clip（）将当前的路径转换为裁剪路径
只能用一次，后续再用，不起作用
代码语言：javascript复制<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>day5-1</title>
<style type="text/css">
canvas{border:1px solid black;}
</style>
</head>
<body onload="draw()">
<canvas id="tutorial" width="150" height="150">
</canvas>
<script type="text/javascript">
function draw(){
var canvas = document.getElementById('tutorial')
if(canvas.getContext){//判断浏览器是否支持getContext属性
var ctx = canvas.getContext('2d');
ctx.fillRect(0,0,150,150);
ctx.translate(75,75);
ctx.beginPath();
ctx.arc(0,0,60,0,Math.PI*2,true);
ctx.clip();
var lingrad = ctx.createLinearGradient(0, -75, 0, 75)//渐变位置
lingrad.addColorStop(0,'#232256')
lingrad.addColorStop(1,'#143778')
ctx.fillStyle=lingrad
ctx.fillRect(-75,-75,150,150)
var f = function(a){
setTimeout(function(){
ctx.save();
ctx.fillStyle = "#fff";
ctx.translate(75-Math.floor(Math.random()*150),
75-Math.floor(Math.random()*150));
drawStar(ctx,Math.floor(Math.random()*4) 2);
ctx.restore();
},100*a)
}
for(var j=0;j<100;j ){
f(j)
}
function drawStar(ctx,r){
ctx.save();
ctx.beginPath();
ctx.moveTo(r,0);
for(var i=0;i<9;i ){
ctx.rotate(Math.PI/5);
if(i%2==0){
ctx.lineTo((r/0.525731)*0.200811,0);
}else{
ctx.lineTo(r,0);
}
}
ctx.closePath();
ctx.fill();
ctx.restore();
}
}else{}
}
</script>
</body>
</html>
