How does VNC continuously repaint windows?

Question

How does VNC send REPAINT messages to windows even when a user is not active?

I would like to implement this in C sharp - I've had a look at the PrintWindow, SendMessage methods and none of them achieve the same thing as VNC (tested by capturing images and its black) but with VNC I get the full picture.

What techniques are they using to do this and can this be implemented in C sharp to get windows to always repaint even when a user is not active (i.e. RDP is closed, minimised or similar).

Thanks all

Answer 1

You could use the technique used by video games, which consists in redrawing permanently a window during CPU idle time.

I found a C# implementation here.

You just have to adapt it to your needs.

Answer 2

VNC does NOT send WM_PAINT messages

Windows does (and it does not care whether a user is active). See also

Is it possible to screenshot a minimized application

How to get the screenshot of a minimized application programmatically?

Capturing screenshots of a minimized remote desktop