Unity3D射线检测。

int groundLayerIndex = LayerMask.GetMask (Tags.Ground);

Ray ray = Camera.main.ScreenPointToRay (Input.mousePosition);
RaycastHit hitInfo;
if(Physics.Raycast (ray, out hitInfo, 200, groundLayerIndex))
{
　　　Vector3 target = hitInfo.point;
 　　 target.y = transform.position.y;
　　　transform.LookAt(target);
}

Ray ray = new Ray (transform.position,transform.forward);
RaycastHit hitInfo;
if(Physics.Raycast (ray, out hitInfo))
{
   lineRender.SetPosition(1,hitInfo.point);
}
else
{
   lineRender.SetPosition(1,transform.position + transform.forward * 100);
}