Ray Tracing News

"Light Makes Right"

July 15, 1991

Volume 4, Number 2

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

All contents are copyright (c) 1991, 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:


Introduction

I admit it, I've strayed from the One True Way of pure ray tracing: I've been dabbling in radiosity. We recently finished a film of Ronchamp chapel illuminated with radiosity techniques, rendered with an a-buffer, and with stochastic ray traced beams of lights streaming in the windows, coming to a film show near you (SIGGRAPH and Eurographics, I hope). My one piece of advice from doing the film is this: try to make everything originate from you. The rights to music are amazingly expensive (in our case, thousands of dollars for just one showing at SIGGRAPH), and tracking down and obtaining permission to use quotes, drawings, or photos can be a real hassle.

If you want to know how we did the beams of light effect, get the "Frontiers in Rendering" course notes (or even go to the course). There should be some good & weird topics at this course, such as Charlie Gunn's animations of hyperbolic space (where dodecahedra meet 8 at a corner) and Peter Kochevar's shading computations via cellular automata ("the lunatic fringe of rendering", as he puts it). Me, I'm going to talk about ray casting for radiosity, and also all the things that drive me crazy about radiosity (with lots of dirty laundry pictures showing where and how radiosity falls apart, and some solutions).

As usual, there will be a ray tracing researchers get-together at SIGGRAPH, open to anyone. On Thursday from 5:15 to 6:30 at room N223 in the convention center we'll meet and gab about this and that. No planned activities, just a place and time to connect names to faces.

When our son Ryan was born, Zap Andersson sent a nice little GIF from his ray tracer of a cigar in an ashtray as congratulations; the texture mapped smoke was particularly well done. Zap was just married, so I was able to send two interlinked rings with his wife's & his names inscribed in them. Definitely a future trend: graphical greeting cards/presents by e-mail.

The wedding rings picture was also my first worthwhile test image using the two-pass software we've developed to blend radiosity and ray-tracing. The nice thing about two-pass algorithms is that you generally get soft shadows cheaply, as the radiosity mesh picks up the shadows adaptively and so saves the ray tracer much shadow-testing time. You also get all the nice features of ray tracing, including exact geometry: spheres are truly spherical, instead of straight radiosity's polygonalized representation. Being able to combine the sampling mesh from radiosity and the geometry from ray tracing is usually a great combination.

Just so it is not buried in the bits: note that Greg Ward's Radiance ray tracer with radiosity effects built in (see his SIGGRAPH paper) is now available via FTP. As important, he has also begun a directory of "test" radiosity scenes which researchers can use to attempt to compare radiosities generated for these scenes. For those of you trying to write your own radiosity system this is a valuable tool for checking if you're getting anything near the right answer. Finally, Greg has also collected various object models and made them available.

Books of note: _Digital Image Warping_ by George Wolberg (IEEE Computer Society Press Monograph, 1990) is very handy if you're involved in texture mapping. Many different topics are covered, with good illustrations and sample code. It's not the ultimate book from a theory standpoint, but is very practical and understandable. Recommended.

Last issue someone mentioned the book _Fractal Programming and Ray Tracing with C++_ by Roger Stevens (M&T Books for $30, $20 more for the disk of code). I bought it, and cannot recommend it to the general reader. If you are getting your feet wet with C++ it might be of some interest, and beginning PC programmers might find bits of it useful. The author takes Steve Koren's QRT input language and develops a C++ ray tracer for it. One major problem with such a ray tracer is that there is no definition for a general polygon; only triangles and parallelograms are provided. There's a lot of padding in the book, with 20 or 30 page stretches of nothing but code listings, and 70 pages of data file listings (42 pages for his version of "sphereflake" alone - he could have printed the listings for the whole SPD package in that space!). The index is somewhat dysfunctional, e.g. minor variations on the words "bounding boxes" are given separate listings, some with wrong page numbers. References to almost all other work in ray tracing is missing, and the interested reader is given almost no help on where to go for more information. I wish it had been better.

Coming out at SIGGRAPH is "Graphics Gems II", edited by Jim Arvo this time around. Does anyone else know of good books to look for there? The other SIGGRAPH question: any guesses on how many times humorous references to "Monte Carlo" techniques will be made?

Get a job: one subscriber pointed out an interesting relationship between public domain ray tracers and future employment. The authors of two of the more popular public domain ray tracers (MTV by Mark VandeWettering and RayShade by Craig Kolb) are currently employed by PIXAR. Now if David Buck of DKBtrace gets a job there (no, I have no idea if he's even looking for work) this relationship can become a firmly established principle...

Finally: I've pretty much stopped culling USENET for news in comp.graphics, figuring that most everyone plows through this stuff by now. What convinced me was looking at my file of comp.graphics clippings and seeing that the accumulation surpassed half a megabyte! Updating the ray tracing and radiosity bibliographies, mailing list, and the FTP site list are time consuming enough; also running a clipping service was too much.

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New People, Address Changes, etc

The first subscriber connected across the now-slagged Iron Curtain:

# Janusz Kalinowski - density clouds (metaballs), parallelism, textures # Technical University of Wroclaw, Computing Center # Wybrzeze Wyspianskiego 27 # Wroclaw, Poland alias janusz_kalinowski [email protected]

I am a lecturer at Technical University of Wroclaw. I am mainly involved in CG-related subjects, but also in system software. We are preparing a metaballs system (modeller, renderer). I made my MS in DataFlow (I wrote an emulator of Manchester Prototype Dataflow System), but I prefer CG now. Maybe I will marry both domains in the future?

________

# Chris Green - efficiency, fancy primitives, radiosity, textures
# Commodore Business Machines
# 1200 Wilson Drive
# West Chester, PA 19380
# (215)-431-9100
alias   chris_green njin!cbmvax.cbm.commodore.com!chrisg

When I've got spare time away from working on Amiga graphics, and doing contract work on 3d games, I spend it working on my ray tracer. My ray tracer is extremely fast, due to being written completely in 680x0 assembly with all fixed point math. I support spheres, triangles, hypertexture (!), and general implicit functions. It also has depth of field, penumbras, procedural textures, and more. The efficiency scheme used is my own invention and is especially fast for radiosity ray tracing (some day) and penumbras (now).

