axiosengine/axios/Common/Decomposition/CDT/Delaunay/Sweep/AdvancingFront.cs

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// Changes from the Java version
//   Removed BST code, but not all artifacts of it
// Future possibilities
//   Eliminate Add/RemoveNode ?
//   Comments comments and more comments!

using System;
using System.Text;

namespace Poly2Tri.Triangulation.Delaunay.Sweep
{
    /**
     * @author Thomas Åhlen (thahlen@gmail.com)
     */

    public class AdvancingFront
    {
        public AdvancingFrontNode Head;
        protected AdvancingFrontNode Search;
        public AdvancingFrontNode Tail;

        public AdvancingFront(AdvancingFrontNode head, AdvancingFrontNode tail)
        {
            Head = head;
            Tail = tail;
            Search = head;
            AddNode(head);
            AddNode(tail);
        }

        public void AddNode(AdvancingFrontNode node)
        {
            //_searchTree.put(node.key, node);
        }

        public void RemoveNode(AdvancingFrontNode node)
        {
            //_searchTree.delete( node.key );
        }

        public override string ToString()
        {
            StringBuilder sb = new StringBuilder();
            AdvancingFrontNode node = Head;
            while (node != Tail)
            {
                sb.Append(node.Point.X).Append("->");
                node = node.Next;
            }
            sb.Append(Tail.Point.X);
            return sb.ToString();
        }

        /// <summary>
        /// MM:  This seems to be used by LocateNode to guess a position in the implicit linked list of AdvancingFrontNodes near x
        ///      Removed an overload that depended on this being exact
        /// </summary>
        private AdvancingFrontNode FindSearchNode(double x)
        {
            // TODO: implement BST index 
            return Search;
        }

        /// <summary>
        /// We use a balancing tree to locate a node smaller or equal to given key value
        /// </summary>
        public AdvancingFrontNode LocateNode(TriangulationPoint point)
        {
            return LocateNode(point.X);
        }

        private AdvancingFrontNode LocateNode(double x)
        {
            AdvancingFrontNode node = FindSearchNode(x);
            if (x < node.Value)
            {
                while ((node = node.Prev) != null)
                    if (x >= node.Value)
                    {
                        Search = node;
                        return node;
                    }
            }
            else
            {
                while ((node = node.Next) != null)
                    if (x < node.Value)
                    {
                        Search = node.Prev;
                        return node.Prev;
                    }
            }
            return null;
        }

        /// <summary>
        /// This implementation will use simple node traversal algorithm to find a point on the front
        /// </summary>
        public AdvancingFrontNode LocatePoint(TriangulationPoint point)
        {
            double px = point.X;
            AdvancingFrontNode node = FindSearchNode(px);
            double nx = node.Point.X;

            if (px == nx)
            {
                if (point != node.Point)
                {
                    // We might have two nodes with same x value for a short time
                    if (point == node.Prev.Point)
                    {
                        node = node.Prev;
                    }
                    else if (point == node.Next.Point)
                    {
                        node = node.Next;
                    }
                    else
                    {
                        throw new Exception("Failed to find Node for given afront point");
                        //node = null;
                    }
                }
            }
            else if (px < nx)
            {
                while ((node = node.Prev) != null)
                {
                    if (point == node.Point)
                    {
                        break;
                    }
                }
            }
            else
            {
                while ((node = node.Next) != null)
                {
                    if (point == node.Point)
                    {
                        break;
                    }
                }
            }
            Search = node;
            return node;
        }
    }
}