From: blythe@sgi.com (David Blythe)
Subject: Re: Reality Engine performance
Organization: Silicon Graphics, Inc., Mountain View, CA
Date: Fri, 24 Jul 1992 11:07:43 GMT

In article <31505@adm.brl.mil> SERRER@odin.nrc.ca (Martin Serrer) writes:
>Hi,
>
>  I had been in the process of writing a proposal for a new machine thinking
>that the new Venice Graphics would really haul ass. I was disappointed however
>when I saw David Blythes posting showing that the polygon performance is still
>at the same level as the VGX. (1.1 million polygons/sec (meshed, flat-shaded))
>  While I realize that in other areas there have been improvements I'm still
>sitting here waiting for a machine that can do an order of magnitude better.
>While some people need the realism of textures (which seems to be where SGI
>is spending their money), our geometry is purely representational.
>  My applications are designed to interactively view simulations of coastal
>processes including wave disturbance, sediment transport, ice floes etc.
>Typical grid sizes are 400x400, so to view a single wave disturbance animation
>at 'real rate' (15 frames/sec.) I need to be able to crunch 4.8 Million tmeshed
>polys/sec. On top of that I have a need to concurrently display at least 2
>surfaces. If we want to increase the size of our grid things get even worse.
>And on and on and on...
>  Rendering to video tape (which we do now) kills the interactive nature of
>the visualization.
>  So my question to SGI is... Are we going to see a machine that can do
>>10 million polys/sec. anytime in the near future?
>  Comments, flames and criticism welcome... Martin

just a few more cents:

the VGX has a peak tmesh rate around 1 million triangles.  many customers
find this rate difficult to achieve because you have to be using a fairly
narrow set of modes to take advantage of this high-performance path (frequently
referred to as the fast path).  Another problem is that this number
can be considered somewhat contrived since it assumes uniform 
10x10x10 triangles, (i.e. the usual benchmark problems).

The Reality Engine tries to better address problems real applications were
experiencing, plus offer new important features (no-penalty anti-aliasing,
no-penalty texturing, ... okay minimal penalty). The peak transform rate may
still look close to the VGX number, but many many more applications may
approach this performance now because of the substantial improvement in the
fill rate, more sophisticated implementation of lighting, ....

Unfortunately, it may be a little while before you get 10 million polygons
per second.  Given our traditional lit vertex represention of 3+3 floats
plus 1 or 2 words overhead, you would need ~10*8 = 80 megawords per second
or 320 megabytes per second sustained bandwdith to the graphics pipe.
The MP machines currently have a bus rated at 16Mwords/sec, so we need to up
the bandwidth first.  Crimson has memory bandwith of 400 Mbytes/sec, but the
same MP-bus limit for graphics engine.  We are moving in the right general
direction ...

Incidentally, at first glance the texture mapping seems like some feature
for improving realism, but its also important for scientific visualization.
3D textures open up many new possibilties for fast volume rendering and
1&2D texture mapping make it much simpler to get the same kind of
pseudo-texturing (false colour maps) effects people were using colour index
mode to achieve, but now allows you to stay in RGB mode and get better
lighting, transparency, and anti-aliasing.  So don't sell it short too
quickly.
	-db
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