🚀 go-pugleaf

rjg@iSC.intel.com (Richard Greco) writes:
>One clarification to several other poster's comments.  The Pike
>patent covers the notion of backing store and not save unders.

Pike's paper only covered a particular implementation of backing store,
not the general concept.  Now, if the reference X server code had in
fact used Pike's algorithms (which it does not), there would be a problem.

In particular:

The essence of Pike's approach was to represent the obscured portions
of a window with a list of rectangular bitmaps, the union of which
constituted the obscured area of the screen.  This way, the memory
used for backing store for a window was directly proportional to the
area of the window that was obscured.  This separates the approach
from previous backing store schemes, which simply kept around a
full-size bitmap of the window's contents.  Pike also wrote a clever
wrapper around "bitblt" which automagically copied pieces of the source
bitmap into the appropriate destination (either the actual screen buffer
or one of the obscured rectangle bitmaps).

The MIT reference X server, on the other hand, keeps around a full
size image of the window, as did several systems before Pike's.  Now,
from my (admittedly casual) understanding of the MIT server code, the
only way it might infringe on Pike's work is that drawing operations
are distributed between the visible screen buffer and the backing
store as they are done, instead of always drawing to the backing
store, and then copying to the screen.  However, the mechanism and the
underlying representation are quite different.  There are, in fact,
comments in the code that refer to Pike's work and point out
contrasts.  Go take a look at the file ".../mit/server/ddx/mi/mibstore.c".

Of course, I'm not a lawyer, and it may require MIT going to court
against AT&T, but so far I think MIT has the better case.

-- 
Amanda Walker						      amanda@visix.com
Visix Software Inc.					...!uunet!visix!amanda
--
"When power leads man towards arrogance, poetry reminds him of his limitations.
 When power narrows the area of man's concern, poetry reminds him of the
 richness and diversity of his existence.  When power corrupts, poetry
 cleanses."	--John F. Kennedy