title: WPF event on re-draw
body: <p>I have some code which renders the contents of a Canvas to a bitmap. Periodically, child elements of the Canvas can change visually and I need a way of discerning when this has happened so that I can re-draw the Bitmap. My initial idea was to override <code>Canvas.OnRender</code> but this doesn't seem to get called when a child re-renders.</p>
  
  <p>Any advice would be much appreciated</p>