Borland Programmer's Resource/Borland_Programmers_Resource_CD_1995.iso/code/graphics/rtnews/rtnews5

Text File | 1995-05-19 | 93.0 KB | 2,198 lines

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            "Light Makes Right"

             October 3, 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
    New Addresses and People
    Bitmap Stuff, Jeff Goldsmith
    More Comments on Kay/Kajiya
    Questions and Answers (for want of a better name)
    More on MTV's Public Domain Ray Tracer (features, bug fixes, etc)
    NFF File Format, by Eric Haines

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

Intro

    IMPORTANT:  Around October 16th I'm losing the `saponara' account at
    Cornell.  So, in case you haven't heeded my earlier warnings, this is
    truly the one!  Please write to me at:

    hpfcla!hpfcrs!eye![e-mail]

    If you have never tried to write me at this address, you should try now
    (submit something for the News while you're at it...).

    This issue is something of a queue clearer for me: a lot has been posted
    on USENET concerning Mark VandeWettering's public domain ray tracer.  I
    include all of this and more at the end.  If you're not interested, I hope
    you can wade through it all until the end, as I would appreciate comments
    on the "neutral file format" I use in the SPD package.

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

New Addresses and People

    Remember that you can ask me any time for the latest version of the RT News
mailing list.

Andrew Glassner has settled down and bought some bookshelves, and is at:

# Andrew Glassner        Andrew Glassner
# Xerox PARC            690 Sharon Park Drive
# 3333 Coyote Hill Road        Apt. #17
# Palo Alto, CA  94304        Menlo Park, CA  94025
# (415) 494 - 4467        (415) 854 - 4285
alias    andrew_glassner    [e-mail]

For those of you who receive only the email version of the Ray Tracing News:
you should contact Andrew, as he is the editor of the hardcopy version of
the RT News.  The hardcopy contains many articles which do not appear in the
email version, so be sure to get both.

--------

# K.R.Subramanian
# The University of Texas at Austin
# Dept. of Computer Sciences
# Taylor Hall 2.124
# Austin, Tx-78712.

alias  krs  [e-mail] (ARPA)
 or
alias  krs  {uunet...}!cs.utexas.edu!subramn (UUCP).

Interests in Ray Tracing:

    Use of hierarchical search structures for efficient ray tracing,
investigating better space partitioning techniques, trying to apply
ray tracing to practical applications.

    Currently a PhD student in Computer Sciences at The University of
Texas at Austin.

One suggestion on the RT round table: We must have a portion of time
where we can talk to other RT people on a more personal basis. At least,
I find it easier to talk to people.

On the RT news: I would like to see practical applications of ray tracing
described here. What applications really require mirror reflections,
refraction etc. Havent seen applications where ray tracing was the way
to go.

--------

From: mcvax!ecn-nlerf.com![e-mail] (Jack van Wijk)

Via my old colleagues at Delft University of Technology I received
a copy of your Ray Tracing News. I am delighted by this initiative, since
it provides a fast, informal way to communicate with colleagues working
in this sensational area.

At the moment I do not do research with respect to ray tracing, but
I expect that in the coming year the blood will creep again where it can't go
(old Dutch proverb). The institute where I work now is very interested
in high quality graphics, scientific data visualization and parallellism,
so I expect that ray tracing can be made a topic here.

I would be very happy if you could put me on the mailing list. Here is
a short auto-biography:

# Jarke J. (Jack) van Wijk - Geometric modelling, intersection algorithms,
#                            parallel algorithms.
# Netherlands Energy Research Foundation, ECN
# P.O. Box 1, 1755 ZG  Petten (NH), The Netherlands
alias    jack_van_wijk    ecn![e-mail]

I have done research on ray-tracing at Delft University of Technology
from 1982 to 1986 together with Wim Bronsvoort and Erik Jansen.
My thesis is: "On new types of solid models and their visualization with
ray-tracing", Delft University Press, 1986, which title summarizes my
main interests. I have developed intersection algorithms for sweep-defined
objects (translational, rotational, sphere), and blending. Also research was
done on curved surfaces, modelling languages and on improving the efficiency.
Currently I am interested in intersection algorithms, efficiency, and
parallel algorithms, and the use of ray tracing for Scientific Data
Visualization.

