🚀 go-pugleaf

In article <a_rubin.721333938@dn66> a_rubin@dsg4.dse.beckman.com (Arthur Rubin) writes:
>In <1992Nov6.183318.5344@netcom.com> danwood@netcom.com (Daniel J Wood) writes:
>>I have a little "windowing" package I've written; when you open up a window
>>on top of another, it saves the contents of the window(s) behind it by
>>reading the ASCII/color bytes from the display buffer, and socks it away
>>for restoration after the window is closed. THE PROBLEM is that this technique
>>only would work in "text" mode, not in one of the various graphics modes
>>where characters are painted to the screen.
>
>Doesn't this violate the "Backing Store" patent?  (Proof once again that the
>patent was obvious.)

Only if he uses the same algorithm and data structures as that patent
specifies.  Here are the relevant claims from the patent (4,555,775):

    1. A computer terminal display system comprising
    a display surface,
    means for simultaneously displaying a plurality of overlapping
	    rectangular graphic layers on said surface, wherein
	    each of said graphic layers comprises an autonomous
	    level of graphical information,
    means for associating each of said graphic layers with an independent
	    computer program,
    means for storing a complete bitmap for each of said graphic layers, and
    means responsive to the associated one of said independent computer
	    programs for continuously updating each of said bitmaps.

In other words, a windowed display system.  Pike would have a real hard
time defending his claim to have invented windowed displays within a year
before 1982 when he filed for his patent; the Xerox Alto was well known in
the industry in the late 70's.

    2. The display system according to claim 1 wherein said bitmaps
    for all partially obscured ones of said graphic layers comprise
    a plurality of partial bitmaps of obscured layers linked together.

Notice the specific mention of "linked together".  The descriptive part of
the patent (which I've read, but don't have online) goes into more details
about the data structures and algorithms that make use of them.

Daniel Wood's description sounds more like X's "save under" feature for
temporary windows (similar also to the MIT Lisp Machine's pop-up temporary
window facility, which was described in documentation around 1980, a couple
of years before Pike filed for his patent).  Instead of keeping a linked
list of obscured regions it just saves away everything under the new
window.

-- 
Barry Margolin
System Manager, Thinking Machines Corp.

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