________

Russ Tuck
[email protected]
MasPar Computer Corporation, 749 N. Mary Ave, Sunnyvale, CA 94086

(Old: [email protected])

________

# Billy Ferrer - ray tracing on the Atari STe, efficiency.
# University of California, Irvine
# 2520 Golden Ave.
# Long Beach, CA 90806
# (213) 595-5279
alias bill_ferrer [email protected]

I am a sophomore at University of California, Irvine studying computer science. My interest in ray tracing stemmed from seeing impressive displays from Amiga, NCGA and Siggraph shows. I am just a beginner in the ray tracing programming department, but during my spare, spare, spare time I am writing a ray tracing program for the Atari STe because first there isn't a good and reliable ray tracing program on the ST/STe and second to write a ray tracing program for learning purposes. Currently my program traces checkered floors, spheres, and reflections. Right now, my effort is going towards texture mapping the floor by mapping an image on the floor. Hopefully my program will support refractions and other various 3d object formats.

________

Name:    Thomas Michael Burgey
Goals:   modelling of objects, modelling of textures, RT art
Company: Cadlab - Kooperation Uni-GH Paderborn / Siemens Nixdorf AG
         Bahnhofstrasse 32
         W-4790 Paderborn
Tel:     +49 5251 284 151
Mail:    [email protected]

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Ray Tracing related FTP sites (and maintainers), 7/15/91 compiled by Eric Haines, [email protected]

[Ironically, we still don't have our FTP connection yet (it's been "one month away" since last December...), so I can't verify much of this data! Please do send me any updates & corrections.]

Some highlights:

RayShade - a great ray tracer for workstations on up.
DKBtrace - another good ray tracer, from all reports; works on PCs.
Radiance - a ray tracer w/radiosity effects, a la Greg Ward (who wrote it).
VORT,QRT,MTV,DBW - yet more ray tracers, some with interesting features.
prt, VM_pRAY - parallel ray tracers.
SIPP - scanline Z-buffer renderer.
VOGLE - graphics learning environment (device portable).

SPD - a set of procedural databases for testing ray tracers. NFF - simplistic file format used by SPD. OFF - another file format.

RT News - collections of articles on ray tracing. RT bib - all known (by me) articles on ray tracing, in "refer" format. RT abstracts - collection of abstracts of many many RT articles.

Utah Raster Toolkit - nice image manipulation tools.
FBM - another set of image manipulation tools.
Graphics Gems - code from the ever so useful book.

(*) means site is an "official" distributor, so is most up to date.

weedeater.math.yale.edu [130.132.23.17]: /pub - *Rayshade 3.0 ray tracer*, *color quantization code*, *SPD*, *RT News*, *Wilson's RT abstracts*, "RT bib*, *new Utah raster toolkit*, newer FBM, *Graphics Gems code*. Craig Kolb ([email protected])

rascal.ics.utexas.edu [128.83.144.1]: /misc/mac/inqueue - VISION-3D facet based modeller, can output RayShade files.

ccu1.aukuni.ac.nz [130.216.1.5]: ftp/mac/architec - *VISION-3D facet based modeller, can output RayShade files*. P.D. Bourke ([email protected])

alfred.ccs.carleton.ca [134.117.1.1]: /pub/dkbtrace - *DKB ray tracer*. David Buck ([email protected])

hobbes.lbl.gov [128.3.12.38]: Radiance ray trace/radiosity package. Greg Ward ([email protected])

nic.funet.fi [128.214.6.100]: pub/graphics/papers - *Paper bank project, including Pete Shirley's entire thesis (with pics)*, *Wilson's RT abstracts in PostScript*, Kouhia Juhana Krister ([email protected])

isy.liu.se [130.236.1.3]: pub/sipp-2.0.tar.Z scan line z-buffer and Phong shading renderer. Jonas Yngvesson ([email protected])

calpe.psc.edu [128.182.66.148]: pub/p3d - p3d_2_0.tar P3D lispy scene language & renderers. Joel Welling ([email protected])

ftp.ee.lbl.gov [128.3.254.68]: *pbmplus.tar.Z*, RayShade data files. Jef Poskanzer ([email protected])

irisa.fr [131.254.2.3]: */iPSC2/VM_pRAY ray tracer*, SPD, /NFF - many non-SPD NFF format scenes, RayShade data files (Americans: check ftp.ee.lbl.gov first). Didier Badouel ([email protected])

wuarchive.wustl.edu [128.252.135.4]: /mirrors/unix-c/graphics - Rayshade ray tracer, MTV ray tracer, Vort ray tracer, FBM, PBM, popi, Utah raster toolkit. /mirrors/msdos/graphics - DKB ray tracer, FLI RayTracker demos. Tracey Bernath ([email protected])

tolsun.oulu.fi [128.214.5.6]: *FLI RayTracker animation files (PC VGA)*, *RayScene demos* (Americans: check wustl first). Jari Kahkonen ([email protected])

cs.uoregon.edu [128.223.4.13]: /pub - *MTV ray tracer*, *RT News*, *RT bibliography*, other raytracers (including RayShade, QRT, VM_pRAY), SPD/NFF, OFF objects, musgrave papers, some Netlib polyhedra, Roy Hall book source code, Hershey fonts, old FBM. Mark VandeWettering ([email protected])

hanauma.stanford.edu [36.51.0.16]: /pub/graphics/Comp.graphics - best of comp.graphics (very extensive), ray-tracers - DBW, MTV, QRT, and more. Joe Dellinger ([email protected])

freedom.graphics.cornell.edu [128.84.247.85]: *RT News back issues*, *source code from Roy Hall's book "Illumination and Color in Computer Generated Imagery"*, SPD package, *Heckbert/Haines ray tracing article bibliography*, Muuss timing papers.

