Unity_2D游戏对象的移动

using UnityEngine;
using System.Collections;

public class SwanMove : MonoBehaviour {

public float speed;
private float width;
private float height;
private Vector3 startPosition;

// Use this for initialization
void Start () {

//计算精灵自身的长度的一半
width = transform.GetComponent<Renderer>().bounds.extents.x;
//将屏幕坐标系转化成世界坐标系
//屏幕主要转视窗位置
Vector3 moveWidth = Camera.main.ScreenToWorldPoint(new Vector3(Screen.width, 0, 0));
startPosition = new Vector3(moveWidth.x + width,0, 0);
//把天鹅放在起始位置
transform.position = startPosition;
}

// Update is called once per frame
void Update () {
//如果精灵在屏幕内移动
if (transform.position.x<-startPosition.x)
{
//如果精灵超出屏幕的边界  那么就重新置位起始位置
transform.position = startPosition;

}transform.Translate(Vector3.right * -speed * Time.deltaTime);
}
}