HTML5 canvas如何绘制圆形？（代码实例）

function draw() {

    var canvas = document.getElementById('SimpleCanvas');

    if ( ! canvas || ! canvas.getContext ) {

          return false;

    }

    var cx = 360;   

    var cy = 400;   

    var radius = 36;

    var context = canvas.getContext('2d');

    context.beginPath();

    context.arc(cx, cy, radius, 0, 2 * Math.PI, false);

    context.fillStyle = '#9fd9ef';

    context.fill();

    context.lineWidth = 1;

    context.strokeStyle = '#00477d';

    context.stroke();

    context.beginPath();

    context.moveTo(0, 0);

    context.lineTo(cx, cy);

    context.stroke();

    }