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Xref: sserve comp.org.eff.talk:9497 misc.int-property:596 comp.unix.bsd:6623 Newsgroups: comp.org.eff.talk,misc.int-property,alt.suit.att-bsdi,comp.unix.bsd Path: sserve!manuel.anu.edu.au!munnari.oz.au!metro!mama!andy From: andy@research.canon.oz.au (Andy Newman) Subject: Re: Patents: What they are. What they aren't. Other factors. Message-ID: <Bw6w0D.D0t@research.canon.oz.au> Sender: news@research.canon.oz.au Organization: Canon Information Systems Research Australia References: <id.6S0U.TRE@ferranti.com> <1992Oct13.055638.23596@netcom.com> <1992Oct14.033523.13036@u.washington.edu> Date: Fri, 16 Oct 1992 00:57:48 GMT Lines: 37 tzs@stein.u.washington.edu (Tim Smith) writes: >peter@ferranti.com (peter da silva) writes: >>They haven't just harmed individuals. For example, the Pike patent prevents >>people from building a window system that uses backing store in a certain >>way -- which happens to be the obvious and most effective way. This harms >>everyone who uses a computer system running a window system, since it forces >>them to use about twice as much RAM or a much faster CPU. > >If Pike's backing store is what I'm guessing (storing off-screen images of >the parts of windows that are obscured by other windows), then if it's so >obvious, how come Apple, Commodore, Microsoft, and many others overlooked >this technique? The 128K Mac was rather pressed for memory -- I would have >expected them to come up with any "obvious" methods to save RAM. > >--Tim Smith Pike's method stores only the occluded areas in off-screen memory. His rendering code can traverse a list of rectangular "framebuffer" areas when putting pixel values into memory. Apple did indeed overlook his technique, they used a method that doesn't use any memory to save occluded memory by forcing the program to redraw "damaged" areas. Commodore, in the Amiga, DO use Pikes technique, they even use the same names for the basic data structures (the Amiga's window system can also do Mac-style forced redraw to save more memory). I don't know what Microsoft do in Windows. The aim of backing store is to hide the details of any windowing from the user program. The program just thinks its got a graphics display of X by Y and draws into it. It doesn't have to care about areas of windows that are obscured by other windows. Pike's method does this memory efficiently. Other systems, notably X11, an entire copy of the window in off-screen memory rather than just the obscured areas. -- Andy Newman (andy@research.canon.oz.au) "Giving money and power to governments is like giving whiskey and car keys to teenage boys" - P.J.O'Rourke