--------

Linda Roy's mail address:

# Linda Roy - all aspects of ray tracing especially efficiency
# Silicon Graphics Inc.
# 2011 Shoreline Blvd.
# Mountain View, California 94039-7311
# 415-962-3684

--------

Mark VW's mail address:

# Mark VandeWettering
# c/o Computer and Information Sciences Dept.
# University of Oregon
# Eugene, OR 97403

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

Bitmap Stuff, by Jeff Goldsmith

   [The following is for VMS people.  UNIX/C people should contact anyone at
the University of Utah for information on their "Utah RLE Toolkit", which has
all kinds of bitmap manipulation tools using pipes (in the style of Tom Duff).
It's a nice toolkit (and includes the famous mandrill picture), and can be
had by ftp from cs.utah.edu. - EAH]

   I have some bitmap utilities that I can put somewhere
if there's interest.  They aren't intended to be anywhere
nearly so portable as poskbitmaps, but they seem to have more tools.
I'm pretty curious what a good total set of tools would be;
maybe this can spark such a list.  Mine work only under VMS
(does direct mapping to files--FAST) and use a bizarre format
that is really just 1024 bytes of header followed by pixels.
Here's a list of the tools:
    Cutout:        Cuts a rectangle out
    Dissolve:    Fades from one picture to another
    Gamma:        Channel-independent contract change
    Filter:        2x2 boxfilter
    Lumin:        Color to Black and White via luminosity
    Pastein:    Pastes a rectangle into another picture
    Poke:        Mess with header data, e.g. offsets
    Resam:        Change from 1-1 to 5-4 aspect ratio fast
    Reverse:    Inverse video
    Switch:        Swap red, green, blue channels around
    Thresh:        Sets pixel<theshhold = 0.  Ramps rest
    Xzoom:        Horizontal stretch.  Floating point factor
    Zoom:        Floating point rescale.
None of these are super-robust, but they are pretty fast.  The
slowest is zoom and it runs in 1-2 minutes on a VAX 780.  On a
newer machine, they'd be ok-fast.

By the way, I've used each of them in animations, so the transformations
are smooth.  Also, they are clearly useful.

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

More Comments on Kay/Kajiya

From Jeff Goldsmith:

I do a quick check on the children to determine the key for the sort.
I just use the largest component of the current ray as the direction
along which to check and then just use the minimum (or maximum) extent
of the bounding volume to generate a key.  Tim Kay says that that is
not what they meant in the paper, but it's close enough and seems to
work.  However, before the sorter ever gets to deal with a new bounding
volume, I check to see if the leading edge of the bounding volume is
beyond the current hit.  John Salmon added the trick that all illumination
rays get a pseudo-hit at the light source position, so that automatically
rejects all objects that cannot cast shadows.  (Of course, it deals with
objects on the other side of the ray origin, too.)  I also, of course,
don't sort the illumination rays' bounding volumes.

A further note: I did not find that the sorting cost was trivial; in
fact, it made up for most of the time saved in avoiding bounding volume
checking.  It was more useful before we added all the other hacks to
avoid things, though.

Good references for heap sort algorithms are:
    Standish, _Data Structure Techniques_     and
        Knuth, of course.

Heap sort is the right algorithm, I think, because a total order
is not needed on all the objects.  We need to pull off one object
(bounding volume) at a time from the head of the list, and once
we find a hit, we discard the rest of the list.  There's no point
in sorting stuff that we will never check.

----

I ended up tossing the heap sort version completely, in order to
save memory space.  (Odd, it's been a long time since I've had to
worry about code size.)  I think that I could gain all of their
savings and then some by just postprocessing the tree so that the
left child is closer to the eye than the right child.  Most non-
illumination rays go in the general direction of "away from the eye,"
so that would help them.  I-rays don't need sorting anyway.  Alternatively,
as you suggested, putting the bigger boxes (whatever) on the left would
work, too, maybe.  If I ever have time to futz with it, I'd like to
try some of that.

