Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!munnari.oz.au!labtam!krite!graeme
From: graeme@krite.labtam.oz (Graeme Gill)
Newsgroups: comp.windows.x
Subject: Re: BackingStore Always (was:PC X servers / backing store)
Summary: Thanks. It would be nice if this was documented a bit better.
Message-ID: <10102@krite.labtam.oz>
Date: 7 Mar 91 01:35:06 GMT
References: <9103051609.AA02015@devnull.Eng.Sun.COM>
Organization: Labtam Australia Pty. Ltd., Melbourne, Australia
Lines: 36

In article <9103051609.AA02015@devnull.Eng.Sun.COM>, dshr@eng.sun.COM (David Rosenthal) writes:
> Correct behaviour is defined by the protocol spec (page 474 of the Digital
> Press 2nd edition):
> 
> 	"This event [Expose] is reported to clients selecting Exposure on
> 	the window.  It is generated when no valid contents are available
> 	for regions of the window,  and either:
> 
> 	-	the regions are visible,
> 	-	the regions are viewable and the server is (perhaps newly)
> 		maintaining backing store on the window,
> 	-	or the window is not viewable but the server is (perhaps
> 		newly) honoring [the] window's backing-store attribute of
> 		Always or WhenMapped.

	The problem was that our server is capable of setting BackingStore
to Always as a default. (Setting the default to something other than NotUseful
is a way of invoking backing store for clients that do not set the attribute
themselves)

	It seems to me that there is the possibility of others being
confused by this if they created a window with this attribute. The Xlib
Programming Manual (Second Edition) page 94 says about attributes:

	"A second group is provided to allow clients to improve their
	redrawing performance under certain conditions. These are backing_pixel,
	backing_planes, backing_store, bit gravity and save_under. These
	attributes do not affect the appearance or operation of a client."

	It appears that the operation of the client will be affected unless
Exposure events are solicited from the window before BackingStore Always is
selected.

	Graeme Gill
	Labtam Australia Pty. Ltd.
	graeme@labtam.oz.au