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From: ekberg@asl.dl.nec.COM (Tom Ekberg)
Newsgroups: comp.windows.x
Subject: Re: PC X servers / backing store
Message-ID: <9103041710.AA12610@asl.dl.nec.com>
Date: 4 Mar 91 17:10:29 GMT
Sender: daemon@athena.mit.edu (Mr Background)
Organization: The Internet
Lines: 22

From: boing!dale@bloom-beacon.mit.edu (Dale Luck)
 > This is absolutely untrue. Backing store is a feature just like colors,
 > visuals, shape extensions, pex and everything else. ...

I have do disagree with that.  From the X11R4 protocol document:

	Backing-stores indicates when the server supports backing stores for
	this screen, although it may be storage limited in the number of
	windows it can support at once.  If save-unders is True, the server can
	support the save-under mode in CreateWindow and ChangeWindowAttributes,
	although again it may be storage limited.

This means that backing store may be supported by a server, and that a server
that supports it may choose to not honor advice that it should maintain the
contents of obscured regions when the window is mapped.  Checking to see if the
server supports backing store via the macro DoesBackingStore(screen) is not
enough.  The same is true for save-unders and the DoesSaveUnders(screen) macro.

As was stated earlier, X clients should always be prepared to handle expose
events.

  -- tom, ekberg@aslss02.asl.dl.nec.com (x3503)