canvas-star0.html

<!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.lineWidth = 10;

                drawStar(context,200,300,400,400,30)

            }else{

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

            }

        }

        // x,y是偏移量 rot 偏移量

        function drawStar(cxt,r,R,x,y,rot){

            cxt.beginPath();

            for(var i=0;i<5;i++){

                //假设大圆内径300

                cxt.lineTo(Math.cos( (18+i*72 - rot) / 180 * Math.PI )*R+x,

                                -Math.sin( (18+i*72 - rot) / 180 * Math.PI )*R+y);

                //假设小圆内径150

                cxt.lineTo(Math.cos( (54+i*72 - rot) / 180 * Math.PI )*r+x,

                                -Math.sin( (54+i*72 - rot) / 180 * Math.PI )*r+y);

            }

            cxt.closePath();

            cxt.stroke();

        }

    </script>

</body>

</html>
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