h5教程html5如何使用canvas画空心圆与实心圆

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

var canvas=document.getElementById("canvas");
     var cxt=canvas.getContext("2d");
     //画一个空心圆
     cxt.beginPath();
     cxt.arc(200,200,50,0,360,false);
     cxt.lineWidth=5;
     cxt.strokeStyle="green";
     cxt.stroke();//画空心圆
     cxt.closePath();
     //画一个实心圆
     cxt.beginPath();
     cxt.arc(200,100,50,0,360,false);
     cxt.fillStyle="red";//填充颜色,默认是黑色
     cxt.fill();//画实心圆
     cxt.closePath();
     //空心和实心的组合
     cxt.beginPath();
     cxt.arc(300,300,50,0,360,false);
     cxt.fillStyle="red";
     cxt.fill();
     cxt.strokeStyle="green";
     cxt.stroke();
     cxt.closePath();