeadingLeftHorz(Active ae)
        {
            return (double.IsPositiveInfinity(ae.dx));
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static void SwapActives(ref Active ae1, ref Active ae2)
        {
            (ae2, ae1) = (ae1, ae2);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static PathType GetPolyType(Active ae)
        {
            return ae.localMin.polytype;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static bool IsSamePolyType(Active ae1, Active ae2)
        {
            return ae1.localMin.polytype == ae2.localMin.polytype;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static void SetDx(Active ae)
        {
            ae.dx = GetDx(ae.bot, ae.top);
        }


        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static Vertex NextVertex(Active ae)
        {
            if (ae.windDx > 0)
                return ae.vertexTop!.next!;
            return ae.vertexTop!.prev!;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static Vertex PrevPrevVertex(Active ae)
        {
            if (ae.windDx > 0)
                return ae.vertexTop!.prev!.prev!;
            return ae.vertexTop!.next!.next!;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static bool IsMaxima(Vertex vertex)
        {
            return ((vertex.flags & VertexFlags.LocalMax) != VertexFlags.None);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static bool IsMaxima(Active ae)
        {
            return IsMaxima(ae.vertexTop!);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static Active? GetMaximaPair(Active ae)
        {
            Active? ae2;
            ae2 = ae.nextInAEL;
            while (ae2 != null)
            {
                if (ae2.vertexTop == ae.vertexTop) return ae2; // Found!
                ae2 = ae2.nextInAEL;
            }
            return null;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static Vertex? GetCurrYMaximaVertex(Active ae)
        {
            Vertex? result = ae.vertexTop;
            if (ae.windDx > 0)
                while (result!.next!.pt.Y == result.pt.Y) result = result.next;
            else
                while (result!.prev!.pt.Y == result.pt.Y) result = result.prev;
            if (!IsMaxima(result)) result = null; // not a maxima
            return result;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static Active? GetHorzMaximaPair(Active horz, Vertex maxVert)
        {
            // we can't be sure whether the MaximaPair is on the left or right, so ...
            Active? result = horz.prevInAEL;
            while (result != null && result.curX >= maxVert.pt.X)
            {
                if (result.vertexTop == maxVert) return result;  // Found!
                result = result.prevInAEL;
            }
            result = horz.nextInAEL;
            while (result != null && TopX(result, horz.top.Y) <= maxVert.pt.X)
            {
                if (result.vertexTop == maxVert) return result;  // Found!
                result = result.nextInAEL;
            }
            return null;
        }

        private struct IntersectListSort : IComparer<IntersectNode>
        {
            public int Compare(IntersectNode a, IntersectNode b)
            {
                if (a.pt.Y == b.pt.Y)
                {
                    if (a.pt.X == b.pt.X) return 0;
                    return (a.pt.X < b.pt.X) ? -1 : 1;
                }
                return (a.pt.Y > b.pt.Y) ? -1 : 1;
            }
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static void SetSides(OutRec outrec, Active startEdge, Active endEdge)
        {
            outrec.frontEdge = startEdge;
            outrec.backEdge = endEdge;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static void SwapOutrecs(Active ae1, Active ae2)
        {
            OutRec? or1 = ae1.outrec; // at least one edge has 
            OutRec? or2 = ae2.outrec; // an assigned outrec
            if (or1 == or2)
            {
                Active? ae = or1!.frontEdge;
                or1.frontEdge = or1.backEdge;
                or1.backEdge = ae;
                return;
            }

            if (or1 != null)
            {
                if (ae1 == or1.frontEdge)
                    or1.frontEdge = ae2;
                else
                    or1.backEdge = ae2;
            }

            if (or2 != null)
            {
                if (ae2 == or2.frontEdge)
                    or2.frontEdge = ae1;
                else
                    or2.backEdge = ae1;
            }

            ae1.outrec = or2;
            ae2.outrec = or1;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static double Area(OutPt op)
        {
            // https://en.wikipedia.org/wiki/Shoelace_formula
            double area = 0.0;
            OutPt op2 = op;
            do
            {
                area += (double)(op2.prev.pt.Y + op2.pt.Y) *
                  (op2.prev.pt.X - op2.pt.X);
                op2 = op2.next!;
            } while (op2 != op);
            return area * 0.5;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static double AreaTriangle(Point64 pt1, Point64 pt2, Point64 pt3)
        {
            return (double)(pt3.Y + pt1.Y) * (pt3.X - pt1.X) +
              (double)(pt1.Y + pt2.Y) * (pt1.X - pt2.X) +
              (double)(pt2.Y + pt3.Y) * (pt2.X - pt3.X);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static OutRec? GetRealOutRec(OutRec? outRec)
        {
            while ((outRec != null) && (outRec.pts == null))
                outRec = outRec.owner;
            return outRec;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static void UncoupleOutRec(Active ae)
        {
            OutRec? outrec = ae.outrec;
            if (outrec == null) return;
            outrec.frontEdge!.outrec = null;
            outrec.backEdge!.outrec = null;
            outrec.frontEdge = null;
            outrec.backEdge = null;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static bool OutrecIsAscending(Active hotEdge)
        {
            return (hotEdge == hotEdge.outrec!.frontEdge);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static void SwapFrontBackSides(OutRec outrec)
        {
            // while this proc. is needed for open paths
            // it's almost never needed for closed paths
            Active ae2 = outrec.frontEdge!;
            outrec.frontEdge = outrec.backEdge;
            outrec.backEdge = ae2;
            outrec.pts = outrec.pts!.next;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static bool EdgesAdjacentInAEL(IntersectNode inode)
        {
            return (inode.edge1.nextInAEL == inode.edge2) || (inode.edge1.prevInAEL == inode.edge2);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        protected void ClearSolution()
        {
            while (_actives != null) DeleteFromAEL(_actives);
            _scanlineList.Clear();
            DisposeIntersectNodes();
            _joinerList.Clear();
            _horzJoiners = null;
            _outrecList.Clear();
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void Clear()
        {
            ClearSolution();
            _minimaList.Clear();
            _vertexList.Clear();
            _currentLocMin = 0;
            _isSortedMinimaList = false;
            _hasOpenPaths = false;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        protected void Reset()
        {
            if (!_isSortedMinimaList)
            {
                _minimaList.Sort(new LocMinSorter());
                _isSortedMinimaList = true;
            }

            _scanlineList.Capacity = _minimaList.Count;
            for (int i = _minimaList.Count - 1; i >= 0; i--)
                _scanlineList.Add(_minimaList[i].vertex.pt.Y);

            _currentBotY = 0;
            _currentLocMin = 0;
            _actives = null;
            _sel = null;
            _succeeded = true;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private void InsertScanline(long y)
        {
            int index = _scanlineList.BinarySearch(y);
            if (index >= 0) return;
            index = ~index;
            _scanlineList.Insert(index, y);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private bool PopScanline(out long y)
        {
            int cnt = _scanlineList.Count - 1;
            if (cnt < 0)
            {
                y = 0;
                return false;
            }

            y = _scanlineList[cnt];
            _scanlineList.RemoveAt(cnt--);
            while (cnt >= 0 && y == _scanlineList[cnt])
                _scanlineList.RemoveAt(cnt--);
            return true;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private bool HasLocMinAtY(long y)
        {
            return (_currentLocMin < _minimaList.Count && _minimaList[_currentLocMin].vertex.pt.Y == y);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private LocalMinima PopLocalMinima()
        {
            return _minimaList[_currentLocMin++];
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private void AddLocMin(Vertex vert, PathType polytype, bool isOpen)
        {
            // make sure the vertex is added only once ...
            if ((vert.flags & VertexFlags.LocalMin) != VertexFlags.None) return;
            vert.flags |= VertexFlags.LocalMin;

            LocalMinima lm = new LocalMinima(vert, polytype, isOpen);
            _minimaList.Add(lm);
        }

        protected void AddPathsToVertexList(Paths64 paths, PathType polytype, bool isOpen)
        {
            int totalVertCnt = 0;
            foreach (Path64 path in paths) totalVertCnt += path.Count;
            _vertexList.Capacity = _vertexList.Count + totalVertCnt;

            foreach (Path64 path in paths)
            {
                Vertex? v0 = null, prev_v = null, curr_v;
                foreach (Point64 pt in path)
                {
                    if (v0 == null)
                    {
                        v0 = new Vertex(pt, VertexFlags.None, null);
                        _vertexList.Add(v0);
                        prev_v = v0;
                    }
                    else if (prev_v!.pt != pt) // ie skips duplicates
                    {
                        curr_v = new Vertex(pt, VertexFlags.None, prev_v);
                        _vertexList.Add(curr_v);
                        prev_v.next = curr_v;
                        prev_v = curr_v;
                    }
                }
                if (prev_v == null || prev_v.prev == null) continue;
                if (!isOpen && prev_v.pt == v0!.pt) prev_v = prev_v.prev;
                prev_v.next = v0;
                v0!.prev = prev_v;
                if (!isOpen && prev_v.next == prev_v) continue;

                // OK, we have a valid path
                bool going_up, going_up0;
                if (isOpen)
                {
                    curr_v = v0.next;
                    while (curr_v != v0 && curr_v!.pt.Y == v0.pt.Y)
                        curr_v = curr_v.next;
                    going_up = curr_v.pt.Y <= v0.pt.Y;
                    if (going_up)
                    {
                        v0.flags = VertexFlags.OpenStart;
                        AddLocMin(v0, polytype, true);
                    }
                    else
                        v0.flags = VertexFlags.OpenStart | VertexFlags.LocalMax;
                }
                else // closed path
                {
                    prev_v = v0.prev;
                    while (prev_v != v0 && prev_v!.pt.Y == v0.pt.Y)
                        prev_v = prev_v.prev;
                    if (prev_v == v0)
                        continue; // only open paths can be completely flat
                    going_up = prev_v.pt.Y > v0.pt.Y;
                }

                going_up0 = going_up;
                prev_v = v0;
                curr_v = v0.next;
                while (curr_v != v0)
                {
                    if (curr_v!.pt.Y > prev_v.pt.Y && going_up)
                    {
                        prev_v.flags |= VertexFlags.LocalMax;
                        going_up = false;
                    }
                    else if (curr_v.pt.Y < prev_v.pt.Y && !going_up)
                    {
                        going_up = true;
                        AddLocMin(prev_v, polytype, isOpen);
                    }
                    prev_v = curr_v;
                    curr_v = curr_v.next;
                }

                if (isOpen)
                {
                    prev_v.flags |= VertexFlags.OpenEnd;
                    if (going_up)
                        prev_v.flags |= VertexFlags.LocalMax;
                    else
                        AddLocMin(prev_v, polytype, isOpen);
                }
                else if (going_up != going_up0)
                {
                    if (going_up0) AddLocMin(prev_v, polytype, false);
                    else prev_v.flags |= VertexFlags.LocalMax;
                }
            }
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void AddSubject(Path64 path)
        {
            AddPath(path, PathType.Subject);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void AddOpenSubject(Path64 path)
        {
            AddPath(path, PathType.Subject, true);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void AddClip(Path64 path)
        {
            AddPath(path, PathType.Clip);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        protected void AddPath(Path64 path, PathType polytype, bool isOpen = false)
        {
            Paths64 tmp = new Paths64(1) { path };
            AddPaths(tmp, polytype, isOpen);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        protected void AddPaths(Paths64 paths, PathType polytype, bool isOpen = false)
        {
            if (isOpen) _hasOpenPaths = true;
            _isSortedMinimaList = false;
            AddPathsToVertexList(paths, polytype, isOpen);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private bool IsContributingClosed(Active ae)
        {
            switch (_fillrule)
            {
                case FillRule.Positive:
                    if (ae.windCount != 1) return false;
                    break;
                case FillRule.Negative:
                    if (ae.windCount != -1) return false;
                    break;
                case FillRule.NonZero:
                    if (Math.Abs(ae.windCount) != 1) return false;
                    break;
            }

            switch (_cliptype)
            {
                case ClipType.Intersection:
                    return _fillrule switch
                    {
                        FillRule.Positive => ae.windCount2 > 0,
                        FillRule.Negative => ae.windCount2 < 0,
                        _ => ae.windCount2 != 0,
                    };

                case ClipType.Union:
                    return _fillrule switch
                    {
                        FillRule.Positive => ae.windCount2 <= 0,
                        FillRule.Negative => ae.windCount2 >= 0,
                        _ => ae.windCount2 == 0,
                    };

                case ClipType.Difference:
                    bool result = _fillrule switch
                    {
                        FillRule.Positive => (ae.windCount2 <= 0),
                        FillRule.Negative => (ae.windCount2 >= 0),
                        _ => (ae.windCount2 == 0),
                    };
                    return (GetPolyType(ae) == PathType.Subject) ? result : !result;

                case ClipType.Xor:
                    return true; // XOr is always contributing unless open

                default:
                    return false;
            }
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private bool IsContributingOpen(Active ae)
        {
            bool isInClip, isInSubj;
            switch (_fillrule)
            {
                case FillRule.Positive:
                    isInSubj = ae.windCount > 0;
                    isInClip = ae.windCount2 > 0;
                    break;
                case FillRule.Negative:
                    isInSubj = ae.windCount < 0;
                    isInClip = ae.windCount2 < 0;
                    break;
                default:
                    isInSubj = ae.windCount != 0;
                    isInClip = ae.windCount2 != 0;
                    break;
            }

            bool result = _cliptype switch
            {
                ClipType.Intersection => isInClip,
                ClipType.Union => !isInSubj && !isInClip,
                _ => !isInClip
            };
            return result;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private void SetWindCountForClosedPathEdge(Active ae)
        {
            // Wind counts refer to polygon regions not edges, so here an edge's WindCnt
            // indicates the higher of the wind counts for the two regions touching the
            // edge. (nb: Adjacent regions can only ever have their wind counts differ by
            // one. Also, open paths have no meaningful wind directions or counts.)

