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canvas-a13prototype.html

2015-11-24 12:13 676 查看

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>扩展方法</title>
</head>
<body>
<canvas id="canvas" style="margin:0 auto;border:1px #ddd solid">
The current browser does not support Canvas, can replace the browser a try!
</canvas>

<script>
var canvas = document.getElementById('canvas');

// 新的API
CanvasRenderingContext2D.prototype.fillStar = function(r,R,x,y,rot){
this.beginPath();
for(var i=0;i<5;i++){
this.lineTo(Math.cos( (18+i*72 -rot)/180*Math.PI )*R+x,
-Math.sin( (18+i*72 -rot)/180*Math.PI  )*R+y);
this.lineTo(Math.cos( (54+i*72 -rot)/180*Math.PI )*r+x,
-Math.sin( (54+i*72 -rot) /180*Math.PI )*r+y);
}
this.closePath();

this.fill();
}

window.onload = function(){

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

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

// begin
context.fillStyle = "#058";
// 调用新的API
context.fillStar(150,300,400,400,0)

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

</script>
</body>
</html>

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