如何开发一个简单的HTML5 Canvas 小游戏

开发一个简单的HTML5 Canvas 小游戏步骤如下：
1创建画布
var canvas = document.createElement("canvas");
var ctx = canvas.getContext("2d");
canvas.width = 512;
canvas.height = 480;
document.body.appendChild(canvas);

2准备图片
var bgReady = false;
var bgImage = new Image();
bgImage.onload = function () {
bgReady = true;
};
bgImage.src = "images/background.png";

3游戏对象
var hero = {
speed: 256, // 每秒移动的像素
x: 0,
y: 0
};
var monster = {
x: 0,
y: 0
};
var monstersCaught = 0;

4处理用户的输入
var keysDown = {};

addEventListener("keydown", function (e) {
keysDown[e.keyCode] = true;
}, false);

addEventListener("keyup", function (e) {
delete keysDown[e.keyCode];
}, false);

5开始一轮游戏
var reset = function () {
hero.x = canvas.width / 2;
hero.y = canvas.height / 2;
monster.x = 32 + (Math.random() * (canvas.width - 64));
monster.y = 32 + (Math.random() * (canvas.height - 64));
};