canvas game greedy snake
直接上效果图：
这个贪食蛇关键地方在于数组，它的长度增加其实是数组的增长，就是数组的向前追加等操作，核心就是数组的操作。
完整代码：
<!DOCTYPE html>
<html>
<body>
<canvas id="myCanvas" width="240" height="240" style="border:1px solid #d3d3d3;">
Your browser does not support the HTML5 canvas tag.
</canvas>
<script>
//r数组表示蛇 ； co表示蛇前进的方向，默认向下 ； e表示食物
var ctx = document.getElementById("myCanvas").getContext("2d"),
r = [{
x: 10,
y: 9
}, {
x: 10,
y: 8
}],
co = 40,
e = null;
/*为了避免按键太快，使定时器没有反应过来，出现bug*/
var offOn=true;
/*这是关卡的开关*/
var offOn01=true;
/*关卡倒计开始值*/
var num=3;
//循环，间隔为200毫秒
var timer=setInterval(doMove, 200);
function doMove() {
//给蛇加上阴影效果
ctx.shadowBlur = 20, ctx.shadowColor = "black";
//游戏是否已经结束
if (check(r[0], 0) || r[0].x < 0 || r[0].x >= 24 || r[0].y < 0 || r[0].y >= 24) return;
//如果有食物，则根据蛇前进的方向判断是否吃到了食物，并且将蛇数组中最后一个元素换到首部
e != null && ((co == 40 && r[0].x == e.x && r[0].y + 1 == e.y) ||
(co == 38 && r[0].x == e.x && r[0].y - 1 == e.y) ||
(co == 37 && r[0].x - 1 == e.x && r[0].y == e.y) ||
(co == 39 && r[0].x + 1 == e.x && r[0].y == e.y)) ?
(r.unshift(e), e = null, r.unshift(r.pop())) : (r.unshift(r.pop()));
//根据方向，重新设定蛇数组首元素的坐标，从而进行移动
(co == 40 || co == 38) ? (r[0].x = r[1].x, r[0].y = r[1].y + (co == 40 ? 1 : -1)) : (r[0].x = r[1].x + (co == 39 ? 1 : -1), r[0].y = r[1].y);
//清空屏幕
ctx.clearRect(0, 0, 240, 240);
//如果有食物，则绘制食物
if (e) ctx.fillRect(e.x * 10, e.y * 10, 10, 10);
//绘制蛇
for (var i = 0; i < r.length; i++) ctx.fillRect(r[i].x * 10, r[i].y * 10, 10, 10);
//如果没有食物，则在随机位置上加入一粒食物
while (e == null || check(e)) e = {
y: (Math.floor(Math.random() * 24)),
x: (Math.floor(Math.random() * 24))
};
/*分数*/
ctx.shadowBlur=0;
ctx.font="12px Arial";
ctx.fillText("分数:"+(r.length - 2),10,10);
ctx.textBaseline="top";
//判断游戏是否结束
if (check(r[0], 0) || r[0].x < 0 || r[0].x >= 24 || r[0].y < 0 || r[0].y >= 24)
alert("game over\n你获得：" + (r.length - 2) + "分");
/*设置一个关卡，就是分数到10分后进入下一关，只设置一个关卡*/
if((r.length-2)==10){
if(offOn01){
clearInterval(timer);
offOn01=false;
var timer0=setInterval(function(){
if(num<=0){
clearInterval(timer0);
}
ctx.clearRect(0, 0, 240, 240);
ctx.font="20px Arial";
ctx.textBaseline="middle";
ctx.textAlign="center";
ctx.fillText("下一关:"+num,120,120);
num=--num<0?0:num;
},1000);
setTimeout(function(){
timer=setInterval(doMove, 100);
},4000);
}
}
offOn=true;
}
//加入键盘事件，用方向键来控制蛇前进的方向
/*(Math.abs(event.keyCode - co) != 2判断不能向后走
left:37,top:38,right:39,bottom:40
反方向刚刚好是相差2
*/
document.onkeydown = function(event) {
if(offOn){
offOn=false;
co = event.keyCode >= 37 &&
event.keyCode <= 40 &&
(Math.abs(event.keyCode - co) != 2) ? event.keyCode : co;
}
}
//判断指定位置是否与蛇重叠
/*这是为了检测自己撞到自己或检测食物在贪食蛇里面的*/
function check(e, j) {
for (var i = 0; i < r.length; i++)
if (j != i && r[i].x == e.x && r[i].y == e.y) return true;
return false;
}</script>
</body>
</html>可以直接复制上面代码看效果；
上面的核心代码：
//如果有食物，则根据蛇前进的方向判断是否吃到了食物，并且将蛇数组中最后一个元素换到首部
e != null && ((co == 40 && r[0].x == e.x && r[0].y + 1 == e.y) ||
(co == 38 && r[0].x == e.x && r[0].y - 1 == e.y) ||
(co == 37 && r[0].x - 1 == e.x && r[0].y == e.y) ||
(co == 39 && r[0].x + 1 == e.x && r[0].y == e.y)) ?
(r.unshift(e), e = null, r.unshift(r.pop())) : (r.unshift(r.pop()));
//根据方向，重新设定蛇数组首元素的坐标，从而进行移动
(co == 40 || co == 38) ? (r[0].x = r[1].x, r[0].y = r[1].y + (co == 40 ? 1 : -1)) : (r[0].x = r[1].x + (co == 39 ? 1 : -1), r[0].y = r[1].y);这是贪食蛇的核心代码，就是数组长度添加，和数组里的值怎么改变。
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