title: How Visual deliver it's list of Drawing objects to rendering system?
body: <p>I'm trying to figure out how WPF rendering system works and now I'm stuck
  for several days with question: </p>
  
  <p>How Visual deliver it's list of Drawing objects to rendering system ?</p>
  
  <p>I don't see members of Visual that serve that purpose.</p>
  
  <p>Simply put, what I have to implement in:</p>
  
  <pre><code>public class MyVisual : Visual
  {
     // ???
  }
  </code></pre>
  
  <p>so that   </p>
  
  <pre><code>DrawingGroup dg = VisualTreeHelper.GetDrawing( new MyVisual() );
  </code></pre>
  
  <p>become non-null (valid DrawingGroup object) ?</p>
  
  <p><strong>Edit (March 14 2013):</strong></p>
  
  <p><strong>I expected this question should be very easy to answer for anyone who
  understand WPF, but as it seems, it's not.</strong></p>
  
  <p><strong>I asked this question more than a week ago and this very specific, concrete,
  and fundamental question about WPF architecture was left unanswered in spite
  of presence of so many experts for WPF around. Is it posible that no one of
  those WPF experts, who answers so many "upper level" questions, actually
  don't know how WPF function at it's base level ?</strong></p>
  
  <p><strong>Actually, my question in fact is: Is there any real expert for WPF or is it
  so mysterious that is beyond human understanding ?</strong> </p>