<h2>需求：</h2>    <p>模拟球形的脉冲运动。</p>    <p>小球的构造函数如下：</p>    <pre>  <code class="language-java">// 圆球的构造函数  function Ball(radius, color) {      if(radius === undefined) { radius = 40; }      if(color === undefined) { color = "#ff0000"; }      this.x = 0;      this.y = 0;      this.radius = radius;      this.rotation = 0;      this.scaleX = 1;      this.scaleY = 1;      this.color = color;      this.lineWidth = 1;  }  Ball.prototype.draw = function(context) {      context.save();      context.translate(this.x, this.y);      context.rotate(this.rotation);      context.scale(this.scaleX, this.scaleY);      context.lineWidth = this.lineWidth;      context.fillStyle = this.color;      context.beginPath();      context.arc(0, 0, this.radius, 0, Math.PI * 2, true);      context.closePath();      context.fill();      if(this.lineWidth > 0) {          context.stroke();      }      context.restore();  }</code></pre>    <h2>二. 思路分析：</h2>    <p>使用正弦值改变球形的比例，即可制造出脉冲效果。</p>    <p>如下：</p>    <pre>  <code class="language-java"><canvas id="canvas" width="200" height="200" style="background: #ccc;"></canvas>    var canvas = document.getElementById("canvas"),      context = canvas.getContext("2d"),      ball = new Ball(),      angle = 5,      centerScale = 1,      range = 0.5,      speed = 0.05;        ball.x = canvas.height / 2;      ball.y = canvas.height / 2;      ball.lineWidth = 0;    (function drawFrame() {      window.requestAnimationFrame(drawFrame, canvas);      context.clearRect(0, 0, canvas.width, canvas.height);      ball.scaleX = ball.scaleY = centerScale + Math.sin(angle) * range;      angle += speed;      ball.draw(context);  })();</code></pre>    <p>演示如下： <a href="/misc/goto?guid=4959677072568858255" rel="nofollow,noindex">http://codepen.io/dengzhirong/pen/PzgygG</a></p>    <p> </p>    <p>来自：http://www.dengzhr.com/js/959</p>    <p> </p>