unity 2D 物体跟随鼠标旋转移动

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

public class FollowMouse:MonoBehaviour {

    // Use this for initialization
    void Start() {

    }

    // Update is called once per frame
    void Update() {
        FollowMouseRotate();
        FollowMouseMove();
    }

    //物体跟随鼠标旋转
    private void FollowMouseRotate() {
        //获取鼠标的坐标，鼠标是屏幕坐标，Z轴为0，这里不做转换  
        Vector3 mouse = Input.mousePosition;
        //获取物体坐标，物体坐标是世界坐标，将其转换成屏幕坐标，和鼠标一直  
        Vector3 obj = Camera.main.WorldToScreenPoint(transform.position);
        //屏幕坐标向量相减，得到指向鼠标点的目标向量，即黄色线段  
        Vector3 direction = mouse - obj;
        //将Z轴置0,保持在2D平面内  
        direction.z = 0f;
        //将目标向量长度变成1，即单位向量，这里的目的是只使用向量的方向，不需要长度，所以变成1  
        direction = direction.normalized;
        //物体自身的Y轴和目标向量保持一直，这个过程XY轴都会变化数值  
        transform.up = direction;
    }

    //跟随鼠标移动
    private void FollowMouseMove() {
        float moveSpeed = 3.0f;
        if(Input.GetMouseButton(0))    //如果按下鼠标左键，移动速度变快
        {
            moveSpeed = 6.0f;
            transform.Translate(Vector3.up * moveSpeed * Time.deltaTime);
        } else {
            transform.Translate(Vector3.up * moveSpeed * Time.deltaTime);
        }
    }
}