1.为飞机大战定义状态

 //定义游戏状态
        const START = 0;
        const STRATING = 1;
        const RUNNING = 2;
        const PAUSE = 3
        const END = 4;

 //初始化一个加载图片logo
        const copyright =new Image();
    copyright.src="img/START.jpg"

setInterval(() => {
                switch (state){
                    case START:
                        sky.judge();
                        sky.paint(context);
                        //渲染飞机大战LOGO
                        //图片原始宽高
                        let logo_x = (480 - copyright.naturalWidth)/2;
                        let logo_y = (650 - copyright.naturalHeight)/2;
                        context.drawImage(copyright,logo_x,logo_y)
                        break;
                    case STARING:
                        sky.judge();
                        sky.paint(context);
                        //这里需要一个飞机加载的loading
                        break;
                    case RUNNING:
                        sky.judge();
                        sky.paint(context);
                        //加载敌机
                        break;
                    case PAUSE:
                        sky.judge();
                        sky.paint(context);
                        //加载暂停页面
                        break;
                    case END:
                        sky.judge();
                        sky.paint(context);
                        //加载游戏结束字样
                        break;
                }

            }, 10);