🚀 go-pugleaf

I have an application that draws graphics in a window. I want to save the
contents of the window across task switches so they can be restored when my
application is reactivated. At what point should I take a snapshot of the
screen? 

Some obvious answers present themselves. Upon receiving WM_ACTIVATE with
wParam=WA_INACTIVE seems a good place. The problem is that if WM_ACTIVATE was
generated as a result of ALT-TAB, there is a rectangular ALT-TAB window sitting
on top of my window when the WM_ACTIVATE message is received. The snapshot then
includes the ALT-TAB window. 

The same problem holds for WM_KILLFOCUS. 

Since some of the graphics drawn in the window manifest animation, it is not
useful to consider a metafile approach to redrawing the window. 

I also do not wish to draw on a memory context and a device context at each
grapics call. While this would maintain the necessary snapshot, I believe
the performance hit would be unacceptable. 

I am still looking for a good answer to this problem.