uunet.uu.net [192.48.96.2]: /graphics - RT News back issues (not complete), NURBS models, other graphics related material.

iear.arts.rpi.edu [128.113.6.10]: /pub - *Kyriazis stochastic Ray Tracer*. qrt, ohta's ray tracer, prt, other RT's (including one for the AT&T Pixel Machine), RT News, *Wilson's RT abstracts*, Graphics Gems, wave ray tracing using digital filter method. George Kyriazis ([email protected])

jyu.fi [128.214.7.5]: /pub/graphics/ray-traces - many ray tracers, including VM_pRAY, DBW, DKB, MTV, QRT, RayShade, some RT News, NFF files. Jari Toivanen ([email protected])

life.pawl.rpi.edu [128.113.10.2]: /pub/ray - *Kyriazis stochastic Ray Tracer*. George Kyriazis ([email protected])

ab20.larc.nasa.gov [128.155.23.64]: /amiga - DBW,
        /usenet/comp.{sources|binaries}.amiga/volume90/applications -
        DKBTrace 2.01.  ([email protected])

munnari.oz.au [128.250.1.21]: pub/graphics/vort.tar.Z - *VORT CSG and algebraic surface ray tracer*, *VOGLE*, /pub - DBW, pbmplus. David Hook ([email protected])

gondwana.ecr.mu.oz.au [128.250.1.63]: pub - *VORT ray tracer*, *VOGLE*, Wilson's ray tracing abstracts. Bernie Kirby ([email protected])

freebie.engin.umich.edu [141.212.68.23]: *Utah Raster Toolkit*, Spencer Thomas ([email protected]) or Rod Bogart ([email protected]).

cs.utah.edu [128.110.4.21]: /pub - Utah raster toolkit, *NURBS databases*. Jamie Painter ([email protected])

gatekeeper.dec.com [16.1.0.2]: /pub/DEC/off.tar.Z - *OFF objects*, /pub/misc/graf-bib - *graphics bibliographies (incomplete)*. Randi Rost ([email protected])

expo.lcs.mit.edu [18.30.0.212]: contrib - *pbm.tar.Z portable bitmap package*, *poskbitmaptars bitmap collection*, *Raveling Img*, xloadimage. Jef Poskanzer ([email protected])

venera.isi.edu [128.9.0.32]: */pub/Img.tar.z and img.tar.z - some image manipulation*, /pub/images - RGB separation photos. Paul Raveling ([email protected])

wuarchive.wustl.edu [128.252.135.4]: /mirrors/unix-c/graphics - Rayshade ray tracer, MTV ray tracer, Vort ray tracer, FBM, PBM, popi, Utah raster toolkit. /mirrors/msdos/graphics - DKB ray tracer.

ucsd.edu [128.54.16.1]: /graphics - utah rle toolkit, pbmplus, fbm, databases, MTV, DBW and other ray tracers, world map, other stuff. Not updated much recently.

okeeffe.berkeley.edu [128.32.130.3]: /pub - TIFF software and pics. Sam Leffler ([email protected])

surya.waterloo.edu [129.97.129.72]: /graphics - FBM, ray tracers

vega.hut.fi [128.214.3.82]: /graphics - RTN archive, ray tracers (MTV, QRT, others), NFF, some models

gondwana.ecr.mu.oz.au [128.250.1.63]: SPD, NFF & OFF databases, Graphics Gems code. Bernie Kirby ([email protected])

hp4nl.nluug.nl [192.16.202.2]: /pub/graphics/raytrace - DBW.microray, MTV, etc.

ftp.brl.mil [128.63.16.158]: /old/brl-cad - information on how to get the BRL CAD package & ray tracer.

karazm.math.uh.edu [129.7.7.6]: pub/Graphics/rtabs.shar.12.90.Z - *Wilson's RT abstracts*, VM_pRAY. J. Eric Townsend ([email protected])

maeglin.mt.luth.se [130.240.0.25]: graphics/raytracing/Doc - *Wilson's RT abstracts*.

ftp.fu-berlin.de []: /pub/unix/graphics/rayshade4.0/inputs - aq.tar.Z is RayShade aquarium (Americans: check ftp.ee.lbl.gov first). Heiko Schlichting ([email protected])

apple.apple.com [130.43.2.2?]: /pub/ArchiveVol2/prt.

netlib automatic mail replier: UUCP - research!netlib, Internet - [email protected]. *SPD package*, *polyhedra databases*. Send one line message "send index" for more info, "send haines from graphics" to get the SPD.

UUCP archive: avatar - RT News back issues. For details, write Kory Hamzeh ([email protected])

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Ray Tracing, the way I do it, by Haakan 'Zap' Andersson

[See the RayTracker description later in this issue for what his system looks like. I don't agree with the usefulness of some of these, but find them interesting reading. I particularly like the idea of hashing, though as John Woolverton points out, this idea has problems with soft shadows. - EAH]

* TIGHT screen space bounding.
  Some people neglect screen space bounding, and don't use it. MANY people
  use it, but they project the 3D bounding box onto screen space, potenti-
  ally getting a lot of 'slack' around 'em.
     Gain: Speedier bounding box generation
     Loss: Slack around objects = more wasteful intersections.
  My Way: Do a vector rendering and get minmax screen coordinates from
          that.  Yes, a vector rendering might take time, but hey, what's that
          compared to the tracing time, eh?
  (Yes I know about the method of doing a Z buffer rendering first... but
   then you have to write a Z buffer renderer first, right?)
  Comments:
    Think about the standard axis-aligned bounding box around an object.
    Seen from the vector 1,1,1 you will have the corners 'sticking out'
    maximally. Also, bounding box intersection takes this 'n that amount
    of FP operation. A screen space bounding box is done with four integer
    compares. For eye rays I NEVER intersect the actual bounding boxes at
    all, ONLY use the screenspace bounding, plus a stored minimum distance
    to the eye for each bounding box. So my bounding box intersection for
    eye rays is 4 integer and one FP compare.

