canvas-a13prototype.html

时间：2023-12-04 22:53:14
<!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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