简单的canvas祖玛小游戏

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
<style>
*{ margin:0; padding:0;}
body{ background:black;}
#div1{ background:white; 600px; margin:20px auto;}
</style>
<script>
window.onload = function(){
var oC = document.getElementById('c1');
var oGC = oC.getContext('2d');

var i = 0;

var yImg = new Image();

yImg.src = 'person.png';

yImg.onload = function(){

setInterval(function(){

oGC.clearRect(0,0,oC.width,oC.height);

oGC.beginPath();
//弧度 = 角度 * Math.PI/180
oGC.arc(300,200,200,-90*Math.PI/180,180*Math.PI/180,false);
oGC.stroke();

oGC.beginPath();
oGC.arc(250,200,150,180*Math.PI/180,360*Math.PI/180,false);
oGC.stroke();
oGC.beginPath();
oGC.arc(400,200,20,0*Math.PI/180,360*Math.PI/180,false);
oGC.stroke();

for(var i=0;i<ball.length;i++){

oGC.beginPath();
oGC.moveTo(ball[i].x,ball[i].y);
oGC.arc(ball[i].x,ball[i].y,20,0*Math.PI/180,360*Math.PI/180,false);
oGC.fill();
}

oGC.save();
oGC.translate(300,200);
oGC.rotate(iRotate);
oGC.translate(-40,-40);
oGC.drawImage(yImg,0,0);
oGC.restore();

for(var i=0;i<bullet.length;i++){

oGC.save();
oGC.fillStyle = 'red';
oGC.beginPath();
oGC.moveTo(bullet[i].x,bullet[i].y);
oGC.arc(bullet[i].x,bullet[i].y,20,0*Math.PI/180,360*Math.PI/180,false);
oGC.fill();
oGC.restore();
}

oGC.save();
oGC.font = '60px impact';
oGC.textBaseline = 'top';
oGC.fillStyle = 'red';
oGC.shadowOffsetX = 10;
oGC.shadowOffsetY = 10;
oGC.shadowColor = 'green';
oGC.shadowBlur = 5;
var w = oGC.measureText('简易祖玛').width;
var h = 60;
oGC.fillText('简易祖玛', (oC.width - w)/2 , 450 );
oGC.restore();

},1000/60);

setInterval(function(){

for(var i=0;i<ball.length;i++){

ball[i].num++;

if( ball[i].num == 270 ){
ball[i].r = 150;
ball[i].startX = 250;
ball[i].startY = 50;
}

if( ball[i].num == 270 + 180 ){
alert('游戏结束');
window.location.reload();
}

ball[i].x = Math.sin(ball[i].num*Math.PI/180) * ball[i].r + ball[i].startX;
ball[i].y = ball[i].r - Math.cos(ball[i].num*Math.PI/180) * ball[i].r + ball[i].startY;

}

for(var i=0;i<bullet.length;i++){
bullet[i].x = bullet[i].x + bullet[i].sX;
bullet[i].y = bullet[i].y + bullet[i].sY;
}

for(var i=0;i<bullet.length;i++){

for(var j=0;j<ball.length;j++){

if( pz(bullet[i].x,bullet[i].y,ball[j].x,ball[j].y) ){

bullet.splice(i,1);
ball.splice(j,1);
break;

}

}

}

},30);

var ball = [];

setInterval(function(){

ball.push({
x : 300,
y : 0,
r : 200,
num : 0,
startX : 300,
startY : 0
});

},350);

var iRotate = 0;

oC.onmousemove = function(ev){
var ev = ev || window.event;

var x = ev.clientX - oC.offsetLeft;
var y = ev.clientY - oC.offsetTop;

var a = x - 300;
var b = y - 200;

var c = Math.sqrt(a*a + b*b);

if(a>0 && b>0){
iRotate = Math.asin(b/c) + 90*Math.PI/180;
}
else if(a>0){
iRotate = Math.asin(a/c);
}

if(a<0 && b>0){
iRotate = -(Math.asin(b/c) + 90*Math.PI/180);
}
else if(a<0){
iRotate = Math.asin(a/c);
}

};

var bullet = [];

oC.onmousedown = function(ev){
var ev = ev || window.event;

var x = ev.clientX - oC.offsetLeft;
var y = ev.clientY - oC.offsetTop;

var a = x - 300;
var b = y - 200;

var c = Math.sqrt(a*a + b*b);

var speed = 5;

var sX = speed * a/c;
var sY = speed * b/c;

bullet.push({
x : 300,
y : 200,
sX : sX,
sY : sY
});

};

};

function pz(x1,y1,x2,y2){

var a = x1 - x2;
var b = y1 - y2;

var c = Math.sqrt(a*a + b*b);

if(c < 40){
return true;
}
else{
return false;
}

}

};
</script>
</head>