Collection of Tools & Utilities/Collection of Tools and Utilities.iso/graphic/rtnews.zip/RTNEWS4

Text File | 1992-09-13 | 73KB | 1,813 lines

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            "Light Makes Right"

             September 5, 1988

Compiled by Eric Haines, 3D/Eye Inc, ...!hplabs!hpfcla!hpfcrs!eye!erich
All contents are US copyright (c) 1988 by the individual authors

Contents:
    Intro, by Eric Haines
    Capsule Autobiographies, by lots of new people
    SIGGRAPH '88 RT Roundtable Summary, by Paul Strauss and Jeff Goldsmith
    Commercial Ray Tracing Software & SIGGRAPH, by Eric Haines & others
    A Letter, Jeff Goldsmith
    Best of USENET

-----------------------------------------------------------------------------

Intro

    Well, I'm back from my honeymoon, I've just moved into a new house, and
    I have returned to work and am confronted with a heavy duty schedule.
    However, the workstation's on the fritz for a few hours so here's my
    chance to compile an issue of the RT News.

    Other major changes around here are that Michael Cohen (of radiosity
    fame, and a subscriber) has begun his cross-country drive from Ithaca
    to Salt Lake City.  He'll be continuing his education at the University
    of Utah's computer graphics facility.  Roy Hall is taking over Michael's
    place at the Cornell Program of Computer Graphics, and should be added to
    this mailing list soon.  Andrew Glassner is now with Xerox PARC, and his
    new address should be available by next issue, too.

    I plan to get another issue out within a week, as there is also an
    interesting research idea that I need to talk about with a few people
    before presenting it here.  Stay tuned...and please feel free to submit to
    the next issue.

-----------------------------------------------------------------------------

Capsule Biographies

    What follows are short self-descriptions by various new people at the
    roundtable at SIGGRAPH.  These are simply in the order I received them.
    The latest address list (email and physical) is attached at the end of
    this issue.

    By the way, if you never submitted an autobiographical sketch, (or if you
    are doing something that's different from your last sketch) please feel
    free to send one on to me for the next issue.


# Russ Tuck - SIMD parallel algorithms and architectures for ray tracing
# Computer Science Dept, Univ. of North Carolina

My dissertation research is on parallel methods of programming SIMD parallel
computers.  I have developed a measure of program portability, and a system
which lets the programmer specify in advance how portable a program must be.
The compiler can then provide (and enforce) this amount of portability.  I
call this an "optimally portable" programming system.  I'll be presenting my
work at "Frontiers 88: The 2nd Symp. on the Frontiers of Massively Parallel
Computation" in October.  Thinking about ways to do ray tracing (and radiosity)
on massively parallel SIMD machines is a fun sidelight.  (Some of my ideas
were in the June '88 hardcopy Ray Tracing News.)


# Greg Ward - accuracy and realism, daylight, efficient light sources.
# Lawrence Berkeley Laboratory

The purpose of my work is the development of more accurate calculations
for lighting design and engineering.  Electric lighting contributes
directly or indirectly to about 20% of the nation's energy
consumption.  Although significant progress has been made in the area
of energy-efficient light sources, wasteful installations frequently
result from poor building design rather than low fixture efficiency.
It is hoped that with better computational tools, architects and
engineers will produce more energy-efficient designs.  I am currently
working on a validated reflection model and method for measuring
surface properties using a digitizing camera.  By streamlining the
measurement process, it should be possible to obtain accurate
simulations of designs using a realistic variety of construction
materials.  I am also comparing the accuracy and applicability of
different classes of lighting calculation, and exploring the use of
animation in design visualization.


# Pete Litwinowicz -- realistic image sythesis, etc.
# Apple Computer, INC

Working on 3D animation, rendering and modelling at Apple.


# Tom Malley - parallelism, complex scenes, space subdiv., shading methods
# Evans & Sutherland Computer Corporation

My interests are primarily in how to make ray traced images that are
significantly more realistic than the computer generated images we
often see now. The complexity of the models must increase for realism.
If we want to ray trace large databases on many processors, we must
determine efficient ways to make pieces of the data set available
dynamically to processors as they perform intersection searches.
Additionally, I'm interested in analysis of reflection models to see
where the typical simplifying assumptions steer us wrong, and what the
alternatives may be.  I'd also like to see more closed loop
comparisons of computer generated images with real scenes.


# Chuck Grant - tracing fewer rays, coherency, antialiasing
# Lawrence Livermore National Laboratory

I am interested in algorithms and data structures for most areas of image
synthesis: visible surface algorithms, volumetric visualization, antialiasing,
texturing, shading, etc., etc... Ray tracing is a big part of my interests but
not all. I am currently working on a comparison of all existing visible surface
algorithms, and have invented several new ones as a result. I am not interested
in "Scientific Data Visualization" but the demands of my job make me spend a
lot of time doing just that. I am finishing my PhD. in computer graphics at the
University of California at Davis.


# Steve Stepoway -- efficient intersection calc., parallelism

My interests in ray tracing these days are centering around finding more
efficient ray-object intersection calculations, as well as issues of
parallelism in rendering. I am working with Sam Uselton (U. Tulsa) and
Mark Lee (AMOCO) on developing some new space sub-division techniques
(next year's SIGGRAPH paper).


# Daniel Bass - Realism, diffraction & wavelength effects
# Apollo Computer Inc.

[no autobiographical note]


# Ken Joy - intersection tests, efficiency, coherency
# Computer Graphics Research Lab, Computer Science Division,
# University of California, Davis

[no autobiographical note]


# Fred Fisher - realism, radiosity enhancements, ray tracing manufacturing
#   databases

Hello. I'm now working at DEC doing electronics design for a
geometry pipeline. My interest in ray tracing has involved rendering
polygonal databases (presumably ones similar to those used in
a quick-Gouraud-render CAD environment ). I've been writing a lot
of software on my own (ray-tracing and otherwise) to understand the
image synthesis process better, with the intent of designing hardware
to help the rendering phase.


# Pierre Poulin - illumination models, natural phenomenon
# University of Toronto
# Department of Computer Science

I am a graduate student working right now on a model for anisotropic reflection
that would save the world and computing time. This should be my introduction in
the fascinating science of the simulation of natural phenomenon (or how to
deceive the eye with less than 1 million polygons...).


# Andrew C. Woo - intersection culling algorithms and complexity
# University of Toronto
# Department of Computer Science

I am currently a first year (fast approaching second year) master's student
at the University of Toronto.  My current thesis work is on a new approach
to shadow acceleration (beyond trans-warp drive, of course) and comparing
it to existing shadow accelerators (eg. the impulse-power "light buffer"
--> just kidding, Eric).


# Chuan Chee  -  natural phenomena, ray tracing, animation
# University of Toronto
# Department of Computer Science

I am finishing my first year as a master's student at the University of
Toronto.  I currently do not have a thesis topic.


# Robert E. Webber, Prof. - ray tracing large databases of volume density data.
# Computer Science Department
# Rutgers University, Busch Campus

Am currently tuning a ray tracer that handles hierarchically arranged
voxel data.  The basic unit of organization is a 16 by 16 by 16
``voxel'' block where each voxel contains 32 bits of information.
This information is interpreted as either a density description of the
contents of that voxel or a pointer to another voxel block
representing a recursive decomposition of the current block.  16 by 16
by 16 times 4 bytes means that my basic block is 16k, which is a size
that fits our local disk system rather well from the point of view of
i/o overhead.  The program is organized to allow the database to be
spread over a number of files (max 255) thus avoiding the 4 gigabyte unix file
size problem (since the pointers only have to be able to address the
start of each 16k block, 32 bit pointers can address a terabyte of
data -- should we ever be lucky enough to have it) as well as the
problem of finding alot of space inside of a single disk partition.
Rutgers currently organizes its computing around a cluster of a
hundred networked Sun workstations including 2's, 3's, and 4's.

The current status of the system is that 5 megabyte scenes (roughly
400 blocks) representing densities at the 256 by 256 by 256 level have
been ray traced.  Surface interpolation permitted images of
demonstrating shadows, shading, and inter-reflection to be generated.
Various techniques for determining the surface represented by a local
cluster of voxel densities are being experimented with.  Will soon be
running the ray tracer in parallel (don't expect much bus contention
as the system is currently extremely cpu bound).  We are also
installing some WORM drives locally and so soon expect to have yet
another layer of memory hierarchy to fiddle with.