* Self sorting list
  Most objects in my structure has the minimum distance to the eye recorded.
  When intersection the object, the first thing you do is to see if the
  currently valid 't' is smaller than this distance. If so we have already
  hit a closer object, and can never hit this object. Also, when the ray-
  intersection checker has found the closest object, this is put first in
  the list and will be checked first next time.

  Since the intersection check function is called recursively when we enter
  a bounding box, objects INSIDE the bounding box is also sorted, so for
  each 'level' in the ray tree we always have the object we hit last first.

* Light buffer
  Similar to the 2d bounding boxes on screen for eye rays, shadow rays have
  their 2d bounding boxes, but since a light source can shine all around and
  is not limited to one direction, this is done in polar coordinates (a
  spherical coordinate system). So, for shadow rays I don't intersect any
  real bounding boxes either, but do some more compare operations. And since
  the ranges for a spherical coordinate system is fixed (i.e. 2 pi * pi)
  there is no point in using floating point, so fixed point integers can be
  used instead.

  The minimum distance to each object is also constant for each light, and
  may then be calculated and stored when we set up things and do the wire
  frame rendering.

* Reflected/fracted rays
  This is the only case where I actually intersect bounding boxes. And now
  to the next weird issue: I do NOT use axis-aligned bounding boxes, they
  are transformed together with the rest of things, since my bounding boxes
  actually work as "transformers" for my objects. But FIRST, for each box,
  I check the MINIMUM distance with the current 't' and if bigger, just
  discard.

  To find the minimum distance, I am helped by the fact that my bounding
  boxes are stored as a center point and x, y and z extends from that
  centre. So I can use a rough (distance to center) - (x_size + y_size +
  z_size), and I get a value that is guaranteed to be SMALLER than the
  actual distance. And to avoid square roots, my actual comparisons is
  of course done on the distances squared, i.e. from the ray origin, I take
  the x distance to the bbox centre squared, plus y distance squared, plus
  z distance squared. Now I have the distance from ray origin to the
  center of the bbox squared. Now subtract from that (x_size + y_size +
  z_size) squared, and compare that to 't' squared. If 't' is smaller, we
  can never hit that bounding box.

* Transformed bounding boxes
  I've always been in love with tight bounding volumes, because they avoid
  unnecessary TRUE intersections. Thus, my bounding boxes are transformed
  with everything else. Actually, it works like this (pseudo code-ish):

  trace_ray(first_object,ray)
  {
    object = first_object;

    while (object)
    {
      .
      .
      (( do the 2d intersection checking, either eye-ray 2d or
         polar 2d for lamps. only do rest of code if 2d hit, and
         distance is below current 't' ))
      .
      (( Ok, we hit 2D-wise, OR this was a reflected/fracted ray then:
         transform ray to object's coordinate system ))
      .
      switch(object->type)
      {
         case SPHERE: /* Intersect sphere(oids) */
                 .
                 .
         case BOUNDING_BOX:
                ((check boundbox intersection, if refl/frac ray,
                  if not refl/frac ray, set hit to true.))

                if (hit)
                {
                   /* Ok, let's trace rays in this new coordinate system
                      we are in now */
                   trace_ray(object->bbox->contents_of_box,transformed_ray);
                }
      }
      object = object->next;
    }
  }


  What this gives me, besides the ability to twiddle my bounding boxes, is
  local coordinate systems WITHIN those boxes. So if I have a HUNDRED objects
  that would feel happy if they got their bounding boxes tilted 30 degrees
  to the right, I could create ONE bounding box that transforms the ray 30
  degrees to the right, and then use axis-aligned boxes (which of course are
  faster) INSIDE the box for each of the hundred objects, making them happy.

  Also, it helps animating stuff a lot. Move the bounding box, ans wham you
  have an aggregate object. Move a box within the box, and Wham you have
  hierarchical motion control without sweating too much.

* Filtering texture maps
  The way I filter texture maps may be considered "nasty" but it works OK
  for me. I know the resolution, and I also know (from reverse engineering
  my perspective ray creator ;-) how "big" the screen is in units, I can
  easily calculate how "big" one pixel is in the screen plane. Deeper into
  the model, the pixel covers a larger area, increasing linearly. So, the
  distance an object is from the eye, guide the "pixel size" at that point
  in a very simple and linear way.

  Now the first error you do when you want to sample from your texture map
  is to sample an area that is pixel_size * pixel_size large. Well, that is
  correct for planes that are facing you. But if we are looking almost para-
  llell to the surface? No, the actual area covered by the pixel is roughly
  pixel_size / cos(view_angle), and since cos() is simply a dot product
  (that you'll need later anyway) it's easily calculated. Now I simply grab
  a square area that is this size large, and average it. Nasty, but looks
  quite OK without overwhelming calculations.

   Oh yes, there is the pathetic case where you are supposed to sample
  10000 x 10000 pixels and average. Well, I never sample more than 8 x 8,
  then I start to pick out 64 pixels at random within an n x n grid, and I
  don't bother if I get the same one twice, since the impact of that on an
  average of 64 pixels is mostly killed by the dithering noise anyway ;-)

  Also, I use the eye-distance calculation ALL THE WAY DOWN THE RAY TREE,
  which looks very OK as soon as the mirroring surfaces are flat, or there
  is no heavy refraction going on. But now let's move on to other anti-
  aliasing.

* Hashing anti aliasing
  I never use color difference as my subdivision criteria for supersampling.
  What I do is this:

  Before each sample for a pixel, set hash_number to 0.
  The trace_ray() procedure does the following:
    If it hits an object
      Is it a smoothed patch mesh or similar?
         Add its "smoothing group" or anything else that is
         same for all faces smoothed together (I use the vertexlist
         pointer) to the hashnumber
      else
         Add something unique for the object, its "number" or the
         objectpointer to the hashnumber.

      Set shadow_count to zero
      For each light source:
         Check shadows. If in shadow, shadow_count++.

      hash_number += shadow_count < 5 (or whatever);

      If object is reflecting/fracting, call trace_ray() recursively
      as always in a raytracer....