            Active? ae2 = ae.prevInAEL;
            // find the nearest closed path edge of the same PolyType in AEL (heading left)
            PathType pt = GetPolyType(ae);
            while (ae2 != null && (GetPolyType(ae2) != pt || IsOpen(ae2))) ae2 = ae2.prevInAEL;

            if (ae2 == null)
            {
                ae.windCount = ae.windDx;
                ae2 = _actives;
            }
            else if (_fillrule == FillRule.EvenOdd)
            {
                ae.windCount = ae.windDx;
                ae.windCount2 = ae2.windCount2;
                ae2 = ae2.nextInAEL;
            }
            else
            {
                // NonZero, positive, or negative filling here ...
                // when e2's WindCnt is in the SAME direction as its WindDx,
                // then polygon will fill on the right of 'e2' (and 'e' will be inside)
                // nb: neither e2.WindCnt nor e2.WindDx should ever be 0.
                if (ae2.windCount * ae2.windDx < 0)
                {
                    // opposite directions so 'ae' is outside 'ae2' ...
                    if (Math.Abs(ae2.windCount) > 1)
                    {
                        // outside prev poly but still inside another.
                        if (ae2.windDx * ae.windDx < 0)
                            // reversing direction so use the same WC
                            ae.windCount = ae2.windCount;
                        else
                            // otherwise keep 'reducing' the WC by 1 (i.e. towards 0) ...
                            ae.windCount = ae2.windCount + ae.windDx;
                    }
                    else
                        // now outside all polys of same polytype so set own WC ...
                        ae.windCount = (IsOpen(ae) ? 1 : ae.windDx);
                }
                else
                {
                    //'ae' must be inside 'ae2'
                    if (ae2.windDx * ae.windDx < 0)
                        // reversing direction so use the same WC
                        ae.windCount = ae2.windCount;
                    else
                        // otherwise keep 'increasing' the WC by 1 (i.e. away from 0) ...
                        ae.windCount = ae2.windCount + ae.windDx;
                }

                ae.windCount2 = ae2.windCount2;
                ae2 = ae2.nextInAEL; // i.e. get ready to calc WindCnt2
            }

            // update windCount2 ...
            if (_fillrule == FillRule.EvenOdd)
                while (ae2 != ae)
                {
                    if (GetPolyType(ae2!) != pt && !IsOpen(ae2!))
                        ae.windCount2 = (ae.windCount2 == 0 ? 1 : 0);
                    ae2 = ae2!.nextInAEL;
                }
            else
                while (ae2 != ae)
                {
                    if (GetPolyType(ae2!) != pt && !IsOpen(ae2!))
                        ae.windCount2 += ae2!.windDx;
                    ae2 = ae2!.nextInAEL;
                }
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private void SetWindCountForOpenPathEdge(Active ae)
        {
            Active? ae2 = _actives;
            if (_fillrule == FillRule.EvenOdd)
            {
                int cnt1 = 0, cnt2 = 0;
                while (ae2 != ae)
                {
                    if (GetPolyType(ae2!) == PathType.Clip)
                        cnt2++;
                    else if (!IsOpen(ae2!))
                        cnt1++;
                    ae2 = ae2!.nextInAEL;
                }

                ae.windCount = (IsOdd(cnt1) ? 1 : 0);
                ae.windCount2 = (IsOdd(cnt2) ? 1 : 0);
            }
            else
            {
                while (ae2 != ae)
                {
                    if (GetPolyType(ae2!) == PathType.Clip)
                        ae.windCount2 += ae2!.windDx;
                    else if (!IsOpen(ae2!))
                        ae.windCount += ae2!.windDx;
                    ae2 = ae2!.nextInAEL;
                }
            }
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static bool IsValidAelOrder(Active resident, Active newcomer)
        {
            if (newcomer.curX != resident.curX)
                return newcomer.curX > resident.curX;

            // get the turning direction  a1.top, a2.bot, a2.top
            double d = InternalClipper.CrossProduct(resident.top, newcomer.bot, newcomer.top);
            if (d != 0) return (d < 0);

            // edges must be collinear to get here

            // for starting open paths, place them according to
            // the direction they're about to turn
            if (!IsMaxima(resident) && (resident.top.Y > newcomer.top.Y))
            {
                return InternalClipper.CrossProduct(newcomer.bot,
                  resident.top, NextVertex(resident).pt) <= 0;
            }

            if (!IsMaxima(newcomer) && (newcomer.top.Y > resident.top.Y))
            {
                return InternalClipper.CrossProduct(newcomer.bot,
                  newcomer.top, NextVertex(newcomer).pt) >= 0;
            }

            long y = newcomer.bot.Y;
            bool newcomerIsLeft = newcomer.isLeftBound;

            if (resident.bot.Y != y || resident.localMin.vertex.pt.Y != y)
                return newcomer.isLeftBound;
            // resident must also have just been inserted
            if (resident.isLeftBound != newcomerIsLeft)
                return newcomerIsLeft;
            if (InternalClipper.CrossProduct(PrevPrevVertex(resident).pt,
                  resident.bot, resident.top) == 0) return true;
            // compare turning direction of the alternate bound
            return (InternalClipper.CrossProduct(PrevPrevVertex(resident).pt,
              newcomer.bot, PrevPrevVertex(newcomer).pt) > 0) == newcomerIsLeft;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private void InsertLeftEdge(Active ae)
        {
            Active ae2;

            if (_actives == null)
            {
                ae.prevInAEL = null;
                ae.nextInAEL = null;
                _actives = ae;
            }
            else if (!IsValidAelOrder(_actives, ae))
            {
                ae.prevInAEL = null;
                ae.nextInAEL = _actives;
                _actives.prevInAEL = ae;
                _actives = ae;
            }
            else
            {
                ae2 = _actives;
                while (ae2.nextInAEL != null && IsValidAelOrder(ae2.nextInAEL, ae))
                    ae2 = ae2.nextInAEL;
                ae.nextInAEL = ae2.nextInAEL;
                if (ae2.nextInAEL != null) ae2.nextInAEL.prevInAEL = ae;
                ae.prevInAEL = ae2;
                ae2.nextInAEL = ae;
            }
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static void InsertRightEdge(Active ae, Active ae2)
        {
            ae2.nextInAEL = ae.nextInAEL;
            if (ae.nextInAEL != null) ae.nextInAEL.prevInAEL = ae2;
            ae2.prevInAEL = ae;
            ae.nextInAEL = ae2;
        }

        private void InsertLocalMinimaIntoAEL(long botY)
        {
            LocalMinima localMinima;
            Active? leftBound, rightBound;
            // Add any local minima (if any) at BotY ...
            // NB horizontal local minima edges should contain locMin.vertex.prev
            while (HasLocMinAtY(botY))
            {
                localMinima = PopLocalMinima();
                if ((localMinima.vertex.flags & VertexFlags.OpenStart) != VertexFlags.None)
                {
                    leftBound = null;
                }
                else
                {
                    leftBound = new Active
                    {
                        bot = localMinima.vertex.pt,
                        curX = localMinima.vertex.pt.X,
                        windDx = -1,
                        vertexTop = localMinima.vertex.prev,
                        top = localMinima.vertex.prev!.pt,
                        outrec = null,
                        localMin = localMinima
                    };
                    SetDx(leftBound);
                }

                if ((localMinima.vertex.flags & VertexFlags.OpenEnd) != VertexFlags.None)
                {
                    rightBound = null;
                }
                else
                {
                    rightBound = new Active
                    {
                        bot = localMinima.vertex.pt,
                        curX = localMinima.vertex.pt.X,
                        windDx = 1,
                        vertexTop = localMinima.vertex.next, // i.e. ascending
                        top = localMinima.vertex.next!.pt,
                        outrec = null,
                        localMin = localMinima
                    };
                    SetDx(rightBound);
                }

                // Currently LeftB is just the descending bound and RightB is the ascending.
                // Now if the LeftB isn't on the left of RightB then we need swap them.
                if (leftBound != null && rightBound != null)
                {
                    if (IsHorizontal(leftBound))
                    {
                        if (IsHeadingRightHorz(leftBound)) SwapActives(ref leftBound, ref rightBound);
                    }
                    else if (IsHorizontal(rightBound))
                    {
                        if (IsHeadingLeftHorz(rightBound)) SwapActives(ref leftBound, ref rightBound);
                    }
                    else if (leftBound.dx < rightBound.dx)
                        SwapActives(ref leftBound, ref rightBound);
                    //so when leftBound has windDx == 1, the polygon will be oriented
                    //counter-clockwise in Cartesian coords (clockwise with inverted Y).
                }
                else if (leftBound == null)
                {
                    leftBound = rightBound;
                    rightBound = null;
                }

                bool contributing;
                leftBound!.isLeftBound = true;
                InsertLeftEdge(leftBound);

                if (IsOpen(leftBound))
                {
                    SetWindCountForOpenPathEdge(leftBound);
                    contributing = IsContributingOpen(leftBound);
                }
                else
                {
                    SetWindCountForClosedPathEdge(leftBound);
                    contributing = IsContributingClosed(leftBound);
                }

                if (rightBound != null)
                {
                    rightBound.windCount = leftBound.windCount;
                    rightBound.windCount2 = leftBound.windCount2;
                    InsertRightEdge(leftBound, rightBound); ///////

                    if (contributing)
                    {
                        AddLocalMinPoly(leftBound, rightBound, leftBound.bot, true);
                        if (!IsHorizontal(leftBound) && TestJoinWithPrev1(leftBound))
                        {
                            OutPt op = AddOutPt(leftBound.prevInAEL!, leftBound.bot);
                            AddJoin(op, leftBound.outrec!.pts!);
                        }
                    }

                    while (rightBound.nextInAEL != null &&
                           IsValidAelOrder(rightBound.nextInAEL, rightBound))
                    {
                        IntersectEdges(rightBound, rightBound.nextInAEL, rightBound.bot);
                        SwapPositionsInAEL(rightBound, rightBound.nextInAEL);
                    }

                    if (!IsHorizontal(rightBound) && TestJoinWithNext1(rightBound))
                    {
                        OutPt op = AddOutPt(rightBound.nextInAEL!, rightBound.bot);
                        AddJoin(rightBound.outrec!.pts!, op);
                    }

                    if (IsHorizontal(rightBound))
                        PushHorz(rightBound);
                    else
                        InsertScanline(rightBound.top.Y);
                }
                else if (contributing)
                    StartOpenPath(leftBound, leftBound.bot);

                if (IsHorizontal(leftBound))
                    PushHorz(leftBound);
                else
                    InsertScanline(leftBound.top.Y);
            } // while (HasLocMinAtY())
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private void PushHorz(Active ae)
        {
            ae.nextInSEL = _sel;
            _sel = ae;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private bool PopHorz(out Active? ae)
        {
            ae = _sel;
            if (_sel == null) return false;
            _sel = _sel.nextInSEL;
            return true;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static bool TestJoinWithPrev1(Active e)
        {
            // this is marginally quicker than TestJoinWithPrev2
            // but can only be used when e.PrevInAEL.currX is accurate
            return IsHotEdge(e) && !IsOpen(e) &&
                   (e.prevInAEL != null) && (e.prevInAEL.curX == e.curX) &&
                   IsHotEdge(e.prevInAEL) && !IsOpen(e.prevInAEL) &&
                   (InternalClipper.CrossProduct(e.prevInAEL.top, e.bot, e.top) == 0);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static bool TestJoinWithPrev2(Active e, Point64 currPt)
        {
            return IsHotEdge(e) && !IsOpen(e) &&
                   (e.prevInAEL != null) && !IsOpen(e.prevInAEL) &&
                   IsHotEdge(e.prevInAEL) && (e.prevInAEL.top.Y < e.bot.Y) &&
                   (Math.Abs(TopX(e.prevInAEL, currPt.Y) - currPt.X) < 2) &&
                   (InternalClipper.CrossProduct(e.prevInAEL.top, currPt, e.top) == 0);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static bool TestJoinWithNext1(Active e)
        {
            // this is marginally quicker than TestJoinWithNext2
            // but can only be used when e.NextInAEL.currX is accurate
            return IsHotEdge(e) && !IsOpen(e) &&
                   (e.nextInAEL != null) && (e.nextInAEL.curX == e.curX) &&
                   IsHotEdge(e.nextInAEL) && !IsOpen(e.nextInAEL) &&
                   (InternalClipper.CrossProduct(e.nextInAEL.top, e.bot, e.top) == 0);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static bool TestJoinWithNext2(Active e, Point64 currPt)
        {
            return IsHotEdge(e) && !IsOpen(e) &&
                   (e.nextInAEL != null) && !IsOpen(e.nextInAEL) &&
                   IsHotEdge(e.nextInAEL) && (e.nextInAEL.top.Y < e.bot.Y) &&
                   (Math.Abs(TopX(e.nextInAEL, currPt.Y) - currPt.X) < 2) &&
                   (InternalClipper.CrossProduct(e.nextInAEL.top, currPt, e.top) == 0);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private OutPt AddLocalMinPoly(Active ae1, Active ae2, Point64 pt, bool isNew = false)
        {
            OutRec outrec = new OutRec();
            _outrecList.Add(outrec);
            outrec.idx = _outrecList.Count - 1;
            outrec.pts = null;
            outrec.polypath = null;
            ae1.outrec = outrec;
            ae2.outrec = outrec;

            // Setting the owner and inner/outer states (above) is an essential
            // precursor to setting edge 'sides' (ie left and right sides of output
            // polygons) and hence the orientation of output paths ...

