html5 js canvas中画星星的函数

function drawStar(cxt, x, y, outerR, innerR, rot) {
             cxt.beginPath();
             for (var i = ; i < ; i++) {
                 cxt.lineTo(Math.cos((+i*-rot)/*Math.PI)*outerR+x,
                 -Math.sin((+i*-rot)/*Math.PI)*outerR+y);
                 cxt.lineTo(Math.cos(( + i *  - rot) /  * Math.PI) * innerR + x,
                     -Math.sin(( + i *  - rot) /  * Math.PI) * innerR + y);
             }
             cxt.closePath();

             cxt.fillStyle = "#fb3";
             cxt.strokeStyle = "#fd5";
             cxt.lineWidth = ;
             cxt.lineJoin = "rount";

             cxt.fill();
             cxt.stroke();
         }

function draw() {
             for (var i = ; i < ; i++) {
                 var r = Math.random() *  + ;
                 var x = Math.random() * cvs.width;
                 var y = Math.random() * cvs.height;
                 var a = Math.random() * ;
                 drawStar(context, x, y, r, r / 2.0, a);
             }
         }