# Michael Natkin
# Brown University

No current paragrapho for now, as i'm rewriting our whole environment
at the moment, no time for ray-tracing.

---------

That's all for now, with about 6 people who are new but haven't contacted
me yet.

-----------------------------------------------------------------------------

SIGGRAPH '88 RT Roundtable Summary, by Paul Strauss and Jeff Goldsmith

0.  Women don't talk about ray tracing.
1.  It would be nice to have something that does both ray tracing and
    radiosity.
2.  It would be nice to have caustics.
3.  It would be nice to do analytical anti-aliasing.
4.  Motion blur is a Good Thing.
5.  Adaptive subsampling don't work good.
6.  There are many ways to minimize ray-object intersection tests.
7.  Hardware would be nice.  Maybe later.
8.  We should use ray tracing for real applications.

-------------------------------------------------------------------------------

Commercial Ray Tracing Software and SIGGRAPH, by Eric Haines and others

    Last issue I listed all the commercially available ray tracers I knew as of
SIGGRAPH.  There were a few new entries I saw this year:

    - ElectroGIG, from England, shown at the Meiko booth, is the first
      commercial ray tracer based on using constructive solid geometry
      that I've seen.

    - SoftImage, (the people with the nice rocks image) from Montreal,
      had a nice looking Wavefront/Alias/etc-looking package with a ray
      tracer.  They claim it was the fastest ray tracer on the floor (it
      runs on a number of machines) and seemed to use octree subdivision.
      I never got to see the demo, but people tell me that it was fast,
      and that the programmer is a very careful and efficient coder.

    - Shima-Seiki, from Japan.  They claim to have a ray-tracer with
      hardware assistance (whatever that means), though they're not
      marketing it yet and couldn't tell us anything about it.  The
      realtime texturing system from Mars, with lots of cool buttons and
      knobs, was pretty impressive though.  System cost is $500K, $300K,
      or "we haven't decided", depending on when you talked with them.

    - Ray Tracing Corp is now Ray Tracing Research Corp, and they released
      a ray tracer for the Mac II for $895.

    - Apollo: not a product, but their ray tracer was fun to watch as a
      demo of both the speed of their new DN10000 (not sure about the
      number of zeros in that one) super-mini-super-workstation and of
      Apollo's networking abilities.  Darn fast.

    - Silicon Graphics: also not a product, they had a very nice demo
      (which, sadly, a number of their marketing people didn't know about)
      showing a scene from a god's-eye point of view, with rays shooting
      through the image plane and bouncing around.  The image would build
      up scan line by scan line on both the image plane in the scene and
      in a separate window.  You could also change the god's-eye view
      interactively as the scene was being ray-traced.  Nice.


Other things of interest:  AT&T Pixel Machines' ray tracer is now even faster,
purely due to software tuning.  They plan to cut even more time by further
changes.  "Sphereflake", which ran at about 30 seconds last year, now runs
at around 16 seconds.  There is a public domain modeller which should be
out in mid-October which will run on the Iris 3130 and on the Pixel Machine.
It was developed by NASA (demoed at AT&T), and since they're governmental they
can't make it a for-profit product.  In a month and a half contact their
distributor, "COSMIC" (which stands for something), at 404-542-3265.  They
won't really know much about it until then.

SGI showed radiosity images on the floor, though there is no announced product
yet.  They seemed to have developed their own adaptive refinement technique.
HP showed ray tracing film loops and stills, and radiosity images and on-the-fly
adaptive refinement (which will be a product sometime this winter).  The new
radiosity technique introduced by Cornell this year has the promise of being
"radiosity for the rest of us".

Those were my major impressions (other than the usual "the art show was better
this year", "course lunches were worse", etc) - anyone else care to add their
two cents?


Jeff Goldsmith points out:

    Cray Research has "Oasis," Gray Lorig's ray tracer, available,
I think, for free.  Of course, you have to buy a Cray at $20 million
first....

    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.


Gray Lorig responded to my query for info on Oasis:

  The current status of the Oasis package, which is basically a
raytracing animation package, is it's an unsupported product.
What that really means is that we will give it to Cray customers
for free, give them updates every once and a while, and provide
support only when I feel like it.


John Peterson says:

  I would add RenderMan to your list of commercial ray tracers - I think you
can explicitly implement classical ray tracing by writing some code in their
magic shading language.

Also, the ray tracer I wrote at Utah is (or at least may be) commercially
available.  It specializes in ray tracing NURB (B-spline) surfaces, and
supports the usual suspects of features (refract/flection, shadows (with
penumbra), texture mapping, anti-aliasing (with stochastic sampling) and
motion blur).  It comes bundled with a geometric modelling system called
Alpha_1, distributed by Engineering Geometry Systems in Salt Lake City.

The contact is:
    Engineering Geometry Systems
    275 East South Temple, Suite 305
    Salt Lake City, UT, 84111

I think the price is something like $10K for commerical sites and < $1K for
government or university sites.  The ray tracer isn't available separately,
but the modelling package is so full of goodies it's worth looking at in its
own right.

-------------------------------------------------------------------------------

A Letter [my response is in brackets]

   1) A student of mine found a typographical error in
your "Intro to Ray Tracing" notes.  (I gave him some
pages from same to teach him about texture mapping; good
job!)  In Equation set E11, the third line should
read: Qvy = -Nb/Dv2 rather than Nc.  I noted that you didn't
catch it in this years' issue.  (Better typesetting, though.)
Thanks for publishing that.

[Thanks!  If anyone else notices typoes, omissions, or anything else that bugs
them in the "Intro" SIGGRAPH notes, please contact Andrew Glassner or me
or the individual author ASAP.]


    2) Does anyone know where I can obtain 2D wood texture maps?
FTP, email, tape, disc, whatever, is fine.

[Any leads, anyone?  I'm interested, too.]

-- Jeff Goldsmith

-------------------------------------------------------------------------------

Best of USENET
---- -- ------

[What follows are things posted to USENET that might be of interest here.
Many readers either don't receive USENET or haven't the time to perform chaff
separation.  What follow are my own winnowings. - EAH]

-------------------------

Thomas Palmer writes:

Has anyone done any work on vectorizing ray-object intersection
calculations?  The vectorizing C compiler on a Cray X/MP will not
(automatically) vectorize loops smaller than about 5 or 6 iterations
(nor should it - the vector register load time outweighs the gain).
Typical ray tracing vector operations involve vectors of length 3 or 4.

  -Tom

 Thomas C. Palmer    NCI Supercomputer Facility
 c/o PRI, Inc.        Phone: [phone]
 PO Box B, Bldg. 430    Uucp: ...!uunet!ncifcrf.gov!palmer
 Frederick, MD 21701    Arpanet: [e-mail]

-----

>From: [e-mail] (Stephen Spencer)
Subject: Re: Vectorizing ray-object intersection calculations
Organization: Ohio State Computer & Info Science

There was an article in IEEE CG&A about four years ago about vectorizing
ray-sphere intersections on a Cyber which included an algorithmic workup
of how it worked.

As far as ray-polygon intersection goes, the article in SIGGRAPH '87 dealing
with tesselation of polygonal objects (it had the pictures of grass and the
Statue of Liberty in it) included the algorithm for fast ray-polygon
intersection, and I did implement it and it did vectorize quite nicely.
I unfortunately no longer seem to have that piece of code, but it wasn't
difficult.  Of course you still have to do the sorting of the intersection
points but the heavy intersection calculations can be done quickly.

-----------------

>From: [e-mail] (John M. Olsen)
Newsgroups: comp.graphics
Subject: Polygon teapot ftp'able
Summary: Come 'n get it.
Organization: University of Utah, Computer Science Dept.

One of the kind and generous People In Charge compressed the Utah Teapot
and has made it available (for a week or so) as ~ftp/pub/teapot.Z so those
who want the polygon version of it can get it now.  It compressed to about
270K from 990K, so it's not too bad to transfer.  The machine name is
cs.utah.edu.  Have fun with it, and let me know if you have any problems
getting it transferred.

Just so I don't get hate mail, and you don't think your software is
broken:  The Utah teapot
was designed with a hole in the bottom.  I had forgotten about this,
but was reminded by someone (Jean Favre?) who rendered it.