  So what is all this? Well the hashnumber we get we compare with the
  hashnumber for last pixel and the pixel in the last scanline. If it is
  different then:
    * We have hit different objects than last pixel/line
    * We are in/out of different number than shadows than last pixel/line
  AND THIS IS FOR THE ENTIRE RAY TREE! So if we hit anything else, ANYWHERE
  down the tree, the hashnumber is bound to be different.

  Oh yes, there are a number of weird cases where you just HAPPEN to miss
  a supersample just because we get out of shadow the same time we move
  from object 0 to object 32, and thereby by mistake get the same hash
  number. But who cares? Don't worry, be happy.

* Surface acne [NEW! NEW! NEW! NEW! NEW?] ??? Or is it? You tell me...

  How to avoid it. Well, somebody proposed normal vector testing, and that
  is OK for the system with well behaved users. The rest of us do a small
  epsilon to avoid it. But someone said that this epsilon might be too big
  or small for a given scene. And the funniest of them all (I laughed quite
  a while), he proposed scaling it to the "diameter of the scene" or
  something else. Why on earth do things like this?

  The epsilon for displacing the ray for any object, is of course related
  to the pixel_size as described above! I use pixel_size / 4 and it works
  like a charm even if I model molecules or the solar system (which I have
  done both, actually!) even in the same scene!!

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More Thoughts on Anti-Aliasing, John Woolverton ([email protected])

[Zap Andersson also talks about this problem and independently invented this hashing method. I neglected to publish a rough draft of Zap's idea last issue - see his article this issue for a more polished version. - EAH]

I was also troubled by the fact that my ray-tracer was anti-aliasing across textures (causing massive thrashing on my machine), and took the problem to the local gurus.

I got back the suggestion of building a hash code, and putting all the things I wanted to detect for in the hash calculation.

So I hashed together, object pointers, and light sources (when they weren't shadowed, or outside the cone of a spotlight...). So first I'd check the hash code, skipping color changes due purely to textures. Only if the hash differed, would I check the colors, just so I didn't SSamp a smooth edge also.

   However, this didn't fix sampling across a soft shadow edge.

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Spatial Measures for Accelerated Ray Tracing, by John Spackman

[Here are some interesting passages from a note from him to me]

...Mind you, my thesis is more to do with the navigation of oct-trees AFTER they have been constructed with interval analysis. This navigation seems more efficient than all that ARTS nonsense (navigating only half the vertical steps), naturally runs under integer addition and bit-shifting in a Bresenham- type way BUT WITHOUT the concept of a global driving axis, and being completely immune to division by zero requires no exception handling. I called the SMART method (Spatial Measures for Accelerated Ray Tracing) - perhaps my jocularity has back-fired & no-ones taking me seriously. I can ray-trace 20,000+ triangles with two light sources & shadows at 512x512 in under 8 minutes on a Sun SparcStation - in fact (outrageous claim time) SMART has been observed to achieve constant time ray tracing INDEPENDENT of object count. Each ray simply navigates a few empty voxels, whose number is independent of the global object count, until reaching the first non-empty voxel where generally only one object need be intersected & accepted as the nearest struck. For example, I rendered a single torus in 7 mins 23 secs and 80 tori in 7 mins 20 secs. This is all AFTER constructing the octtree - O(N) but very efficient with interval analysis. Interval analysis allows one to decompose right down to the surface of a primitive or CSG object (none of this bounding box nonsense propounded in RTNews a couple of years back). You'll be able to see some of the pictures of the Octtrees in my thesis - at a fine resolution they look great!

[...]

I think the work of Adrian Bowyer & John Woodwark at Bath would interest you - they're attacking things from a CAD/CAM angle (Adrian is a Mechanical Engineer) - email `[email protected]'. Another pocket of isolated English ray-tracing is established at Leeds university (which I only stumbled across recently). They also have a CAD/CAM bent, & are particularly into multi- processors. If you're interested, email Professor Peter Dew at `[email protected]'. A Dr Stuart Green also did some multi-processor work (using your SPD data base) at Bristol University, but has now moved out to industry & I don't have his new email address. I've recently moved to Edinburgh to take advantage of a 420 Meiko transputer surface - there's quite a lot of knowledge in ray tracing accumulating here (Fractal planets etc).

... Arvo & Kirk's formation of candidate lists for their 5D ray tracing efficiency scheme? I'm not a great fan of this I'm afraid - the old problem, too much over-approximation for concave objects. Consider a hoop with large major radius, small minor radius (e.g. bicycle tyre tube). A view frustrum can easily intersect the hoops bounding box by passing through the hoop's central hole WITHOUT striking the tyre anywhere!

Lazy Oct-tree construction is the one for me, with nice tight decompositions right down to object surfaces, allowing rays to pass through the centre of such hoops whilst ignoring them, (or indeed lazy Hex-tree construction for animated scenes...), and reduced storage & construction costs. It's a bit difficult to convey the efficiency of the scheme without recourse to a black board, but the long and the short of it is that most rays missing all objects end up querying none (hoorah!) whilst those hitting an object end up querying only that (ie just one) object. One can't do much better than that on a ray by ray basis, and I gave up on ray coherence ages ago (not that it's not got great potential, but I got awful headaches trying to work out the action of a complex CSG object e.g. reflective engine block on a single incoming pyramid of rays, never mind refraction - perhaps you've got further ... ?). Oh, and you get free adaptive anti-aliasing with octtrees ..

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Barcelona Workshop Summary, by Arjan Kok ([email protected])

[There were many interesting papers at this workshop. What follows is excerpted from Arjan's summary, focusing on those papers directly concerned with classical ray tracing (e.g. not including Monte Carlo methods, two-pass methods, etc). The finished papers will be available from Springer-Verlag in book form some time next year.]

