cnsy@vax5.CIT.CORNELL.EDU (06/22/89)
In order to keep my name off the "Ten Most Posted" list, I'm trimming these
USENET posted issues of USENET cullings, since it's a waste to echo what
I like of what's been posted in the past month or so. If you want to get this
stuff, go to the skinner.cs.uoregon.edu FTP site and grab the whole issue.
If you can't FTP, I can't help you much - your best bet is to read this
newsgroup!
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' ) ) / ' ) )
/--' __. __ , --/ __ __. _. o ____ _, / / _ , , , _
/ \_(_/|_/ (_/_ (_/ / (_(_/|_(__<_/ / <_(_)_ / (_</_(_(_/_/_)_
/ /|
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"Light Makes Right"
June 21, 1989
Volume 2, Number 4
Compiled by Eric Haines, 3D/Eye Inc, 2359 Triphammer Rd, Ithaca, NY 14850
607-257-1381, hpfcla!hpfcrs!eye!erich@hplabs.hp.com, cornell!eye!erich
All contents are US copyright (c) 1989 by the individual authors
Contents:
Introduction
Hardcopy News (Andrew Glassner)
New People (Stuart Green, Craig Kolb (and Ken Musgrave), Kaveh Kardan)
Comments on "Free" Ray Tracers and on Renderman (Kaveh Kardan)
Minimum Bounding Sphere, continued (Jack Ritter)
Comments on "A Review of Multi-Computer Ray-Tracing" (Thierry Priol)
======== USENET cullings follow ========
Query: Dataflow Architectures and Ray Tracing (George Kyriazis)
More on Pixar's Noise Function (Jon Buller)
DBW_render for Sun 3 (Tad Guy)
Steel Colors (Eugene Miya)
Dirty Little Tricks (Jack Ritter)
Obfuscated Ray Tracer (George Kyriazis)
Contents of FTP archives, skinner.cs.uoregon.edu (Mark VandeWettering)
-----------------------------------------------------------------------------
Introduction
------------
First off, please note that I now have a second mail address:
eye!erich@wrath.cs.cornell.edu
This is a lot more direct than hopping the HP network through Palo Alto and
Colorado just to get to Ithaca. We have the connection courtesy of the
Computer Science Dept at Cornell, and they have asked us to try to keep our
traffic down. So, please don't be a funny guy and send me image files or
somesuch.
I just noticed that Andrew and I are out of sync: his hardcopy version is on
Volume 3, and I'm on Volume 2. One excuse is that the first year of the email
edition is labeled "Volume 0", since it wasn't even called "The Ray Tracing
News" at that point. An alternate excuse is that I program in "C", and so
start from 0. Anyway, until maybe the new year, I'll stick with the current
scheme (hey, no one even noticed that last issue was misnumbered (and corrected
on the USENET copy)).
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Hardcopy News
-------------
by Andrew Glassner
The latest issue of the hardcopy Ray Tracing News (Volume 3, Number 1, May
1989) goes into the mail today, 31 May. Everyone who is on the softcopy
mailing list should receive a copy. If you don't get a copy in a week or two,
please let me know (glassner.pa@xerox.com). It would help if you include your
physical mailing address, so I can at least confirm that your issue was
intended to go to the right place.
Contributions are now being solicited for Vol. 3, No. 2. Start working on
those articles!
-----------------------------------------------------------------------------
New (and Used?) People
----------------------
The Cornell Program of Computer Graphics computers have all changed their
addresses. Any computer with the name "*.tn.cornell.edu" is now
"*.graphics.cornell.edu".
------------
Stuart Green - multiprocessor systems for realistic image synthesis
Department of Computer Science
University of Bristol
Queen's Building
University Walk
Bristol. BS8 1TR
ENGLAND.
green@uk.ac.bristol.compsci
I am working on multiprocessor implementations of algorithms for realistic
image synthesis. So far, this has been restricted to straightforward ray
tracing, but I hope to look at enhanced ray tracing algorithms and radiosity.
I've implemented a ray tracer on a network of Inmos Transputers which uses
mechanisms for distributing both computation and the model data amongst the
processors in a distributed memory MIMD system.
------------
Craig Kolb (and Ken Musgrave)
My primary interests include modeling natural phenomena, realistic image
synthesis, and animation.
I can be reached at:
Dept. of Mathematics
Yale University
P.O. Box 2155
Yale Station
New Haven, CT 06520-2155
(203) 432-7053
alias craig_kolb craig@weedeater.math.yale.edu
alias ken_musgrave musgrave-forest@yale.edu
...I've just started looking into ray/spline intersection. We do a lot of
heightfield-tracing 'round here, and in the past have rendered them using a
triangle tessellation. I'm giving splines a shot in order to render some
pictures of eroded terrain for our SIGGRAPH talk. I notice that you list
spline intersection among your primary interests. What sort of methods have
you investigated? At the moment I've implemented (what I assume is) the
standard Newton's method in tandem with a DDA-based cell traversal scheme (as
per our SIGGRAPH paper). Although this works, it's not exactly blindingly
fast... Do you know of any 'interesting' references?
