How did Gnome/KDE do it?

[G B <gbpublicemailaddress yahoo com>]

How did Gnome/KDE make, for example, the linux
terminal, or any window who's background can be set to
the desktop (I'm not interested in setting the BG
image to the desktop in particular, but an arbitrary
image), and allow scrolling text over that image. 

Note, I don't mean tile the background of a text edit
widget and scroll down the tiles upon which the text
is permanently place, but actual scrolling text over a
non-scrolling image.

Hint: I notice that the text scrolling is done line by
line, not by a single, or arbitrary number of pixels.
Thanks,
Gary


                
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