WPF is a retained composition engine. What it means is you don't have to do the rendering yourself hooking the Rendering event, but rather compose an image using nodes that you will put in a tree. See here for details on WPF architecture: WPF Architecture. I can assure you if you understand perfectly this document as well as the Layout System link Rick Sladkey sent, you should also understand why you should change your code if you want to continue with WPF.

If you play it right with WPF (ie: use dependency properties, override Measure & Arrange methods for example), you will see it's a very powerful engine capable of displaying thousands of nodes in the graphical tree. I suggest another useful reading: ZoomableApplication2: A Million Items