Ray Tracing News

"Light Makes Right"

September 11, 1988

Volume 1, Number 9

Compiled by Eric Haines [email protected] . Opinions expressed are mine.

All contents are copyright (c) 1988, all rights reserved by the individual authors

Archive locations: anonymous FTP at ftp://ftp-graphics.stanford.edu/pub/Graphics/RTNews/,
wuarchive.wustl.edu:/graphics/graphics/RTNews, and many others.

You may also want to check out the Ray Tracing News issue guide and the ray tracing FAQ.


Contents:


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

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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
# (301) 698-5797
alias tom_palmer [email protected]

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 [email protected], 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
# (518) 276-6491
alias phil_getto [email protected]

______________

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

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
# (614) 292-3416
alias stephen_spencer [email protected]

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
# (919) 962-1918
alias greg_turk [email protected]

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
# (607)255-6711
alias roy_hall [email protected]

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
# [email protected]
alias mark_vandewettering [email protected]

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.

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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 [email protected].

Thank you,

Mark

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Public Domain Ray Tracer Q & A, by Mark VandeWettering

Reply-To: [email protected] (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 cs.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

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Public Domain Ray Tracer Utilities, by Tom Vijlbrief

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

In article ([email protected]) [email protected] (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: +31 34 63 62 77
3769 DE  Soesterberg                    E-mail: tnosoes![email protected]
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]

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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]

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

From: [email protected] (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![email protected] (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
(303) 772-3400
...sun!stan!dave

________________

>From: [email protected] (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: [email protected] (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: [email protected] (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:  mbc%[email protected]

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

________________

>From: [email protected] (Stephen Spencer)

[included in last issue]

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The Ray Tracer I Wrote, by George Kyriazis

From: [email protected] (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
        [email protected]

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New Bitmaps Library Available, Jef Poskanzer

Reply-To: Jef Poskanzer ([email protected])
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
    [email protected]
    {ucbvax, lll-crg, sun!pacbell, apple, hplabs}!well!pokey

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Eric Haines / [email protected]