----

My reply to Jeff:

    Sorting on distance to eye sounds good - in fact, I was going to
try it, but I use the item buffer and so the eye rays are mostly taken care
of.  If anything, sorting with objects farther away might help me:  the
reflection rays, etc etc will probably be in a direction away from the eye
rays!  Oh, another good post-process might be to sort each list of sons on
the difficulty of sorting (or did I mention this already?) - try the sphere
before the spline.

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

Questions and Answers (for want of a better name)

Wood Texture Request Filled:

Jeff Goldsmith's request for wood texture bitmaps was generously filled by
Rod Bogart, who made four bitmaps (wood.img[1-4]) available for ftp at
cs.utah.edu.  These are still there (I just grabbed them), though I don't
know how long they'll remain available.  These are scanned images from an
artist's book of textures.

--------

Efficiency Question

From Mark VandeWettering:

How can we efficiently manage the intersect lists that get passed
between the various procedures.  Heckbert statically allocates arrays
within the stack frames of various procedures, which seems a little odd,
because you never really know how much space to allocate.  Also, merging
them using Roth's CSG scheme requires alot of copying: can this be
avoided?

--------

From Jack Ritter:

A simple method for fast ray tracing has occurred to me,
and I haven't seen it in the literature, particularly
Procedural Elements for Computer Graphics.
It is a way to trivially reject rays that don't
intersect with objects. It works for primary
rays only (from the eye).  It is:

Do once for each object:
   compute its minimum 3D bounding box. Project
   the box's 8 corners unto pixel space. Surround the
   cluster of 8 pixel points with a minimum 2D bounding box.
   (a tighter bounding volume could be used).

To test a ray against an object, check if the pixel
through which the ray goes is in the object's 2D box.
If not, reject it.

It sure beats line-sphere minimum distance calculation.

Surely this has been tried, hasn't it?

----

An Answer, by Eric Haines:

It's true, this really hasn't appeared in the literature, per se.  However, it
has been done.

The idea of the item buffer has been presented by Hank Weghorst, Gary Hooper,
and Donald P. Greenberg in "Improved Computational Methods for Ray Tracing",
ACM TOG, Vol. 3, No. 1, January 1984, pages 52-69.  Here they cast polygons
onto a z-buffer, storing the ID of the closest item for each pixel.  During
ray tracing the z-buffer is then sampled for which items are probably hit
by the eye ray.  These are checked, and if one is hit you're done.  If none
are hit then a standard ray trace is performed.  Incidentally, this is the
method Wavefront uses for eye rays when they perform ray tracing.  It's
fairly useful, as Cornell's research found that there are usually more eye
rays than reflection and refraction rays combined.  There's still all those
shadow rays, which was why I created the light buffer (but that's another
story...see IEEE CG&A September 1986 if you're interested).

In the paper the authors do not describe how to insert non-polygonal objects
into the buffer.  In Weghorst's (and I assume Hooper's, too) thesis he
describes the process, which is essentially casting the bounding box onto
the screen and getting its x and y extents, then shooting rays within this
extent at the object as a pre-process.  This is the idea you outlined.
However, theirs avoids all testing of the extents by doing the work as
a per object (instead of per ray) preprocess.  A per object basis means they
don't have to test extents: all they do is loop through the extent itself and
shoot rays at the object for each pixel.

--------

Efficient Polygon Intersection Question, from Mark VandeWettering

Another problem I have been considering arose from a profile of my
raytracer when run on the "gears" database.  A large amount of time
(~40%) was spent in the polygon intersection code, which is greater than
other scenes which used polygons.  The reason:  the polygon intersection
routine which you described in the Siggraph Course Notes is linear in
the number of sides of the object.  For the case of the gear, the number
of sides is 144, which is a very large number.

Perhaps a better way of trying to intersect polygons is to decompose the
complex polygons into triangles, and then arrange them in your favorite
hierarchy scheme.  The simplest way would be to subdivide prior to the
raytracing in a preprocessing step.  Several very quick algorithms exist
for intersection with triangles, and I think that this may be a better
way to implement polygon intersection.

"Back of the envelope" calculations:

Haines' method of intersection:        O(n) to intersect polygon
Triangular decomposition:        O(1) to intersect triangle
                    * number of triangles searched
                      inside your hierarchy scheme.

