Path: utzoo!attcan!uunet!ginosko!brutus.cs.uiuc.edu!tut.cis.ohio-state.edu!bloom-beacon!LARRY.MCRCIM.MCGILL.EDU!mouse
From: mouse@LARRY.MCRCIM.MCGILL.EDU (der Mouse)
Newsgroups: comp.windows.x
Subject: Re:  backing store
Message-ID: <8909140158.AA17629@Larry.McRCIM.McGill.EDU>
Date: 14 Sep 89 01:58:20 GMT
Sender: daemon@bloom-beacon.MIT.EDU
Organization: The Internet
Lines: 42

> 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.

Sounds like a buggy server.

> 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?

What does backing-store do?  It asks (not tells) the server to keep a
copy of the whole window so you don't have to regenerate portions of it
yourself, just as you seem to expect it to.  (I would have liked a way
to say "this backing-store hint is not really a hint - give me an error
if you can't commit to honoring it".)

> [about the -wm option to someone's server]

> Second request: would people who have been using -wm please comment
> on their experience.  Is using -wm the norm?

Not around here.

> What are the drawbacks?

You pay the penalty for backing-store even on windows where it truly
isn't necessary.  I have a program, for example, that never draws
anything in any window - all the display action happens by setting the
background pixmaps of the windows.  Backing-store would be wholly
wasted on this program.

You, as a programmer, also get the illusion that Expose events don't
happen, so that code doesn't get tested.  Then when run with a server
that doesn't support -wm or was started without it, your program
hiccups unexpectedly.

					der Mouse

			old: mcgill-vision!mouse
			new: mouse@larry.mcrcim.mcgill.edu