    <div class="content"><div class='highlight'><pre>  <span class="hljs-keyword">var</span> Bullet = <span class="hljs-function"><span class="hljs-keyword">function</span><span class="hljs-params">(center, velocity)</span> </span>{
    <span class="hljs-keyword">this</span>.center = center;
    <span class="hljs-keyword">this</span>.size = { x: <span class="hljs-number">3</span>, y: <span class="hljs-number">3</span> };
    <span class="hljs-keyword">this</span>.velocity = velocity;
  };

  Bullet.prototyp