title: I want to force a render, but only draw as fast as possible (InvalidateVisual / CompositionTarget.Rendering)
body: <p>I'm working on a real-time WPF/Silverlight (and soon WP7) visualization component and I'm looking for the best solution to force a redraw of the entire component in a Game-loop style. Redraw should be on-demand, but I don't want to back up the message pump with re-draw calls. Most of the drawing in my component is done using non-WPF primitives (e.g. Bitmap Interop, Direct2D) so my code does not use InvalidateVisual, and as a result, currently looks like this</p>
  
  <pre><code>// Pseudocode, doesnt compile, just to convey the meaning
  public void InvalidateElement()
  {
      if (CurrentlyDrawing)
          return;
  
      Dispatcher.BeginInvoke(() =&gt; 
      {
          CurrentlyDrawing = true;
  
          DoDrawInternal();
  
          CurrentlyDrawing = false;            
      }
  }
  </code></pre>
  
  <p>Ok so this is great. If I call InvalidateElement lots of times I get good responsiveness. However, what I want to do is ensure I can push data to my visualization component as fast as possible but only draw when the component is able to draw, and not keep drawing to catch up with the data once the input stream completes. </p>
  
  <p>No I can't override OnRender, I'm using non-WPF drawing inside WPF ;-)</p>
  
  <p>Basically what I want is something like the old Invalidate() / OnPaint in WindowsForms, or better yet, a game loop in DirectX. </p>
  
  <p>At the moment I get the situation where if I have an external thread that pushes data to the visualization component at a high rate then if I Stop pushing data I get another 20 seconds worth of refreshes to get through before the component stops drawing. I want to stop drawing as soon as data has gone in. </p>
  
  <p>Another idea I had was to handle CompositionTarget.Rendering in the visualization component then implement some sort of rudimentary Queue to push data to and the Rendering event consumes this data as fast as it can. </p>
  
  <p><strong>In Summary</strong> </p>
  
  <p>Given a WPF visualization component, V, and a datasource which pushes it data every 1ms, D, how can I ensure that no matter the datarate of D, V draws data at 30FPS (or whatever it can do) and updates itself in chunks, sort of how a game render loop does in DirectX? </p>
  
  <p>When the data stops, V should redraw everything it has up to now in one go. When the data is too fast, V draws larger chunks at a time to compensate. </p>
  
  <p>If you need more information I'd be happy to share it. Right now I've just posted a synopsis to gauge if there are any quick fixes but a fuller Q with code examples can be provided on request. </p>
  
  <p>Best regards, </p>