-----------------

From: [e-mail] (Mark VandeWettering)
Newsgroups: comp.graphics
Subject: Ray Tracer: Part 01/01
Organization: University of Oregon, Computer Science, Eugene OR
Lines: 2353

Here is the first release of my totally whiz-bang ray tracer.  Okay, so
it isn't TOTALLY whiz bang, but it does have some nice features.  It
uses bounding volumes, has cones, spheres, polygons and cylinders as
primitives, reads Eric Haines NFF file format images and more....

Use it, abuse it, sell it, but be sure to have fun with it.  I had alot
of fun hacking on it.   If any of you find bugs, or better yet fix bugs
and add features, send them to me, and I will try to get them worked
into a future release which I hope might make it into comp.sources.unix.

[ code not included here:  either get it from USENET, or you can write Mark
or myself for a copy.  The source weighs in at about 55K bytes.]

-----------------

Reply-To: [e-mail] (John K. Counsulatant)
Organization: RICH Inc. , Franklin Park,IL

    If anyone is interested in *other* ray tracers, I
have source to DBW Render (an excellent ray tracer ported from the VAX to
the Amiga) and Tracer (a crude spheres only (but a good starter :-) tracer
for the Amiga).  I am in the process of obtaining QRT (quick ray tracer (if
there is such a thingee ;-)) source (also for the Amiga).

I can be reached at:

RealTime (prefered):  1(312)418-1236  (6pm to 10:30pm central time)

USmail:               John Kjellman             E-Mail: [e-mail]
                      17302 Park Ave.
                      Lansing IL 60438

-----------------

Reply-To: [e-mail] (Sean Casey)
Organization: The Leaning Tower of Patterson Office @ The Univ. of KY

In article <[e-mail]> [e-mail] (Mark VandeWettering) writes:
>    Isn't DBW Render copyrighted?  I believe the source code may not
>    be redistributed, I tried to obtain the sources, but aborted
>    because of the restriction on use/redistribution.

The first release of DBW Render was freely redistributable. I believe it
even found it's way to a Fish disk. The story I hear is of an evil employer
seeing $$$ and telling Dave that since he wrote it on the company computer
it belongs to the company and that no further releases may be given away.

The current release uses "Look Up A Word In The Manual" type copy
protection, the most annoying kind I have experienced to date.

If someone really wants to pay for an Amiga ray tracer, I'd send him in the
direction of one of Turbo Silver, Videoscape 3D, or Sculpt 3D, all excellent
products. These products are in fierce competition with each other, and get
better all the time. I saw a pamphlet in Turbo Silver that had an ad for a
fascinating terrain generator module.  Just think, combine a high quality
terrain generator and the logistics of a board wargame...

Oh yeah, I hear that some of the commercial Amiga ray tracing software is
being ported to the Mac II. These products have been around for a while, so
it's a good chance for Mac users to get their hands on some already-evolved
ray-tracing software.

Sean
--
***  Sean Casey                        [e-mail],  [e-mail]
***  (Looking for his towel)           {backbone|rutgers|uunet}!ukma!sean
***  U of K, Lexington Kentucky, USA   Internet site? "talk [e-mail]"
***  ``With a name like Renderman, you know it's good jam.''

-----------------

Reply-To: [e-mail] (George Kyriazis)
Organization: RPI CS Dept.

        Hello world!  I have been using ray tracers for quite some time now,
and I have made many changes to some of them, so I though it was time for
me to write a ray tracer.  So there it is!  It is not supposed to be fast
or anything, but I think it is well commented and easy to understand.
It is very simple also.
        I am willing to give it to anyone that wants it.  Unfortunately,
I don't think I can put it in a place where people can ftp to, so if you
want it, please send me mail.  I'm sure I can put it in some public place
later.
        The ray tracer currently supports only spheres, with ambient,
diffuse, specular lighting, together with reflections and refractions.
I don't use any in-line code for the vector routines, but subroutines, for
readability.
        Hope someone will want to play around with it.

  George Kyriazis

------------------------------

Postscript Ray Tracer, John Hartman and Paul Heckbert

[This was published in the last hardcopy RT News.  Here it is again, for those
not inclined to type a lot]
Reply-To: [e-mail] (John H. Hartman)
Organization: University of California, Berkeley

  Ever worry about all those cycles that are going to waste every night when
you shut off your laserwriter? Well, now you can put them to good use.
Introducing the world's first PostScript ray tracer. Just start it up, wait
a (long) while, and out comes an image that any true graphics type would
die laughing over. As it is currently set up it will trace a scene with
three spheres and two lights. The image resolution is 16x16 pixels.
  Warning: the code is a real kludge. I'm not sure there is much you can
change without breaking it, but you're welcome to try. If, by chance, you
are able to improve the running time please send us the improved version.
  psray.ps is the ray tracer. result.ps is what a 16x16 image should look
like.
  Have fun.

-----------------------------------------------------------------------
John H. Hartman         [e-mail]
UCB/CSD                ucbvax!ernie!jhartman