Summaries of papers presented at the second Eurographics Workshop on Rendering Barcelona, Spain, 13-15 May 1991

Gregory Ward ([email protected])
Adaptive Shadow Testing for Ray Tracing

Method for reducing the number of shadow rays for scenes with a large number of light sources. The sources are sorted on their contribution, and only for the most important sources rays are cast. The influence of the other sources is estimated statistically. Tests are done with different tolerances (threshold to determine whether sources are important) and certainties (rate of accuracy). The method gives good reduction and is able to find the most important shadows because it selects contrast as criterion.

Christophe Schlick ([email protected]_prg.FR)
An Adaptive Sampling Technique for Multidimensional Integration by Ray-
Tracing

Describes a sampling method that includes the following characteristics: adaptivity, irregularity, complete stratification, importance sampling and uncorrelation. It allows a fast reconstruction. Implementation is done using look-up tables.

J.P. Jessel, M. Paulin, R. Caubet An Extended Radiosity Using Parallel Ray-Traced Specular Transfers

Describes a parallel extended radiosity method. The method is implemented on a parallel architecture dedicated to ray-tracing (based on transputers).

Veysi Isler, Cevdet Aykanat, Bulent Ozguc ([email protected]) Subdivision of 3D Space Based on the Graph Partitioning for Parallel Ray Tracing

Describes a heuristic algorithm to subdivide the 3D space by converting the problem into a graph partitioning problem.

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Book Announcement, from Stuart Green

[This is Stuart's thesis, further refined for publication. To see if you might be interested in it, look at: Stuart A. Green & D.J. Paddon, "Exploiting Coherence for Multiprocessor Ray Tracing," IEEE Computer Graphics and Applications, vol 9, no 6, p. 12-26, Nov. 1989. - EAH]

Green, Stuart. "Parallel Processing for Computer Graphics", 1991, in the series "Research Monographs in Parallel and Distributed Computing".

MIT Press, Cambridge, Massachusetts, 02142. ISSN 0953-7767, ISBN 0-262-57087-4.

Pitman Publishing, 12-14 Slaidburn Crescent, Southport PR9 9YF. ISBN 0-273-08834-3.

I don't have the US$ price, but in the UK it costs 27.95 Sterling.

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Spiral Scene Generator, by Tom Wilson

[This is a simple SPD-like scene generator, creating a 3D spiral loop]

There are two loops: one which creates SIZE levels and the other that creates 2^SIZE balls on each level. The balls on each level almost form a circle. the entire structure makes a spiral. The thing I am most displeased with is the texture ("f" line). I created it so that a scene would have a very nonuniform distribution of objects.

#include <stdio.h>
#include <math.h>
#define PI 3.1415926
#define DEFAULTSIZE 10

main(argc,argv)
  int argc;
  char *argv[];
{double r, x, y, z, frac, angle, tmp, invs2;
 int s, s2, w, SIZE, col;

 if (argc > 1)
   sscanf(argv[1],"%d",&SIZE);
 else SIZE = DEFAULTSIZE;
 s2 = (int) pow(2.0,(double)SIZE);
 x = (double) SIZE / 2.0;
 printf("v\nfrom 40 20 -40\n");
 printf("at 0 0 0\n");
 printf("up 0 1 0\nangle 45\nhither 1\nresolution 512 512\n");
 printf("b 0 0 0.3\n");
 printf("l 90 90 0\n");
 printf("l 0 90 -90\n");
 printf("f 0.3 0.3 0.3 0.5 0.5 3 0 0\n");
 printf("p 4\n");
 printf("50 0 50\n");
 printf("50 0 -50\n");
 printf("-50 0 -50\n");
 printf("-50 0 50\n");
 for (s = col = 0; s < SIZE; s++)
  {s2 = (int) pow(2.0,(double) s);
   for (w = 0; w < s2; w++)
    {frac = (double)w / (double)s2;
     r = (double)s + frac;
     angle = 2.0 * PI * frac;
     x = 2*r*cos(angle);
     z = 2*r*sin(angle);
     tmp = (double)(SIZE - s) + (double)(s2 - w - 1) / (double)s2;
     y = tmp*tmp*tmp / (double)(SIZE*SIZE);
     col = (col + 1) & 7;
     printf("f %d %d %d 0.8 0.2 3 0 0\n",(col&4)>0,(col&2)>0,col&1);
     printf("s %g %g %g %g\n",x,y,z,2.0/(double)(s*s+1));
    }
  }
}

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An Announcement From The 'Paper Bank' Project, by Juhana Kouhia ([email protected])

The following new paper is available from nic.funet.fi [128.214.6.100] from the directory pub/graphics/papers/papers.

Eric A. Haines and John R. Wallace
Shaft Culling for Efficient Ray-Traced Radiosity
May 1991, Barcelona
File: hain91.ps.Z   [about 70 kBytes]

If anonymous FTP is not available to you I will mail it if requested.

Please contact me for a full list of the papers.

[We have recently sent Juhana the last version of our paper (with thinko's removed) and so you might want to get this improved version. The new version is called "Shaft Culling for Efficient Ray-Cast Radiosity". It's a nice little algorithm for finding what objects potentially block light between any two given boxes in space. Similar in some ways to Arvo & Kirk 5D but with hierarchy, it has some interesting potential uses and generally speeds up hierarchical bounding volume ray tracers. - EAH]

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Radiance 1.4 via FTP, by Greg Ward

Radiance 1.4 is now available via tape distribution or anonymous ftp (for the first time). Rather than including compiled executables as I have in the previous releases, only the source code and a global make script is provided that should work on most platforms. Please let me know if you have any trouble with it. I have also taken out the example images and the conference room model in order to trim back the distribution. I hope to include these files in other anonymous ftp directories as suggested by Robert Amor since there seems to be general agreement that this is a good idea.

To pick up release 1.4 from anonymous ftp, connect to hobbes.lbl.gov (128.3.12.38) with ftp using the "anonymous" account and enter your e-mail address as the password. Everything is in the directory pub, and the main distribution is called "Radiance1R4.tar.Z". This file is about 3.5 Megabytes, so please do your transfers in binary mode the first time! Also, you will probably experience less network traffic in the morning, when most computer scientists are asleep.