            if (IsOpen(ae1))
            {
                outrec.owner = null;
                outrec.isOpen = true;
                if (ae1.windDx > 0)
                    SetSides(outrec, ae1, ae2);
                else
                    SetSides(outrec, ae2, ae1);
            }
            else
            {
                outrec.isOpen = false;
                Active? prevHotEdge = GetPrevHotEdge(ae1);
                // e.windDx is the winding direction of the **input** paths
                // and unrelated to the winding direction of output polygons.
                // Output orientation is determined by e.outrec.frontE which is
                // the ascending edge (see AddLocalMinPoly).
                if (prevHotEdge != null)
                {
                    outrec.owner = prevHotEdge.outrec;
                    if (OutrecIsAscending(prevHotEdge) == isNew)
                        SetSides(outrec, ae2, ae1);
                    else
                        SetSides(outrec, ae1, ae2);
                }
                else
                {
                    outrec.owner = null;
                    if (isNew)
                        SetSides(outrec, ae1, ae2);
                    else
                        SetSides(outrec, ae2, ae1);
                }
            }

            OutPt op = new OutPt(pt, outrec);
            outrec.pts = op;
            return op;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private OutPt? AddLocalMaxPoly(Active ae1, Active ae2, Point64 pt)
        {
            if (IsFront(ae1) == IsFront(ae2))
            {
                if (IsOpenEnd(ae1))
                    SwapFrontBackSides(ae1.outrec!);
                else if (IsOpenEnd(ae2))
                    SwapFrontBackSides(ae2.outrec!);
                else
                {
                    _succeeded = false;
                    return null;
                }
            }

            OutPt result = AddOutPt(ae1, pt);
            if (ae1.outrec == ae2.outrec)
            {
                OutRec outrec = ae1.outrec!;
                outrec.pts = result;
                UncoupleOutRec(ae1);
                if (!IsOpen(ae1))
                    CleanCollinear(outrec);
                result = outrec.pts;

                outrec.owner = GetRealOutRec(outrec.owner);
                if (_using_polytree && outrec.owner is { frontEdge: null })
                    outrec.owner = GetRealOutRec(outrec.owner.owner);
            }
            // and to preserve the winding orientation of outrec ...
            else if (IsOpen(ae1))
            {
                if (ae1.windDx < 0)
                    JoinOutrecPaths(ae1, ae2);
                else
                    JoinOutrecPaths(ae2, ae1);
            }
            else if (ae1.outrec!.idx < ae2.outrec!.idx)
                JoinOutrecPaths(ae1, ae2);
            else
                JoinOutrecPaths(ae2, ae1);

            return result;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static void JoinOutrecPaths(Active ae1, Active ae2)
        {
            // join ae2 outrec path onto ae1 outrec path and then delete ae2 outrec path
            // pointers. (NB Only very rarely do the joining ends share the same coords.)
            OutPt p1Start = ae1.outrec!.pts!;
            OutPt p2Start = ae2.outrec!.pts!;
            OutPt p1End = p1Start.next!;
            OutPt p2End = p2Start.next!;
            if (IsFront(ae1))
            {
                p2End.prev = p1Start;
                p1Start.next = p2End;
                p2Start.next = p1End;
                p1End.prev = p2Start;
                ae1.outrec.pts = p2Start;
                // nb: if IsOpen(e1) then e1 & e2 must be a 'maximaPair'
                ae1.outrec.frontEdge = ae2.outrec.frontEdge;
                if (ae1.outrec.frontEdge != null)
                    ae1.outrec.frontEdge!.outrec = ae1.outrec;
            }
            else
            {
                p1End.prev = p2Start;
                p2Start.next = p1End;
                p1Start.next = p2End;
                p2End.prev = p1Start;

                ae1.outrec.backEdge = ae2.outrec.backEdge;
                if (ae1.outrec.backEdge != null)
                    ae1.outrec.backEdge!.outrec = ae1.outrec;
            }

            // an owner must have a lower idx otherwise
            // it won't be a valid owner
            if (ae2.outrec.owner != null &&
              ae2.outrec.owner.idx < ae1.outrec.idx)
            {
                if (ae1.outrec.owner == null || ae2.outrec.owner.idx < ae1.outrec.owner.idx)
                    ae1.outrec.owner = ae2.outrec.owner;
            }

            // after joining, the ae2.OutRec must contains no vertices ...
            ae2.outrec.frontEdge = null;
            ae2.outrec.backEdge = null;
            ae2.outrec.pts = null;
            ae2.outrec.owner = ae1.outrec; // this may be redundant

            if (IsOpenEnd(ae1))
            {
                ae2.outrec.pts = ae1.outrec.pts;
                ae1.outrec.pts = null;
            }

            // and ae1 and ae2 are maxima and are about to be dropped from the Actives list.
            ae1.outrec = null;
            ae2.outrec = null;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static OutPt AddOutPt(Active ae, Point64 pt)
        {
            OutPt newOp;

            // Outrec.OutPts: a circular doubly-linked-list of POutPt where ...
            // opFront[.Prev]* ~~~> opBack & opBack == opFront.Next
            OutRec outrec = ae.outrec!;
            bool toFront = IsFront(ae);
            OutPt opFront = outrec.pts!;
            OutPt opBack = opFront.next!;

            if (toFront && (pt == opFront.pt)) newOp = opFront;
            else if (!toFront && (pt == opBack.pt)) newOp = opBack;
            else
            {
                newOp = new OutPt(pt, outrec);
                opBack.prev = newOp;
                newOp.prev = opFront;
                newOp.next = opBack;
                opFront.next = newOp;
                if (toFront) outrec.pts = newOp;
            }
            return newOp;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private OutPt StartOpenPath(Active ae, Point64 pt)
        {
            OutRec outrec = new OutRec();
            _outrecList.Add(outrec);
            outrec.idx = _outrecList.Count - 1;
            outrec.owner = null;
            outrec.isOpen = true;
            outrec.pts = null;
            outrec.polypath = null;
            if (ae.windDx > 0)
            {
                outrec.frontEdge = ae;
                outrec.backEdge = null;
            }
            else
            {
                outrec.frontEdge = null;
                outrec.backEdge = ae;
            }

            ae.outrec = outrec;
            OutPt op = new OutPt(pt, outrec);
            outrec.pts = op;
            return op;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private void UpdateEdgeIntoAEL(Active ae)
        {
            ae.bot = ae.top;
            ae.vertexTop = NextVertex(ae);
            ae.top = ae.vertexTop!.pt;
            ae.curX = ae.bot.X;
            SetDx(ae);
            if (IsHorizontal(ae)) return;
            InsertScanline(ae.top.Y);
            if (TestJoinWithPrev1(ae))
            {
                OutPt op1 = AddOutPt(ae.prevInAEL!, ae.bot);
                OutPt op2 = AddOutPt(ae, ae.bot);
                AddJoin(op1, op2);
            }
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static Active? FindEdgeWithMatchingLocMin(Active e)
        {
            Active? result = e.nextInAEL;
            while (result != null)
            {
                if (result.localMin == e.localMin) return result;
                if (!IsHorizontal(result) && e.bot != result.bot) result = null;
                else result = result.nextInAEL;
            }
            result = e.prevInAEL;
            while (result != null)
            {
                if (result.localMin == e.localMin) return result;
                if (!IsHorizontal(result) && e.bot != result.bot) return null;
                result = result.prevInAEL;
            }
            return result;
        }


        private OutPt? IntersectEdges(Active ae1, Active ae2, Point64 pt)
        {
            OutPt? resultOp = null;

            // MANAGE OPEN PATH INTERSECTIONS SEPARATELY ...
            if (_hasOpenPaths && (IsOpen(ae1) || IsOpen(ae2)))
            {
                if (IsOpen(ae1) && IsOpen(ae2)) return null;
                // the following line avoids duplicating quite a bit of code
                if (IsOpen(ae2)) SwapActives(ref ae1, ref ae2);

                if (_cliptype == ClipType.Union)
                {
                    if (!IsHotEdge(ae2)) return null;
                }
                else if (ae2.localMin.polytype == PathType.Subject)
                    return null;

                switch (_fillrule)
                {
                    case FillRule.Positive:
                        if (ae2.windCount != 1) return null; break;
                    case FillRule.Negative:
                        if (ae2.windCount != -1) return null; break;
                    default:
                        if (Math.Abs(ae2.windCount) != 1) return null; break;
                }

                // toggle contribution ...
                if (IsHotEdge(ae1))
                {
                    resultOp = AddOutPt(ae1, pt);
#if USINGZ
          SetZ(ae1, ae2, ref resultOp.pt);
#endif
                    if (IsFront(ae1))
                        ae1.outrec!.frontEdge = null;
                    else
                        ae1.outrec!.backEdge = null;
                    ae1.outrec = null;
                }

                // horizontal edges can pass under open paths at a LocMins
                else if (pt == ae1.localMin.vertex.pt &&
                  !IsOpenEnd(ae1.localMin.vertex))
                {
                    // find the other side of the LocMin and
                    // if it's 'hot' join up with it ...
                    Active? ae3 = FindEdgeWithMatchingLocMin(ae1);
                    if (ae3 != null && IsHotEdge(ae3))
                    {
                        ae1.outrec = ae3.outrec;
                        if (ae1.windDx > 0)
                            SetSides(ae3.outrec!, ae1, ae3);
                        else
                            SetSides(ae3.outrec!, ae3, ae1);
                        return ae3.outrec!.pts;
                    }

                    resultOp = StartOpenPath(ae1, pt);
                }
                else
                    resultOp = StartOpenPath(ae1, pt);

#if USINGZ
        SetZ(ae1, ae2, ref resultOp.pt);
#endif
                return resultOp;
            }

            // MANAGING CLOSED PATHS FROM HERE ON

            // UPDATE WINDING COUNTS...

            int oldE1WindCount, oldE2WindCount;
            if (ae1.localMin.polytype == ae2.localMin.polytype)
            {
                if (_fillrule == FillRule.EvenOdd)
                {
                    oldE1WindCount = ae1.windCount;
                    ae1.windCount = ae2.windCount;
                    ae2.windCount = oldE1WindCount;
                }
                else
                {
                    if (ae1.windCount + ae2.windDx == 0)
                        ae1.windCount = -ae1.windCount;
                    else
                        ae1.windCount += ae2.windDx;
                    if (ae2.windCount - ae1.windDx == 0)
                        ae2.windCount = -ae2.windCount;
                    else
                        ae2.windCount -= ae1.windDx;
                }
            }
            else
            {
                if (_fillrule != FillRule.EvenOdd)
                    ae1.windCount2 += ae2.windDx;
                else
                    ae1.windCount2 = (ae1.windCount2 == 0 ? 1 : 0);
                if (_fillrule != FillRule.EvenOdd)
                    ae2.windCount2 -= ae1.windDx;
                else
                    ae2.windCount2 = (ae2.windCount2 == 0 ? 1 : 0);
            }

            switch (_fillrule)
            {
                case FillRule.Positive:
                    oldE1WindCount = ae1.windCount;
                    oldE2WindCount = ae2.windCount;
                    break;
                case FillRule.Negative:
                    oldE1WindCount = -ae1.windCount;
                    oldE2WindCount = -ae2.windCount;
                    break;
                default:
                    oldE1WindCount = Math.Abs(ae1.windCount);
                    oldE2WindCount = Math.Abs(ae2.windCount);
                    break;
            }

            bool e1WindCountIs0or1 = oldE1WindCount == 0 || oldE1WindCount == 1;
            bool e2WindCountIs0or1 = oldE2WindCount == 0 || oldE2WindCount == 1;

            if ((!IsHotEdge(ae1) && !e1WindCountIs0or1) || (!IsHotEdge(ae2) && !e2WindCountIs0or1)) return null;

            // NOW PROCESS THE INTERSECTION ...