# to unpack, cut here and run the following shell archive through sh
# contents: psray.ps result.ps
#
echo extracting psray.ps
sed 's/^X//' <<'EOF10807' >psray.ps
X%!
X% Copyright (c) 1988  John H. Hartman and Paul Heckbert
X%
X% This source may be copied, distributed, altered or used, but not sold for
X% profit or incorporated into a product except under licence from the authors.
X% This notice should remain in the source unaltered.
X%   John H. Hartman [e-mail]
X%   Paul Heckbert   [e-mail]
X
X%    This is a PostScript ray tracer. It is not a toy - don't let the kids
X%  play with it. Features include: shadows, recursive specular reflection
X%  and refraction, and colored surfaces and lights (bet you can't tell!).
X%  To use this thing just send it to your favorite Postscript printer.
X%  Then take a long nap/walk/coffee break/vacation. Running time for
X%  a recursive depth of 3 and a size of 16x16 is about 1000 seconds
X%  (roughly 20 minutes) or 4 seconds/pixel.
X%    There are a few parameters at the beginning of the file that you can
X%  change.  The rest of the code is pretty indecipherable. It is translated
X%  from a C program written by Paul Heckbert, Darwyn Peachey, and Joe Cychosz
X%  for the Minimal Ray Tracing Programming Contest in comp.graphics in
X%  May 1987.  Some changes have been made to improve the running time.
X%  Don't even bother trying to figure out how this works if you are looking
X%  for a good example of a ray tracer.
X%
X/starttime usertime def
X/DEPTH 3 def   % recursion depth
X/SIZE 16 def   % image resolution
X/TIMEOUT SIZE dup mul 10 mul cvi 120 add def  % approximately 10 sec/pixel
X/NUM_SPHERES 5 def
X/AOV 25.0 def    % angle of view
X/AMB [0.02 0.02 0.02] def  % ambient light
X% list of spheres/lights in scene
X%            x    y    z     r   g   b   rad  kd   ks  kt   kl  ir
X/SPHERES [[[ 0.0  6.0  0.5] [1.0 1.0 1.0] 0.9 0.05 0.2 0.85 0.0  1.7]
X          [[-1.0 8.0 -0.5] [1.0 0.5 0.2] 1.0 0.7  0.3 0.0  0.05  1.2]
X          [[ 1.0 8.0 -0.5] [0.1 0.8 0.8] 1.0 0.3  0.7 0.0  0.0   1.2]
X      [[ 3.0 -6.0 15.0] [1.0 0.8 1.0] 7.0 0.0  0.0 0.0  0.6  1.5]
X      [[-3.0 -3.0 12.0] [0.8 1.0 1.0] 5.0 0.0  0.0 0.0  0.5  1.5]
X     ] def
X
Xstatusdict begin
XTIMEOUT setjobtimeout
X/waittimeout TIMEOUT def
Xend
X/initpage {
X   /Courier findfont
X   10 scalefont setfont
X} def
X
X/X 0 def
X/Y 1 def
X/Z 2 def
X/TOL 5e-4 def
X/BLACK [0.0 0.0 0.0] def
X/WHITE [1.0 1.0 1.0] def
X/U 0.0 def
X/B 0.0 def
X% index of fields in sphere array
X/cen 0 def
X/col 1 def
X/rad 2 def
X/kd 3 def
X/ks 4 def
X/kt 5 def
X/kl 6 def
X/ir 7 def
X/NEG_SIZE SIZE neg def
X/MATRIX [SIZE 0 0 NEG_SIZE 0 SIZE] def
X/vec {3 array} def
X/VU vec def
X/vunit_a 0.0 def
X
X% dot product, two arrays of three reals
X/vdot {
X   aload pop
X   4 -1 roll
X   aload pop
X   4 -1 roll mul
X   2 -1 roll 4 -1 roll mul add
X   3 -2 roll mul add
X} def
X
X% vcomb, sa, a, sb, b  returns new array of sa*a + sb*b
X
X/vcomb {
X   aload pop
X   4 -1 roll dup dup
X   5 1 roll 3 1 roll mul
X   5 1 roll mul
X   4 1 roll mul 3 1 roll
X   5 -2 roll aload pop
X   4 -1 roll dup dup
X   5 1 roll 3 1 roll mul
X   5 1 roll mul
X   4 1 roll mul 3 1 roll
X   4 -1 roll add 5 1 roll
X   3 -1 roll add 4 1 roll
X   add 3 1 roll
X   vec astore
X} def
X
X/vsub {
X   aload pop
X   4 -1 roll aload pop
X   4 -1 roll sub 5 1 roll
X   3 -1 roll sub 4 1 roll
X   exch sub 3 1 roll
X   vec astore
X} def
X
X/smul {
X   aload pop
X   4 -1 roll dup dup
X   5 1 roll 3 1 roll mul
X   5 1 roll mul
X   4 1 roll mul 3 1 roll
X   vec astore
X} def
X
X/vunit {
X   /vunit_a exch store
X   1.0 vunit_a dup vdot sqrt div vunit_a smul
X} def
X
X/grayscale {
X   % convert to ntsc, then to grayscale
X   0.11 mul exch
X   0.59 mul add exch
X   0.30 mul add
X   255.0 mul
X   cvi
X} def
X
X
X/intersect { % returns best, tmin, rootp
X   7 dict begin
X   /d exch def
X   /p exch def
X   /best -1 def
X   /tmin 1e30 def
X   /rootp 0 def
X   0 1 NUM_SPHERES 1 sub {
X      /i exch def
X      /sphere SPHERES i get def
X      /VU sphere cen get p vsub store
X      /B d VU vdot store
X      /U B dup mul VU dup vdot sub sphere rad get dup mul add store
X      U 0.0 gt
X      {
X     /U B U sqrt sub store
X     U TOL lt
X     {
X        /U 2.0 B mul U sub store
X        /B 1.0 store
X     }
X     { /B -1.0 store }
X     ifelse
X     U TOL ge
X     U tmin lt and
X     {
X        /best i store
X        /tmin U store
X        /rootp B store
X     }
X     if
X      }
X      if
X   } for
X   best tmin rootp
X   end
X} def
X
X/trace {
X   13 dict begin
X   /d exch def
X   /p exch def
X   /level exch def
X   /saveobj save def
X   /color AMB vec copy def
X   /level level 1 sub store
X   p d intersect
X   /root exch def
X   /v exch def
X   /s exch def
X   -1 s ne
X   {
X      /sphere SPHERES s get def
X      /p 1.0 p v d vcomb store
X      /n
X      sphere cen get p
X      root 0.0 lt { exch } if
X      vsub vunit def
X      sphere kd get 0.0 gt
X      {
X     0 1 NUM_SPHERES 1 sub
X     {
X        /i exch def
X        /light SPHERES i get def
X        light kl get 0.0 gt
X        {
X           /VU light cen get p vsub vunit store
X           /v light kl get
X           n VU vdot
X           mul store
X           v 0.0 gt
X           p VU intersect
X           /B exch store
X           /nd exch def
X           i eq
X           and
X          { /color 1.0 color v light col get vcomb def }
X           if
X        } if
X     } for
X      } if
X      color aload pop
X      sphere col get aload vec copy /VU exch store
X      4 -1 roll mul
X      5 1 roll
X      3 -1 roll mul
X      4 1 roll
X      mul
X      3 1 roll
X      color astore pop
X      /nd d n vdot neg store
X      /color
X      sphere ks get
X      sphere kd get color sphere kl get VU vcomb
X      0 level eq
X     { BLACK vec copy}
X     { level p 1.0 d 2 nd mul n vcomb trace vec astore }
X      ifelse
X      1.0 3 -1 roll vcomb store
X      root 0.0 gt
X     { /v sphere ir get store }
X     { /v 1.0 sphere ir get div store }
X      ifelse
X      /U 1 v dup mul 1 nd dup mul sub mul sub store
X      U 0.0 gt
X      {
X     /color
X     1.0 color sphere kt get
X     0 level eq
X        { BLACK vec copy}
X        { level p v d v nd mul U sqrt sub n vcomb trace vec astore }
X     ifelse
X     vcomb store
X      } if
X   } if
X   color aload pop
X   saveobj restore
X   end
X} def
X
X/main {
X   initpage
X   /data SIZE dup mul string def
X   /half SIZE 0.5 mul def
X   /i 0 def
X   /dy half AOV cvr 0.5 mul dup cos exch sin div mul def
X   /temp vec def
X   0 1 SIZE 1 sub
X   {
X      /y exch def
X      0 1 SIZE 1 sub
X      {
X     /x exch def
X         data i
X     /saveobj save def
X     VU X x cvr half sub put
X     VU Y  dy put
X     VU Z half y cvr sub put
X     DEPTH BLACK VU vunit trace
X         grayscale
X     saveobj restore
X           put
X     /i i 1 add store
X      } for
X   } for
X   gsave
X   100 300 translate 400 400 scale SIZE SIZE 8 MATRIX {data} image
X   grestore
X   100 200 moveto
X   (Statistics: ) show
X   100 190 moveto
X   (Size: ) show SIZE 10 string cvs show
X   100 180 moveto
X   (Depth: ) show DEPTH 3 string cvs show
X   100 170 moveto
X   (Running time: ) show usertime starttime sub 1000 div 20 string cvs show
X   showpage
X} def
X/main load bind
Xmain
Xstop
EOF10807
echo extracting result.ps
sed 's/^X//' <<'EOF10808' >result.ps
X%!
X/picstr 16 string def
X100 300 translate
X400 400 scale
X16 16 8 [16 0 0 -16 0 16]
X{currentfile picstr readhexstring pop} image
X0505050505050d0e1114140505050505
X050505050518231c1136472c05050505
X0505050528231b262729364b58050505
X05050525251c0e2528280e3a52550505
X050505241b0c0d0d0d0d0d0c3c540505
X050505080a0b0b0c0c0b0b0b0a080505
X0505620608090a0a0a0a090908072805
X056873170607070808080707060c2e2a
X57676e94050505060606060505752d29
X525e6456310505050505050514722825
X45512f2e2b0a06050505050111141420
X35402726240b0b0b0509040410111119
X1e2c1e1d1b0b0b0b050904040c0d0d0c
X0b121312100b0b0b0504040407080807
X050b0b0b0b0b0b050505040404040404
X05050505050505050505050505050505
Xshowpage
EOF10808
exit

-------------------------------------------------------------------------------

END OF RTNEWS

 _ __                 ______                         _ __
' )  )                  /                           ' )  )
 /--' __.  __  ,     --/ __  __.  _. o ____  _,      /  / _  , , , _
/  \_(_/|_/ (_/_    (_/ / (_(_/|_(__<_/ / <_(_)_    /  (_</_(_(_/_/_)_
             /                               /|
            '                               |/

            "Light Makes Right"

             September 11, 1988

Compiled by Eric Haines, 3D/Eye Inc, ...!hplabs!hpfcla!hpfcrs!eye!erich
All contents are US copyright (c) 1988 by the individual authors

Contents:
    Intro
    Capsule Autobiographies, by more new people
    The Continuing Saga of MTV's Raytracer, by Mark VandeWettering
    Public Domain Ray Tracer Q & A, by Mark VandeWettering
    Public Domain Ray Tracer Utilities, by Tom Vijlbrief
    Sorting Unnecessary on Shadow Rays for Kay/Kajiya?
    by Eric Haines and Mark VandeWettering
    Summary of Replies to Vectorizing Ray-Object Intersection Query,
    by Tom Palmer
    The Ray Tracer I Wrote, by George Kyriazis
    New Bitmaps Library Available, Jef Poskanzer

-----------------------------------------------------------------------------

Intro

    Let's see, there's Whitted's, VandeWettering's, Kyriazis', Ohta's,
Hartman/Heckbert's, "Pearl" on the Amiga & Atari, and a whole slew of them by
Heckbert and friends (the Minimal Ray Tracer contest on USENET) - we're now at
the point where the number of public domain ray tracers cannot be counted on
one hand (and that's even if you count all the minimal RTs from Paul Heckbert's
contest as worth one).  If nothing else, this proves ray tracing's a pretty
trivial algorithm in its simplest form.

