title: WPF FrameworkElement manipulation after OnRender
body: <p>I create a custom control and draw some objects in OnRender.</p>
  
  <p>Now the question is: Assume I draw 5 rectangles in OnRender. Is there a way to delete eg the 1. rectangle without to retrigger OnRender and redraw rectangles 2-5?</p>
  
  <p>Or in general, is there another way, where you can update or add/remove rendering instructions, instead of rebuilding the drawing in OnRender every time something changes?</p>
  
  <hr>
  
  <p>@ dsdel: Ok, the idea is, that the calculations in OnRender might be very heavy. You can render Text, Geometric shapes. And I ask myself, why shall I create all the Geometry and FormatedText again, if the only thing I want, is to change the position of a line. The Rectangles above just were an example. It is more a general question. Is it really necessary to recalculate all elements in a new call to OnRender instead of just updating what has changed. I mean OnRender does not render anything, it just prepares some object structures that get transfered to DirectX for rendering. So I just want to manipulate the existing object structures instead of creating new once every time a little thing changes.</p>