Assuming a good hierarchy, you can expect O(logn) triangles to be
searched.  The problem is finding the constants involved in this.  I do
suspect that this method may in fact be superior, because in the ground
case (intersect a triangle), the two methods are equivalent (actually
since the code may be streamlined for triangles, the second is probably
better), and I expect that as the number of sides grows, the second will
get better relative to the first.

I am torn between trying to formally analyze the run-time, and just
going ahead and implementing the thing, and gaining performance
information from that.  Perhaps I will have some figures for you about
my experience soon.

I would like to hear from anyone on the RT-News who has
information on ray tracing superquadrics.  I am especially interested in
the numerical methods used to solve intersections, but any information
would be useful.

[as I recall Preparata talks about preprocessing polygons into trapezoids
in his book _Computational Geometry_, leading to many fewer edge which
need testing (each trapezoid has but two sides which can intersect, as the
test ray is parallel to the other two edges).  Any other solutions, anyone?
-- EAH]

--------

Bug in Paul Heckbert's Ray Tracer?

From Mark VandeWettering:

As I might have mentioned before, I modelled my raytracer after the one
described in Heckbert's article "Writing a RayTracer".  I have noticed
some ambiguities/anomolies/bugs(?) that might be interesting to examine.

In Heckbert's code, there is some "weirdness" going on in the Shade
procedure. The part of the "Shade" procedure which handles
tranparency is something has a comment like:

/* hit[0].medium and hit.[1].medium are entering and exiting media */

The transmission direction is then calculated using the index of
refraction of the two media.

But hit[0].medium should be the medium that the ray originates in, not
the medium of the object actually hit.  Therefore, the index of
refractions are incorrect and the Transmission direction also is
incorrect.

Perhaps Paul could comment on this.  What seems to be correct is to keep
hit[0] reserved to contain the type of material that the ray originates
in, and hit[1] be the first hit along this ray?  Was this what was
intended?

--------

A Tidbit from USENET

From: Ali T. Ozer

In article <[e-mail]> [e-mail] (Sean Casey) writes:
>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.

For a lot higher price, though... I read that the Mac version of
Byte by Byte's Sculpt 3D and Animate 3D packages will start from $500.

Ali Ozer, [e-mail]

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

More on MTV's Public Domain Ray Tracer (features, bug fixes, etc)

--------

Raytrace to Impress/Postscript Converter, by David Koblas

Contained is a shar for converting MRGB pictures to either
impress or postscript depending on your needs (black and white).

{I'm looking for versatec plotter routines, if you have some I'd be interested}

[Ed. note: there is also a patch for this program posted to USENET.]

[as usual, the code is deleted for space.  Check USENET or contact David for
the program. - EAH]

name : David Koblas         place: MIPS Computers Systems
phone: [phone]         uucp : {ames,decwrl,pyramid,wyse}!mips!koblas

--------

Raytrace to X Image converter, by Paul Andrews

Here's a somewhat primitive program to display one of Marks raytraced pic's
on an X display. There's no makefile, but then there's only one source file.

[e-mail] (Paul Andrews)

[again, code deleted for space.  Check USENET or write Paul]

--------

Better Shading Model for Raytracer, by David Koblas

A better shading model for the MTV raytracer [I probably should have
posted this a while back, while I was sure it all worked]

The two big changes this has are a better shading model, including doing
something diffrent with diffuse reflection.  You can specify the color of
a light, and surfaces have an ambiant and absorbance values [default:
no ambiant and no absorbtion].  The "shine" value is now in the range
from 0.0 -> 1.0 instead of 0 -> infinity.  On balls I ran a sed script
like this: '/^f/s/ 35 / 0.2 /' and got close the the same results.
Also all componants of a surface can be specified with r,g,b values.

