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canvas-star2.html

2015-11-19 17:31 393 查看

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
</head>
<body>
<canvas id="canvas" style="margin:0 auto;">
The current browser does not support Canvas, can replace the browser a try!
</canvas>

<script>

window.onload = function(){
var canvas = document.getElementById('canvas');

canvas.width = 1024;
canvas.height = 768;

if(canvas.getContext('2d')){
var context = canvas.getContext('2d');

context.fillStyle = "#000";
context.fillRect(0,0,canvas.width,canvas.height)

for(var i=0;i<200;i++){
var r = Math.random() * 10 + 10;
var x = Math.random() * canvas.width;
var y = Math.random() * canvas.height;
var a = Math.random() * 360;

drawStar(context , x , y , r , a )
}

}else{
alert('当前游览器不支持Canvas，请更换游览器后再试！');
}
}

function drawStar(cxt,x,y,R,rot){
cxt.save();

cxt.translate(x,y);
cxt.rotate(rot/180*Math.PI);
cxt.scale(0.05*R,0.05*R)

starPath(cxt);

cxt.fillStyle = "#fb3";
cxt.strokeStyle = "#fd5";
cxt.lineWidth = 3;
cxt.lineJoin = "round";

cxt.fill();
cxt.stroke();

cxt.restore()
}

function starPath(cxt){

cxt.beginPath();
for(var i=0;i<5;i++){
cxt.lineTo(Math.cos( (18+i*72) / 180 * Math.PI )*20,
-Math.sin( (18+i*72) / 180 * Math.PI )*20);
cxt.lineTo(Math.cos( (54+i*72) / 180 * Math.PI )*0.5*20,
-Math.sin( (54+i*72) / 180 * Math.PI )*0.5*20);
}
cxt.closePath();
}
</script>
</body>
<script>
/*图形变换

位移 translate(x,y)

旋转 rotate(deg)

缩放 scale(sx,sy)

*/
</script>
</html>

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