JavaScript Canvas 贪吃蛇游戏实现详解

<!DOCTYPE html>
<html lang="en">
<head>
 <meta charset="UTF-8">
 <title>贪吃蛇小游戏</title>
 <style>
*{margin:0; padding:0;}
header {
 display: block;
 margin: 0 auto;
 width: 500px;
 text-align: center;
}
header h1 {
 font-family: Arial;
 font-weight: bold;
}
header #newGameButton {
 display: block;
 margin: 20px auto;
 width: 100px;
 padding: 10px 10px;
 background-color: #8f7a66;
 font-family: Arial;
 color: white;
 border-radius: 10px;
 text-decoration: none;
}
header #newGameButton:hover {
 background-color: #9f8b77;
}
header p {
 font-family: Arial;
 font-size: 25px;
 margin: 20px auto;
}
canvas{
 display:block; 
 border:medium double black;
 margin:4px auto;
}
 </style>
</head>
<body>
 <header>
 <h1>贪吃蛇小游戏</h1>
 <a href="javascript:newgame();" id="newGameButton">New Game</a>
 <p>score:<span id="score">0</span></p>
 </header>
 <canvas id="canvas">
 Your browser doesn't support the <code>canvas</code> element.
 </canvas>
 <script>
 var CANVAS = document.getElementById("canvas");
var CTX = CANVAS.getContext("2d");
var SNAKE = new Array(); //用队列模拟蛇身
var DIR = "right"; //用来控制蛇头的方向
var SIZE = 20; //蛇身的宽度
var FOODX = 0; //食物的x坐标
var FOODY = 0; //食物的y坐标
var HEADX = 0; //蛇头的x坐标
var HEADY = 0; //蛇头的y坐标
var MAXWIDTH = 200; //画布的高度
var MAXHEIGHT = 200; //画布的宽度
var TIME = 400; //蛇的速度
var SCORE = 0; //计算玩家分数
var interval = null;

CANVAS.width = MAXWIDTH;
CANVAS.height = MAXHEIGHT;

window.onload = function(){
 newgame();
};
document.getElementById("newGameButton").click(function(){
 newgame();
});
function newgame(){
 SNAKE = []; //用队列模拟蛇身
 DIR = "right"; //用来控制蛇头的方向
 HEADX = 0; //蛇头的x坐标
 HEADY = 0; //蛇头的y坐标
 SCORE = 0;
 window.clearInterval(interval);
 interval = null;
 //初始化画布
 CTX.clearRect(0, 0, MAXWIDTH, MAXHEIGHT);
 //画一条蛇
 drawSnake();
 //放置食物
 setFood();
 //移动蛇
 interval = window.setInterval(move, TIME);

}
function move(){
 switch(DIR){
 case "up":HEADY = HEADY-SIZE;break;
 case "right":HEADX = HEADX+SIZE;break;
 case "down":HEADY = HEADY+SIZE;break;
 case "left":HEADX = HEADX-SIZE;break;
 }
 if(HEADX>MAXWIDTH-SIZE || HEADY>MAXHEIGHT-SIZE || HEADX<0 || HEADY<0){
 alert("你的分数为："+SCORE+"分，继续努力吧!失败原因：碰壁了.....");
 window.location.reload();
 }
 for(var i=1;i<SNAKE.length;i++){
 if(SNAKE[i][0] == SNAKE[0][0] && SNAKE[i][1] == SNAKE[0][1]){
 alert("你的分数为："+SCORE+"分，继续努力吧！失败原因：撞到自己了.....");
 window.location.reload();
 }
 }
 if(SNAKE.length == MAXWIDTH *MAXHEIGHT){
 alert("好厉害!么么哒~");
 window.location.reload();
 }
 moveIn(HEADX, HEADY);//移动一格
}
document.onkeydown = function(e) { //改变蛇方向
 var code = e.keyCode - 37;
 switch(code){
 case 1 : DIR = "up";break;//上
 case 2 : DIR = "right";break;//右
 case 3 : DIR = "down";break;//下
 case 0 : DIR = "left";break;//左
 }
}
//=============================画一条蛇=======================================================
function drawSnake(){
 CTX.fillStyle = "black";
 //画蛇头
 CTX.fillRect (HEADX, HEADY, SIZE, SIZE);
 SNAKE.push([HEADX, HEADY]);
 
 //画蛇身
 switch(DIR){
 case "up": 
 drawBody(HEADX, HEADY + SIZE, HEADX, HEADY + 2 * SIZE);
 break;
 case "right": 
 drawBody(HEADX - SIZE, HEADY, HEADX - 2 * SIZE, HEADY);
 break;
 case "down": 
 drawBody(HEADX, HEADY - SIZE, HEADX, HEADY - 2 * SIZE);
 break;
 case "left": 
 drawBody(HEADX + SIZE, HEADY, HEADX + 2 * SIZE, HEADY);
 break;
 }
}
function drawBody(x1, y1, x2, y2){
 CTX.fillRect (x1, y1, SIZE, SIZE); 
 CTX.fillRect (x2, y2, SIZE, SIZE); 
 SNAKE.push([x1, y1]);
 SNAKE.push([x2, y2]);
}
//===========================放置食物==============================
function setFood(){
 do{
 FOODX = SIZE * Math.floor(Math.random() * MAXWIDTH / SIZE);
 FOODY = SIZE * Math.floor(Math.random() * MAXHEIGHT / SIZE);
 }while(foodInSnake());
 CTX.fillStyle = "red";
 CTX.fillRect (FOODX, FOODY, SIZE, SIZE);
}
function foodInSnake(){
 for (var i = 0; i < SNAKE.length; i++) {
 if(FOODX == SNAKE[i][0] && FOODY == SNAKE[i][1]){
 return true;
 }
 }
 return false;
}
//========================================移动一格===========================
function moveIn(x, y){
 CTX.fillStyle = "black";
 CTX.fillRect(x, y, SIZE, SIZE);//重画蛇头 
 //把新蛇头添加到 SNAKE 数组
 var newSnake = [[x, y]];
 SNAKE = newSnake.concat(SNAKE);

 if(false == eatFood()){//如果没吃到食物，减少一格蛇尾 
 var snakeTail = SNAKE.pop();//获得蛇尾位置
 CTX.clearRect(snakeTail[0], snakeTail[1], SIZE, SIZE);//去掉蛇尾 
 }
}
function eatFood(){
 if(HEADX == FOODX && HEADY == FOODY){
 CTX.fillStyle = "block";
 CTX.fillRect (FOODX, FOODY, SIZE, SIZE);

 setFood();
 SCORE++;
 //$("#score").text(SCORE);
 document.getElementById("score").innerHTML = SCORE;
 return true;
 }
 return false;
}

 </script>
</html>

function newgame(){
 重置蛇和分数的数据；
 清除interval；
 初始化画布；
 画一条蛇；
 放置食物；
 使用定时器（setInterval）使蛇移动（move函数）；
}
function move(){
 根据方向改变蛇头下一格将要到达的位置；
 判断游戏是否结束，以及显示结束的原因（包含输赢）；
 蛇移动一格（moveIn函数）；
}
对键盘的方向键作监控，当改变方向时，修改全局变量DIR的值（用于存储方向）；
function moveIn(){
 在蛇头的前一格增加一格作为新的蛇头，并将蛇头的坐标作为第一个元素加入到代表蛇的数组中；
 if(没吃到食物){
 删除一格蛇尾，在画布中做相应改变；
 }
}