[Unity算法]点是否在多边形范围内

参考链接：

https://www.zhihu.com/question/26551754

http://www.cnblogs.com/leoin2012/p/6425089.html

原理如下：

代码实现：

using UnityEngine;
using System.Collections.Generic;

public class MathTool {

    /// <summary>
    /// 点是否在多边形范围内
    /// </summary>
    /// <param name="p">点</param>
    /// <param name="vertexs">多边形顶点列表</param>
    /// <returns></returns>
    public static bool IsPointInPolygon(Vector2 p, List<Vector2> vertexs)
    {
        int crossNum = 0;
        int vertexCount = vertexs.Count;

        for (int i = 0; i < vertexCount; i++)
        {
            Vector2 v1 = vertexs[i];
            Vector2 v2 = vertexs[(i + 1) % vertexCount];

            if (((v1.y <= p.y) && (v2.y > p.y))
                || ((v1.y > p.y) && (v2.y <= p.y)))
            {
                if (p.x < v1.x + (p.y - v1.y) / (v2.y - v1.y) * (v2.x - v1.x))
                {
                    crossNum += 1;
                }
            }
        }

        if (crossNum % 2 == 0)
        {
            return false;
        }
        else
        {
            return true;
        }
    }
}