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);

        }

    }

}