using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class UIFollowGameObj : MonoBehaviour {

    public GameObject TargetObj;
    public Camera _camera;
    public Vector3 Offset;
    private Canvas canvas;
    // Use this for initialization
    void Start () {
        canvas = GameObject.Find("Canvas").GetComponent<Canvas>();
        _camera = canvas.GetComponentInChildren<Camera>();
    }
	
	// Update is called once per frame
	void Update () {
        //目标世界坐标转画布坐标  
        Vector3 worldToScreenPoint = Camera.main.WorldToScreenPoint(TargetObj.transform.position);
        //在画布上对应的点  
        worldToScreenPoint = new Vector3(worldToScreenPoint.x, worldToScreenPoint.y, canvas.planeDistance);
        Vector3 screenToWorldPoint = _camera.ScreenToWorldPoint(worldToScreenPoint);
        //得到最终画布坐标系中的投影点  
        Vector3 projPoint = canvas.transform.worldToLocalMatrix.MultiplyPoint(screenToWorldPoint);

        this.transform.localPosition = new Vector3 (projPoint.x,projPoint.y,0)+Offset;
    }
}