Boprs/SweepLine.cs

#if ACAD24
using Autodesk.AutoCAD.EditorInput;
using Autodesk.AutoCAD.Geometry;
using Autodesk.AutoCAD.DatabaseServices;
using Autodesk.AutoCAD.Colors;
using AcAp = Autodesk.AutoCAD.ApplicationServices;
#elif BCAD
using Bricscad.EditorInput;
using Teigha.Geometry;
using Teigha.DatabaseServices;
using Teigha.Colors;
#endif
using System;
using System.Collections.Generic;

namespace Boprs
{
	/// <summary>
	/// Line to sweep through sorted vertices, keeps track of currently intersecting edges.
	/// </summary>
	internal class SweepLine
	{
		/// <summary>
		/// Edges the line is currently intersecting.
		/// </summary>
		/// TODO: Change this into a BST when optimizing.
		private List<SweepEdge> IntersectingEdges { get; }

		/// <summary>
		/// Start tracking an edge identified by its left vertex.
		/// </summary>
		/// <param name="edge">Edge to start tracking.</param>
		/// <param name="allowCollinearity">
		/// If <c>false</c> and the edge is collinear with one of the edges in the sweep line,
		/// an exception will get thrown.
		/// </param>
		internal void Add(SweepEdge edge, bool allowCollinearity)
		{
			int i = 0;

			if (IntersectingEdges.Contains(edge))
			{
				throw new Exception("inserting contained edge");
			}

			// Go through all the edges, find my index for insertion.
			for(; i < IntersectingEdges.Count; i++)
			{
				int comparison = edge.CompareTo(IntersectingEdges[i], edge.LeftVertex.Point.X);
				// If we are below the current edge, that is the correct index.
				if (comparison < 0)
				{
					break;
				}
				// If edges are collinear and it is not allowed, throw an exception
				else if(!allowCollinearity && comparison == 0)
				{
					throw new Exception($"Collinear edges detected. [{edge} & {IntersectingEdges[i]}]");
				}
				// If we are above the last edge, set inserttion index after it.
				else if (i == IntersectingEdges.Count)
				{
					i++;
				}
			}

			// Insert the edge to the correct place.
			IntersectingEdges.Insert(i, edge);
		}

		/// <summary>
		/// Remove an edge from being tracked by the sweep line.
		/// </summary>
		/// <param name="edge">Edge to remove.</param>
		internal void Remove(SweepEdge edge)
		{
			IntersectingEdges.Remove(edge);
		}

		/// <summary>
		/// Returns the edge below curr, or null if curr is the lowest.
		/// </summary>
		/// <param name="curr">Current edge.</param>
		/// <returns>Edge below curr, or null.</returns>
		internal SweepEdge PrevEdge(SweepEdge curr)
		{
			// Get the index of the current edge
			int currIdx = IntersectingEdges.IndexOf(curr);

			// If the current edge isn't the lowest, return the edge below it.
			if(currIdx != 0)
			{
				return IntersectingEdges[currIdx - 1];
			}

			// Otherwise return null.
			return null;
		}

		/// <summary>
		/// Returns the edge above curr, or null if curr is the highest.
		/// </summary>
		/// <param name="curr">Current edge.</param>
		/// <returns>Edge above curr, or null.</returns>
		internal SweepEdge NextEdge(SweepEdge curr)
		{
			// Get the index of the current edge
			int currIdx = IntersectingEdges.IndexOf(curr);

			// If the current edge isn't the highest, return the edge above it.
			if (currIdx != IntersectingEdges.Count - 1)
			{
				return IntersectingEdges[currIdx + 1];
			}

			// Otherwise return null.
			return null;
		}

		/// <summary>
		/// Constructor.
		/// </summary>
		internal SweepLine()
		{
			IntersectingEdges = new List<SweepEdge>();
		}
	}
}