line segment

   /// <summary>
    /// 判定某点是否在线段上
    /// </summary>
    /// <param name="lineStart"></param>
    /// <param name="lineEnd"></param>
    /// <param name="midPoint"></param>
    /// <returns></returns>
    public static bool IsPointOnLine(Vector3 lineStart,Vector3 lineEnd,Vector3 midPoint)
    {
        //if (midPoint.x == lineStart.x || midPoint.x == lineEnd.x)
        //{

        //}
        //if (midPoint.x >= Mathf.Min(lineStart.x, lineEnd.x) && midPoint.x <= Mathf.Max(lineStart.x, lineEnd.x))
        //{
        //    if ((midPoint.z - lineStart.z) / (midPoint.x - lineStart.x) == ((midPoint.z - lineEnd.z) / (midPoint.x - lineEnd.x)))
        //    {
        //        return true;
        //    }
        //}
        float StartToEnd =Mathf.Sqrt((lineEnd.x - lineStart.x) * (lineEnd.x - lineStart.x) + (lineEnd.z - lineStart.z)*(lineEnd.z - lineStart.z));
        float StartToMid = Mathf.Sqrt((midPoint.x - lineStart.x) * (midPoint.x - lineStart.x) + (midPoint.z - lineStart.z) * (midPoint.z - lineStart.z));
        float MidToEnd = Mathf.Sqrt((lineEnd.x - midPoint.x) * (lineEnd.x - midPoint.x) + (lineEnd.z - midPoint.z) * (lineEnd.z - midPoint.z));
        if (StartToEnd == StartToMid + MidToEnd)
            return true;
        return false;
    }


    /// <summary>
    /// 根据两条线段端点判断是否相交
    /// </summary>
    /// <param name="pointAStart"></param>
    /// <param name="pointAEnd"></param>
    /// <param name="pointBStart"></param>
    /// <param name="pointBEnd"></param>
    /// <returns></returns>
    public static bool IsInterSect(Vector3 lineAStart,Vector3 lineAEnd,Vector3 lineBStart,Vector3 lineBEnd)
    {
        #region 特例太多
        //求斜率 暴力点
        float k1;
        float k2;
        float b1;
        float b2;
        //特殊情况 斜率正无穷
        if (lineAEnd.x == lineAStart.x|| lineBEnd.x == lineBStart.x)
        {
            if (lineAEnd.x == lineAStart.x&&lineBEnd.x == lineBStart.x)//巧了，平行
            {
                if (lineAStart.x == lineBStart.x)//更巧了，直线重合
                {
                    //判断线段是否重合
                    if ((Mathf.Max(lineAStart.z, lineAEnd.z) >= Mathf.Min(lineBStart.z, lineBEnd.z)) && (Mathf.Min(lineAStart.z, lineAEnd.z) <= Mathf.Max(lineBStart.z, lineBEnd.z)))
                    {
                        return true;
                    }
                    else
                    {
                        return false;
                    }
                }
                else
                {
                    return false;
                }
            }
            else
            {
                if (lineAEnd.x == lineAStart.x)
                {
                    k2 = (lineBEnd.z - lineBStart.z) / (lineBEnd.x - lineBStart.x);
                    b2 = lineBStart.z - k2 * lineBStart.x;
                    float z2 = k2 * lineAEnd.x + b2;
                    if (z2 < Mathf.Max(lineBStart.z, lineBEnd.z) && z2 > Mathf.Min(lineBStart.z, lineBEnd.z) && z2 < Mathf.Max(lineAStart.z, lineAEnd.z) && z2 > Mathf.Min(lineAStart.z, lineAEnd.z))
                    {
                        return true;
                    }
                    else
                    {
                        return false;
                    }
                }else if (lineBEnd.x == lineBStart.x)
                {

                    k1 = (lineAEnd.z - lineAStart.z) / (lineAEnd.x - lineAStart.x);
                    b1 = lineAStart.z - k1 * lineAStart.x;
                    float z1= k1 * lineBEnd.x + b1;
                    if (z1 < Mathf.Max(lineBStart.z, lineBEnd.z) && z1 > Mathf.Min(lineBStart.z, lineBEnd.z) && z1 < Mathf.Max(lineAStart.z, lineAEnd.z) && z1 > Mathf.Min(lineAStart.z, lineAEnd.z))
                    {
                        return true;
                    }
                    else
                    {
                        return false;
                    }
                }
            }
        }

        //斜率存在情况
        k1 = (lineAEnd.z - lineAStart.z) / (lineAEnd.x - lineAStart.x);
        k2 = (lineBEnd.z - lineBStart.z) / (lineBEnd.x - lineBStart.x);
        b1 = lineAStart.z - k1 * lineAStart.x;
        b2 = lineBStart.z - k2 * lineBStart.x;
        if (k1 == k2)//平行
        {
            
            if (b1 != b2)
            {
                return false;//平行不重合
            }
            else
            {
                if (Mathf.Max(lineAStart.x, lineAEnd.x) >= Mathf.Min(lineBStart.x, lineBEnd.x) && Mathf.Min(lineAStart.x, lineAEnd.x) <= Mathf.Max(lineBStart.x, lineBEnd.x))
                {
                    return true;//重合
                }
                else
                {
                    return false;
                }
            }
        }
        else//有交点
        {
            float interSectX = (b2 - b1) / (k1 - k2);
            if (interSectX <= Mathf.Max(lineAStart.x, lineAEnd.x) && interSectX >= Mathf.Min(lineAStart.x, lineAEnd.x)&&
                interSectX<=Mathf.Max(lineBStart.x,lineBEnd.x)&&interSectX>=Mathf.Min(lineBStart.x,lineBEnd.x))//交点在线段上
            {
                return true;
            }
            else
            {
                return false;
            }
        }

        
    }