Path: utzoo!attcan!uunet!husc6!uwvax!oddjob!ncar!ames!ucsd!ucsdhub!hp-sdd!hplabs!hpda!hp-sde!hpfcdc!hpfclp!diamant
From: diamant@hpfclp.SDE.HP.COM (John Diamant)
Newsgroups: comp.windows.x
Subject: Re: changing menu widget behavior
Message-ID: <9740035@hpfclp.SDE.HP.COM>
Date: 1 Jul 88 19:26:33 GMT
References: <11393@steinmetz.ge.com>
Organization: HP SDE, Fort Collins, CO
Lines: 30

>     Unfortunately, there's a flaw with backing store:  you can't insist on
>     it.
> 
> You can't insist on it because there are servers out there (e.g., the
> X terminal that was being shown at Usenix) with a fixed amount of
> memory, and they simply can't commit to all backing store requests.

Yes, that's true.  Unfortunately, that makes it considerably less useful than
it would be otherwise.  If you have an application that needs backing store
or something like it to run effectively (a paint program that allows arbitrary
pixels to be turned on and off is an example) then you are forced to maintain
your own backing store via pixmaps and/or images, since you can never be
assured that the server will honor your backing store.  That means even if
it has the memory and will honor all uses of it, you still have to manange 
your own duplicate copy.  That's a waste of time and resources (though you
still get the benefit of the server's ability to be more efficient in
handling it when it can).

What might help would be a way to ask the server to reserve backing storage
space for a particular window such that it could decide at the beginning
whether it had the maximum space required and reserve it right then.  If it
refuses (whether it had the space or not), then the application could fall
back to the local maintenance approach.  This would avoid the redundancy for
most servers (workstations with large virtual memory).


John Diamant
Software Development Environments
Hewlett-Packard Co.		ARPA Internet: diamant@hpfclp.sde.hp.com
Fort Collins, CO		UUCP:  {hplabs,hpfcla}!hpfclp!diamant