マウスでクリックした位置にポリゴン(多角形)を作成するサンプル

操作方法

マウスの左クリックで頂点を打ち、最後の頂点の位置で右クリックするとポリゴンが生成されます。頂点は10個まで打てます。

修正したファイル

【Triangulator.cs】

using UnityEngine;
using System.Collections.Generic;
 
public class Triangulator
{
    private List<Vector2> m_points = new List<Vector2>();
	private Vector3 m_cameraPosition;
 
    public Triangulator (Vector2[] points, Vector3 cameraPosition)
	{
		m_points = new List<Vector2> (points);
		m_cameraPosition = cameraPosition;
    }
 
    public int[] Triangulate ()
	{
		List<int> indices = new List<int> ();
		
		int n = m_points.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)
				break;
 
			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;
			}
		}
		
		bool reversFlag = true;
		int i0 = indices [0];
		int i1 = indices [1];
		int i2 = indices [2];
		Vector3 pos0 = new Vector3 (m_points [i0].x, m_points [i0].y, 0f);
		Vector3 pos1 = new Vector3 (m_points [i1].x, m_points [i1].y, 0f);
		Vector3 pos2 = new Vector3 (m_points [i2].x, m_points [i2].y, 0f);
		Vector3 v1 = pos1 - pos0;
		Vector3 v2 = pos2 - pos1;
		Vector3 crossVec = Vector3.Cross (v1, v2);
		Debug.Log(Vector3.Dot (m_cameraPosition, crossVec));
		if (Vector3.Dot (m_cameraPosition, crossVec) > 0) {
			reversFlag = false;
		}
		if (reversFlag) {
			indices.Reverse ();
		}

		return indices.ToArray ();
	}
 
    private float Area () {
        int n = m_points.Count;
        float A = 0.0f;
        for (int p = n - 1, q = 0; q < n; p = q++) {
            Vector2 pval = m_points[p];
            Vector2 qval = m_points[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 = m_points[V[u]];
        Vector2 B = m_points[V[v]];
        Vector2 C = m_points[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 = m_points[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));
    }
}

関連情報

Simple Concave 2D Triangulator for Unity Jasper Stocker
http://www.jasperstocker.com/2013/02/21/simple-concave-2d-triangulator-for-unity/

ポリゴンの三角形への分割についてのアルゴリズムを調べたい時は「triangulation algorithm」なんてワードで検索すると良さげ。

Polygon triangulation - Wikipedia, the free encyclopedia
http://en.wikipedia.org/wiki/Polygon_triangulation