    I had hoped to talk with Tim Kay about a project he proposed at the ray
tracing roundtable at SIGGRAPH this year, but he's in New York until the 20th.
The kernel of the idea that he proposed was setting up ftp space on one of the
Caltech computers and letting people check in their test ray-tracers there.

    In the meantime this issue quickly filled up with biographical sketches
and the winnowings of USENET, especially Mark VandeWettering's efforts.  His
ray tracer looks fairly nice, doing much more than spheres - check it out!

-- Eric

-----------------------------------------------------------------------------

Biographical Sketches, old and new


# Ben Trumbore - photorealism, efficiency, interactive ray tracing
# Cornell University Program of Computer Graphics staff

Greetings!  I am a candidate from the Reformed Radiosity party.  My campaign
pledge:  I will not be satisfied until computer generated images are
indistinguishable from photographs.  Like all right-thinking Americans, I
believe ray tracing is the means to this end.  Better images at better
runtimes!  And I strenuously deny allegations that I spend too much time
working with stochastic textures - every modern life needs balance.  I foresee
a world where interaction and ray tracing live in harmony, and I want you to
be a part of that world.  Thank you!

--------------

A few more new people have joined our ranks since last issue.

#
# Tom Palmer - applied ray tracing: realism & modeling for molecular graphics
# National Cancer Institute
# P.O. Box B  Bldg 430
# Frederick, MD 21701
# [phone]
alias tom_palmer [e-mail]

I'm currently interested in vectorizing ray-object intersection calculations.
However, my primary interest is in applied ray tracing.  The wide variety of
primitives and the realistic rendering make ray tracing an ideal (if slow)
method for creating images of extremely complex molecular models.  I'm
currently working with a (chemist) collaborator experimenting with visualizing
electon density, electrostatic potential, molecular orbitals, etc. via ray
tracing primitives.


A note from Tom Palmer:

Doug Turner has left UNC and is now with Apple in Cupertino doing ray casting
and textures on their Cray.  I would guess his email address to be
[e-mail], but don't hold me to it.

--------------

#
# Phillip Getto - Real-time radiant energy simulation :-), sampling,
#                 object-oriented rendering, efficient intersections calcs.
# CII 7309
# Center for Interactive Computer Graphics
# Rensselaer Polytechnic Institute
# 110 8th St.
# Troy, NY 12180-3590
# [phone]
alias    phil_getto    [e-mail]

--------------

#
# George Kyriazis - parallel ray-tracing
# ECSE Dept., JEC,
# R.P.I.,
# Troy, NY 12180
# e-mail: [e-mail]
#    [e-mail]
alias    george_kyriazis    [e-mail]

I will (pretty soon) be parallelizing a ray tracer to work with an AT&T Pixel
Machine.  One of the problems there will be sharing pixels when doing
anti-aliasing.  Stochastic sampling may be considered.  Also implementing
algorithms for high hit/miss ratio in intersection calculations.

--------------

#
# Stephen Spencer - accurate diffuse light calculation, antialiasing
# The Ohio State University Advanced Computing Center for the Arts and Design
# 1224 Kinnear Road
# Columbus Ohio  43212
# [phone]
alias    stephen_spencer    [e-mail]

Currently employed by The Ohio State University Advanced Computing Center for
the Arts and Design as a Graphics Research Specialist I designing graphics
software for research and instructional use by students and staff working in
computer animation and industrial design.  Graphics interests include ray-
tracing (somewhat obviously) and radiosity, and improving the realism of
computer-generated images in general.

--------------

# Greg Turk - rendering equation & tracing from lights
# UNC at Chapel Hill
# P.O. Box 26
# Chapel Hill, NC 27514
# [phone]
alias greg_turk [e-mail]

I'm currently looking at ways to speed up collision detection for complex
objects.  I'm betting that collision detection can be made fast enough to
be useful for interactive graphics applications, and I plan to see how far
I can get on Pixel-planes, my favorite one-of-a-kind graphics engine.

--------------

#
# Roy Hall
# Program of Computer Graphics
# 120 Rand Hall
# Cornell University
# Ithaca, NY 14853
# [phone]
alias    roy_hall    [e-mail]

    I've been writing renderer's commercially for some time and have
    been concentrating on efficiency and eas of use.  Recently I returned
    to academics as faculty at Cornell.  I expect to be pursuing research
    for a variety of rendering techniques, ray tracing being high on the
    list.  Just finished a book "Illumination and Color in Computer
    Generated Imagery" - pub. by Springer-Verlag - should be out Sept
    or Oct.  In addition to graphics research I'm teaching architecture
    classes in lighting and acoustics, and computer applications to
    architecture.

--------------

#
# Mark VandeWettering
# Master's Student
# University of Oregon Computer And Information Sciences
# [e-mail]
alias    mark_vandewettering    [e-mail]

I am currently interested in most aspects of raytracing, radiosity and
realistic image synthesis.  I am the author of a public domain raytracer
that has been distributed via USENET and is available from me via e-mail
and via anonymous ftp.  I am interested in developing a "library" of
public domain code for doing image synthesis, and learning as much as I
can in the mean time.

To download my raytracer, ftp to drizzle.cs.uoregon.edu (128.223.4.1)
and login as ftp, with your name as a password.  The README file in the
pub directory can guide you further.


[by way of introduction, attached is Mark's reply to some of my comments about
his ray tracer]

I would be pleased to see my raytracer compared to other raytracers.  I am not
a "serious" graphics person, my Master's thesis work is in functional
programming languages and parallelism, but I do seem to spend alot of my off
hours trying to hack graphics stuff.

I chose Kajiya/Kay bounding volumes because they seemed much simpler than
octree methods, and still offered good speed.

As for all your suggestions:

    - The `t' option is not mentioned the `?' options list. [This option
    prints out a `.' after each scan-line is computed]

    Thanks, will include it.  I just hacked -t in to get some idea
    of how fast the raytracer was...

    - how does your implementation of Kay/Kajiya work?  That is, what
      sorting algorithm is going on with insert/delete that ensures you
      of getting the lowest key at the beginning of the list?  It's been
      but 10 years since I last studied sorting algorithms, so I am
      not up-to-date on what your scheme is all about (the powers of
      two comparisons and swaps).

    I use a simple heap implementation and use it as a priority
    queue.  I forget which data structures book I hauled it out of,
    but it isn't the most efficient in the world.  But then again,
    when I profiled it, it wasn't in the "Top Ten Most Deadly" list
    either, so I guess its okay for now.  The next release will try
    to document it better.

    - More comments throughout the code would be a plus.  If you spend an
      hour or two now, you'll save us all a lot of time.  Most of the stuff
      looks fairly straightforward, but stuff like the Kay queue sort
      could use at least a reference as to where to go next.

    Guilty as charged.  That is why I didn't try to post it to
    comp.sources.unix.  The next release will be cleaned up,
    commented, and have a better Makefile.

You comments on the lighting model are good, the lighting model needs to be
reworked at least slightly, and probably a lot more than slightly.  I haven't
got to it yet, but it is coming.

Compilation and link problems: I have a much more generic Makefile for it, but
I accidently distributed my "totally hacked one".  The next release will
probably be configurable to a wider variety of systems.

I have already received mail from a person at Tek Research Labs who is possibly
thinking of adapting my raytracer to their new Motorola 88000 based workstation
as a demo.  I said he could send me one if it sold any :-) I am glad to see my
effort so warmly received, and treated with some level of enthusiasm.  Nobody
has come back and said "Gosh, how stupid" so I will probably wish to extend
some further effort to keep it up.

-----------------------------------------------------------------------------

The Continuing Saga of MTV's Raytracer, by Mark VandeWettering

I thought I would take the time to present a list of the software
that I am making available via anonymous ftp.  All these things have
been distributed via netnews over the past few years, so I dusted them
off and made them available.

