8. 贪吃蛇版本迭代（V8）
- 张大为
- 辽宁师范大学计算机与信息技术学院@大连
- https://daweizh.github.io/h5/ QQ:1243605845
8.1 需求说明
- 放置第一份食物
- 吃到食物长长蛇身，再次投放食物
- 判断食物投放是否越界
8.2 效果设计
8.3 编程过程
- 加载游戏时投放食物
putFood(); - 吃到食物后长长身体并再次投放食物
if((foodX*snakeUnitSize)==x && (foodY*snakeUnitSize)==y){ snakeLength++; putFood(); } - 判断食物是否越界
if(foodX*size>fieldWidth-size) foodX = foodX - 1; if(foodY*size>fieldHeight-size) foodY = foodY - 1;
8.4 代码注解
<script type="text/javascript">
... ...
window.onload = function(){ //v1
... ...
//随机放置第一份食物
putFood();
window.setInterval(snakeMove, speed); //v3
}
... ...
function snakeMove(){ //v3
... ...
//如果蛇头碰到了食物
if((foodX*snakeUnitSize)==x && (foodY*snakeUnitSize)==y){ //v8
//吃掉食物，身体长长
snakeLength++; //v8
//重新放置食物
putFood(); //v8
}
}
function putFood(){ //v2
... ...
foodX = Math.ceil(Math.random() * (fieldWidth/size)); //v2
//判断食物位置是否在水平边界以外
if(foodX*size>fieldWidth-size) //v8
//做越界处理
foodX = foodX - 1; //v8
foodY = Math.ceil(Math.random() * (fieldHeight/size)); //v2
//判断食物位置是否在垂直边界以外
if(foodY*size>fieldHeight-size) //v8
//做越界处理
foodY = foodY - 1; //v8
game.fillRect(foodX*size, foodY*size, size, size); //v2
}
</script>
8.5 核心代码
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>Greedy Snake</title>
<style type="text/css">
div { /*v1*/
width:400px;
margin:0 auto;
}
canvas { /*v1*/
background:#abcdef;
border:1px solid #000000;
}
</style>
<script type="text/javascript">
var field; //v1
var game; //v1
var fieldWidth; //v2
var fieldHeight; //v2
var speed = 160; //v2
var foodX = foodY = 0; //v2
var snakeUnitSize = 8; //v2
var x = y = snakeUnitSize; //v3
var direction = 3; //v4
var snakeLength = 20; //v6
var pathMap = []; //v6
window.onload = function(){ //v1
field = document.getElementById("field"); //v1
game = field.getContext("2d"); //v1
fieldWidth = field.width; //v2
fieldHeight = field.height; //v2
//随机放置第一份食物
putFood(); //v8
window.setInterval(snakeMove, speed); //v3
}
document.onkeydown = function(e) { //v5
var code = e.keyCode - 37; //v5
switch(code){ //v5
case 0 : //按向左键
direction = 0;
break;
case 1 : //按向上键
direction = 1;
break;
case 2 : //按向右键
direction = 2;
break;
case 3 : //按向下键
direction = 3;
break;
}
}
function snakeMove(){ //v3
switch(direction){ //v4
case 0: //向左走
x = x - snakeUnitSize;
break;
case 1: //向上走
y = y - snakeUnitSize;
break;
case 2: //向右走
x = x + snakeUnitSize;
break;
case 3: //向下走
y = y + snakeUnitSize;
break;
}
if(x>fieldWidth || y>fieldHeight || x<0 || y<0){ //v4
alert("你挂了，继续努力吧!失败原因：碰壁了....."); //v4
window.location.reload(); //v4
}
for(var i=0; i<pathMap.length; i++){ //v7
if( parseInt(pathMap[i].x)==x && parseInt(pathMap[i].y)==y){ //v7
alert("你挂了，继续努力吧！失败原因：撞到自己了....."); //v7
window.location.reload(); //v7
}
}
if (pathMap.length>snakeLength) { //v6
var snakeTail = pathMap.shift(); //v6
game.clearRect(snakeTail['x'], snakeTail['y'], snakeUnitSize, snakeUnitSize); //v6
}
pathMap.push({'x':x,'y':y}); //v6
game.fillStyle = "#006699"; //v3
game.strokeStyle = "#006699"; //v3
game.fillRect(x, y, snakeUnitSize, snakeUnitSize); //v3
//如果蛇头碰到了食物
if((foodX*snakeUnitSize)==x && (foodY*snakeUnitSize)==y){ //v8
//吃掉食物，身体长长
snakeLength++; //v8
//重新放置食物
putFood(); //8
}
}
function putFood(){ //v2
var size = snakeUnitSize; //v2
game.fillStyle = "#ff0000"; //v2
game.strokeStyle = "#000000"; //v2
foodX = Math.ceil(Math.random() * (fieldWidth/size)); //v2
//判断食物位置是否在水平边界以外
if(foodX*size>fieldWidth-size) //v8
//做越界处理
foodX = foodX - 1; //v8
foodY = Math.ceil(Math.random() * (fieldHeight/size)); //v2
//判断食物位置是否在垂直边界以外
if(foodY*size>fieldHeight-size) //v8
//做越界处理
foodY = foodY - 1; //v8
game.fillRect(foodX*size, foodY*size, size, size); //v2
}
</script>
</head>
<body>
<!-- v1 -->
<h2 align="center">Greedy Snake</h2>
<!-- v1 -->
<div>
<!-- v1 -->
<canvas id="field" width="400" height="600">
This is the field that snake snaking.
</canvas>
</div>
</body>
</html>
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