________

Information on Models, Test Environments, etc for Radiance:

I've just set up an anonymous ftp archive site at hobbes.lbl.gov (128.3.12.38) for sharing Radiance models and programs. In addition to the standard source distribution, this archive contains the following:

pub/generators - Programs for generating specialized objects & shapes pub/libraries - Libraries of patterns, textures, fonts, etc. pub/mac - MacIntosh applications and utilities (for Radiance) pub/models - Complete Radiance scene descriptions pub/objects - Objects for including in Radiance scenes pub/programs - Miscellaneous programs and utilities pub/tests - Test scenes for validating global illumination programs pub/translators - CAD file translators and image format converters

For those of you who I haven't dragged aside and told already, Radiance is free ray tracing software for lighting simulation and rendering that does a lot of neat stuff and tries very hard to do it accurately.

If you are interested in picking up or leaving off some nice environment models, this is a good place to do it. Most of the scene descriptions are in Radiance format, but writing a translator shouldn't be too much work, and I'm willing to offer whatever help I can.

If you are working on your own radiosity or ray tracing program and want to compare results, please check out the pub/tests directory. There is not much there now, but with your help we can make this archive into a valuable resource for researchers in global illumination.

Please send any questions or comments to [email protected].

________

I finally finished putting together a library of objects from the various models I've created for Radiance. It is in pub/objects/gjward.tar.Z. I hope people find it useful. It took me quite some time to get the my miscellany into a usable form.

If you have objects you are willing to submit, please take a look at the way this initial library is set up first.

________

>From Paul D. Bourke ([email protected]) [130.216.1.5]

The public domain modeller Vision-3D for the Mac II family is about to support Radiance data files as an export option. This has already been done but the copy on our FTP site hasn't yet been updated (I want to put some more features in the next release) If anyone is interested however the current version of Vision-3D with Radiance file export can be made available.

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Proceedings of Graphics Interface '91 Availability, by Irene Gargantini

In the USA: Morgan Kaufmann Publishers
Order Fulfillment Center
P.O. Box 50490
Palo Alto, Ca 94303 USA, phone (415) 965 4081

The proceedings should be available by now, and they can take your order in advance.

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NFF Previewers, by Bernie Kirby, Patrick Flynn, Mike Gigante, Eric Haines

>From Bernie Kirby ([email protected]):

There is an NFF previewer available for anonymous FTP on gondwana.ecr.mu.oz.au [128.250.1.63] pub/preview.c. It uses the vogle library which is also available as pub/vogle.tar.Z

>From Patrick Flynn ([email protected]):

If anyone on this side of the pond wants the preview.c program, it's now available for anonymous FTP from shillelagh.cse.nd.edu (129.74.9.7). You can get the VOGLE library from uunet. I tried the previewer; it does what I need.

>From Mike Gigante ([email protected]):

There is a NFF previewer for Silicon Graphics workstations available on godzilla.cgl.rmit.oz.au (131.170.14.2). Make sure you grab the readme file also. It uses the hardware lighting and Zbuffer on the SGI machines to give a very fast preview.

>From Eric Haines:

I also have two previewers for NFF files which work on HP workstations (one is static, the other uses the mouse for rotating & viewing the object). I can send them to anyone who wants them (no FTP right now).

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RayTracker Demos Available, by Jari Kahkonen

My Swedish friend Haakan Andersson sent me some RayTracker animation- demos and now they are ftp'able from tolsun.oulu.fi [128.214.5.6]. You need PC with VGA to run these animations.

Because I'm sure that raytracer-fans have lotsa questions about RayTracker, after they have seen these animations, please mail all questions to the author, i.e. to Haakan Andersson, [email protected] If you have problems with animations (they don't unpack etc...) flame or hate-mail me...

You can find animations from /pub/rayscene/zap, though it has nothing to do with Rayscene. /pub/rayscene/anim.PC contains raytraced animations made with Rayscene and DKBtracer (my animations...). /pub/rayscene/anim.AMIGA contains raytraced animations for Amiga made with Rayscene and DKBTracer (animations by Panu Hassi).

Animations are packed with Lharc 2.05. All animations are self-extracting archives (= .exe-files). So, "run" them and they will unpack themselves. For examples: If you have "car.exe"-animation, just type "car". Animation-arc- hives includes short README.TXT and animation (.fli). If you want to give these animations to your friends, *do not* separate these parts. Give .exe, since README.TXT contains contact-information to Haakan Andersson. Also, every animation has little text for contact address. (except "mesh", I didn't wanna "spoil" it...it moves so smoothly...:). Remember to set "type binary" when downloading files...

These animations need Autodesk Animation Player, and if you don't have it, you can pick it from /pub/rayscene/anim.PC. That directory contains my demos made with Rayscene. Filename is "aaplay.exe".

Animations run faster if you are running them from RAM-disk. If you have mouse it's easier to control aaplay.exe. Adjust animation speed to your machine.

Some animations are not full-screen because of their original size.

Little description of animations:

BIKE.FLI: Fly-by over a bike in a brick basement.

HP-RIP2.FLI: The 'famous' one of a Camshaft emerging from its own drawing. Created for the 'Mechslide' demo video, available from Emt Inc in USA. The name 'HP-RIP' comes from the fact that the 'idea' of a camshaft came from Hewlett-Packard's well known raytraced 'Camshaft on bed of ravioli' by Eric Haines, a friend of mine.

ART.FLI: Fly-by over a pen, a few bolts, a drawing and a book placed on a wooden table under a green metal table lamp.

BLAHBLAH.FLI: Here's a (relatively) new one: Demo of 1.55 Beta's transparent, animated texturemaps, using Autodesks 'BOSSTALK'. Even funnier is to use animated bump-maps. To see them, watch out for 'Spaceman Spiff' at a theatre near you.

BOING.FLI: Newer version of BOUNCE. A Red, bouncing chrome sphere on top of a texture map from Imagetects(tm). Rendered and Animated in RayTracker 1.4 Beta.

BOUNCE.FLI: Very very simple animated bouncing ball. The first RayTracker animation EVER!

