Question: I am drawing to a regular `HwndRengerTarget` but other windows, which have nothing to do with Direct2D, overlap it. 

The problem is that these windows get painted over when I draw to the `HwndRengerTarget`.

I would like to tell Direct2D not to touch a specific region of the `HwndRengerTarget` (i.e. don't touch the pixels that are already on the screen), so that these windows remain correctly visible.

Is that possible?

If I draw normally then call `RedrawWindow` on the windows, it flickers a lot.

Thanks.

Answer: 
Why not arrange the windows (HWNDs) so that the Direct2D one is at the bottom of the z-index? It should be the first child of its parent. Then clipping will be automatic. You may need the WS\_CLIPSIBLINGS window style.
I had the same problem.

Fixed by calling CreateWindowEx LAST for the D2D child HWND.
So AFTER all the other child windows are created.