canvas-star1.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.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 , r , 2*r ,x , y , a )
                }
    

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

            cxt.fill();
            cxt.stroke();
        }
    </script>
</body>
</html>

 

posted @ 2015-11-19 17:30  Cynthia娆墨旧染  阅读(190)  评论(0)    收藏  举报