109 lines
3.9 KiB
C#
109 lines
3.9 KiB
C#
/*
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* Farseer Physics Engine:
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* Copyright (c) 2012 Ian Qvist
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*/
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using System.Collections.Generic;
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using System.Diagnostics;
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using FarseerPhysics.Common.Decomposition.Seidel;
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using Microsoft.Xna.Framework;
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using Point = FarseerPhysics.Common.Decomposition.Seidel.Point;
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namespace FarseerPhysics.Common.Decomposition
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{
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/// <summary>
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/// Convex decomposition algorithm created by Raimund Seidel
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///
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/// Properties:
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/// - Decompose the polygon into trapezoids, then triangulate.
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/// - To use the trapezoid data, use ConvexPartitionTrapezoid()
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/// - Generate a lot of garbage due to incapsulation of the Poly2Tri library.
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/// - Running time is O(n log n), n = number of vertices.
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/// - Running time is almost linear for most simple polygons.
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/// - Does not care about winding order.
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///
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/// For more information, see Raimund Seidel's paper "A simple and fast incremental randomized
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/// algorithm for computing trapezoidal decompositions and for triangulating polygons"
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///
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/// See also: "Computational Geometry", 3rd edition, by Mark de Berg et al, Chapter 6.2
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/// "Computational Geometry in C", 2nd edition, by Joseph O'Rourke
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///
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/// Original code from the Poly2Tri project by Mason Green.
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/// http://code.google.com/p/poly2tri/source/browse?repo=archive#hg/scala/src/org/poly2tri/seidel
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///
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/// This implementation is from Dec 14, 2010
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/// </summary>
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internal static class SeidelDecomposer
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{
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/// <summary>
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/// Decompose the polygon into several smaller non-concave polygons.
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/// </summary>
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/// <param name="vertices">The polygon to decompose.</param>
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/// <param name="sheer">The sheer to use if you get bad results, try using a higher value.</param>
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/// <returns>A list of triangles</returns>
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public static List<Vertices> ConvexPartition(Vertices vertices, float sheer = 0.001f)
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{
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Debug.Assert(vertices.Count > 3);
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List<Point> compatList = new List<Point>(vertices.Count);
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foreach (Vector2 vertex in vertices)
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{
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compatList.Add(new Point(vertex.X, vertex.Y));
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}
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Triangulator t = new Triangulator(compatList, sheer);
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List<Vertices> list = new List<Vertices>();
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foreach (List<Point> triangle in t.Triangles)
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{
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Vertices outTriangles = new Vertices(triangle.Count);
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foreach (Point outTriangle in triangle)
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{
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outTriangles.Add(new Vector2(outTriangle.X, outTriangle.Y));
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}
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list.Add(outTriangles);
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}
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return list;
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}
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/// <summary>
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/// Decompose the polygon into several smaller non-concave polygons.
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/// </summary>
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/// <param name="vertices">The polygon to decompose.</param>
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/// <param name="sheer">The sheer to use if you get bad results, try using a higher value.</param>
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/// <returns>A list of trapezoids</returns>
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public static List<Vertices> ConvexPartitionTrapezoid(Vertices vertices, float sheer = 0.001f)
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{
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List<Point> compatList = new List<Point>(vertices.Count);
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foreach (Vector2 vertex in vertices)
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{
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compatList.Add(new Point(vertex.X, vertex.Y));
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}
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Triangulator t = new Triangulator(compatList, sheer);
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List<Vertices> list = new List<Vertices>();
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foreach (Trapezoid trapezoid in t.Trapezoids)
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{
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Vertices verts = new Vertices();
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List<Point> points = trapezoid.GetVertices();
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foreach (Point point in points)
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{
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verts.Add(new Vector2(point.X, point.Y));
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}
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list.Add(verts);
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}
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return list;
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}
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}
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} |