Give it a try, and if you have any bugs/problems/sugestions, let me
know and I'll give them a try/fix.

name : David Koblas         place: MIPS Computers Systems
phone: [phone]         uucp : {ames,decwrl,pyramid,wyse}!mips!koblas

[code deleted for space: check USENET or write David for the new model]

--------

From Irv Moy:

    I have Mark VandeWettering's raytracer running on a Sun 3/260
and Version 2.4 of Eric Haines' SPD (I took the SPD that Mark posted and
applied the patch that Eric posted to get Ver. 2.4).  I display the output
of the raytracer on a Targa 32; I had to add an extra byte in the output
file for the Targa's alpha channel.  The output of 'balls.c' looks great;
I now have my very own "sphereflake"!!!
    I tried 'gears' at a size factor of 4 and the resulting output is
quite dark.  The background is a nice UNC blue but the gear surfaces are
very dark and so is the reflecting polygon underneath the gears.
Has anyone else tried to raytrace 'gears' with Mark's program yet???
Enquiring minds want to know.....(BTW, if you look closely at 'sphereflake',
you can see Elvis (recursively, of course)).

                Irv Moy
                UUCP: ..!chinet!musashi
                Internet: [e-mail]

--------

From Ron Hitchens:

   This may have some bearing on the problem:

vixen% ray -i gears.nff -o gears.pic -t
ray: (9345 prims, 5 lights)
ray: inputfile = "gears.nff"
ray: resolution 512 512
ray: after adding bounding volumes, 10516 prims
                    ^^^^^

   From defs.h:

#define MAXPRIMS        (10000)
             ^^^^^

   I ran gears.nff last night and got the same results.  I bumped MAXPRIMS to
11000 and ran it again, seemed to work fine.  I only ran a 128x128 version,
the resolution was so low that most of the gears looked like fuzzy blobs, but
it seemed to be properly lighted and plenty colorful.  I have a 512x512 run
going now, should be finished in about 12 hours (I love my Sun 3/60FC, but it
sure would be handy to have a Cray now and then).

> (BTW, if you look closely at 'sphereflake',
> you can see Elvis (recursively, of course)).

   Naw, that's the spirit of Tom Snyder, Elvis is way too busy channelling
through an unemployed truck driver in Muncie, Indiana.

   To Mark VandeWettering: Hey, thanks for the ray tracer.  I don't suppose
you could send me a disk drive to store all these picture files on could you?

Ron Hitchens        [e-mail]    [e-mail]

--------

From: Steve Holzworth

There is a bug in the screen.c routine of Mark's raytracer.
Specifically, everywhere he does a malloc, the code is of the form:

foo = (Pixel *) malloc (xres * sizeof (Pixel)) + 1;

The actual intent is to allocate xres+1 Pixels, thusly:

foo = (Pixel *) malloc ((xres + 1) * sizeof (Pixel));

There are three occurences of the former in the code; they should be changed
similarly to the later.  (Note: I never ran over this bug until I tried
to run a 1024x1024 image.  It worked fine on 512x512 or less images.)

Other than that, its a good raytracer.  Congrats, Mark!  I'm working on
a better lighting model and a better camera model.  I'll send them on
when (if) I finish them.

                        Steve Holzworth
                        rti!tachyon!sch

--------

Teapot Database for Ray Tracing, by Ron Hitchens

Subject: Ray traced teapot

   Below is a modification of a program that Dean S. Jones posted a few weeks
ago that draws the well known teapot in wire frame using SunCore.  I changed
it so that it would use the same data to produce an NFF file that Mark
VandeWettering's ray tracer can use.  The result looks surprisingly good.
Using the default step value of 6 is satisfactory, 12 looks very nice.

   I'd like to know what's causing the little specks on the spout and the
handle.  I don't know if it's a problem with how this guy generates the
NFF file, or some glitch in Mark's ray tracer.  I don't have the time to
investigate.

   The original program that Dean posted was Sun specific, since it used
SunCore.  This one is not Sun-specific, all it does is some computation
and spit out some text data, so it should run most anywhere.  You'll probably
need to remove the -f68881 from the makefile spec if you compile it on a
non-Sun system though.

   Enjoy.

Ron Hitchens        [e-mail]    [e-mail]

[code deleted for space.  Check USENET or write Ron Hitchens for the code]

--------

From Mark VandeWettering (to me):

Your final comments regarding Kay/Kajiya BVs were basically
in line with the thinking that I have done, and with the current state
of my raytracer.  I now provide cutoffs for shadow testing, and cull
objects immediately if they are beyond the maximum distance that we need
to look.