            // if both edges are 'hot' ...
            if (IsHotEdge(ae1) && IsHotEdge(ae2))
            {
                if ((oldE1WindCount != 0 && oldE1WindCount != 1) || (oldE2WindCount != 0 && oldE2WindCount != 1) ||
                    (ae1.localMin.polytype != ae2.localMin.polytype && _cliptype != ClipType.Xor))
                {
                    resultOp = AddLocalMaxPoly(ae1, ae2, pt);
#if USINGZ
          if (resultOp != null)
            SetZ(ae1, ae2, ref resultOp.pt);
#endif
                }
                else if (IsFront(ae1) || (ae1.outrec == ae2.outrec))
                {
                    // this 'else if' condition isn't strictly needed but
                    // it's sensible to split polygons that ony touch at
                    // a common vertex (not at common edges).
                    resultOp = AddLocalMaxPoly(ae1, ae2, pt);
                    OutPt op2 = AddLocalMinPoly(ae1, ae2, pt);
#if USINGZ
          if (resultOp != null)
            SetZ(ae1, ae2, ref resultOp.pt);
          SetZ(ae1, ae2, ref op2.pt);
#endif
                    if (resultOp != null && resultOp.pt == op2.pt &&
                      !IsHorizontal(ae1) && !IsHorizontal(ae2) &&
                      (InternalClipper.CrossProduct(ae1.bot, resultOp.pt, ae2.bot) == 0))
                        AddJoin(resultOp, op2);
                }
                else
                {
                    // can't treat as maxima & minima
                    resultOp = AddOutPt(ae1, pt);
#if USINGZ
          OutPt op2 = AddOutPt(ae2, pt);
          SetZ(ae1, ae2, ref resultOp.pt);
          SetZ(ae1, ae2, ref op2.pt);
#else
                    AddOutPt(ae2, pt);
#endif
                    SwapOutrecs(ae1, ae2);
                }
            }

            // if one or other edge is 'hot' ...
            else if (IsHotEdge(ae1))
            {
                resultOp = AddOutPt(ae1, pt);
#if USINGZ
        SetZ(ae1, ae2, ref resultOp.pt);
#endif
                SwapOutrecs(ae1, ae2);
            }
            else if (IsHotEdge(ae2))
            {
                resultOp = AddOutPt(ae2, pt);
#if USINGZ
        SetZ(ae1, ae2, ref resultOp.pt);
#endif
                SwapOutrecs(ae1, ae2);
            }

            // neither edge is 'hot'
            else
            {
                long e1Wc2, e2Wc2;
                switch (_fillrule)
                {
                    case FillRule.Positive:
                        e1Wc2 = ae1.windCount2;
                        e2Wc2 = ae2.windCount2;
                        break;
                    case FillRule.Negative:
                        e1Wc2 = -ae1.windCount2;
                        e2Wc2 = -ae2.windCount2;
                        break;
                    default:
                        e1Wc2 = Math.Abs(ae1.windCount2);
                        e2Wc2 = Math.Abs(ae2.windCount2);
                        break;
                }

                if (!IsSamePolyType(ae1, ae2))
                {
                    resultOp = AddLocalMinPoly(ae1, ae2, pt);
#if USINGZ
          SetZ(ae1, ae2, ref resultOp.pt);
#endif
                }
                else if (oldE1WindCount == 1 && oldE2WindCount == 1)
                {
                    resultOp = null;
                    switch (_cliptype)
                    {
                        case ClipType.Union:
                            if (e1Wc2 > 0 && e2Wc2 > 0) return null;
                            resultOp = AddLocalMinPoly(ae1, ae2, pt);
                            break;

                        case ClipType.Difference:
                            if (((GetPolyType(ae1) == PathType.Clip) && (e1Wc2 > 0) && (e2Wc2 > 0)) ||
                                ((GetPolyType(ae1) == PathType.Subject) && (e1Wc2 <= 0) && (e2Wc2 <= 0)))
                            {
                                resultOp = AddLocalMinPoly(ae1, ae2, pt);
                            }

                            break;

                        case ClipType.Xor:
                            resultOp = AddLocalMinPoly(ae1, ae2, pt);
                            break;

                        default: // ClipType.Intersection:
                            if (e1Wc2 <= 0 || e2Wc2 <= 0) return null;
                            resultOp = AddLocalMinPoly(ae1, ae2, pt);
                            break;
                    }
#if USINGZ
          if (resultOp != null) SetZ(ae1, ae2, ref resultOp.pt);
#endif
                }
            }

            return resultOp;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private void DeleteFromAEL(Active ae)
        {
            Active? prev = ae.prevInAEL;
            Active? next = ae.nextInAEL;
            if (prev == null && next == null && (ae != _actives)) return; // already deleted
            if (prev != null)
                prev.nextInAEL = next;
            else
                _actives = next;
            if (next != null) next.prevInAEL = prev;
            // delete &ae;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private void AdjustCurrXAndCopyToSEL(long topY)
        {
            Active? ae = _actives;
            _sel = ae;
            while (ae != null)
            {
                ae.prevInSEL = ae.prevInAEL;
                ae.nextInSEL = ae.nextInAEL;
                ae.jump = ae.nextInSEL;
                ae.curX = TopX(ae, topY);
                // NB don't update ae.curr.Y yet (see AddNewIntersectNode)
                ae = ae.nextInAEL;
            }
        }

        protected void ExecuteInternal(ClipType ct, FillRule fillRule)
        {
            if (ct == ClipType.None) return;
            _fillrule = fillRule;
            _cliptype = ct;
            Reset();
            if (!PopScanline(out long y)) return;
            while (_succeeded)
            {
                InsertLocalMinimaIntoAEL(y);
                Active? ae;
                while (PopHorz(out ae)) DoHorizontal(ae!);
                ConvertHorzTrialsToJoins();
                _currentBotY = y; // bottom of scanbeam
                if (!PopScanline(out y))
                    break; // y new top of scanbeam
                DoIntersections(y);
                DoTopOfScanbeam(y);
                while (PopHorz(out ae)) DoHorizontal(ae!);
            }

            if (_succeeded) ProcessJoinList();
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private void DoIntersections(long topY)
        {
            if (BuildIntersectList(topY))
            {
                ProcessIntersectList();
                DisposeIntersectNodes();
            }
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private void DisposeIntersectNodes()
        {
            _intersectList.Clear();
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private void AddNewIntersectNode(Active ae1, Active ae2, long topY)
        {
            if (!InternalClipper.GetIntersectPt(
              ae1.bot, ae1.top, ae2.bot, ae2.top, out Point64 ip))
                ip = new Point64(ae1.curX, topY);

            if (ip.Y > _currentBotY || ip.Y < topY)
            {
                double absDx1 = Math.Abs(ae1.dx);
                double absDx2 = Math.Abs(ae2.dx);
                if (absDx1 > 100 && absDx2 > 100)
                {
                    if (absDx1 > absDx2)
                        ip = InternalClipper.GetClosestPtOnSegment(ip, ae1.bot, ae1.top);
                    else
                        ip = InternalClipper.GetClosestPtOnSegment(ip, ae2.bot, ae2.top);
                }
                else if (absDx1 > 100)
                    ip = InternalClipper.GetClosestPtOnSegment(ip, ae1.bot, ae1.top);
                else if (absDx2 > 100)
                    ip = InternalClipper.GetClosestPtOnSegment(ip, ae2.bot, ae2.top);
                else
                {
                    if (ip.Y < topY) ip.Y = topY;
                    else ip.Y = _currentBotY;
                    if (absDx1 < absDx2) ip.X = TopX(ae1, ip.Y);
                    else ip.X = TopX(ae2, topY);
                }
            }
            IntersectNode node = new IntersectNode(ip, ae1, ae2);
            _intersectList.Add(node);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static Active? ExtractFromSEL(Active ae)
        {
            Active? res = ae.nextInSEL;
            if (res != null)
                res.prevInSEL = ae.prevInSEL;
            ae.prevInSEL!.nextInSEL = res;
            return res;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static void Insert1Before2InSEL(Active ae1, Active ae2)
        {
            ae1.prevInSEL = ae2.prevInSEL;
            if (ae1.prevInSEL != null)
                ae1.prevInSEL.nextInSEL = ae1;
            ae1.nextInSEL = ae2;
            ae2.prevInSEL = ae1;
        }

        private bool BuildIntersectList(long topY)
        {
            if (_actives == null || _actives.nextInAEL == null) return false;

            // Calculate edge positions at the top of the current scanbeam, and from this
            // we will determine the intersections required to reach these new positions.
            AdjustCurrXAndCopyToSEL(topY);

            // Find all edge intersections in the current scanbeam using a stable merge
            // sort that ensures only adjacent edges are intersecting. Intersect info is
            // stored in FIntersectList ready to be processed in ProcessIntersectList.
            // Re merge sorts see https://stackoverflow.com/a/46319131/359538

            Active? left = _sel, right, lEnd, rEnd, currBase, prevBase, tmp;

            while (left!.jump != null)
            {
                prevBase = null;
                while (left != null && left.jump != null)
                {
                    currBase = left;
                    right = left.jump;
                    lEnd = right;
                    rEnd = right.jump;
                    left.jump = rEnd;
                    while (left != lEnd && right != rEnd)
                    {
                        if (right!.curX < left!.curX)
                        {
                            tmp = right.prevInSEL!;
                            for (; ; )
                            {
                                AddNewIntersectNode(tmp, right, topY);
                                if (tmp == left) break;
                                tmp = tmp.prevInSEL!;
                            }

                            tmp = right;
                            right = ExtractFromSEL(tmp);
                            lEnd = right;
                            Insert1Before2InSEL(tmp, left);
                            if (left == currBase)
                            {
                                currBase = tmp;
                                currBase.jump = rEnd;
                                if (prevBase == null) _sel = currBase;
                                else prevBase.jump = currBase;
                            }
                        }
                        else left = left.nextInSEL;
                    }

                    prevBase = currBase;
                    left = rEnd;
                }
                left = _sel;
            }

            return _intersectList.Count > 0;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private void ProcessIntersectList()
        {
            // We now have a list of intersections required so that edges will be
            // correctly positioned at the top of the scanbeam. However, it's important
            // that edge intersections are processed from the bottom up, but it's also
            // crucial that intersections only occur between adjacent edges.

            // First we do a quicksort so intersections proceed in a bottom up order ...
            _intersectList.Sort(new IntersectListSort());

            // Now as we process these intersections, we must sometimes adjust the order
            // to ensure that intersecting edges are always adjacent ...
            for (int i = 0; i < _intersectList.Count; ++i)
            {
                if (!EdgesAdjacentInAEL(_intersectList[i]))
                {
                    int j = i + 1;
                    while (!EdgesAdjacentInAEL(_intersectList[j])) j++;
                    // swap
                    (_intersectList[j], _intersectList[i]) =
                      (_intersectList[i], _intersectList[j]);
                }

                IntersectNode node = _intersectList[i];
                IntersectEdges(node.edge1, node.edge2, node.pt);
                SwapPositionsInAEL(node.edge1, node.edge2);

                if (TestJoinWithPrev2(node.edge2, node.pt))
                {
                    OutPt op1 = AddOutPt(node.edge2.prevInAEL!, node.pt);
                    OutPt op2 = AddOutPt(node.edge2, node.pt);
                    if (op1 != op2) AddJoin(op1, op2);
                }
                else if (TestJoinWithNext2(node.edge1, node.pt))
                {
                    OutPt op1 = AddOutPt(node.edge1, node.pt);
                    OutPt op2 = AddOutPt(node.edge1.nextInAEL!, node.pt);
                    if (op1 != op2) AddJoin(op1, op2);
                }
            }
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private void SwapPositionsInAEL(Active ae1, Active ae2)
        {
            // preconditon: ae1 must be immediately to the left of ae2
            Active? next = ae2.nextInAEL;
            if (next != null) next.prevInAEL = ae1;
            Active? prev = ae1.prevInAEL;
            if (prev != null) prev.nextInAEL = ae2;
            ae2.prevInAEL = prev;
            ae2.nextInAEL = ae1;
            ae1.prevInAEL = ae2;
            ae1.nextInAEL = next;
            if (ae2.prevInAEL == null) _actives = ae2;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static bool ResetHorzDirection(Active horz, Active? maxPair,
            out long leftX, out long rightX)
        {
            if (horz.bot.X == horz.top.X)
            {
                // the horizontal edge is going nowhere ...
                leftX = horz.curX;
                rightX = horz.curX;
                Active? ae = horz.nextInAEL;
                while (ae != null && ae != maxPair) ae = ae.nextInAEL;
                return ae != null;
            }

            if (horz.curX < horz.top.X)
            {
                leftX = horz.curX;
                rightX = horz.top.X;
                return true;
            }
            leftX = horz.top.X;
            rightX = horz.curX;
            return false; // right to left
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static bool HorzIsSpike(Active horz)
        {
            Point64 nextPt = NextVertex(horz).pt;
            return (horz.bot.X < horz.top.X) != (horz.top.X < nextPt.X);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static void TrimHorz(Active horzEdge, bool preserveCollinear)
        {
            bool wasTrimmed = false;
            Point64 pt = NextVertex(horzEdge).pt;

            while (pt.Y == horzEdge.top.Y)
            {
                // always trim 180 deg. spikes (in closed paths)
                // but otherwise break if preserveCollinear = true
                if (preserveCollinear &&
                (pt.X < horzEdge.top.X) != (horzEdge.bot.X < horzEdge.top.X))
                    break;

                horzEdge.vertexTop = NextVertex(horzEdge);
                horzEdge.top = pt;
                wasTrimmed = true;
                if (IsMaxima(horzEdge)) break;
                pt = NextVertex(horzEdge).pt;
            }
            if (wasTrimmed) SetDx(horzEdge); // +/-infinity
        }

        private void DoHorizontal(Active horz)
        /*******************************************************************************
         * Notes: Horizontal edges (HEs) at scanline intersections (i.e. at the top or    *
         * bottom of a scanbeam) are processed as if layered.The order in which HEs     *
         * are processed doesn't matter. HEs intersect with the bottom vertices of      *
         * other HEs[#] and with non-horizontal edges [*]. Once these intersections     *
         * are completed, intermediate HEs are 'promoted' to the next edge in their     *
         * bounds, and they in turn may be intersected[%] by other HEs.                 *
         *                                                                              *
         * eg: 3 horizontals at a scanline:    /   |                     /           /  *
         *              |                     /    |     (HE3)o ========%========== o   *
         *              o ======= o(HE2)     /     |         /         /                *
         *          o ============#=========*======*========#=========o (HE1)           *
         *         /              |        /       |       /                            *
         *******************************************************************************/
        {
            Point64 pt;
            bool horzIsOpen = IsOpen(horz);
            long Y = horz.bot.Y;

            Vertex? vertex_max = null;
            Active? maxPair = null;

            if (!horzIsOpen)
            {
                vertex_max = GetCurrYMaximaVertex(horz);
                if (vertex_max != null)
                {
                    maxPair = GetHorzMaximaPair(horz, vertex_max);
                    // remove 180 deg.spikes and also simplify
                    // consecutive horizontals when PreserveCollinear = true
                    if (vertex_max != horz.vertexTop)
                        TrimHorz(horz, PreserveCollinear);
                }
            }

            bool isLeftToRight =
              ResetHorzDirection(horz, maxPair, out long leftX, out long rightX);

            if (IsHotEdge(horz))
                AddOutPt(horz, new Point64(horz.curX, Y));

