title: HTML Canvas doesn't update
body: <p>When I call move() the "y" variable is changed but the box is still rendered in the same position.</p>
  
  <pre><code>var c = document.getElementById("can");  //my canvas id is "can"  
  var pen = c.getContext("2d");
  var y = 200;
  setInterval(render(y), 1000/30); //update 30 times per second
  
  function move(dir){
      y=y+dir;
  }
  
  function render(height) {
      pen.beginPath();
      pen.clearRect(0,0,888,500);
      pen.beginPath();
      pen.rect(30,height,50,50); //Draw the player
      pen.fillStyle="green";
      pen.fill();
  }
  </code></pre>