This also allows me to implement some of the "shadow caching" and other
optimizations suggested by you in the March 28, 1988 RT-News.   Most of
these were trivial to implement, and will be incorporated in a
better/stronger/faster version of my raytracer.

--

Gosh, I just can't keep quiet can I?  I just wanted you to know that a
new and improved version of my raytracer is available for anonymous ftp.
It employs some of the stuff regarding Kay/Kajiya bounding volumes, and
shadow caches for an improvement in speed as well.  (Roughly 30%
improvement).  I can now do the sphereflake is less than 5 hours on a
Sun 3 w/68881 coprocessor.

For the future, I am thinking of CSG, antialiasing, and Goldsmith and
Salmon style hierarchy generation.  Things that have been put off, but I
would like to include would be more complex primitives, but I just can't
deal with numerical analysis at the moment :-)

Soon it will be back to the world of functional programming and my
thesis so I better get this all done.  *sigh*

--

New Ideas: an ObjectDesc -> NFF compiler

One possible project that I have thought of doing is an Object to NFF
compiler.  The compiler could be a procedural language which could be
used to define hierarchical objects, with facilities for rotation,
translation and scaling.  The output would be an NFF file for the scene.

For instance, we might have primitive object types  CUBE, SPHERE, POLYGON
and CONE.  Each of these might represent the canonical "unit" primitive.
We could then build new objects out of these primitives.

A hypothetical example program to create a checkerboard might be:

#
# checkboard.obj
#
define object check {
    polygon (0.0 0.0 0.0)
            (1.0 0.0 0.0)
            (1.0 1.0 0.0)
            (0.0 1.0 0.0) ;
    }
#
# Check4 contains 4 squares...
#
define object check4 {
    check, color white ;
    check, translate(1.0, 0.0, 0.0), color black ;
    check, translate(0.0, 1.0, 0.0), color white ;
    check, translate(1.0, 1.0, 0.0), color black ;
    }
#
# Board 4 is 1/4 of a checkerboard...
#
define object board4 {
    check4 ;
    check4, translate(2.0, 0.0, 0.0) ;
    check4, translate(0.0, 2.0, 0.0) ;
    check4, translate(2.0, 2.0, 0.0) ;
    }

#
# Board is a full sized checkerboard...
#
define object board {
    board4 ;
    board4, translate(4.0, 0.0, 0.0) ;
    board4, translate(0.0, 4.0, 0.0) ;
    board4, translate(4.0, 4.0, 0.0) ;
    }

#
# the scene to be rendered...
#

define scene {
    board ;
    }

--

I would also like it to support CSG, and maybe even procedural (looping
constructs).  I don't know if I will get up enough steam to implement
this, but it would make scenes easier to specify for the average user.

Ideally, such a language would be interesting to use for specifying
motion as well, although I have no real ideas about the ideal way to
specify (or implement) this.

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

Neutral File Format (NFF), by Eric Haines

[This is a description of the format used in the SPD package.  Any comments
on how to expand this format are appreciated.  Some extensions seem obvious
to me (e.g. adding directional lights, circles, and tori), but I want to take
my time, gather opinions, and get it more-or-less right the first time. -EAH]

Draft document #1, 10/3/88

The NFF (Neutral File Format) is designed as a minimal scene description
language.  The language was designed in order to test various rendering
algorithms and efficiency schemes.  It is meant to describe the geometry and
basic surface characteristics of objects, the placement of lights, and the
viewing frustum for the eye.  Some additional information is provided for
esthetic reasons (such as the color of the objects, which is not strictly
necessary for testing rendering algorithms).

Future enhancements include:  circle and torus objects, spline surfaces
with trimming curves, directional lights, characteristics for positional
lights, CSG descriptions, and probably more by the time you read this.
Comments, suggestions, and criticisms are all welcome.

At present the NFF file format is used in conjunction with the SPD (Standard
Procedural Database) software, a package designed to create a variety of
databases for testing rendering schemes.  The SPD package is available
from Netlib and via ftp from drizzle.cs.uoregon.edu.  For more information
about SPD see "A Proposal for Standard Graphics Environments," IEEE Computer
Graphics and Applications, vol. 7, no. 11, November 1987, pp. 3-5.

