导图：
image.png
html内容：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>flappy_bird</title>
<style>
canvas {
border:1px solid red;
}
img {
display: none;
}
</style>
</head>
<body>
<canvas id="cvs" width="500" height="500"></canvas>
<script src="./js/util.js"></script>
<script src="./js/bird.js"></script>
<script src="./js/land.js"></script>
<script src="./js/pipe.js"></script>
<script src="./js/sky.js"></script>
<script src="./js/gameScene.js"></script>
<script src="./js/overScene.js"></script>
<script>
var cvs = document.querySelector( '#cvs' );
var ctx = cvs.getContext( '2d' );
util.loadImage({
bird: './img/bird.png',
land: './img/land.png',
pipeDown: './img/pipeDown.png',
pipeUp: './img/pipeUp.png',
sky: './img/sky.png'
}, function( imgObj ) {
// 根据背景的大小设置画布的大小
cvs.width = imgObj.sky.width;
cvs.height = imgObj.sky.height;
// 游戏场景是否继续
var isRun = true;
// 创建游戏场景
var gameScene = getGameScene( ctx, imgObj );
// 创建游戏结束场景
var overScene = getOverScene( ctx );
// 添加小鸟死亡的听众
gameScene.addListener( function() {
isRun = false; // 游戏场景退场
overScene.draw(); // 结束场景切入
} );
// 切入游戏场景，开始游戏
(function run() {
gameScene.draw();
if ( isRun ) {
requestAnimationFrame( run );
}
}());
});
</script>
</body>
</html>
