[vtkusers] vtk annotations/MFC drawing on the CDC

[John Biddiscombe]

> I tried it but as soon as any transformations happen then the drawing
> disappears.  Anybody else tried this?  I need to do some annotation in

Apologies for delayed response...

You need to watch out....When you call Paint() or similar, a WM_PAINT
handler gets acivated (generally) and your callback paint handler will work
as fine.

As soon as you click on the screen and start rotating stuff, the interactor
(see vtkInteractorStyle and subclasses) will call a Renderwindow->Render()
This doesn't go through the same sequence and no WM_PAINT related stuff
happens.

If you want to overlay drawings on top of vtk renders, you need to delve a
bit deeper and intercept calls further up the foodchain if you follow me.

JB