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From: mlm@odi.com (Mitchell Model)
Newsgroups: comp.windows.x
Subject: backing store
Message-ID: <1989Sep13.193303.15857@odi.com>
Date: 13 Sep 89 19:33:03 GMT
Reply-To: mlm@odi.com (Mitchell Model)
Organization: Object Design Inc., Burlington, MA
Lines: 42

[X11R3, 12mb Sun 3/60, OS 4.03, high-res monitor]

Having used other window systems which save the contents of obscured
windows (Smalltalk, various Lisp machines) I have been disconcerted by
my inability to get this feature working in X.  Setting backing store
to WhenMapped in my application's windows results in strange behavior,
including displaying pieces of other windows.

First request: would someone who understands backing store in X
please give the rest of us an explanation of what it does, how it
works, and how to use it?

Yesterday, after a year of using X in several environments, I noticed
for the first time the -wm option to Xserver, which the man page
describes as follows:

     -wm     forces the default backing-store of all  windows  to
             be   WhenMapped;   a  cheap  trick  way  of  getting
             backing-store to apply to all windows.

I tried starting up x with:
	xinit -- -wm
and it worked just fine.  The redisplay flash that otherwise occurs
when GNU Emacs is raised to the top doesn't happen, my application
doesn't get expose events when it is raised, etc.  Looking at the SIZE
output of "ps avx", I can see that -wm is costing me a little less
than a megabyte, with several xterms, GNU Emacs running in an 81x75
window, my application (a structure graphics program for developing
object-oriented database schemata) in a 1500x1200 window, and a few
other things.

Second request: would people who have been using -wm please comment on
their experience.  Is using -wm the norm?  What are the drawbacks?
Etc.  (Depending on those responses, if any, you could also interpret
this posting as sharing my discovery of -wm, which you might want to
try out.)
 
-- 
	Mitchell L Model		    Object Design, Inc.
	Director, HeadStart Program	    1 New England Executive Park
		  			    Burlington MA 01803
	mlm@odi.com, odi!mlm@uunet.uu.net   (617) 270-9797