So in my case I can not hide the form, I need to make it visible to the client all the time
i think that is only available with DirectX.
Magnification is not the way to do it and will not work in conjunction with DWM.
EDIT:
without hide or minimize your form.. see
Zitat:
Windows doesen't render invisible parts of the screen due to performance issues. At least older Windows versions didn't render invisible parts of the screen.
if the form hidden or minimized then a simple BitBlt Call should work on all Window Versions to
greets