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From: jonnyg@ROVER.UMD.EDU (Jon Greenblatt)
Newsgroups: comp.windows.x
Subject: Backing store
Message-ID: <8712022158.AA19000@rover.UMD.EDU>
Date: Wed, 2-Dec-87 16:58:40 EST
Article-I.D.: rover.8712022158.AA19000
Posted: Wed Dec  2 16:58:40 1987
Date-Received: Sun, 6-Dec-87 06:58:01 EST
Sender: usenet@ucbvax.BERKELEY.EDU
Organization: The ARPA Internet
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	I have a temporary solution for those awaiting backing store.  I
found this very useful for me so I thought I'd share it.  I am working on a
image processing package that runs on X11 and needed some way to preserve
and restore the image when it got abscured and needed this process to be
automatic (sounds like backing store to me...).  The way I simulated this
was to create a pixmap the same size and depth of the window I was
displaying and made this my background pixmap for the window (this will work
in X10 on some servers).  When ever I do a graphic command to the window I
first do it to the background pixmap then to the window itself, the results
are SIMULAR to backing store.  For those of you who try this under X10, keep
in mind that you can not execute graphics commands on a pixmap the way you
can in X11.  One thing to watch out for:  you should paint the window and
the background pixmap the same color before starting, the window is usualy
white by default and the pixmap may be black or just garbage by default.

	By the way for those of you having problems with X11 image
processing bugs, I put up the image by scan lines using vectors, I use
points for vectors of lenght 1, they didn't show up otherwise.  I have other
reasons for using vectors instead of the image processing routines but
thought I would throw this tidbit in anyway.

					Jon Greenblatt.

					(pcproj@gymble.umd.edu 128.8.128.16)
					(jonnyg@rover.umd.edu 128.8.2.73)