            OutPt? op;
            for (; ; )
            {
                if (horzIsOpen && IsMaxima(horz) && !IsOpenEnd(horz))
                {
                    vertex_max = GetCurrYMaximaVertex(horz);
                    if (vertex_max != null)
                        maxPair = GetHorzMaximaPair(horz, vertex_max);
                }

                // loops through consec. horizontal edges (if open)
                Active? ae;
                if (isLeftToRight) ae = horz.nextInAEL;
                else ae = horz.prevInAEL;

                while (ae != null)
                {
                    if (ae == maxPair)
                    {
                        if (IsHotEdge(horz))
                        {
                            while (horz.vertexTop != ae.vertexTop)
                            {
                                AddOutPt(horz, horz.top);
                                UpdateEdgeIntoAEL(horz);
                            }
                            op = AddLocalMaxPoly(horz, ae, horz.top);
                            if (op != null && !IsOpen(horz) && op.pt == horz.top)
                                AddTrialHorzJoin(op);
                        }

                        DeleteFromAEL(ae);
                        DeleteFromAEL(horz);
                        return;
                    }

                    // if horzEdge is a maxima, keep going until we reach
                    // its maxima pair, otherwise check for break conditions
                    if (vertex_max != horz.vertexTop || IsOpenEnd(horz))
                    {
                        // otherwise stop when 'ae' is beyond the end of the horizontal line
                        if ((isLeftToRight && ae.curX > rightX) ||
                            (!isLeftToRight && ae.curX < leftX)) break;

                        if (ae.curX == horz.top.X && !IsHorizontal(ae))
                        {
                            pt = NextVertex(horz).pt;
                            if (isLeftToRight)
                            {
                                // with open paths we'll only break once past horz's end
                                if (IsOpen(ae) && !IsSamePolyType(ae, horz) && !IsHotEdge(ae))
                                {
                                    if (TopX(ae, pt.Y) > pt.X) break;
                                }
                                // otherwise we'll only break when horz's outslope is greater than e's
                                else if (TopX(ae, pt.Y) >= pt.X) break;
                            }
                            else
                            {
                                // with open paths we'll only break once past horz's end
                                if (IsOpen(ae) && !IsSamePolyType(ae, horz) && !IsHotEdge(ae))
                                {
                                    if (TopX(ae, pt.Y) < pt.X) break;
                                }
                                // otherwise we'll only break when horz's outslope is greater than e's
                                else if (TopX(ae, pt.Y) <= pt.X) break;
                            }
                        }
                    }

                    pt = new Point64(ae.curX, Y);

                    if (isLeftToRight)
                    {
                        op = IntersectEdges(horz, ae, pt);
                        SwapPositionsInAEL(horz, ae);

                        if (IsHotEdge(horz) && op != null &&
                          !IsOpen(horz) && op.pt == pt)
                            AddTrialHorzJoin(op);

                        if (!IsHorizontal(ae) && TestJoinWithPrev1(ae))
                        {
                            op = AddOutPt(ae.prevInAEL!, pt);
                            OutPt op2 = AddOutPt(ae, pt);
                            AddJoin(op, op2);
                        }

                        horz.curX = ae.curX;
                        ae = horz.nextInAEL;
                    }
                    else
                    {
                        op = IntersectEdges(ae, horz, pt);
                        SwapPositionsInAEL(ae, horz);

                        if (IsHotEdge(horz) && op != null &&
                          !IsOpen(horz) && op.pt == pt)
                            AddTrialHorzJoin(op);

                        if (!IsHorizontal(ae) && TestJoinWithNext1(ae))
                        {
                            op = AddOutPt(ae, pt);
                            OutPt op2 = AddOutPt(ae.nextInAEL!, pt);
                            AddJoin(op, op2);
                        }

                        horz.curX = ae.curX;
                        ae = horz.prevInAEL;
                    }
                } // we've reached the end of this horizontal

                // check if we've finished looping through consecutive horizontals
                if (horzIsOpen && IsOpenEnd(horz))
                {
                    if (IsHotEdge(horz))
                    {
                        AddOutPt(horz, horz.top);
                        if (IsFront(horz))
                            horz.outrec!.frontEdge = null;
                        else
                            horz.outrec!.backEdge = null;
                    }
                    horz.outrec = null;
                    DeleteFromAEL(horz); // ie open at top
                    return;
                }

                if (NextVertex(horz).pt.Y != horz.top.Y) break;

                // there must be a following (consecutive) horizontal
                if (IsHotEdge(horz))
                    AddOutPt(horz, horz.top);
                UpdateEdgeIntoAEL(horz);

                if (PreserveCollinear && !horzIsOpen && HorzIsSpike(horz))
                    TrimHorz(horz, true);

                isLeftToRight = ResetHorzDirection(horz, maxPair, out leftX, out rightX);

            } // end for loop and end of (possible consecutive) horizontals

            if (IsHotEdge(horz))
            {
                op = AddOutPt(horz, horz.top);
                if (!IsOpen(horz))
                    AddTrialHorzJoin(op);
            }
            else
                op = null;

            if ((horzIsOpen && !IsOpenEnd(horz)) ||
              (!horzIsOpen && vertex_max != horz.vertexTop))
            {
                UpdateEdgeIntoAEL(horz); // this is the end of an intermediate horiz.
                if (IsOpen(horz)) return;

                if (isLeftToRight && TestJoinWithNext1(horz))
                {
                    OutPt op2 = AddOutPt(horz.nextInAEL!, horz.bot);
                    AddJoin(op!, op2);
                }
                else if (!isLeftToRight && TestJoinWithPrev1(horz))
                {
                    OutPt op2 = AddOutPt(horz.prevInAEL!, horz.bot);
                    AddJoin(op2, op!);
                }
            }
            else if (IsHotEdge(horz))
                AddLocalMaxPoly(horz, maxPair!, horz.top);
            else
            {
                DeleteFromAEL(maxPair!);
                DeleteFromAEL(horz);
            }
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private void DoTopOfScanbeam(long y)
        {
            _sel = null; // sel_ is reused to flag horizontals (see PushHorz below)
            Active? ae = _actives;
            while (ae != null)
            {
                // NB 'ae' will never be horizontal here
                if (ae.top.Y == y)
                {
                    ae.curX = ae.top.X;
                    if (IsMaxima(ae))
                    {
                        ae = DoMaxima(ae); // TOP OF BOUND (MAXIMA)
                        continue;
                    }

                    // INTERMEDIATE VERTEX ...
                    if (IsHotEdge(ae))
                        AddOutPt(ae, ae.top);
                    UpdateEdgeIntoAEL(ae);
                    if (IsHorizontal(ae))
                        PushHorz(ae); // horizontals are processed later
                }
                else // i.e. not the top of the edge
                    ae.curX = TopX(ae, y);

                ae = ae.nextInAEL;
            }
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private Active? DoMaxima(Active ae)
        {
            Active? prevE;
            Active? nextE, maxPair;
            prevE = ae.prevInAEL;
            nextE = ae.nextInAEL;

            if (IsOpenEnd(ae))
            {
                if (IsHotEdge(ae)) AddOutPt(ae, ae.top);
                if (!IsHorizontal(ae))
                {
                    if (IsHotEdge(ae))
                    {
                        if (IsFront(ae))
                            ae.outrec!.frontEdge = null;
                        else
                            ae.outrec!.backEdge = null;
                        ae.outrec = null;
                    }
                    DeleteFromAEL(ae);
                }
                return nextE;
            }

            maxPair = GetMaximaPair(ae);
            if (maxPair == null) return nextE; // eMaxPair is horizontal

            // only non-horizontal maxima here.
            // process any edges between maxima pair ...
            while (nextE != maxPair)
            {
                IntersectEdges(ae, nextE!, ae.top);
                SwapPositionsInAEL(ae, nextE!);
                nextE = ae.nextInAEL;
            }

            if (IsOpen(ae))
            {
                if (IsHotEdge(ae))
                    AddLocalMaxPoly(ae, maxPair, ae.top);
                DeleteFromAEL(maxPair);
                DeleteFromAEL(ae);
                return (prevE != null ? prevE.nextInAEL : _actives);
            }

            // here ae.nextInAel == ENext == EMaxPair ...
            if (IsHotEdge(ae))
                AddLocalMaxPoly(ae, maxPair, ae.top);

            DeleteFromAEL(ae);
            DeleteFromAEL(maxPair);
            return (prevE != null ? prevE.nextInAEL : _actives);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static bool IsValidPath(OutPt op)
        {
            return (op.next != op);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static bool PtsReallyClose(Point64 pt1, Point64 pt2)
        {
            return (Math.Abs(pt1.X - pt2.X) < 2) && (Math.Abs(pt1.Y - pt2.Y) < 2);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static bool IsVerySmallTriangle(OutPt op)
        {
            return op.next!.next == op.prev &&
              (PtsReallyClose(op.prev.pt, op.next.pt) ||
                  PtsReallyClose(op.pt, op.next.pt) ||
                  PtsReallyClose(op.pt, op.prev.pt));
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static bool IsValidClosedPath(OutPt? op)
        {
            return (op != null && op.next != op &&
              (op.next != op.prev || !IsVerySmallTriangle(op)));
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static bool ValueBetween(long val, long end1, long end2)
        {
            // NB accommodates axis aligned between where end1 == end2
            return ((val != end1) == (val != end2)) &&
              ((val > end1) == (val < end2));
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static bool ValueEqualOrBetween(long val, long end1, long end2)
        {
            return (val == end1) || (val == end2) || ((val > end1) == (val < end2));
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static bool PointEqualOrBetween(Point64 pt, Point64 corner1, Point64 corner2)
        {
            // NB points may not be collinear
            return
              ValueEqualOrBetween(pt.X, corner1.X, corner2.X) &&
              ValueEqualOrBetween(pt.Y, corner1.Y, corner2.Y);
        }

        private static bool PointBetween(Point64 pt, Point64 corner1, Point64 corner2)
        {
            // NB points may not be collinear
            return
              ValueBetween(pt.X, corner1.X, corner2.X) &&
              ValueBetween(pt.Y, corner1.Y, corner2.Y);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static bool CollinearSegsOverlap(Point64 seg1a, Point64 seg1b,
          Point64 seg2a, Point64 seg2b)
        {
            // precondition: seg1 and seg2 are collinear      
            if (seg1a.X == seg1b.X)
            {
                if (seg2a.X != seg1a.X || seg2a.X != seg2b.X) return false;
            }
            else if (seg1a.X < seg1b.X)
            {
                if (seg2a.X < seg2b.X)
                {
                    if (seg2a.X >= seg1b.X || seg2b.X <= seg1a.X) return false;
                }
                else
                {
                    if (seg2b.X >= seg1b.X || seg2a.X <= seg1a.X) return false;
                }
            }
            else
            {
                if (seg2a.X < seg2b.X)
                {
                    if (seg2a.X >= seg1a.X || seg2b.X <= seg1b.X) return false;
                }
                else
                {
                    if (seg2b.X >= seg1a.X || seg2a.X <= seg1b.X) return false;
                }
            }

            if (seg1a.Y == seg1b.Y)
            {
                if (seg2a.Y != seg1a.Y || seg2a.Y != seg2b.Y) return false;
            }
            else if (seg1a.Y < seg1b.Y)
            {
                if (seg2a.Y < seg2b.Y)
                {
                    if (seg2a.Y >= seg1b.Y || seg2b.Y <= seg1a.Y) return false;
                }
                else
                {
                    if (seg2b.Y >= seg1b.Y || seg2a.Y <= seg1a.Y) return false;
                }
            }
            else
            {
                if (seg2a.Y < seg2b.Y)
                {
                    if (seg2a.Y >= seg1a.Y || seg2b.Y <= seg1b.Y) return false;
                }
                else
                {
                    if (seg2b.Y >= seg1a.Y || seg2a.Y <= seg1b.Y) return false;
                }
            }
            return true;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static bool HorzEdgesOverlap(long x1a, long x1b, long x2a, long x2b)
        {
            const long minOverlap = 2;
            if (x1a > x1b + minOverlap)
            {
                if (x2a > x2b + minOverlap)
                    return !((x1a <= x2b) || (x2a <= x1b));
                return !((x1a <= x2a) || (x2b <= x1b));
            }

            if (x1b > x1a + minOverlap)
            {
                if (x2a > x2b + minOverlap)
                    return !((x1b <= x2b) || (x2a <= x1a));
                return !((x1b <= x2a) || (x2b <= x1a));
            }
            return false;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static Joiner? GetHorzTrialParent(OutPt op)
        {
            Joiner? joiner = op.joiner;
            while (joiner != null)
            {
                if (joiner.op1 == op)
                {
                    if (joiner.next1 != null &&
                        joiner.next1.idx < 0) return joiner;
                    joiner = joiner.next1;
                }
                else
                {
                    if (joiner.next2 != null &&
                        joiner.next2.idx < 0) return joiner;
                    joiner = joiner.next1;
                }
            }
            return joiner;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static bool OutPtInTrialHorzList(OutPt op)
        {
            return op.joiner != null &&
             ((op.joiner.idx < 0) || GetHorzTrialParent(op) != null);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private bool ValidateClosedPathEx(ref OutPt? op)
        {
            if (IsValidClosedPath(op)) return true;
            if (op != null)
                SafeDisposeOutPts(ref op);
            return false;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static OutPt InsertOp(Point64 pt, OutPt insertAfter)
        {
            OutPt result = new OutPt(pt, insertAfter.outrec)
            { next = insertAfter.next };
            insertAfter.next!.prev = result;
            insertAfter.next = result;
            result.prev = insertAfter;
            return result;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static OutPt? DisposeOutPt(OutPt op)
        {
            OutPt? result = (op.next == op ? null : op.next);
            op.prev.next = op.next;
            op.next!.prev = op.prev;
            // op == null;
            return result;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private void SafeDisposeOutPts(ref OutPt op)
        {
            OutRec? outRec = GetRealOutRec(op.outrec);
            if (outRec!.frontEdge != null)
                outRec.frontEdge.outrec = null;
            if (outRec.backEdge != null)
                outRec.backEdge.outrec = null;

            op.prev.next = null;
            OutPt? op2 = op;
            while (op2 != null)
            {
                SafeDeleteOutPtJoiners(op2);
                op2 = op2.next;
            }
            outRec.pts = null;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private void SafeDeleteOutPtJoiners(OutPt op)
        {
            Joiner? joiner = op.joiner;
            if (joiner == null) return;

            while (joiner != null)
            {
                if (joiner.idx < 0)
                    DeleteTrialHorzJoin(op);
                else if (_horzJoiners != null)
                {
                    if (OutPtInTrialHorzList(joiner.op1))
                        DeleteTrialHorzJoin(joiner.op1);
                    if (OutPtInTrialHorzList(joiner.op2!))
                        DeleteTrialHorzJoin(joiner.op2!);
                    DeleteJoin(joiner);
                }
                else
                    DeleteJoin(joiner);
                joiner = op.joiner;
            }
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private void AddTrialHorzJoin(OutPt op)
        {
            // make sure 'op' isn't added more than once
            if (!op.outrec.isOpen && !OutPtInTrialHorzList(op))
                _horzJoiners = new Joiner(op, null, _horzJoiners);

