Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site utah-cs.UUCP Path: utzoo!watmath!clyde!burl!ulysses!allegra!oliveb!hplabs!utah-cs!b-davis From: b-davis@utah-cs.UUCP (Brad Davis) Newsgroups: net.graphics Subject: Re: exclusive-ORed cursors (Patent) Message-ID: <3486@utah-cs.UUCP> Date: Wed, 31-Dec-69 18:59:59 EDT Article-I.D.: utah-cs.3486 Posted: Wed Dec 31 18:59:59 1969 Date-Received: Sat, 12-Oct-85 15:26:29 EDT References: <588@stc-b.stc.UUCP> <5988@utzoo.UUCP> <914@turtlevax.UUCP> <745@terak.UUCP> <6018@utzoo.UUCP> <6026@utzoo.UUCP> <544@ecsvax.UUCP> Reply-To: b-davis@utah-cs.UUCP (Brad Davis) Organization: University of Utah VCIS Group Lines: 41 Summary: In article <544@ecsvax.UUCP> hes@ecsvax.UUCP (Henry Schaffer) writes: >> > The use of exclusive-OR to draw and erase cursors, rubber band lines, >> > etc. is covered by patent number 4,197,590... >> >> (Forgot this in my previous response) It would also be nice to know the >> date of the patent. >> >Date: Apr. 8, 1980 In my Principles of Interactive Computer Graphics, Second Edition, William M. Newman and Robert F. Sproull, McGraw-Hill Book Company, Copyright 1979, 1973, ISBN 0-07-046338-7, pages 256-259 the following algorithm is described. F-1 is the inverse of f. "... we simply apply to each pixel value 'x' the function 'f(x) = a - x' where 'a' is the maximum value that the frame buffer can record for a pixel. Then the function 'f-1 (x) = a - x' will invert the transformation." If a = 1 then the functions are f(x) = 1 - x and f-1 (x) = 1 - x. Anyone can show that for 1 bit the function 1 - x is the same as 1 xor x. 1 - x = f(x) 1 xor x = f(x) 0 | 1 0 | 1 1 | 0 1 | 0 Since the Newman and Sproull algorithm also works for color I will continue to use it and not be in violation of any patent, even though the general case seems to have been described in literature 1 year before the patent was awarded for the simple case. I wonder what NuGraphics does about software that was written before their patent was awarded that uses xor to do cursors and rubber banding. I might have even wrote such software in 1978. If someone has some old SIGGRAPH's it might be interesting to look for some references. Also, the bibliography in Newman and Sproull has a number of references that talk about raster graphics. -- Brad Davis {ihnp4, decvax, seismo}!utah-cs!b-davis b-davis@utah-cs.ARPA