CAR.FLI: Looking at a red car in sunset. Image Rendered and Animated in RayTracker 0.6 Beta. Model built in AutoCAD R10 by: Bertil Heden, Autodesk, Sweden. Thanks, Bert!

MESH.FLI: Fly-round a bowling pin of glass and a bowling ball on a plate suspended in space. New effect in this version of RayTracker is the ability create a feel of space via 'space mapping' a background to the universe.

ALARMCLK.FLI: An image of an alarmclock, a matchbox, a table, and a wooden table lamp. Suddenly, without warning, we fly past the clock and up the lamp. Why? Beats me.

________

Tracey Bernath ([email protected]) notes:

I recently uploaded the raytraced animations from tolsun.oulu.fi to wuarchive.wustl.edu to try and cut down the trans-ocean net travel. I can't upload to SIMTEL because we have a lousy connection, and I always get the usual "Too many anonymous users, Try Again" 8-}

in /pub/zap are the raytraced and animated images, some are really good, some, well... in /pub/raytracker are the original animations, including aaplay.lzh (I don't know if aaplay.exe works, but I know the aaplay.lzh does )

Enjoy!

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RayTracker Info, by Zap Andersson

[Though a commercial product, I thought I would include this info, since the FLI demos used this software to generate them. Also, the interactive features are of interest. I received a demo copy to review, and it seemed pretty nice (though I didn't do any serious rendering with my no-math-coprocessor 386).]

Current version (1.71)
Date: 24 april 1991

RayTracker is a commercial raytracing program, especially created to render geometries from the well-known CAD software AutoCAD. RayTracker reads models in the AutoCAD DXF format, or in Autodesk 3D Studio 'ASCII' format.

RayTracker runs on MS-DOS PC computers, with a math co-processor, but porting to other platforms (mainly Sparc, Amiga and Mac) are being considered. It utilizes Expanded (EMS) memory if it is found in the system.

RayTracker has a graphical user interface (GUI) with dialog boxes, pull-down menus, and a built in hypertext help-system. It runs in two modes, a graphical mode (which requires an EGA/VGA display) and a text mode fore those lacking graphics. On a VGA you may also see the image as it is being rendered. You may view the finished image with a supplied program on your VGA, Super-VGA or on your CAD display, if it has an AutoSHADE compatible real mode ADI driver with version 4.0 or higher and at least 256 colors.

Materials are easily assigned to objects by simply loading them from the provided material library, containing many useful materials. You may also create your own materials by setting parameters for color, ambient, diffuse and specular reflection, mirroring, transparency, index of refraction, trans- lucency, shadow-casting and many many other things.

The mapping functions in RayTracker use a very generalized model of a map. A 'map' can be any number of patterns, mixed or overlaid, placed on different parts of one single surface, or repeated all over. Each pattern can be both a bitmapped graphic image (GIF, Targa 16/24/32, Animator CEL, Animator FLI and Amiga IFF format is accepted), or one of the built in mathematically defined functions (wood, marble, random noise, wavy, checkered etc.).

Each 'map' can be applied in many ways:

* Texture map - Changing the color of the surface. This is the only thing that more primitive renderers, such as 'Big D' can do. Certain parts of a texturemap can also have a transparent color allowing one single surface to depict a complex object such as a tree or a person as a 'coulisse'. Naturally, the shadow has the contour of the tree or person also.

* Bump map - The 'brightness' at each spot in the map guides the surface 'altitude', allowing you to create dented, scraped, wrinkled, engraved or in any other minor surface deviation.

* Mix map - Allows you to mix between two totally different surface descriptions on one surface, such as a checkered pattern where some squares are of red glass and others of wood.

* Reflect. map- Allows you to simulate reflections without the increased rendering time using true mirroring. Curved objects looks just as convincing with a reflection map. You may also add amusing effects, such as 'window reflections' like in the film 'Tin Toy' from Pixar.

Aside from this, a map can also be applied as the 'slide' in a slide projector light source, or as the screen fore- or background.

Lightsources include point sources, directed, spotlights and slide- projectors. Light falloff can be none, linear or quadratic. All types of lights can cast shadows of two types: Raytraced shadows, that are sharp and accurate but requires one extra step in the ray tracing algo- rithm, and shadows using a "shadow map", that can have 'fuzzy edges' and work very quickly.

To ease the production of images, RayTracker renders every 16:th pixel first, then every 8:th and so on, allowing you to quickly determine if there is something wrong with the light, or a material. You may also create 'test renderings' on parts of your model by simply marking two points on the initial wireframe.

Three modes are available, Quick Track, ignoring shadows and reflections, Medium Track, accounting for shadows, but not reflection and refraction, and finally Ray Track, performing the full raytracing calculation.

RayTracker can generate walkthrough animations from just a small set of 'key' views, using a 7 dimensional spline interpolation technique. The images can be automatically concatenated to an Animator compatible FLI file.

The output format from RayTracker is GIF or Targa 16/24/32 (with alpha channel in the 32 bit format) in any resolution (up to your diskspace limit). A conversion utility is also provided to convert a Targa file to a Amiga HAM format.

RayTracker is *NOT* a PD or ShareWare program, it is a commercial product, available from the addresses supplied below. If you have any technical questions about its capabilities, you can contact me, the program author on email address:

    [email protected]

....or you can send ordinary mail to the LAST (Scandinavian) address listed below, and attach my name: Hakan 'Zap' Andersson

U.S.A.                  Europe:             Scandinavia:
=================       =================   ===================
EMT Inc.  #250          EMT Ltd.            EMT Ab
199 N. Commercial st.   PO Box 103          Box 40
Bellingham, WA          Rickmansworth       S-178 21 Ekeroe
98255 USA               Herts WD3 5RF       SWEDEN
                        U.K.
Phone:
(USA)-206 647 2426     (UK)-923 285 496     (SW)-756 320 20
Fax:
(USA)-206 647 2890     (UK)-923 285 496     (SW)-756 346 50

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Eric Haines / [email protected]