------------
Kaveh Kardan
Visual Edge Software Ltd.
3870 Cote Vertu
Montreal, Quebec H4R 1V4
(514)332-6430
larry.mcrim.mcgill.edu!vedge!kaveh
I graduated with a BS in Math from MIT in 1985, did some work in molecular
graphics at the Xerox Research Centre of Canada (XRCC), wrote the renderer at
Neo-Visuals (now known as SAS Canada) -- which included a raytracer --, and the
animation stuff at Softimage. I'm currently working at Visual Edge on the UIMX
package: an X Windows user interface design system.
Regarding the Softimage raytracer: it was written by Mike Sweeney (who used
to be at Abel, and who did "Crater Lake" at Waterloo).
I will also be acting as a mail forwarder for Mike, as Softimage is not on any
networks. So in effect, you should probably include Mike in the mailing list
as well, with my address -- or somehow let people know that he can be reached
tc/o me.
If I may make some comments about the stuff I have read so far in the back
issues:
====================
Jeff Goldsmith writes:
> I don't get it. Why doesn't every CG Software vendor supply a
>ray tracer. It's definitely the easiest renderer to write. Yes,
>they are slo-o-o-o-o-o-w, but they sound glitzy and (I bet) would
>stimulate sales, even if buyers never used them.
Having worked at two CG Software companies, I know firsthand how the "to do"
list grows faster than you can possibly implement features (no matter how many
programmers you have -- c.f."The Mythical Man-Month").
Jeff is right that ray tracing sounds glitzy, and, yes, it is another factor to
toss into the sales pitch -- but it is not at all clear that it is worth the
effort.
Most (if not all) ray tracers assume either infinite rendering time or infinite
disk space. In the real world (a 68020 and a 144Meg disk) this is not the
case. The raytracer I wrote at Neo Visuals was written in Fortran -- ergo no
dynamic memory allocation -- so I had to work on optimizing it without
significantly increasing the memory used. This mostly involved intelligently
choosing when to fire rays. The renderer performs a Watkins-style rendering,
and fires secondary rays from a pixel only if the surface at that pixel needs
to be raytraced. Memory constraints prevented me from using any spatial
subdivision methods.
Yes, ray traced images are great sales tools. They are also sometimes not
entirely honest -- novice users ("I want a system to animate Star Wars quality
images, about ten minutes of animation a day on my XT") are not aware of the
expense of raytracing, and very few salesmen go out of their way to point this
out. However, these same users, unsure of the technology, put together a list
of buzzwords (amongst them "raytracing") and go out to find that piece of
software which has the most features on their list. Hence I coined the phrase
"buzzword compatible" while at Neo-Visuals (and also "polygons for polygons
sake" -- but that's another story).
I have also seen demos, animations, and pictures at trade shows, presented by
hardware and software vendors, which were extremely and deliberately
misleading. A very common example is to show nice animation that was not
really created with your software product. The animation having been typically
created by special programs and add-ons. An obvious example was Abel,
marketing their "Generation 2" software with "Sexy Robot", "Gold", "Hawaiian
Punch", etc. I only mention Abel because they are no longer in business -- I
don't want to mention any names of existing companies.
I hadn't intended this to be a flame. But that sums up why not all software
vendors bother with raytracing, and how it can be abused if not handled
carefully.
====================
On Steve Upstill's remarks on the Renderman standard:
Disclaimer: I have not read the Renderman specs, and have spoken to people who
liked it and people who didn't.
I would like to say that while I was at Neo-Visuals, Tom Porter and Pat
Hanrahan did indeed drop by to ask us about our needs, and to ensure that the
interface would be compatible with our system. As I recall, we asked that the
interface be able of handling arbitrary polygons (n vertices, concave, etc).
As I recall, I was playing devil's advocate at the meeting, questioning
whether rendering had settled down enough to be standardized. So yes, at
least Neo-Visuals did get to have a say and contribute to the interface.
I spoke to one rendering person at Siggraph who didn't appreciate the way Pixar
had handed down the interface and said "thou shalt enjoy." Well the
alternative would be a PHIGS-like process: years spent in committees trying to
hash out a compromise which will in all likelihood be obsolete before the ink
is dry. In fact, two hardware vendors decided to take matters into their own
hands and came up with PHIGS+.
Yes, the interface is probably partly a marketing initiative by Pixar. Why
would they do it otherwise? Why should they do it otherwise? I would guess
that Pixar hopes to have the standard adopted, then come out with a board which
will do Renderman rendering faster than anyone else's software. This seems a
natural progression. More and more rendering features have been appearing in
hardware -- 2D, 3D, flat shaded, Gouraud, and now Phong and texture maps. It
is very probable that in a few years, "renderers" will be hardware, except for
experimental, research, and prototype ones.
