[Gllug] XOR

[Gordon Joly]

At 18:07 +0100 2004/04/15, Richard Jones wrote:
>On Thu, Apr 15, 2004 at 05:33:17PM +0100, Andrew Halliwell wrote:
>>  Even the sinclair zx spectrum has "OVER 1" mode, which turned on XOR for
>>  screen writing. (Used in that case for games written in BASIC, and of
>>  course, for things like underline, creating umlauts from 2 normal
>>  characters, u and " iirc, etc)
>
>There's even a bogus patent on using XOR for cursor drawing IIRC.  See
>John Walker's page about bogus patents:
>
>http://www.fourmilab.ch/autofile/www/chapter2_105.html
>
>Rich.


Indeed.

http://en.wikipedia.org/wiki/List_of_notorious_software_patents

But it what sense is it bogus?


http://www.wired.com/news/linux/0,1411,61631,00.html

"...California-based Cadtrak owns a much-disputed patent on using a 
simple mathematical operation, known as XOR, to draw a cursor over an 
image on screen."

http://nothings.org/computer/patents.html

"Closely related is a patent which apparently covers results, not 
process. The exclusive-or-cursor patent is a simple example of this. 
There are a number of mathematically equivalent ways of expressing 
the xor algorithm, but it appears to be widely believed that all of 
them are covered by the patent. The patent apparently is understood 
to cover the idea of representing an onscreen cursor by complementing 
each "visible" pixel of the cursor with the contents of whatever is 
on screen."


Gordo.

-- 
"Think Feynman"/////////
http://pobox.com/~gordo/
gordon.joly at pobox.com///
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