I encourage anyone who has some interesting programs to contribute to
send me mail.  Unfortunately, I cannot allow people to upload directly,
because our space is VERY tight here (the anonymous ftp login puts you
in a subdirectory of mine, and I have a puny quota), but I would like to
maintain a library of freely distributable source code for computer
graphic applications.  I hope to have viewers for sun and X11 soon, as
well as an imagen printer dump.  Anyone working on such things, write me
if you would like to have your work distributed.

Anyway, here is the current contents of the directory ~/pub on
drizzle.cs.uoregon.edu (128.223.4.1):

-cut-cut-cut-cut-cut-cut-cut-cut-cut-cut-cut-cut-cut-cut-cut-cut-cut-cut



This directory contains:

    raytrace.shar        my raytracer as it was posted to usenet's
                comp.graphics group

    rpi-tracer.shar        A raytracer written by George Kyriazis,
                posted to comp.graphics.

    teapot.nff.Z        compressed nff file of the famous
                "teapot", as patches for the above
                raytracer.

    mini-ray.shar        The winner to paul heckbert's minimal
                raytracing contest.  Wow!  Fits on a
                screen, once it has been "raped".

    ohta-tracer.shar    A REALLY FAST spheres only raytracer.
                Was originally posted to comp.graphics.

    haines.shar        A slightly out of date version of Eric
                Haines' NFF Standard Procedural Database
                stuff.  I am working on getting the
                latest and greatest from netlib, but
                they seem to be slow.

Any questions or bugs with this software can be send to [e-mail].

Thank you,

Mark

-----------------------------------------------------------------------------

Public Domain Ray Tracer Q & A, by Mark VandeWettering

Reply-To: [e-mail] (Mark VandeWettering)
Organization: University of Oregon, Computer Science, Eugene OR

[Mark's public domain RT was posted to USENET a week or two ago.  This is a
note he posted to USENET just recently.]


First of all thanks to everyone who has expressed an interest in my raytracer.
I wish to address some questions globally rather than to each individual.

Q:    The raytracer seems to work, but how do I display it on my XXX
    brand workstation?

A:    Well, there are many answers to this.  We only have black and
    white sun workstations here, so I have to display my images on
    an ancient and probably quite rare Tek4115 graphics terminal
    which has only 8 bitplanes.

    What I do is take the output of this raytracer, and pipe it
    through a program to convert it to the Utah Raster Toolkit
    format that we use here at the U of O.  We have several programs
    to display these files on a wide variety of devices.  The utah
    Raster Toolkit is available via anonymous FTP from cis.utah.edu,
    or you can send them some amount of money, and they can make you
    a tape (I don't have exact details here).

    The only problem with this is the guts of my conversion program
    are not original, they consist of some code that Eugene Miya
    posted to this group awhile ago (never write what you can beg,
    borrow or steal!), and I would have to contact him before I
    distributed said program.  Also you would have to get the Utah
    Raster stuff as well.

    If I get enough mail to warrant posting this stuff, and if I can
    verify it with Eugene Miya, I will post my programs.

    My advice:  Don't bother hacking pic.c too much.  Write a
    program to display general raster images of an rgb bitmap to
    whatever device you have on hand.  Use dithering if you want
    black and white.  And then POST such programs, so that others
    can use/improve them.

Q:    Where can I get Eric Haines' NFF package?

A:    Simple:  I will be reposting it right after this message.

Q:    Does anyone have any nifty NFF file objects to trace?

A:    Well, I just converted the teapot to NFF file format (using
    faceted polygons) but it is pretty big.  If someone can suggest
    an anonymous FTP site where I could put some of these, as well
    as other revisions to my programs, I would make them available
    from there.

Q:    What else am I working on?

    Well, I would like to add motion blur, and statistically
    optimized anti-aliasing.  I added code so that you can specify
    colors by name rather than by guessing colors.  Parametric
    patches, tori, and surfaces of revolution would be nice to add
    too. As soon as I feel the raytracer has been significantly
    extended, I will repost.

Finally, a bug fix (courtesy of Cameron Elliot):

Your program will crash on some machines unless you do the following...
(The buf array was too small.)

Modify screen.c:

/* Was before cam...
    [Ed:  Gadzooks, Mark can sure be stupid sometimes....]
        curbuf = (Pixel *) malloc (xres * sizeof (Pixel)) + 1 ;
        buf = (Pixel *) malloc (xres * sizeof (Pixel)) + 1;
*/
        curbuf = (Pixel *) malloc ((xres+1) * sizeof (Pixel)) ;
        buf = (Pixel *) malloc ((xres+1) * sizeof (Pixel));

        ---
        Cameron Elliott        Portable Cellular Communications
        Path: ...!uw-beaver!tikal!ptisea!cam

Thanks again for the bug fix, and the nice comments!

Keep the mail coming!

Mark VandeWettering

-----------------------------------------------------------------------------

Public Domain Ray Tracer Utilities, by Tom Vijlbrief

>From: [e-mail] (Tom Vijlbrief)
Newsgroups: comp.graphics
Organization: TNO Institute for Perception, Soesterberg, The Netherlands

In article <[e-mail]> [e-mail] (Mark VandeWettering) writes:

>    My advice:  Don't bother hacking pic.c too much.  Write a
>    program to display general raster images of an rgb bitmap to
>    whatever device you have on hand.  Use dithering if you want
>    black and white.  And then POST such programs, so that others
>    can use/improve them.

This is a posting of two programs which convert the output
of the raytracing program to Sun rasterfile format.

Ray2sun maps to greyscale.

Cray2sun maps to color (3 bit red, 3 bit green and 2 bit blue)

The program Ray2sun works fine, but Cray2sun should be much smarter
to produce better quality pictures.  (E.g. use dithering...)

Tom

Tom Vijlbrief
TNO Institute for Perception
P.O. Box 23                Phone: [phone]
3769 DE  Soesterberg            E-mail: tnosoes![e-mail]
The Netherlands                    or:    uunet!mcvax!tnosoes!tom

[Code is 200+ lines, so is left out.  Either check USENET or write Tom or
me for the code. - Eric]

------------------------------------------------------------------------------

Sorting Unnecessary on Shadow Rays for Kay/Kajiya?
    by Eric Haines and Mark VandeWettering

[What follows is a discussion (still ongoing - please do add your two cents)
between Mark and I about the Kay/Kajiya efficiency scheme.  Mark uses
Kay/Kajiya in his ray tracer for shadow rays, which I feel is superfluous.
It's a minor point, as the sorting, as Mark points out, is usually not a
killer as far as where the time is spent.  However, it was worth it to me
as I found I misunderstood a part of the algorithm and found a better way
(I think) to implement Kay/Kajiya than was originally presented.  Tim Kay:
care to comment?]

Eric's first note:

- Note that Kay/Kajiya sorting is unnecessary for shadow rays.  This
  is because you don't care about the closest object, but rather
  whether any object blocks the light.  As soon as you get a shadow
  test hit, you can skip the rest of the intersection test - you're
  done.

----------------

Mark's reply:

    Is this totally correct?  What we want to know is if there is a
    shadow between the light source and the point we hit.  If we
    sort the list, we can stop when we find the first item, but we
    can also stop when the bounding volumes or the intersection are
    greater than the distance to the shadow (the point isn't
    shadowed)  Because the heap insertion/deletion routines take so
    little time, it would seem that this would be a good
    optimization.  But yes, I agree that some optimization of shadow
    rays could be made.

----------------

Eric's response:

The way a sorted list is created is to intersect a BV, get its distance, and
put its children on the list using this distance as a key.  For shadowing, the
distance to the light acts as the maximum cutoff from the start.  So, when a BV
is intersected it is either beyond the light or not.  If beyond, its children
are not put on the candidate list.  If not beyond, the children can be placed
anywhere within the candidate list (since we want any intersection).
Essentially, there should never be anything on the candidate list which is
keyed as having a distance beyond the light.  Only when you actually test the
candidate can you tell if it is beyond, at which point you throw it out.  So,
there should never be a point where you can say "all these candidates are
beyond the light", as such candidates should not be on the test list, no matter
whether the list is sorted or not.  QED, the sorting is unneeded.  I should
mention that Jeff Goldsmith also figured this out independently - has anyone
else noticed that sorting is unnecessary for shadowing?

