[游戏开发]Unity 依据Polygon Collider 2D 绘制 mesh

参考文章：
mesh的简介
创建mesh
简单多边形三角化(暴力)（削耳朵）

偶尔需要依据多边形创建平面mesh，所以在网上浏览了很多资料，再修修补补才凑出一段代码。

    [ContextMenu("Create_Mesh_For_PolygonCollider2D")]
    void Create_Mesh_For_PolygonCollider2D()
    {

        PolygonCollider2D pc = GetComponent<PolygonCollider2D>();
        //获取多边形碰撞体的顶点
        Vector3[] v_vertices = new Vector3[pc.points.Length];
        for (int i = 0; i < pc.points.Length; i++)
        {
            v_vertices[i] = new Vector3(pc.points[i].x, pc.points[i].y, 0);
        }
        DoCreatPloygonMesh(v_vertices);
    }

    //*****  创建mesh
    void DoCreatPloygonMesh(Vector3[] s_Vertives)
    {

        //新建一个空物体进行进行绘制自定义多边形
        GameObject tPolygon = new GameObject("tPolygon");
        tPolygon.transform.parent = transform;
        //绘制所必须的两个组件
        tPolygon.AddComponent<MeshFilter>();
        tPolygon.AddComponent<MeshRenderer>();

        //新申请一个Mesh网格
        Mesh tMesh = new Mesh();

        //存储所有的顶点
        Vector3[] tVertices = s_Vertives;

        //存储画所有三角形的点排序
        List<int> tTriangles = Calculate_Triangles_CutEar_Method(tVertices);

        //赋值多边形顶点
        tMesh.vertices = tVertices;

        //赋值三角形点排序
        tMesh.triangles = tTriangles.ToArray();

        //重新设置UV，法线
        tMesh.RecalculateBounds();
        tMesh.RecalculateNormals();

        //将绘制好的Mesh赋值
        tPolygon.GetComponent<MeshFilter>().mesh = tMesh;
        tPolygon.transform.localPosition = Vector3.zero;
    }

    //***********  计算并获取三角形数组-削耳朵法，详看参考文章
    List<int> Calculate_Triangles_CutEar_Method(Vector3[] s_Vertives)
    {

        List<Vector3> v_vertives = new List<Vector3>();                     //此处的v_vertives的z为s_Vertives的序号
        for (int i = 0; i < s_Vertives.Length; i++)
        {
            v_vertives.Add(new Vector3(s_Vertives[i].x, s_Vertives[i].y, i));
        }

        int sn = 0;
        List<int> tTriangles = new List<int>();
        int layer = 0;
        while (v_vertives.Count > 3 && layer < 1000)
        {
            List<Vector2> v_points = new List<Vector2>();
            for (int i = 0; i < v_vertives.Count; i++)
            {
                v_points.Add(v_vertives[i]);
            }
            int sna = sn - 1;
            if (sna < 0)
                sna = v_points.Count - 1;
            int snb = sn;
            int snc = sn + 1;
            if (snc >= v_points.Count)
                snc = 0;

            List<Vector2> v_triangle = new List<Vector2>();
            v_triangle.Add(v_points[sna]);
            v_triangle.Add(v_points[snb]);
            v_triangle.Add(v_points[snc]);


            bool bl_haveOtherPointInTriangle = false;
            for (int i = 0; i < v_points.Count; i++)
            {
                if (i != sna && i != snb && i != snc)
                {
                    if (Check_Point_InPolygon(v_points[i], v_triangle) == true)
                    {
                        bl_haveOtherPointInTriangle = true;
                        break;
                    }
                }
            }
            bool bl_cutEar = false;
            if (bl_haveOtherPointInTriangle == false)
            {
                Vector2 v_center = (v_triangle[0] + v_triangle[1] + v_triangle[2]) / 3;
                if (Check_Point_InPolygon(v_center, v_points) == true)
                {
                    int ta = (int)v_vertives[sna].z;
                    int tb = (int)v_vertives[snb].z;
                    int tc = (int)v_vertives[snc].z;
                    tTriangles.Add(tc);
                    tTriangles.Add(tb);
                    tTriangles.Add(ta);

                    v_vertives.RemoveAt(snb);
                    bl_cutEar = true;
                }
            }
            if (bl_cutEar == false)
            {
                sn++;
            }
            if (sn >= v_vertives.Count)
                sn = 0;
            layer++;


        }
        if (v_vertives.Count == 3)
        {
            int ta = (int)v_vertives[0].z;
            int tb = (int)v_vertives[1].z;
            int tc = (int)v_vertives[2].z;
            tTriangles.Add(tc);
            tTriangles.Add(tb);
            tTriangles.Add(ta);


        }
        Debug.Log("tTriangles.Count : " + tTriangles.Count + "  layer : " + layer);
        return tTriangles;
    }

    //***********   判断是否在多边形内，射线法
    //***********   从检查点发射一条射线，若该射线碰到的边的数量为奇数，则该点在多边形内部
    bool Check_Point_InPolygon(Vector2 v_check, List<Vector2> v_points)
    {
        //从检查点向右做线，若碰到两点之间的线段，则num_across++
        int num_across = 0;
        int count = 0;
        int i = 0;
        while (count < v_points.Count)
        {
            Vector2 v1 = v_points[i];
            if (i == v_points.Count - 1)
                i = -1;
            Vector2 v2 = v_points[i + 1];

            if (v1.y == v2.y)
            {

            }
            else if (v1.y == v_check.y && v1.x >= v_check.x)
            {
                num_across++;
            }
            else if (v2.y == v_check.y && v2.x >= v_check.x)
            {
                num_across++;
            }
            else if (Mathf.Sign(v1.y - v_check.y) == Mathf.Sign(v2.y - v_check.y))
            {

            }
            else
            {
                float x_line = v1.x + (v2.x - v1.x) * (v_check.y - v1.y) / (v2.y - v1.y);
                if (x_line >= v_check.x)
                {
                    num_across++;
                }
            }

            i++;
            count++;
        }

        if (num_across % 2 == 1)
            return true;
        return false;
    }

注：
代码尝试次数不多，所以可能会出错
在绘制Polygon Collider 2D时，节点要逆时针排列