之前一篇文章里写了一种差乘判断方法：

虽然用3D空间的差乘，但是只适用于2D空间

 

bool IsIntersection(Vector3 a, Vector3 b, Vector3 c, Vector3 d){    var crossA = Mathf.Sign(Vector3.Cross(d - c, a - c).y);    var crossB = Mathf.Sign(Vector3.Cross(d - c, b - c).y);    if (Mathf.Approximately(crossA, crossB)) return false;    var crossC = Mathf.Sign(Vector3.Cross(b - a, c - a).y);    var crossD = Mathf.Sign(Vector3.Cross(b - a, d - a).y);    if (Mathf.Approximately(crossC, crossD)) return false;    return true;}

 

 

后来我找到了另一个封装好的函数，不仅可以判断相交而且能查到是否相交于虚交点，是否平行等等。

原版的编写语言是java，但出处弄丢了

 

以下是我修改的Unity版本：

public static int GetIntersection(Vector3 a, Vector3 b, Vector3 c, Vector3 d, out Vector3 contractPoint){    contractPoint = new Vector3(0, 0);    if (Mathf.Abs(b.z - a.z) + Mathf.Abs(b.x - a.x) + Mathf.Abs(d.z - c.z)            + Mathf.Abs(d.x - c.x) == 0)    {        if ((c.x - a.x) + (c.z - a.z) == 0)        {            //Debug.Log("ABCD是同一个点！");        }        else        {            //Debug.Log("AB是一个点，CD是一个点，且AC不同！");        }        return 0;    }    if (Mathf.Abs(b.z - a.z) + Mathf.Abs(b.x - a.x) == 0)    {        if ((a.x - d.x) * (c.z - d.z) - (a.z - d.z) * (c.x - d.x) == 0)        {            //Debug.Log("A、B是一个点，且在CD线段上！");        }        else        {            //Debug.Log("A、B是一个点，且不在CD线段上！");        }        return 0;    }    if (Mathf.Abs(d.z - c.z) + Mathf.Abs(d.x - c.x) == 0)    {        if ((d.x - b.x) * (a.z - b.z) - (d.z - b.z) * (a.x - b.x) == 0)        {            //Debug.Log("C、D是一个点，且在AB线段上！");        }        else        {            //Debug.Log("C、D是一个点，且不在AB线段上！");        }        return 0;    }    if ((b.z - a.z) * (c.x - d.x) - (b.x - a.x) * (c.z - d.z) == 0)    {        //Debug.Log("线段平行，无交点！");        return 0;    }    contractPoint.x = ((b.x - a.x) * (c.x - d.x) * (c.z - a.z) -            c.x * (b.x - a.x) * (c.z - d.z) + a.x * (b.z - a.z) * (c.x - d.x)) /            ((b.z - a.z) * (c.x - d.x) - (b.x - a.x) * (c.z - d.z));    contractPoint.z = ((b.z - a.z) * (c.z - d.z) * (c.x - a.x) - c.z            * (b.z - a.z) * (c.x - d.x) + a.z * (b.x - a.x) * (c.z - d.z))            / ((b.x - a.x) * (c.z - d.z) - (b.z - a.z) * (c.x - d.x));    if ((contractPoint.x - a.x) * (contractPoint.x - b.x) <= 0            && (contractPoint.x - c.x) * (contractPoint.x - d.x) <= 0            && (contractPoint.z - a.z) * (contractPoint.z - b.z) <= 0            && (contractPoint.z - c.z) * (contractPoint.z - d.z) <= 0)    {        //Debug.Log("线段相交于点(" + contractPoint.x + "," + contractPoint.z + ")！");        return 1; // '相交      }    else    {        //Debug.Log("线段相交于虚交点(" + contractPoint.x + "," + contractPoint.z + ")！");        return -1; // '相交但不在线段上      }}