Take a screenshot of a X window that is not visibled or covered or minimized

[pioz]

Hi all, Im new with X.
I have a question:
Is it possible with Xlib, XComposite or other extensions to take a
screenshot of a X window that is not visible, or is cover by another
window, or is minimized, or is to another desktop that is not active?

I know the XID of the window and I would like to get a png image of the
window.
If this is possible can you tell me the way to do this?
Thanks.

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