title: Call function while rendering heatmap HTML canvas
body: <p>I'm using <a href="http://www.patrick-wied.at/static/heatmapjs/" rel="nofollow">heatmap.js</a> on my website, which looks great. One slight issue is that when the event to generate the heat map is triggered, the page becomes unusable for a few seconds while the canvas loads.</p>
  
  <p>I've created a modal dialog with a load bar that will eventually hide the page during this process, I'm just having difficulty creating a function to call the modal.</p>
  
  <p>On another (slightly less useful) heat map library called <a href="https://github.com/sunng87/heatcanvas" rel="nofollow">heatcanvas</a>, there are two functions to handle this:</p>
  
  <pre><code>heatmap.onRenderingStart = function(){document.getElementById('status').innerHTML = 'rendering...'}
  heatmap.onRenderingEnd = function(){document.getElementById('status').innerHTML = 'ready'}
  </code></pre>
  
  <p>Is there a way I can create two similar functions with the heatmap.js (http://www.patrick-wied.at/static/heatmapjs/) library?</p>
  
  <p>Thanks</p>