射线，克隆，画线

using UnityEngine;
using System.Collections;

public class Drawwarnline : MonoBehaviour {

    // Use this for initialization
    private Vector3 pos1;//第一个点的位置
    private Vector3 pos2;//第二个点的位置
    private RaycastHit hit;
    private Ray ray;
    private int num = 0;

    public bool ischoose;//是否开始画线
    public GameObject warnline;//线模型
    void Update()
    {
       
        if (Input.GetMouseButtonDown(0))//按下鼠标左键
        {
            ray = Camera.main.ScreenPointToRay(Input.mousePosition);//从主相机投射一条射线到鼠标位置
            if (Physics.Raycast(ray,out hit))//在场景中投下可与所有碰撞器碰撞的一条光线。
            {
                if (hit.collider != null)//碰撞到碰撞器
                {
                    if (!ischoose)
                    {
                        pos1 = new Vector3(hit.point.x, hit.point.y, hit.point.z);//记录第一个点坐标
                        //Debug.Log(pos1);
                        ischoose = true;
                    }
                    else
                    {
                        num++;
                        pos2 = new Vector3(hit.point.x, hit.point.y, hit.point.z);//第二个点坐标
                        //Debug.Log(pos2);
                        var distance = Vector3.Distance(pos2, pos1);//两点之间距离，这里var为float类型，使用var，var会自动检测类型
                        Vector3 direction = (pos2 - pos1).normalized;//要花的线的方向单位向量
                        GameObject warnobj = GameObject.Instantiate(warnline, (pos2 - pos1) / 2, Quaternion.identity) as GameObject;//克隆警戒线
                       warnobj.name = "warnline" + num;
                        
                        warnobj.transform.localScale = new Vector3(100f, 10f, distance * 70);//根据父对象调整大小
                        warnobj.transform.position = warnobj.transform.position + pos1;//位置
                        warnobj.transform.forward = direction;
                        warnobj.transform.parent = GameObject.Find("pwarnline").transform;
                        //Debug.Log(direction);
                        ischoose = false;
                    }
                }
            }
            
        }
       
    }
}