Kay/Kajiya is something of a Catch-22 (but a great method, nonetheless), since
the sort key is the candidate's parent's distance, and what we really would
like is to have the sort key be the candidate's distance.  To get this distance
we intersect the candidate.  Now we have the distance (if any) we would have
liked to used to sort the candidate, but it's too late: we've intersected the
candidate and so taken it off the candidate list (possibly replacing it with
its children).

However, there might actually be a slight gain in practice if the list is
sorted by distance for shadow rays.  Say you have two bounding volumes, each
with N objects.  If both BV's are intersected, and the further bounding volume
contains the light, then it's probably worth intersecting the objects in the
closer BV first.  This is because the further bounding volume probably contains
objects which are beyond the light, while the closer one has objects more or
less between the light and the test point.  I believe this gain is negated by
the following counter-argument: what if the closer BV contains the intersection
point, and the further does not contain the light or the intersection point?
By the previous logic, we should intersect the further BV's children first.
"Scene dependence" seems to be the key phrase here: are your shadowing objects
closer to the intersection point (e.g. a board with a bunch of nails pounded
into it seems worth testing the closer nails first), or closer to the light
source (e.g. the light source has a lampshade).

In light (ho ho) of this, I maintain that Kay & Kajiya sorting is unnecessary
for shadow rays.  However, there are certainly other interesting sorting
strategies worth considering for shadow rays.  Some possibilities:

  - Object complexity (i.e. if you have a choice, try intersecting the
    sphere before trying the spline surface).
  - Object size (big objects cast big shadows.  This idea actually
    helps enhance "shadow caching", where the last object to shadow a
    light is then tested first for the next shadow ray for that light.
    A big object will have more shadow coherence and so will result
    in less having to find another shadowing object.  Say a light is
    blocked by both a sphere and a fine mesh of polygons.  The sphere
    will have much more shadow coherence than each polygon, resulting
    in many fewer misses).
  - Function sorting.  I haven't thought about this much, but one might be
    able to come up with a function which simulates the probability
    that a given object will be intersected.  The function could be based
    on the closest intersection distance, or the farthest, or some of each.
    One possible theory:  BV's which neither overlap the light or the
    intersection point have a higher probability of containing a shadowing
    object, for the reasons given earlier.

Anyway, just some thoughts. - Eric Haines

----------------

Mark's response:

    > The way a sorted list is created is to intersect a BV,
    > get its distance, and put its children on the list using
    > this distance as a key.

This isn't the way it is currently implemented in my raytracer, and
glancing back at Kay/Kajiya, it seems contrary to their intent as well.
If I intersect the parent volume, I intersect with the bounding volume
of each of the children, and use THAT distance as the key for insertion.
This does seem to require alot more bounding box intersections, but
still has exactly the same number of ray/object intersections.

> Kay/Kajiya is something of a Catch-22 (but a great method,
> nonetheless), since the sort key is the candidate's parent's distance,
> and what we really would like is to have the sort key be the
> candidate's distance.  To get this distance we intersect the
> candidate.  Now we have the distance (if any) we would have liked to
> used to sort the candidate, but it's too late: we've intersected the
> candidate and so taken it off the candidate list (possibly replacing it
> with its children).

I think that this argument falls in light of my correction above.  Each
time an object is queued, it is keyed by the actual distance to its own
bounding volume, not the distance to the parent.

My feeling is that if you add the proper cutoffs, that Kajiya/Kay
testing for shadows is still just about the same cost as not bothering
to sort.   I actually implemented early cutoffs within the framework of
Kajiya/Kay BVs, and it only gave an improvement of 2% on average for the
Standard Procedural Database objects.  This DOESN'T mean that it is
correct, because I am uncertain just how "typical" the SPD stuff is, but
it would seem to be that for certain objects, the gain is small.

----------------

Eric's response:  Well, I made a semantic error.  Kay/Kajiya calls a
"candidate" an object (real or BV) whose bounding volume has been hit and
whose children have not been intersected.  So, you're right in that the
algorithm does put an intersected BV on the list as a candidate, and not
its children.  In practical terms this will mean less sorting: you only
have to insert the intersected BV into the list, and not all its children
(all of which have the same key).  My confusion arose from the fact that
Kay/Kajiya puts a bounding volume around every object, which I don't (a simple
triangle or a sphere is about the same to intersect than a bounding box, and
a BV around a sphere (which is a BV, after all), seems excessive).

    Interestingly enough, looking over the original paper, I now have to agree
with you:  sorting on shadow rays using their original algorithm makes sense.
However, I have found that there is an inefficiency in the Kay/Kajiya algorithm
as presented at SIGGRAPH (which I never noticed before):  in their figure 7,
where they outline the algorithm, (page 275 of the SIGGRAPH '86 proceedings)
it is stated, "if the ray hits the BV, insert the child into the heap".  Then
when they get to the "while" loop they state that "while heap is non-empty and
distance to top node < t" the loop should be performed.  Seems to me that they
are inserting children which could be immediately culled.  I believe a faster
algorithm results from:

    If the ray hits the bounding volume and distance < t
        Insert the child into the heap

In other words, if the distance to the BV is greater than the present t (which
is the closest intersection distance of a real object), its child can
immediately be discarded (instead of inserting it into the heap).

    Using this slight modification of Kay/Kajiya now means that sorting is
unnecessary.  In the original, it was worth checking the distance because
objects which were beyond the present t distance (for shadowing, the distance to
the light) were actually inserted on the heap.  By realizing that these
children have no business on the heap (they're beyond the light, right?) and
not inserting them in the first place, there is then no reason to sort what
is then actually put on the heap.

[This is where things stand for now.  My original mistake of misreading Kay
and Kajiya was partly due to my using a more efficient algorithm:  not adding to
the heap if the child cannot possibly be hit.  I had never noticed that this
was not how they wrote it up, as I assumed they would compare all intersections
against the closest real intersection distance. - Eric]

------------------------------------------------------------------------------

Summary of Replies to Vectorizing Ray-Object Intersection Query, by Tom Palmer

From: [e-mail] (Thomas Palmer)
Newsgroups: comp.graphics


This is a summary of the replies I received to my query regarding
vectorizing ray-object intersection calculations.

----------------

>From: stan!dodge![e-mail] (Dave Plunkett)

   You might try any of:

   "The Vectorization of a Ray Tracing Program for Image Generation",
   with J.M. Cychosz and M.J. Bailey.
   Cyber 200 Applications Seminar, NASA Goddard, October 1983.

   "Ray Tracing on a Cyber 205",
   Conference Proceedings VIM-40,
   San Francisco, CA, April 1984.

   "A Vectorized Ray Tracing Algorithm",
   Masters Thesis,
   Purdue University, West Lafayette, IN.  August 1984.

   "The Vectorization of a Ray Tracing Algorithm for Improved Execution Speed",
   with M.J. Bailey.  IEEE Computer Graphics and Applications,
   Vol. 5, No. 8, August 1985.

   The last two of these are more readily accessible.  These papers describe my
Master's research, a vectorized ray tracing algorithm for use on csg objects
that was written using explicit vector syntax on the 205.  If you have any
specific questions, I'd be glad to answer any that I can.

Dave Plunkett
Solbourne Computer, Inc.
Longmont, CO 80501
[phone]
...sun!stan!dave

----------------

>From: [e-mail] (Joe Cychosz)

I have developed a vectorized ray tracing package for the CYBER 205.  Part of
the work is discussed in Plunkett's CG&A paper.  Nelson Max also had a paper on
vectorized intersections of height fields used to produce Carlos' Island.  Saul
Youseff at Florida State has also been doing some work using raytracing for
collector plate design.

Both Plunkett and myself use a ray queue to collect rays, and then vectorize
such that serveral rays are intersected with an object.  This approach does
make it difficult to implement these accelerated ray traces such as Mike
Kaplan's "Constant Time Ray Tracing".

I have a variation of Kaplan's approach that sub-divides the object space and
uses bit operators to elliminate unnecessary intersection calculations.

Joe Cychosz

----------------

>From: mcvax!tokaido.irisa.fr![e-mail] (Thierry Priol -- Equipe Hypercubes)

There are few works on vectorization of the ray-object intersection.  One of
these works was done by Plunkett on a CDC-CYBER. The reference is:

[reference same as in Plunkett's note]

Personally, I work in ray-tracing on a parallel MIMD (hypercube iPSC/2)
computer.

