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- From: peterb@perturb.esd.sgi.com (Peter Birch)
- Subject: Re: Indigo Graphics and Z-Buffering
- Message-ID: <tnl0lm0@zola.esd.sgi.com>
- Followup-To: comp.sys.sgi
- Sender: news@zola.esd.sgi.com (Net News)
- Organization: Silicon Graphics, Inc. Mountain View, CA
- References: <92350.143855SML108@psuvm.psu.edu> <1glhm0INNlu@fido.asd.sgi.com> <3201@contex.contex.com>
- Date: Thu, 17 Dec 92 20:23:07 GMT
- Lines: 40
-
- [discussion about z-buffering on XS, and how OpenGL will provide a software
- z-buffering mechanism for XS]
-
- In article <3201@contex.contex.com>, frank@marvin.contex.com writes:
- > Regarding zbuffering, I have wondered about this also, and suspected
- > something like this was coming. I think G.T. did the zbuffer stuff in
- > the Entry graphics. He must laugh and feel vindicated when people
- > note that the Crimson entry graphics can draw P zbuffered polygons
- > per second, but when you install the XS&Z "upgrade", zbuffered polygon
- > performance drops to something like P/3! I suspect that for tuned
- > code on the R4000A, this is like P/10.....good thing this is going
- > away some time soon.
-
- Your post is very misleading, and deserves some clarification:
-
- 1) 'XS&Z', or a XS system with optional hardware z-buffer, will provide fast
- z-buffering, faster than any configuration (Crimson or Indigo) of Entry
- graphics. A few examples:
-
- primitive Crimson Entry Crimson XS&Z
- --------------------------------------------------
- tmesh, flat Z 20K 80K
- tmesh, gouraud light Z 13K 50K
- ind. quads, flat Z 16K 35K
-
- 2) Currently, an XS without a z-buffer card does NOT support z-buffering, at any
- speed. The reason for this is that the architecture is designed for a hardware
- z-buffer, and making a software z-buffer for it would be inefficient.
-
- 3) OpenGL will require that software z-buffering be supported on XS. This
- doesn't mean that it will be an ideal solution for people who care about fast
- z-buffered primitives. Entry graphics was specially architected and carefully
- tuned for a software z-buffer mechanism. Software z-buffering on XS will not be
- fast, OpenGL or not. If you really care about z-buffer performance, buying the
- XS with Z-buffer hardware is well worth the money, in terms of price performance.
-
- peter
-
- .....Peter Birch.....peterb@perturb.esd.sgi.com.....MTS, Graphics Hardware.....
- ......Silicon Graphics, Inc.....Mountain View, CA 94039.....(415)390-1512......
-