title: HTML5 Canvas - Buttons doesn't work once scroll down the page
body: <p>I used HTML canvas to create a gun model as well as the control buttons (e.g. fire buttons), but the buttons doesn't work once scrolls the page down, the buttons only work when scroll to top of the page. Any ideas?</p>
  
  <p>I used the following code to detecting the clicks/ rollovers - </p>
  
  <pre><code>function defineRollovers() {
      dartsOver = hudCheck(hudLX,dy-(60*units),colHalf,140*units);
      missilesOver = hudCheck(hudLX+colHalf,dy-(60*units),colHalf,140*units);
      explodeOver = hudCheck(dx,dy+(230*units),60*units,50*units);
      dartFireOver = hudCheck(dx+(70*units),dy+(230*units),60*units,50*units);
      missileFireOver = hudCheck(dx+(140*units),dy+(230*units),60*units,50*units);
      rotateYOver = hudCheck(dx-(116*units),fullY-(116*units),108*units,116*units);
      rotateXOver = hudCheck(dx-(224*units),fullY-  (116*units),108*units,116*units);
     }
  </code></pre>