move images

[T.C. Zhao]

Sorry for asking maybe a novice question:

I now have a need to move a rectangular frame around the screen.
I know of XOR but I also know it is not very portable. The way
I am now doing it is to save whatever underneath the frame before
putting the rectangular frame and restore it when the frame is moved.
It works nicely except it is slow(rectread and rectwrite.) I noticed
that when open a new window, moving the frame around is quite fast,
how is that done ? Any help would be appreciated.

Thanks in advance.