效果图：
代码如下：
<!doctype html>
<html>
<head>
<meta http-equiv="content-type" content="text/html;charset=utf-8" />
<title>canvas 画多边形</title>
</head>
<body>
<canvas id="mycanvas" width="500" height="500"></canvas>
</body>
<script>
var canvas = document.getelementbyid("mycanvas");
var ctx = canvas.getcontext('2d');
function draw(x,y,n,r){
var i,ang;
ang= math.pi*2/n;
ctx.save();
ctx.fillstyle = 'rgba(255,0,0,.3)';
ctx.strokestyle = 'hsl(120,50%,50%)';
ctx.linewidth = 1;
ctx.translate(x,y);
ctx.moveto(0,-r);
ctx.beginpath();
for(i=0;i<n;i++){
ctx.rotate(ang);
ctx.lineto(0,-r);
}
ctx.closepath();
ctx.fill();
ctx.stroke();
ctx.restore();
}
draw(100,100,3,40);
draw(200,100,4,40);
draw(300,100,5,40);
draw(100,200,6,40);
draw(200,200,7,40);
draw(300,200,8,40);
</script>
</html>
更多canvas绘制多边形。