        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static Joiner? FindTrialJoinParent(ref Joiner joiner, OutPt op)
        {
            Joiner? parent = joiner;
            while (parent != null)
            {
                if (op == parent.op1)
                {
                    if (parent.next1 != null && parent.next1.idx < 0)
                    {
                        joiner = parent.next1;
                        return parent;
                    }
                    parent = parent.next1;
                }
                else
                {
                    if (parent.next2 != null && parent.next2.idx < 0)
                    {
                        joiner = parent.next2;
                        return parent;
                    }
                    parent = parent.next2;
                }
            }
            return null;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private void DeleteTrialHorzJoin(OutPt op)
        {
            if (_horzJoiners == null) return;

            Joiner? joiner = op.joiner;
            Joiner? parentH, parentOp = null;
            while (joiner != null)
            {
                if (joiner.idx < 0)
                {
                    // first remove joiner from FHorzTrials
                    if (joiner == _horzJoiners)
                        _horzJoiners = joiner.nextH;
                    else
                    {
                        parentH = _horzJoiners;
                        while (parentH!.nextH != joiner)
                            parentH = parentH.nextH;
                        parentH.nextH = joiner.nextH;
                    }

                    // now remove joiner from op's joiner list
                    if (parentOp == null)
                    {
                        // joiner must be first one in list
                        op.joiner = joiner.next1;
                        // joiner == null;
                        joiner = op.joiner;
                    }
                    else
                    {
                        // the trial joiner isn't first
                        if (op == parentOp.op1)
                            parentOp.next1 = joiner.next1;
                        else
                            parentOp.next2 = joiner.next1;
                        // joiner = null;
                        joiner = parentOp;
                    }
                }
                else
                {
                    // not a trial join so look further along the linked list
                    parentOp = FindTrialJoinParent(ref joiner, op);
                    if (parentOp == null) break;
                }
                // loop in case there's more than one trial join
            }
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static bool GetHorzExtendedHorzSeg(ref OutPt op, out OutPt op2)
        {
            OutRec outRec = GetRealOutRec(op.outrec)!;
            op2 = op;
            if (outRec.frontEdge != null)
            {
                while (op.prev != outRec.pts &&
                  op.prev.pt.Y == op.pt.Y) op = op.prev;
                while (op2 != outRec.pts &&
                  op2.next!.pt.Y == op2.pt.Y) op2 = op2.next;
                return op2 != op;
            }

            while (op.prev != op2 && op.prev.pt.Y == op.pt.Y)
                op = op.prev;
            while (op2.next != op && op2.next!.pt.Y == op2.pt.Y)
                op2 = op2.next;
            return op2 != op && op2.next != op;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private void ConvertHorzTrialsToJoins()
        {
            while (_horzJoiners != null)
            {
                Joiner? joiner = _horzJoiners;
                _horzJoiners = _horzJoiners.nextH;
                OutPt op1a = joiner.op1;
                if (op1a.joiner == joiner)
                {
                    op1a.joiner = joiner.next1;
                }
                else
                {
                    Joiner joinerParent = FindJoinParent(joiner, op1a);
                    if (joinerParent.op1 == op1a)
                        joinerParent.next1 = joiner.next1;
                    else
                        joinerParent.next2 = joiner.next1;
                }
                // joiner = null;

                if (!GetHorzExtendedHorzSeg(ref op1a, out OutPt op1b))
                {
                    if (op1a.outrec.frontEdge == null)
                        CleanCollinear(op1a.outrec);
                    continue;
                }

                OutPt op2a;
                bool joined = false;
                joiner = _horzJoiners;
                while (joiner != null)
                {
                    op2a = joiner.op1;
                    if (GetHorzExtendedHorzSeg(ref op2a, out OutPt op2b) &&
                      HorzEdgesOverlap(op1a.pt.X, op1b.pt.X, op2a.pt.X, op2b.pt.X))
                    {
                        // overlap found so promote to a 'real' join
                        joined = true;
                        if (op1a.pt == op2b.pt)
                            AddJoin(op1a, op2b);
                        else if (op1b.pt == op2a.pt)
                            AddJoin(op1b, op2a);
                        else if (op1a.pt == op2a.pt)
                            AddJoin(op1a, op2a);
                        else if (op1b.pt == op2b.pt)
                            AddJoin(op1b, op2b);
                        else if (ValueBetween(op1a.pt.X, op2a.pt.X, op2b.pt.X))
                            AddJoin(op1a, InsertOp(op1a.pt, op2a));
                        else if (ValueBetween(op1b.pt.X, op2a.pt.X, op2b.pt.X))
                            AddJoin(op1b, InsertOp(op1b.pt, op2a));
                        else if (ValueBetween(op2a.pt.X, op1a.pt.X, op1b.pt.X))
                            AddJoin(op2a, InsertOp(op2a.pt, op1a));
                        else if (ValueBetween(op2b.pt.X, op1a.pt.X, op1b.pt.X))
                            AddJoin(op2b, InsertOp(op2b.pt, op1a));
                        break;
                    }
                    joiner = joiner.nextH;
                }
                if (!joined)
                    CleanCollinear(op1a.outrec);
            }
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private void AddJoin(OutPt op1, OutPt op2)
        {
            if ((op1.outrec == op2.outrec) && ((op1 == op2) ||
              // unless op1.next or op1.prev crosses the start-end divide
              // don't waste time trying to join adjacent vertices
              ((op1.next == op2) && (op1 != op1.outrec.pts)) ||
              ((op2.next == op1) && (op2 != op1.outrec.pts)))) return;

            Joiner joiner = new Joiner(op1, op2, null) { idx = _joinerList.Count };
            _joinerList.Add(joiner);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static Joiner FindJoinParent(Joiner joiner, OutPt op)
        {
            Joiner result = op.joiner!;
            for (; ; )
            {
                if (op == result.op1)
                {
                    if (result.next1 == joiner) return result;
                    result = result.next1!;
                }
                else
                {
                    if (result.next2 == joiner) return result;
                    result = result.next2!;
                }
            }
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private void DeleteJoin(Joiner joiner)
        {
            // This method deletes a single join, and it doesn't check for or
            // delete trial horz. joins. For that, use the following method.
            OutPt op1 = joiner.op1, op2 = joiner.op2!;

            Joiner parentJnr;
            if (op1.joiner != joiner)
            {
                parentJnr = FindJoinParent(joiner, op1);
                if (parentJnr.op1 == op1)
                    parentJnr.next1 = joiner.next1;
                else
                    parentJnr.next2 = joiner.next1;
            }
            else
                op1.joiner = joiner.next1;

            if (op2.joiner != joiner)
            {
                parentJnr = FindJoinParent(joiner, op2);
                if (parentJnr.op1 == op2)
                    parentJnr.next1 = joiner.next2;
                else
                    parentJnr.next2 = joiner.next2;
            }
            else
                op2.joiner = joiner.next2;

            _joinerList[joiner.idx] = null;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private void ProcessJoinList()
        {
            // NB can't use foreach here because list may 
            // contain nulls which can't be enumerated
            for (int i = 0; i < _joinerList.Count; i++)
            {
                Joiner? j = _joinerList[i];
                if (j == null) continue;
                OutRec outrec = ProcessJoin(j);
                CleanCollinear(outrec);
            }
            _joinerList.Clear();
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static bool CheckDisposeAdjacent(ref OutPt op, OutPt guard, OutRec outRec)
        {
            bool result = false;
            while (op.prev != op)
            {
                if (op.pt == op.prev.pt && op != guard &&
                  op.prev.joiner != null && op.joiner == null)
                {
                    if (op == outRec.pts) outRec.pts = op.prev;
                    op = DisposeOutPt(op)!;
                    op = op.prev;
                }
                else
                    break;
            }

            while (op.next != op)
            {
                if (op.pt == op.next!.pt && op != guard &&
                op.next.joiner != null && op.joiner == null)
                {
                    if (op == outRec.pts) outRec.pts = op.prev;
                    op = DisposeOutPt(op)!;
                    op = op.prev;
                }
                else
                    break;
            }
            return result;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static double DistanceFromLineSqrd(Point64 pt, Point64 linePt1, Point64 linePt2)
        {
            // perpendicular distance of point (x0,y0) = (a*x0 + b*y0 + C)/Sqrt(a*a + b*b)
            // where ax + by +c = 0 is the equation of the line
            // see https://en.wikipedia.org/wiki/Distance_from_a_point_to_a_line
            double a = (linePt1.Y - linePt2.Y);
            double b = (linePt2.X - linePt1.X);
            double c = a * linePt1.X + b * linePt1.Y;
            double q = a * pt.X + b * pt.Y - c;
            return (q * q) / (a * a + b * b);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static double DistanceSqr(Point64 pt1, Point64 pt2)
        {
            return (double)(pt1.X - pt2.X) * (pt1.X - pt2.X) +
                   (double)(pt1.Y - pt2.Y) * (pt1.Y - pt2.Y);
        }

        private OutRec ProcessJoin(Joiner j)
        {
            OutPt op1 = j.op1, op2 = j.op2!;
            OutRec or1 = GetRealOutRec(op1.outrec)!;
            OutRec or2 = GetRealOutRec(op2.outrec)!;
            DeleteJoin(j);

            if (or2.pts == null) return or1;
            if (!IsValidClosedPath(op2))
            {
                SafeDisposeOutPts(ref op2);
                return or1;
            }
            if ((or1.pts == null) || !IsValidClosedPath(op1))
            {
                SafeDisposeOutPts(ref op1);
                return or2;
            }
            if (or1 == or2 &&
                ((op1 == op2) || (op1.next == op2) || (op1.prev == op2))) return or1;

            CheckDisposeAdjacent(ref op1, op2, or1);
            CheckDisposeAdjacent(ref op2, op1, or2);
            if (op1.next == op2 || op2.next == op1) return or1;

            OutRec result = or1;
            for (; ; )
            {
                if (!IsValidPath(op1) || !IsValidPath(op2) ||
                  (or1 == or2 && (op1.prev == op2 || op1.next == op2))) return or1;

                if (op1.prev.pt == op2.next!.pt ||
                    ((InternalClipper.CrossProduct(op1.prev.pt, op1.pt, op2.next.pt) == 0) &&
                     CollinearSegsOverlap(op1.prev.pt, op1.pt, op2.pt, op2.next.pt)))
                {
                    if (or1 == or2)
                    {
                        // SPLIT REQUIRED
                        // make sure op1.prev and op2.next match positions
                        // by inserting an extra vertex if needed
                        if (op1.prev.pt != op2.next.pt)
                        {
                            if (PointEqualOrBetween(op1.prev.pt, op2.pt, op2.next.pt))
                                op2.next = InsertOp(op1.prev.pt, op2);
                            else
                                op1.prev = InsertOp(op2.next.pt, op1.prev);
                        }

                        // current              to     new
                        // op1.p[opA] >>> op1   ...    opA \   / op1
                        // op2.n[opB] <<< op2   ...    opB /   \ op2
                        OutPt opA = op1.prev, opB = op2.next;
                        opA.next = opB;
                        opB.prev = opA;
                        op1.prev = op2;
                        op2.next = op1;
                        CompleteSplit(op1, opA, or1);
                    }
                    else
                    {
                        // JOIN, NOT SPLIT
                        OutPt opA = op1.prev, opB = op2.next;
                        opA.next = opB;
                        opB.prev = opA;
                        op1.prev = op2;
                        op2.next = op1;

                        //SafeDeleteOutPtJoiners(op2);
                        //DisposeOutPt(op2);

