canvas之画圆

<canvas id="canvas" width="500" height="500" style="background-color: yellow;"></canvas>

 1 var canvas=document.getElementById("canvas");
 2     var cxt=canvas.getContext("2d");
 3     //画一个空心圆
 4     cxt.beginPath();
 5     cxt.arc(200,200,50,0,360,false);
 6     cxt.lineWidth=5;
 7     cxt.strokeStyle="green";
 8     cxt.stroke();//画空心圆
 9     cxt.closePath();
10     //画一个实心圆
11     cxt.beginPath();
12     cxt.arc(200,100,50,0,360,false);
13     cxt.fillStyle="red";//填充颜色,默认是黑色
14     cxt.fill();//画实心圆
15     cxt.closePath();
16 
17     //空心和实心的组合
18     cxt.beginPath();
19     cxt.arc(300,300,50,0,360,false);
20     cxt.fillStyle="red";
21     cxt.fill();
22     cxt.strokeStyle="green";
23     cxt.stroke();
24     cxt.closePath();