-----------------------------------------------------------------------------
Minimum Bounding Sphere, continued
----------------------------------
by Jack Ritter, {ames,apple,sun,pyramid}!versatc!ritter
I noticed in "The Ray Tracing News" an answer to my query about minimum
bounding spheres. The answer following my question assumes there are 3 points.
(Search for "Ray Traced Bounding Spheres"). This is wrong; I meant n points in
3 space. Since then, Lyle Rains, Wolfgang Someone and I have arrived at a fast
way to find a tight bounding sphere for n points in 3 space:
1) Make 1 pass through pts. Find these 6 pts:
pt with min x, max x, min/max y, min/max z.
Pick the pair with the widest dimensional span. This describes the
diameter of the initial bounding sphere. If the pts are anywhere near
uniform, this sphere will contain most pts.
2) Make 2nd pass through pts: for each pt still outside current sphere, update
current sphere to the larger sphere passing through the pt on 1 side,
and the back side of the old sphere on the other side. Each new sphere
will (barely) contain its previous pts, plus the new pt, and probably
some new outsiders as well. Step 2 should need to be done only a small
fraction of total num pts.
The following is code (untested as far as I know) to increment sp:
typedef double Ordinate;
typedef double Distance;
typedef struct { Ordinate x; Ordinate y; Ordinate z; } Point;
typedef struct { Point center; Distance radius; } Sphere;
Distance separation(pa, pb)
Point *pa;
Point *pb;
{
Distance delta_x, delta_y, delta_z;
delta_x = pa->x - pb->x;
delta_y = pa->y - pb->y;
delta_z = pa->z - pb->z;
return (sqrt(delta_x * delta_x + delta_y * delta_y + delta_z * delta_z));
}
Sphere *new_sphere(s, p)
Sphere *s;
Point *p;
{
Distance old_to_p;
Distance old_to_new;
old_to_p = separation(&s->center, p);
if (old_to_p > s->radius) { /* could test vs r**2 here */
s->radius = (s->radius + old_to_p) / 2.0;
old_to_new = old_to_p - s->radius;
s->center.x =
(s->radius * s->center.x + old_to_new * p->x) / old_to_p;
s->center.y =
(s->radius * s->center.y + old_to_new * p->y) / old_to_p;
s->center.z =
(s->radius * s->center.z + old_to_new * p->z) / old_to_p;
}
return (s);
}
Jack Ritter, S/W Eng. Versatec, 2710 Walsh Av, Santa Clara, CA 95051
Mail Stop 1-7. (408)982-4332, or (408)988-2800 X 5743
UUCP: {ames,apple,sun,pyramid}!versatc!ritter
[This looks to be a good quick algorithm giving a near-optimal solution. Has
anyone come up with an absolutely optimal solution? The "three point" solution
(in last issue) gives us a tool to do a brute force search of all triplets, but
this is insufficient to solve the problem. For example, a tetrahedron's
bounding sphere cannot be found by just searching all the triplets, as all such
spheres would leave out the fourth point. - EAH]
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Comments on "A Review of Multi-Computer Ray-Tracing"
---------------------------------------------------
by Thierry Priol
I read with a great interest in the hardcopy "Ray Tracing News (May 1989)" "A
Review of Multi-Computer Ray-Tracing". But, D.A.J. Jevans said that our work
presented in CGI "may even serve to cloud the important issues in
multi-computer ray-tracing"! I do not agree with this remark. The
presentation at CGI describes only a first step in using multi-processor ray
tracing algorithms. It is true that there were no interesting results in this
paper. D.A.J. Jevans also said that a hypercube architecture is hardware
specific. I do not agree. This kind of architecture represents a great part
of distributed memory architectures. Our algorithm is not specific for this
topology and can work on a SYMULT-2010 which uses a mesh topology. However, I
agree when he said that our algorithm provides little in the way of new
algorithms, since we used Cleary's algorithm. But we think that for the
moment, the main problem is not to create new algorithms but to make
experiments with some algorithms presented by several authors because most of
them have been simulated but not implemented. Our experiments show that many
problems due to distributed computing (not only load and memory balancing) were
not solved by the authors.
At present, our algorithm has been modified to take into account load balancing
and we have several results not yet published. These new results may give some
important conclusions about the Cleary approach (processor-volume association).
We are working now on a new algorithm based on a global memory on distributed
memory architectures! For my mind it is the best solution to obtain load and
memory balancing. The ray coherence property is a means to have a sort of
locality when data is read in the global memory (best use of caches).
We are very interested (D. Badouel, K. Bouatouch and myself) in submitting to
the "Ray-tracing News" a short paper which summarizes our work in parallel
ray-tracing algorithm for distributed memory architecture. This contribution
should present two ray tracing algorithms with associated results. This work
has not been yet published outside France.
======== USENET cullings follow ===============================================
{deleted from USENET edition, since all of these articles were on USENET}