By providing a minimal interface, NFF is meant to act as a simple format to
allow the programmer to quickly write filters to move from NFF to the
local file format.  Presently the following entities are supported:
     A simple perspective frustum
     A positional (vs. directional) light source description
     A background color description
     A surface properties description
     Polygon, polygonal patch, cylinder/cone, and sphere descriptions

Files are output as lines of text.  For each entity, the first line
defines its type.  The rest of the first line and possibly other lines
contain further information about the entity.  Entities include:

"v"  - viewing vectors and angles
"l"  - positional light location
"b"  - background color
"f"  - object material properties
"c"  - cone or cylinder primitive
"s"  - sphere primitive
"p"  - polygon primitive
"pp" - polygonal patch primitive


These are explained in depth below:

Viewpoint location.  Description:
    "v"
    "from" Fx Fy Fz
    "at" Ax Ay Az
    "up" Ux Uy Uz
    "angle" angle
    "hither" hither
    "resolution" xres yres

Format:

    v
    from %g %g %g
    at %g %g %g
    up %g %g %g
    angle %g
    hither %g
    resolution %d %d

The parameters are:

    From:  the eye location in XYZ.
    At:    a position to be at the center of the image, in XYZ world
       coordinates.  A.k.a. "lookat".
    Up:    a vector defining which direction is up, as an XYZ vector.
    Angle: in degrees, defined as from the center of top pixel row to
       bottom pixel row and left column to right column.
    Resolution: in pixels, in x and in y.

  Note that no assumptions are made about normalizing the data (e.g. the
  from-at distance does not have to be 1).  Also, vectors are not
  required to be perpendicular to each other.

  For all databases some viewing parameters are always the same:
    Yon is "at infinity."
    Aspect ratio is 1.0.

  A view entity must be defined before any objects are defined (this
  requirement is so that NFF files can be used by hidden surface machines).

--------

Positional light.  A light is defined by XYZ position.  Description:
    "b" X Y Z

Format:
    l %g %g %g

    All light entities must be defined before any objects are defined (this
    requirement is so that NFF files can be used by hidden surface machines).
    Lights have a non-zero intensity of no particular value [this definition
    may change soon, with the addition of an intensity and/or color].

--------

Background color.  A color is simply RGB with values between 0 and 1:
    "b" R G B

Format:
    b %g %g %g

    If no background color is set, assume RGB = {0,0,0}.

--------

Fill color and shading parameters.  Description:
     "f" red green blue Kd Ks Shine T index_of_refraction

Format:
    f %g %g %g %g %g %g %g %g

    RGB is in terms of 0.0 to 1.0.

    Kd is the diffuse component, Ks the specular, Shine is the Phong cosine
    power for highlights, T is transmittance (fraction of light passed per
    unit).  Usually, 0 <= Kd <= 1 and 0 <= Ks <= 1, though it is not required
    that Kd + Ks == 1.  Note that transmitting objects ( T > 0 ) are considered
    to have two sides for algorithms that need these (normally objects have
    one side).

    The fill color is used to color the objects following it until a new color
    is assigned.

--------

Objects:  all objects are considered one-sided, unless the second side is
needed for transmittance calculations (e.g. you cannot throw out the second
intersection of a transparent sphere in ray tracing).

Cylinder or cone.  A cylinder is defined as having a radius and an axis
    defined by two points, which also define the top and bottom edge of the
    cylinder.  A cone is defined similarly, the difference being that the apex
    and base radii are different.  The apex radius is defined as being smaller
    than the base radius.  Note that the surface exists without endcaps.  The
    cone or cylinder description:

    "c"
    base.x base.y base.z base_radius
    apex.x apex.y apex.z apex_radius

Format:
    c
    %g %g %g %g
    %g %g %g %g

    A negative value for both radii means that only the inside of the object is
    visible (objects are normally considered one sided, with the outside
    visible).  Note that the base and apex cannot be coincident for a cylinder
    or cone.

--------

Sphere.  A sphere is defined by a radius and center position:
    "s" center.x center.y center.z radius

Format:
    s %g %g %g %g

    If the radius is negative, then only the sphere's inside is visible
    (objects are normally considered one sided, with the outside visible).

