title: Request Animation Frame issue
body: <p>I've been writing some examples with RequestAnimationFrame and Canvas: </p>
  
  <pre><code>var ctx;
  var x=0,y=0,v_x=5,v_y=5;
  window.addEventListener('load',init);
  window.requestAnimationFrame = (function(){
      return window.requestAnimationFrame ||
      window.webkitRequestAnimationFrame ||
      window.mozRequestAnimationFrame ||
      function(f){
          window.setTimeout(f,1000/60);
      }
  })();
  function init(){
      ctx = document.getElementById("canvas").getContext("2d");
      draw();
  }
  function draw(){
      ctx.beginPath();
      ctx.rect(0,0,50,50);
      ctx.closePath();
      ctx.fill();
      x += v_x;
      y += v_y;
      requestAnimationFrame(draw);
  }
  </code></pre>
  
  <p>The problem is that I want the Rect() to go diagonally down with the variables v_x and v_y and the requestAnimationFrame, then I get the Rectangle fully drawn, but it doesn't move!</p>