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/// 
    /// 判断点是否在多边形内.    /// ----------原理----------    /// 注意到如果从P作水平向左的射线的话，如果P在多边形内部，那么这条射线与多边形的交点必为奇数，    /// 如果P在多边形外部，则交点个数必为偶数(0也在内)。    /// 
    public bool IsInPolygon(Vector3 checkPoint, List
   
     polygonPoints)    {
           bool inside = false;                int pointCount = polygonPoints.Count;        Vector2 p1, p2;        for (int i = 0, j = pointCount - 1; i < pointCount; j = i, i++)        {
               p1 = polygonPoints[i];            p2 = polygonPoints[j];            if (checkPoint.y < p2.y)            {
                   if (p1.y <= checkPoint.y)                {
                       if ((checkPoint.y - p1.y) * (p2.x - p1.x) > (checkPoint.x - p1.x) * (p2.y - p1.y))                    {
                           inside = !inside;                    }                }            }            else if (checkPoint.y < p1.y)            {
                   if ((checkPoint.y - p1.y) * (p2.x - p1.x) < (checkPoint.x - p1.x) * (p2.y - p1.y))                {
                       inside = !inside;                }            }        }        return inside;    }
   

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