Thierry PRIOL
Institut de Recherche en Informatique et Systemes Aleatoires
Campus de Beaulieu
35042 RENNES CEDEX
FRANCE
e-mail : mcvax!inria!irisa!priol

---------------------

>From: [e-mail] (Michael Carter)

     The real problem in the inner ray tracing loop is not ray-object
intersections, but ray-bounding volume intersections.  If you refer to the
article by Kay and Kajiya from SIGGRAPH '86, they describe a method of breaking
down the OBJECT space into a hierarchical data structure, and intersecting rays
against simple bounding volumes constructed from sets of planes.  This method
queries the objects in the order that they occur along the ray, therefore, NO
SORTING IS NEEDED.  It takes at least three pairs of planes to completely
enclose an object, therefore this intersection calculation could be done
efficiently, in parallel (on perhaps more than one object at a time!)  on a
vector machine.  Most of the time is spent in this ray-bounding volume
intersection loop, and not in the ray-object intersection algorithms.

     I realize that this is not something that the C compiler can do
on its own, but remember: no pain -- no gain.  (-:

--
Michael B. Carter
Department of Electrical and Computer Engineering, Oklahoma State University
UUCP:  {cbosgd, ea, ihnp4, isucs1, mcvax, pesnta, uokvax}!okstate!mbc
ARPA:  [e-mail]


[The statement "NO SORTING IS NEEDED" appears to be in error - sorting is an
integral part of the Kay & Kajiya algorithm. - Eric H.]

----------------

>From: [e-mail] (Stephen Spencer)

[included in last issue]

----------------------------------------------------------------------------

The Ray Tracer I Wrote, by George Kyriazis

From: kyriazis@rpics (George Kyriazis)
Newsgroups: comp.graphics
Organization: RPI CS Dept.

    Since I had too many requests for my ray tracer, I am posting it
here [USENET].  Hope that will help people that can't get mail to me.  I finally
had the source put so people can read it, but it's not definite that it'll
stay where it is.  Right now it is on life.pawl.rpi.edu (128.113.10.2) in
pub/ray.  Can you please comment back on it ?  Thanks.

So, here it is:

[Deleted here, again, as it's another 900+ lines of archive.  Check USENET,
write George or me, or ftp it as above to get a copy.  What follows are
excerpts from his README file.]

    Here is a simple ray tracing program developed here at RPI.  It
incorporates shadows, reflections and refraction together with one
non-directional light source.  The light source can diffuse on the surfaces
and can also give specular reflections.  The illumination model used is
by Phong.  The only objects supported right now are spheres, but the data
structure can be easily expanded to incorporate more objects.

[...]

    The ray tracer is written so it can be easily understood (at least
that version), and it is fully commented.  Nevertheless, probably it won't
be understood by a newcomer.

[...]

    Can you please inform me with any bugs that the program might have
or any features that you want the upcoming versions to have.  This software
was written by me, and the subsequent version will probably by produced
by other members of the RPI chapter of the ACM.
                        Good luck!

    George Kyriazis
    [e-mail]

----------------------------------------------------------------------------

New Bitmaps Library Available, Jef Poskanzer

Reply-To: Jef Poskanzer <[e-mail]>
Organization: Paratheo-Anametamystikhood Of Eris Esoteric, Ada Lovelace Cabal

The third release of the Portable Bitmap package is ready for FTPing
from expo.lcs.mit.edu:contrib/pbm.tar.Z.

Answers to some frequently asked questions:
 - The decimal address of expo is 18.30.0.212.
 - Please avoid ftp'ing from expo.lcs.mit.edu in between the hours of
   9am and 6pm east coast, USA time.
 - There may be other places to FTP it from, but I don't know of them.
   In particular, you can't FTP it from lbl-rtsg.  Don't even try.
 - Don't forget to set binary mode when you do the FTP.
 - Pbmtorast and rasttopbm depend on Sun's pixrect library, and will
   compile only on suns.
 - Currently there is no way to get the package other than FTP.  However,
   if comp.sources.misc ever gets going again, perhaps PBM will get
   distributed there.  (I have sent mail to the moderator about it, and
   have received no reply.)

Appended is the README for PBM.  It includes a list of the major enhancements
in this version.
---
Jef

- - - - - - - - - -

                       Portable Bitmap Toolkit
                       Distribution of 31aug88
                    Previous distribution 04apr88


Included are a number of programs for converting various bitmap formats
to and from a portable format; plus some tools for manipulating the
portable bitmaps.

Major changes since the previous distribution:
    The pbm format now has a "magic number".
    New conversion filters brushtopbm, giftopbm, pbmtolj, pbmtomacp,
      pbmtoxwd, and pbmtox10wd.
    Icontopbm converter has a better parser -- it knows to skip over
      any extraneous comments at the beginning of the icon file.
    Pbmtops generates a different PostScript wrapper program -- it should
      handle huge bitmaps better.
    Xwdtopbm now handles byte-swapping correctly.
    Pbmmake takes a flag to specify the color of the new bitmap.
    Pbmpaste now implements 'or', 'and', and 'xor' operations as well
      as the default 'replace'.
Plus various minor bug fixes and enhancements.


Files in this distribution:

    README        this
    FORMATS        descriptions of the various bitmap formats
    Makefile        guess

    brushtopbm.c    convert from Xerox doodle brushes to portable bitmap
    cbmtopbm.c        convert from compact bitmap to portable bitmap
    giftopbm.c        convert from GIF to portable bitmap
    icontopbm.c        convert from Sun icon to portable bitmap
    macptopbm.c        convert from MacPaint to portable bitmap
    rasttopbm.c        convert from Sun raster to portable bitmap
    xbmtopbm.c        convert from X10 or X11 bitmap to portable bitmap
    xwdtopbm.c        convert from X10 or X11 window dump to portable bitmap
    xxxtopbm.c        convert from UNKNOWN BITMAP to portable bitmap

    pbmtoascii.c    convert from portable bitmap to ASCII graphic form
    pbmtocbm.c        convert from portable bitmap to compact bitmap
    pbmtoicon.c        convert from portable bitmap to Sun icon
    pbmtolj.c        convert from portable bitmap to HP LaserJet
    pbmtomacp.c        convert from portable bitmap to MacPaint
    pbmtops.c        convert from portable bitmap to PostScript
    pbmtoptx.c        convert from portable bitmap to Printronix
    pbmtorast.c        convert from portable bitmap to Sun raster
    pbmtoxbm.c        convert from portable bitmap to X11 bitmap
    pbmtox10bm.c    convert from portable bitmap to X10 bitmap
    pbmtoxwd.c        convert from portable bitmap to X11 window dump
    pbmtox10wd.c    convert from portable bitmap to X10 window dump

    pbmcatlr.c        concatenate portable bitmaps left to right
    pbmcattb.c        concatenate portable bitmaps top to bottom
    pbmcrop.c        crop a portable bitmap
    pbmcut.c        cut a rectangle out of a portable bitmap
    pbmenlarge.c    enlarge a portable bitmap N times
    pbmfliplr.c        flip a portable bitmap left for right
    pbmfliptb.c        flip a portable bitmap top for bottom
    pbminvert.c        invert a portable bitmap
    pbmmake.c        create a blank bitmap of a specified size
    pbmpaste.c        paste a rectangle into a portable bitmap
    pbmtrnspos.c    transpose a portable bitmap x for y

    libpbm.c        a few utility routines
    pbm.h        header file for libpbm
    macp.h        definitions for MacPaint files
    x10wd.h        definitions for X10 window dumps
    x11wd.h        definitions for X11 window dumps
    bmaliases        csh script to make aliases for converting formats
    *.1            manual entries for all of the tools
    pbm.5        manual entry for the pbm format
    bitreverse.h    useful include file


Unpack the files, edit Makefile and change the options to suit,
make, and enjoy!  Note that if you're not on a Sun, you won't be
able to compile rasttopbm and pbmtorast.

I've tested this stuff under 4.2 BSD, 4.3 BSD, and System V rel 2,
and on both Suns and Vaxen.  Nevertheless, I'm sure bugs remain.
Feedback is welcome - send bug reports, enhancements, checks, money
orders, etc. to the addresses below.


    Jef Poskanzer
    [e-mail]
    {ucbvax, lll-crg, sun!pacbell, apple, hplabs}!well!pokey

-----------------------------------------------------------------------------

END OF RTNEWS