                        if (or1.idx < or2.idx)
                        {
                            or1.pts = op1;
                            or2.pts = null;
                            if (or1.owner != null &&
                              (or2.owner == null || or2.owner.idx < or1.owner.idx))
                            {
                                or1.owner = or2.owner;
                            }
                            or2.owner = or1;
                        }
                        else
                        {
                            result = or2;
                            or2.pts = op1;
                            or1.pts = null;
                            if (or2.owner != null &&
                              (or1.owner == null || or1.owner.idx < or2.owner.idx))
                            {
                                or2.owner = or1.owner;
                            }
                            or1.owner = or2;
                        }
                    }
                    break;
                }
                if (op1.next!.pt == op2.prev.pt ||
                         ((InternalClipper.CrossProduct(op1.next.pt, op2.pt, op2.prev.pt) == 0) &&
                          CollinearSegsOverlap(op1.next.pt, op1.pt, op2.pt, op2.prev.pt)))
                {
                    if (or1 == or2)
                    {
                        // SPLIT REQUIRED
                        // make sure op2.prev and op1.next match positions
                        // by inserting an extra vertex if needed
                        if (op2.prev.pt != op1.next.pt)
                        {
                            if (PointEqualOrBetween(op2.prev.pt, op1.pt, op1.next.pt))
                                op1.next = InsertOp(op2.prev.pt, op1);
                            else
                                op2.prev = InsertOp(op1.next.pt, op2.prev);
                        }

                        // current              to     new
                        // op2.p[opA] >>> op2   ...    opA \   / op2
                        // op1.n[opB] <<< op1   ...    opB /   \ op1
                        OutPt opA = op2.prev, opB = op1.next;
                        opA.next = opB;
                        opB.prev = opA;
                        op2.prev = op1;
                        op1.next = op2;
                        CompleteSplit(op1, opA, or1);
                    }
                    else
                    {
                        // JOIN, NOT SPLIT
                        OutPt opA = op1.next, opB = op2.prev;
                        opA.prev = opB;
                        opB.next = opA;
                        op1.next = op2;
                        op2.prev = op1;

                        //SafeDeleteOutPtJoiners(op2);
                        //DisposeOutPt(op2);

                        if (or1.idx < or2.idx)
                        {
                            or1.pts = op1;
                            or2.pts = null;
                            if (or1.owner != null &&
                              (or2.owner == null || or2.owner.idx < or1.owner.idx))
                            {
                                or1.owner = or2.owner;
                            }
                            or2.owner = or1;
                        }
                        else
                        {
                            result = or2;
                            or2.pts = op1;
                            or1.pts = null;
                            if (or2.owner != null &&
                              (or1.owner == null || or1.owner.idx < or2.owner.idx))
                            {
                                or2.owner = or1.owner;
                            }
                            or1.owner = or2;
                        }
                    }
                    break;
                }

                if (PointBetween(op1.next.pt, op2.pt, op2.prev.pt) &&
                         DistanceFromLineSqrd(op1.next.pt, op2.pt, op2.prev.pt) < 2.01)
                {
                    InsertOp(op1.next.pt, op2.prev);
                    continue;
                }
                if (PointBetween(op2.next.pt, op1.pt, op1.prev.pt) &&
                         DistanceFromLineSqrd(op2.next.pt, op1.pt, op1.prev.pt) < 2.01)
                {
                    InsertOp(op2.next.pt, op1.prev);
                    continue;
                }
                if (PointBetween(op1.prev.pt, op2.pt, op2.next.pt) &&
                         DistanceFromLineSqrd(op1.prev.pt, op2.pt, op2.next.pt) < 2.01)
                {
                    InsertOp(op1.prev.pt, op2);
                    continue;
                }
                if (PointBetween(op2.prev.pt, op1.pt, op1.next.pt) &&
                         DistanceFromLineSqrd(op2.prev.pt, op1.pt, op1.next.pt) < 2.01)
                {
                    InsertOp(op2.prev.pt, op1);
                    continue;
                }

                // something odd needs tidying up
                if (CheckDisposeAdjacent(ref op1, op2, or1)) continue;
                if (CheckDisposeAdjacent(ref op2, op1, or1)) continue;
                if (op1.prev.pt != op2.next!.pt &&
                  (DistanceSqr(op1.prev.pt, op2.next.pt) < 2.01))
                {
                    op1.prev.pt = op2.next.pt;
                    continue;
                }
                if (op1.next!.pt != op2.prev.pt &&
                  (DistanceSqr(op1.next.pt, op2.prev.pt) < 2.01))
                {
                    op2.prev.pt = op1.next.pt;
                    continue;
                }
                // OK, there doesn't seem to be a way to join after all
                // so just tidy up the polygons
                or1.pts = op1;
                if (or2 != or1)
                {
                    or2.pts = op2;
                    CleanCollinear(or2);
                }
                break;
            }
            return result;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static void UpdateOutrecOwner(OutRec outrec)
        {
            OutPt opCurr = outrec.pts!;
            for (; ; )
            {
                opCurr.outrec = outrec;
                opCurr = opCurr.next!;
                if (opCurr == outrec.pts) return;
            }
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private void CompleteSplit(OutPt? op1, OutPt? op2, OutRec outrec)
        {
            double area1 = Area(op1!);
            double area2 = Area(op2!);
            bool signs_change = (area1 > 0) == (area2 < 0);

            // delete trivial splits (with zero or almost zero areas)
            if (area1 == 0 || (signs_change && Math.Abs(area1) < 2))
            {
                SafeDisposeOutPts(ref op1!);
                outrec.pts = op2;
            }
            else if (area2 == 0 || (signs_change && Math.Abs(area2) < 2))
            {
                SafeDisposeOutPts(ref op2!);
                outrec.pts = op1;
            }
            else
            {
                OutRec newOr = new OutRec() { idx = _outrecList.Count };
                _outrecList.Add(newOr);
                newOr.polypath = null;

                if (_using_polytree)
                {
                    outrec.splits ??= new List<OutRec>();
                    outrec.splits.Add(newOr);
                }

                if (Math.Abs(area1) >= Math.Abs(area2))
                {
                    outrec.pts = op1;
                    newOr.pts = op2;
                }
                else
                {
                    outrec.pts = op2;
                    newOr.pts = op1;
                }

                if ((area1 > 0) == (area2 > 0))
                    newOr.owner = outrec.owner;
                else
                    newOr.owner = outrec;

                UpdateOutrecOwner(newOr);
                CleanCollinear(newOr);
            }
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private void CleanCollinear(OutRec? outrec)
        {
            outrec = GetRealOutRec(outrec);
            if (outrec == null || outrec.isOpen ||
            outrec.frontEdge != null || !ValidateClosedPathEx(ref outrec.pts))
                return;

            OutPt startOp = outrec.pts!;
            OutPt? op2 = startOp;
            for (; ; )
            {
                if (op2!.joiner != null) return;
                // NB if preserveCollinear == true, then only remove 180 deg. spikes
                if ((InternalClipper.CrossProduct(op2.prev.pt, op2.pt, op2.next!.pt) == 0) &&
                  ((op2.pt == op2.prev.pt) || (op2.pt == op2.next.pt) || !PreserveCollinear ||
                  (InternalClipper.DotProduct(op2.prev.pt, op2.pt, op2.next.pt) < 0)))
                {
                    if (op2 == outrec.pts)
                        outrec.pts = op2.prev;
                    op2 = DisposeOutPt(op2);
                    if (!ValidateClosedPathEx(ref op2))
                    {
                        outrec.pts = null;
                        return;
                    }
                    startOp = op2!;
                    continue;
                }
                op2 = op2.next;
                if (op2 == startOp) break;
            }
            FixSelfIntersects(outrec);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private void DoSplitOp(OutRec outrec, OutPt splitOp)
        {
            // splitOp.prev -> splitOp &&
            // splitOp.next -> splitOp.next.next are intersecting
            OutPt prevOp = splitOp.prev;
            OutPt nextNextOp = splitOp.next!.next!;
            outrec.pts = prevOp;
            OutPt result = prevOp;

            InternalClipper.GetIntersectPoint(
                prevOp.pt, splitOp.pt, splitOp.next.pt, nextNextOp.pt, out PointD ipD);
            Point64 ip = new Point64(ipD);

#if USINGZ
      if (_zCallback != null)
        _zCallback(prevOp.pt, splitOp.pt, splitOp.next.pt, nextNextOp.pt, ref ip);
#endif

            double area1 = Area(prevOp);
            double absArea1 = Math.Abs(area1);

            if (absArea1 < 2)
            {
                SafeDisposeOutPts(ref splitOp);
                return;
            }

            // nb: area1 is the path's area *before* splitting, whereas area2 is
            // the area of the triangle containing splitOp & splitOp.next.
            // So the only way for these areas to have the same sign is if
            // the split triangle is larger than the path containing prevOp or
            // if there's more than one self=intersection.
            double area2 = AreaTriangle(ip, splitOp.pt, splitOp.next.pt);
            double absArea2 = Math.Abs(area2);

            // de-link splitOp and splitOp.next from the path
            // while inserting the intersection point
            if (ip == prevOp.pt || ip == nextNextOp.pt)
            {
                nextNextOp.prev = prevOp;
                prevOp.next = nextNextOp;
            }
            else
            {
                OutPt newOp2 = new OutPt(ip, prevOp.outrec) { prev = prevOp, next = nextNextOp };
                nextNextOp.prev = newOp2;
                prevOp.next = newOp2;
            }

            SafeDeleteOutPtJoiners(splitOp.next);
            SafeDeleteOutPtJoiners(splitOp);

            if (absArea2 > 1 &&
                (absArea2 > absArea1 ||
                 ((area2 > 0) == (area1 > 0))))
            {
                OutRec newOutRec = new OutRec();
                newOutRec.idx = _outrecList.Count;
                _outrecList.Add(newOutRec);
                newOutRec.owner = prevOp.outrec.owner;
                newOutRec.polypath = null;
                splitOp.outrec = newOutRec;
                splitOp.next.outrec = newOutRec;

                OutPt newOp = new OutPt(ip, newOutRec) { prev = splitOp.next, next = splitOp };
                newOutRec.pts = newOp;
                splitOp.prev = newOp;
                splitOp.next.next = newOp;
            }
            //else { splitOp = null; splitOp.next = null; }
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private void FixSelfIntersects(OutRec outrec)
        {
            OutPt op2 = outrec.pts!;
            for (; ; )
            {
                // triangles can't self-intersect
                if (op2.prev == op2.next!.next) break;
                if (InternalClipper.SegsIntersect(op2.prev.pt,
                        op2.pt, op2.next.pt, op2.next.next!.pt))
                {
                    DoSplitOp(outrec, op2);
                    if (outrec.pts == null) return;
                    op2 = outrec.pts;
                    continue;
                }
                else
                    op2 = op2.next;
                if (op2 == outrec.pts) break;
            }
        }

        internal static bool BuildPath(OutPt op, bool reverse, bool isOpen, Path64 path)
        {
            if (op.next == op || (!isOpen && op.next == op.prev)) return false;
            path.Clear();

            Point64 lastPt;
            OutPt op2;
            if (reverse)
            {
                lastPt = op.pt;
                op2 = op.prev;
            }
            else
            {
                op = op.next!;
                lastPt = op.pt;
                op2 = op.next!;
            }
            path.Add(lastPt);

            while (op2 != op)
            {
                if (op2.pt != lastPt)
                {
                    lastPt = op2.pt;
                    path.Add(lastPt);
                }
                if (reverse)
                    op2 = op2.prev;
                else
                    op2 = op2.next!;
            }

            if (path.Count == 3 && IsVerySmallTriangle(op2)) return false;
            else return true;
        }


        protected bool BuildPaths(Paths64 solutionClosed, Paths64 solutionOpen)
        {
            solutionClosed.Clear();
            solutionOpen.Clear();
            solutionClosed.Capacity = _outrecList.Count;
            solutionOpen.Capacity = _outrecList.Count;

            foreach (OutRec outrec in _outrecList)
            {
                if (outrec.pts == null) continue;

                Path64 path = new Path64();
                if (outrec.isOpen)
                {
                    if (BuildPath(outrec.pts!, ReverseSolution, true, path))
                        solutionOpen.Add(path);
                }
                else
                {
                    // closed paths should always return a Positive orientation
                    // except when ReverseSolution == true
                    if (BuildPath(outrec.pts!, ReverseSolution, false, path))
                        solutionClosed.Add(path);
                }
            }
            return true;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static bool Path1InsidePath2(OutRec or1, OutRec or2)
        {
            PointInPolygonResult result;
            OutPt op = or1.pts!;
            do
            {
                result = InternalClipper.PointInPolygon(op.pt, or2.path);
                if (result != PointInPolygonResult.IsOn) break;
                op = op.next!;
            } while (op != or1.pts);
            if (result == PointInPolygonResult.IsOn)
                return Area(op) < Area(or2.pts!);
            return result == PointInPolygonResult.IsInside;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static Rect64 GetBounds(Path64 path)
        {
            if (path.Count == 0) return new Rect64();
            Rect64 result = new Rect64(long.MaxValue, long.MaxValue, -long.MaxValue, -long.MaxValue);
            foreach (Point64 pt in path)
            {
                if (pt.X < result.left) result.left = pt.X;
                if (pt.X > result.right) result.right = pt.X;
                if (pt.Y < result.top) result.top = pt.Y;
                if (pt.Y > result.bottom) result.bottom = pt.Y;
            }
            return result;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private bool DeepCheckOwner(OutRec outrec, OutRec owner)
        {
            if (owner.bounds.IsEmpty())
                owner.bounds = GetBounds(owner.path);
            bool isInsideOwnerBounds = owner.bounds.Contains(outrec.bounds);

            // while looking for the correct owner, check the owner's
            // splits **before** checking the owner itself because
            // splits can occur internally, and checking the owner
            // first would miss the inner split's true ownership
            if (owner.splits != null)
                foreach (OutRec asplit in owner.splits!)
                {
                    OutRec? split = GetRealOutRec(asplit);
                    if (split == null || split.idx <= owner.idx || split == outrec) continue;
                    if (split.splits != null && DeepCheckOwner(outrec, split)) return true;

                    if (split.path.Count == 0)
                        BuildPath(split.pts!, ReverseSolution, false, split.path);
                    if (split.bounds.IsEmpty()) split.bounds = GetBounds(split.path);

                    if (split.bounds.Contains(outrec.bounds) && Path1InsidePath2(outrec, split))
                    {
                        outrec.owner = split;
                        return true;
                    }
                }

