5. 贪吃蛇版本迭代（V5）
- 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
5.1 需求说明
- 读取按键码，并转换成0~3四个方向值
5.2 效果设计
5.3 编程过程
- 增加按键事件处理函数
document.onkeydown = function(e) { var code = e.keyCode - 37; switch(code){ 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; } }
5.4 代码注解
<script type="text/javascript">
//v1 ... v4
/*
* 接收键盘按键事件处理功能，用来改变蛇的前进方向。
*/
document.onkeydown = function(e) {
//读取按键码，并转换成0~3四个方向值
var code = e.keyCode - 37;
switch(code){
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;
}
}
</script>
5.5 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
window.onload = function(){ //v1
field = document.getElementById("field"); //v1
game = field.getContext("2d"); //v1
fieldWidth = field.width; //v2
fieldHeight = field.height; //v2
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; //v5
break;
case 1 : //按向上键
direction = 1; //v5
break;
case 2 : //按向右键
direction = 2; //v5
break;
case 3 : //按向下键
direction = 3; //v5
break;
}
}
function snakeMove(){ //v3
switch(direction){ //v4
case 0: //向左走
x = x - snakeUnitSize; //v4
break;
case 1: //向上走
y = y - snakeUnitSize; //v4
break;
case 2: //向右走
x = x + snakeUnitSize; //v4
break;
case 3: //向下走
y = y + snakeUnitSize; //v4
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
}
game.fillStyle = "#006699"; //v3
game.strokeStyle = "#006699"; //v3
game.fillRect(x, y, snakeUnitSize, snakeUnitSize); //v3
}
function putFood(){ //v2
var size = snakeUnitSize; //v2
game.fillStyle = "#ff0000"; //v2
game.strokeStyle = "#000000"; //v2
foodX = Math.ceil(Math.random() * (fieldWidth/size)); //v2
foodY = Math.ceil(Math.random() * (fieldHeight/size)); //v2
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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