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Path: euryale.cc.adfa.oz.au!newshost.anu.edu.au!newshost.nla.gov.au!act.news.telstra.net!psgrain!newsfeed.internetmci.com!in1.uu.net!EU.net!Belgium.EU.net!idefix.CS.kuleuven.ac.be!geert From: geert@cs.KULeuven.ac.be (Geert Uytterhoeven) Newsgroups: comp.os.linux.development.apps,comp.os.linux.development.system,comp.os.linux.x,comp.os.linux.hardware,comp.os.linux.setup,comp.unix.bsd.386bsd.misc,comp.unix.bsd.bsdi.misc,comp.unix.bsd.netbsd.misc,comp.unix.bsd.freebsd.misc Subject: Re: Why to not buy Matrox Millennium Date: 27 Mar 1996 10:55:44 GMT Organization: Department of Computer Science, Katholieke Universiteit Leuven, Belgium Lines: 36 Sender: geert@idefix (Geert Uytterhoeven) Distribution: world Message-ID: <4jb6rg$72q@idefix.CS.kuleuven.ac.be> References: <4j21ph$crr@slappy.cs.utexas.edu> <ROELL.96Mar25214459@blah.xinside.com> <4javnt$qo5@jaws.cs.hmc.edu> NNTP-Posting-Host: idefix.cs.kuleuven.ac.be Xref: euryale.cc.adfa.oz.au comp.os.linux.development.apps:13729 comp.os.linux.development.system:20108 comp.os.linux.x:27758 comp.os.linux.hardware:34522 comp.os.linux.setup:47474 comp.unix.bsd.386bsd.misc:310 comp.unix.bsd.bsdi.misc:2808 comp.unix.bsd.netbsd.misc:2586 comp.unix.bsd.freebsd.misc:16101 In article <4javnt$qo5@jaws.cs.hmc.edu>, mmicek@muddcs.cs.hmc.edu (Michael J. Micek) writes: |> In article <ROELL.96Mar25214459@blah.xinside.com>, |> Thomas Roell <roell@xinside.com> wrote: |> >There are now a couple of real problems with HW acceleration. |> > Because every chip has a different scheme of mapping |> >certain functions to the buffers (like limits/clamping for the |> >z-buffer) you have to write a software emulation of each chip for the |> >cases where the chip cannot render directly a specific thing. As the |> >OpenGL invariance rules state that the same pixels get rendered |> >whether you draw to the backbuffer or the frontbuffer you have a |> >serious limitation here. The next hugeish problem is feeding the |> |> It would be interesting to know what the heck he's talking about. |> Anybody not working in the industry (an engineering student, say) care |> to explicate, just for the heck of it? What's a z-buffer? A z-buffer is used to remember the z (depth) coordinate of every pixel on the screen. If you want to draw a new object, you have to check for every pixel of the new object whether it's in front of or behind the corresponding pixel that's already on the screen. If it's in front of the screen pixel (compare the z position in the z buffer), you have to draw the pixel and update the z buffer. If it's behind, just forget about it. Hardware z buffering is much faster than software, especially combined with polygon drawing. All you have to do is tell the graphics chip the coordinates of the vertices of the polygon, and it will automatically update the frame buffer and the z buffer. Greetings, Geert -- Geert Uytterhoeven Geert.Uytterhoeven@cs.kuleuven.ac.be Wavelets, Linux/m68k on Amiga http://www.cs.kuleuven.ac.be/~geert/ Department of Computer Science -- Katholieke Universiteit Leuven -- Belgium