Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!bcm!dimacs.rutgers.edu!mips!sdd.hp.com!think.com!barmar
From: barmar@think.com (Barry Margolin)
Newsgroups: comp.windows.x
Subject: Re:  AT&T Claims patent on part of MIT's X11 server.
Message-ID: <1991Mar6.215434.3830@Think.COM>
Date: 6 Mar 91 21:54:34 GMT
References: <9102231551.AA01386@lightning.McRCIM.McGill.EDU> <1812@cetia.cetia.fr>
Sender: news@Think.COM
Organization: Thinking Machines Corporation, Cambridge MA, USA
Lines: 28

It looks to me like AT&T's patent-infringement claim is unfounded.  Here is
an excerpt from a comment from server/ddx/mi/mibstore.c in the MIT sample
server:

 *    This is a cross between saving everything and just saving the
 * obscued areas (as in Pike's layers.)

If this comment is correct, and if the patented algorithm is the one used
in "Pike's layers" (seems like a reasonable assumption), MIT's backing
store implementation is explicitly *not* using the patented mechanism.
Claim 9 of the patent (posted by Ritchie to comp.misc and gnu.misc.discuss
-- maybe suppose someone should copy it here) specifically says that the
terminal maintains a separate backing bitmap for each obscured area of a
window and each window maintains a list of its backing bitmaps, and claim
10 says that each backing bitmap list includes a specification of the size
and position of the window.  MIT's code only seems to maintain a single
backing pixmap per window.

Furthermore, claim 1 in the patent specifies that it deals with
*rectangular* windows.  X servers that implement the shape extension
support non-rectangular windows, and don't fall under the claims of the
patent.

--
Barry Margolin, Thinking Machines Corp.

barmar@think.com
{uunet,harvard}!think!barmar