PolygonMesh2D.cs

using UnityEngine;
using System.Linq;
using System.Collections.Generic;

[ExecuteInEditMode]
[RequireComponent (typeof (PolygonCollider2D))]
[RequireComponent (typeof (MeshRenderer))]
[RequireComponent (typeof (MeshFilter))]
/// <summary>
/// Builds a Mesh for a gameObject using the PolygonCollider2D's path</summary>
public class PolygonMesh2D : MonoBehaviour {
	protected PolygonCollider2D polygon;
	protected MeshFilter meshFilter;

	///<summary>The index of the polygon path to use for the mesh</summary>
	int pathIndex = 0;
	///<summary>The Z position for the generated mesh</summary>
	public float zPosition = 0f;

	void Start() {
		polygon = gameObject.GetComponent<PolygonCollider2D>();
		meshFilter = gameObject.GetComponent<MeshFilter>();
	} 

	#if UNITY_EDITOR
	///<summary>
	///(Re)builds the Mesh using the path of the PolygonCollider2D</summary>
	public void OnColliderUpdate() {
		Vector2[] path = polygon.GetPath(pathIndex);
		Mesh msh = new Mesh();

		msh.vertices = path.Select(v => new Vector3(v.x, v.y, zPosition)).ToArray();
		msh.triangles = new Triangulator(path).Triangulate();

		msh.RecalculateNormals();
		msh.RecalculateBounds();
		meshFilter.mesh = msh;

		//recalculate UV
		Bounds bounds = msh.bounds;

		msh.uv = path.Select(v => new Vector2(v.x / bounds.size.x, v.y / bounds.size.y)).ToArray();
	}

	void Update() {
		if (!Application.isPlaying) OnColliderUpdate();
	}
	#endif
}

class Triangulator {
	private List<Vector2> mPoints = new List<Vector2>();
	
	public Triangulator (Vector2[] points) {
		mPoints = new List<Vector2>(points);
	}
	
	public int[] Triangulate() {
		List<int> indices = new List<int>();
	
		int n = mPoints.Count;
		if (n < 3) return indices.ToArray();
	
		int[] V = new int[n];
		if (Area() > 0) {
			for (int v = 0; v < n; v++)
				V[v] = v;
		}
		else {
			for (int v = 0; v < n; v++)
				V[v] = (n - 1) - v;
		}
	
		int nv = n;
		int count = 2 * nv;
		for (int m = 0, v = nv - 1; nv > 2; ) {
			if ((count--) <= 0)
				return indices.ToArray();
	
			int u = v;
			if (nv <= u)
				u = 0;
			v = u + 1;
			if (nv <= v)
				v = 0;
			int w = v + 1;
			if (nv <= w)
				w = 0;
	
			if (Snip(u, v, w, nv, V)) {
				int a, b, c, s, t;
				a = V[u];
				b = V[v];
				c = V[w];
				indices.Add(a);
				indices.Add(b);
				indices.Add(c);
				m++;
				for (s = v, t = v + 1; t < nv; s++, t++)
					V[s] = V[t];
				nv--;
				count = 2 * nv;
			}
		}
	
		indices.Reverse();
		return indices.ToArray();
	}
	
	private float Area () {
		int n = mPoints.Count;
		float A = 0.0f;
		for (int p = n - 1, q = 0; q < n; p = q++) {
			Vector2 pval = mPoints[p];
			Vector2 qval = mPoints[q];
			A += pval.x * qval.y - qval.x * pval.y;
		}
		return (A * 0.5f);
	}
	
	private bool Snip (int u, int v, int w, int n, int[] V) {
		int p;
		Vector2 A = mPoints[V[u]];
		Vector2 B = mPoints[V[v]];
		Vector2 C = mPoints[V[w]];
		if (Mathf.Epsilon > (((B.x - A.x) * (C.y - A.y)) - ((B.y - A.y) * (C.x - A.x))))
			return false;
		for (p = 0; p < n; p++) {
			if ((p == u) || (p == v) || (p == w))
				continue;
			Vector2 P = mPoints[V[p]];
			if (InsideTriangle(A, B, C, P))
				return false;
		}
		return true;
	}
	
	private bool InsideTriangle (Vector2 A, Vector2 B, Vector2 C, Vector2 P) {
		float ax, ay, bx, by, cx, cy, apx, apy, bpx, bpy, cpx, cpy;
		float cCROSSap, bCROSScp, aCROSSbp;
	
		ax = C.x - B.x; ay = C.y - B.y;
		bx = A.x - C.x; by = A.y - C.y;
		cx = B.x - A.x; cy = B.y - A.y;
		apx = P.x - A.x; apy = P.y - A.y;
		bpx = P.x - B.x; bpy = P.y - B.y;
		cpx = P.x - C.x; cpy = P.y - C.y;
	
		aCROSSbp = ax * bpy - ay * bpx;
		cCROSSap = cx * apy - cy * apx;
		bCROSScp = bx * cpy - by * cpx;
	
		return ((aCROSSbp >= 0.0f) && (bCROSScp >= 0.0f) && (cCROSSap >= 0.0f));
	}
}