【unity3d】GUI 图像自动适配屏幕大小

图像大小是固定，直到屏幕的大小小于这个图像大小时，图像在保持自身长宽不变的情况下，缩小到可以在这个屏幕中完整观看的尺寸。

目前需要跑运行模式，而且要作为该图的组件

1. 组织：
   
2. background的Canvas设置
   
3. Panel设置为填满
   
4. Image 加入"AutoUiSize"的组件（下面有代码），设置为居中
   

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

public class AutoUiSize : MonoBehaviour
{
    // Start is called before the first frame update
    void Start()
    {
        
    }

    void UpdateSize(){
        RectTransform rt = GetComponent();
        
        if(rt.rect.width > Screen.width || rt.rect.height > Screen.height){
            if(Screen.width / Screen.height < rt.rect.width / rt.rect.height ){
                float scale =  Screen.width / rt.rect.width;
                rt.localScale = new Vector3(scale, scale, scale);
                Debug.Log("Scale is " + scale);
            }else{
                float scale = Screen.height / rt.rect.height;
                rt.localScale = new Vector3(scale, scale, scale);
                Debug.Log("Scale is " + scale);
            }
        }
    }

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

}