            // only continue when not inside recursion
            if (owner != outrec.owner) return false;

            for (; ; )
            {
                if (isInsideOwnerBounds && Path1InsidePath2(outrec, outrec.owner!))
                    return true;

                outrec.owner = outrec.owner!.owner;
                if (outrec.owner == null) return false;
                isInsideOwnerBounds = outrec.owner.bounds.Contains(outrec.bounds);
            }
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        protected bool BuildTree(PolyPathNode polytree, Paths64 solutionOpen)
        {
            polytree.Clear();
            solutionOpen.Clear();
            solutionOpen.Capacity = _outrecList.Count;

            for (int i = 0; i < _outrecList.Count; i++)
            {
                OutRec outrec = _outrecList[i];
                if (outrec.pts == null) continue;

                if (outrec.isOpen)
                {
                    Path64 open_path = new Path64();
                    if (BuildPath(outrec.pts!, ReverseSolution, true, open_path))
                        solutionOpen.Add(open_path);
                    continue;
                }

                if (!BuildPath(outrec.pts!, ReverseSolution, false, outrec.path)) continue;
                if (outrec.bounds.IsEmpty()) outrec.bounds = GetBounds(outrec.path);
                outrec.owner = GetRealOutRec(outrec.owner);
                if (outrec.owner != null)
                    DeepCheckOwner(outrec, outrec.owner);

                // swap order if outer/owner paths are preceeded by their inner paths
                if (outrec.owner != null && outrec.owner.idx > outrec.idx)
                {
                    int j = outrec.owner.idx;
                    outrec.owner.idx = i;
                    outrec.idx = j;
                    _outrecList[i] = _outrecList[j];
                    _outrecList[j] = outrec;
                    outrec = _outrecList[i];
                    outrec.owner = GetRealOutRec(outrec.owner);
                    BuildPath(outrec.pts!, ReverseSolution, false, outrec.path);
                    if (outrec.bounds.IsEmpty()) outrec.bounds = GetBounds(outrec.path);
                    if (outrec.owner != null)
                        DeepCheckOwner(outrec, outrec.owner);
                }

                PolyPathNode ownerPP;
                if (outrec.owner != null && outrec.owner.polypath != null)
                    ownerPP = outrec.owner.polypath;
                else
                    ownerPP = polytree;
                outrec.polypath = ownerPP.AddChild(outrec.path);
            }
            return true;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public Rect64 GetBounds()
        {
            Rect64 bounds = Clipper.MaxInvalidRect64;
            foreach (Vertex t in _vertexList)
            {
                Vertex v = t;
                do
                {
                    if (v.pt.X < bounds.left) bounds.left = v.pt.X;
                    if (v.pt.X > bounds.right) bounds.right = v.pt.X;
                    if (v.pt.Y < bounds.top) bounds.top = v.pt.Y;
                    if (v.pt.Y > bounds.bottom) bounds.bottom = v.pt.Y;
                    v = v.next!;
                } while (v != t);
            }
            return bounds.IsEmpty() ? new Rect64(0, 0, 0, 0) : bounds;
        }

    } // ClipperBase class


    public class Clipper64 : ClipperBase
    {
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        internal new void AddPath(Path64 path, PathType polytype, bool isOpen = false)
        {
            base.AddPath(path, polytype, isOpen);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        internal new void AddPaths(Paths64 paths, PathType polytype, bool isOpen = false)
        {
            base.AddPaths(paths, polytype, isOpen);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void AddSubject(Paths64 paths)
        {
            AddPaths(paths, PathType.Subject);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void AddOpenSubject(Paths64 paths)
        {
            AddPaths(paths, PathType.Subject, true);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void AddClip(Paths64 paths)
        {
            AddPaths(paths, PathType.Clip);
        }

        public bool Execute(ClipType clipType, FillRule fillRule,
            Paths64 solutionClosed, Paths64 solutionOpen)
        {
            solutionClosed.Clear();
            solutionOpen.Clear();
            try
            {
                ExecuteInternal(clipType, fillRule);
                BuildPaths(solutionClosed, solutionOpen);
            }
            catch
            {
                _succeeded = false;
            }

            ClearSolution();
            return _succeeded;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public bool Execute(ClipType clipType, FillRule fillRule, Paths64 solutionClosed)
        {
            return Execute(clipType, fillRule, solutionClosed, new Paths64());
        }

        public bool Execute(ClipType clipType, FillRule fillRule, PolyTree64 polytree, Paths64 openPaths)
        {
            polytree.Clear();
            openPaths.Clear();
            _using_polytree = true;
            try
            {
                ExecuteInternal(clipType, fillRule);
                BuildTree(polytree, openPaths);
            }
            catch
            {
                _succeeded = false;
            }

            ClearSolution();
            return _succeeded;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public bool Execute(ClipType clipType, FillRule fillRule, PolyTree64 polytree)
        {
            return Execute(clipType, fillRule, polytree, new Paths64());
        }

#if USINGZ
    public ZCallback64? ZCallback {
      get { return this._zCallback; }
      set { this._zCallback = value; } 
    }
#endif

    } // Clipper64 class

    public class ClipperD : ClipperBase
    {
        private static string precision_range_error = "Error: Precision is out of range.";

        private readonly double _scale;
        private readonly double _invScale;

#if USINGZ
    public delegate void ZCallbackD(PointD bot1, PointD top1,
        PointD bot2, PointD top2, ref PointD intersectPt);

    public ZCallbackD? ZCallback { get; set; }

    private void CheckZCallback()
    {
      if (ZCallback != null)
        _zCallback = ZCB;
      else
        _zCallback = null;
    }
#endif

        public ClipperD(int roundingDecimalPrecision = 2)
        {
            if (roundingDecimalPrecision < -8 || roundingDecimalPrecision > 8)
                throw new ClipperLibException(precision_range_error);
            _scale = Math.Pow(10, roundingDecimalPrecision);
            _invScale = 1 / _scale;
        }

#if USINGZ
    private void ZCB(Point64 bot1, Point64 top1,
        Point64 bot2, Point64 top2, ref Point64 intersectPt)
    {
      // de-scale (x & y)
      // temporarily convert integers to their initial float values
      // this will slow clipping marginally but will make it much easier
      // to understand the coordinates passed to the callback function
      PointD tmp = new PointD(intersectPt);
      //do the callback
      ZCallback?.Invoke(
        Clipper.ScalePointD(bot1, _invScale),
        Clipper.ScalePointD(top1, _invScale),
        Clipper.ScalePointD(bot2, _invScale),
        Clipper.ScalePointD(top2, _invScale), ref tmp);
      intersectPt = new Point64(intersectPt.X,
          intersectPt.Y, tmp.z);
    }
#endif

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void AddPath(PathD path, PathType polytype, bool isOpen = false)
        {
            base.AddPath(Clipper.ScalePath64(path, _scale), polytype, isOpen);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void AddPaths(PathsD paths, PathType polytype, bool isOpen = false)
        {
            base.AddPaths(Clipper.ScalePaths64(paths, _scale), polytype, isOpen);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void AddSubject(PathD path)
        {
            AddPath(path, PathType.Subject);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void AddOpenSubject(PathD path)
        {
            AddPath(path, PathType.Subject, true);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void AddClip(PathD path)
        {
            AddPath(path, PathType.Clip);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void AddSubject(PathsD paths)
        {
            AddPaths(paths, PathType.Subject);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void AddOpenSubject(PathsD paths)
        {
            AddPaths(paths, PathType.Subject, true);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void AddClip(PathsD paths)
        {
            AddPaths(paths, PathType.Clip);
        }

        public bool Execute(ClipType clipType, FillRule fillRule,
            PathsD solutionClosed, PathsD solutionOpen)
        {
            Paths64 solClosed64 = new Paths64(), solOpen64 = new Paths64();
#if USINGZ
      CheckZCallback();
#endif

            bool success = true;
            solutionClosed.Clear();
            solutionOpen.Clear();
            try
            {
                ExecuteInternal(clipType, fillRule);
                BuildPaths(solClosed64, solOpen64);
            }
            catch
            {
                success = false;
            }

            ClearSolution();
            if (!success) return false;

            solutionClosed.Capacity = solClosed64.Count;
            foreach (Path64 path in solClosed64)
                solutionClosed.Add(Clipper.ScalePathD(path, _invScale));
            solutionOpen.Capacity = solOpen64.Count;
            foreach (Path64 path in solOpen64)
                solutionOpen.Add(Clipper.ScalePathD(path, _invScale));

            return true;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public bool Execute(ClipType clipType, FillRule fillRule, PathsD solutionClosed)
        {
            return Execute(clipType, fillRule, solutionClosed, new PathsD());
        }

        public bool Execute(ClipType clipType, FillRule fillRule, PolyTreeD polytree, PathsD openPaths)
        {
            polytree.Clear();
            (polytree as PolyPathD).Scale = _scale;
#if USINGZ
      CheckZCallback();
#endif
            openPaths.Clear();
            Paths64 oPaths = new Paths64();
            bool success = true;
            try
            {
                ExecuteInternal(clipType, fillRule);
                BuildTree(polytree, oPaths);
            }
            catch
            {
                success = false;
            }
            ClearSolution();
            if (!success) return false;
            if (oPaths.Count > 0)
            {
                openPaths.Capacity = oPaths.Count;
                foreach (Path64 path in oPaths)
                    openPaths.Add(Clipper.ScalePathD(path, _invScale));
            }

            return true;
        }

        public bool Execute(ClipType clipType, FillRule fillRule, PolyTreeD polytree)
        {
            return Execute(clipType, fillRule, polytree, new PathsD());
        }
    } // ClipperD class

    public abstract class PolyPathNode : IEnumerable
    {
        internal PolyPathNode? _parent;
        internal List<PolyPathNode> _childs = new List<PolyPathNode>();

        public IEnumerator GetEnumerator()
        {
            return new NodeEnumerator(_childs);
        }
        private class NodeEnumerator : IEnumerator
        {
            private int position = -1;
            private readonly List<PolyPathNode> _nodes;

            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            public NodeEnumerator(List<PolyPathNode> nodes)
            {
                _nodes = new List<PolyPathNode>(nodes);
            }

            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            private IEnumerator getEnumerator()
            {
                return (IEnumerator)this;
            }

            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            public bool MoveNext()
            {
                position++;
                return (position < _nodes.Count);
            }

            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            public void Reset()
            {
                position = -1;
            }

            public object Current
            {
                get
                {
                    if (position < 0 || position >= _nodes.Count)
                        throw new InvalidOperationException();
                    return _nodes[position];
                }
            }

        };

        public bool IsHole => GetIsHole();

        public PolyPathNode(PolyPathNode? parent = null) { _parent = parent; }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private bool GetIsHole()
        {
            bool result = true;
            PolyPathNode? pp = _parent;
            while (pp != null)
            {
                result = !result;
                pp = pp._parent;
            }

            return result;
        }

        public int Count => _childs.Count;

        internal abstract PolyPathNode AddChild(Path64 p);

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void Clear()
        {
            _childs.Clear();
        }
    } // PolyPathBase class

    public class PolyPath64 : PolyPathNode
    {
        public Path64? Polygon { get; private set; } // polytree root's polygon == null

        public PolyPath64(PolyPathNode? parent = null) : base(parent) { }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        internal override PolyPathNode AddChild(Path64 p)
        {
            PolyPathNode newChild = new PolyPath64(this);
            (newChild as PolyPath64)!.Polygon = p;
            _childs.Add(newChild);
            return newChild;
        }

        [IndexerName("Child")]
        public PolyPath64 this[int index]
        {
            get
            {
                if (index < 0 || index >= _childs.Count)
                    throw new InvalidOperationException();
                return (PolyPath64)_childs[index];
            }
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public double Area()
        {
            double result = Polygon == null ? 0 : Clipper.Area(Polygon);
            foreach (PolyPathNode polyPathBase in _childs)
            {
                PolyPath64 child = (PolyPath64)polyPathBase;
                result += child.Area();
            }
            return result;
        }
    }

    public class PolyPathD : PolyPathNode
    {
        internal double Scale { get; set; }
        public PathD? Polygon { get; private set; }

        public PolyPathD(PolyPathNode? parent = null) : base(parent) { }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        internal override PolyPathNode AddChild(Path64 p)
        {
            PolyPathNode newChild = new PolyPathD(this);
            (newChild as PolyPathD)!.Scale = Scale;
            (newChild as PolyPathD)!.Polygon = Clipper.ScalePathD(p, 1 / Scale);
            _childs.Add(newChild);
            return newChild;
        }

        [IndexerName("Child")]
        public PolyPathD this[int index]
        {
            get
            {
                if (index < 0 || index >= _childs.Count)
                    throw new InvalidOperationException();
                return (PolyPathD)_childs[index];
            }
        }
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public double Area()
        {
            double result = Polygon == null ? 0 : Clipper.Area(Polygon);
            foreach (PolyPathNode polyPathBase in _childs)
            {
                PolyPathD child = (PolyPathD)polyPathBase;
                result += child.Area();
            }
            return result;
        }
    }

    public class PolyTree64 : PolyPath64 { }

    public class PolyTreeD : PolyPathD
    {
        public new double Scale => base.Scale;
    }

    public class ClipperLibException : Exception
    {
        public ClipperLibException(string description) : base(description) { }
    }
} // namespace