--------

Polygon.  A polygon is defined by a set of vertices.  With these databases,
    a polygon is defined to have all points coplanar.  A polygon has only
    one side, with the order of the vertices being counterclockwise as you
    face the polygon (right-handed coordinate system).  The first two edges
    must form a non-zero convex angle, so that the normal and side visibility
    can be determined.  Description:

    "p" total_vertices
    vert1.x vert1.y vert1.z
    [etc. for total_vertices vertices]

Format:
    p %d
    [ %g %g %g ] <-- for total_vertices vertices

--------

Polygonal patch.  A patch is defined by a set of vertices and their normals.
    With these databases, a patch is defined to have all points coplanar.
    A patch has only one side, with the order of the vertices being
    counterclockwise as you face the patch (right-handed coordinate system).
    The first two edges must form a non-zero convex angle, so that the normal
    and side visibility can be determined.  Description:

    "pp" total_vertices
    vert1.x vert1.y vert1.z norm1.x norm1.y norm1.z
    [etc. for total_vertices vertices]

Format:
    pp %d
    [ %g %g %g %g %g %g ] <-- for total_vertices vertices

--------

Comment.  Description:
    "#" [ string ]

Format:
    # [ string ]

    As soon as a "#" character is detected, the rest of the line is considered
    a comment.

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

            "Light Makes Right"

             November 4, 1988

Compiled by Eric Haines, 3D/Eye Inc, 410 E. Upland Rd, Ithaca, NY 14850
    607-257-1381, hpfcla!hpfcrs!eye![e-mail]
All contents are US copyright (c) 1988 by the individual authors

Contents:
    Intro, by Eric Haines
    New People: David Rogers, Kelvin Thompson, A.T. Campbell III, Tim O'Connor
    Ray/Triangle Intersection with Barycentric Coordinates, by Rod Bogart,
    reply by Jeff Arenberg
    Letter and Replies
    Free On-Line Computer Graphics References, (Eugene Miya for) Baldev Singh
    Latest Mailing List, Short Form, by Eric Haines

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

Intro
-----

    For a switch, there are no articles on MTV's ray tracer!  The major stuff
    this time is Rod Bogart's triangle intersector, and the announcement of
    Baldev Singh's computer graphics reference resource.  There are also many
    letters and short articles, along with the usual cullings of USENET.
    Enjoy.

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

New People
----------

# Professor David F. Rogers
# Aerospace Engineering Department
# U.S. Naval Academy
# Annapolis, MD 21402
# USA
# Tel: [phone]
# ARPANET: [e-mail]
# UUCP:    ~uunet!usna!dfr
alias    david_rogers    [e-mail]



# Kelvin Thompson - hierarchy schemes, procedural objects, animation
# The University of Texas at Austin
# 4412 Ave A. #208
# Austin, TX  78751-3622
alias    kelvin_thompson    [e-mail]

I'm a PhD student in graphics at the University of Texas.  I received a BSEE
from Rice University in 1983, and a Master's in EE from UT in 1984.  My
doctoral project is on hierarchical, multi-scale databases for computer
graphics, and I'm building a ray-tracer as part of my work on that project.
I'm also interested in motion and animation.  I never plan on becoming
President of the United States of America.

-- Kelvin Thompson, Lone Rider of the Apocalypse
   [e-mail]  {...,uunet}!cs.utexas.edu!kelvin



# A. T. Campbell, III - shading models, animation
# Department of Computer Sciences
# University of Texas
# Austin, Texas 78712
# [phone]
alias    at_campbell     [e-mail]

I am in the PhD program in Computer Sciences at the University of Texas.  My
research area is developing a more sophisticated illumination model than those
currently in widespread use.  A modified form of distributed ray tracing is one
of the methods I am considering to evaluate my model.

Animation is another of my interests.  I am putting myself through school by
producing computer graphics animations for a small engineering company.
Sometimes I am called upon to create special effects such as motion blur and
atmospheric effects.  Based on what I heard at this year's ray tracing round
table at SIGGRAPH, it looks as if ray tracing can solve most of my problems.



# Tim O'Connor
# Staff, Cornell Program of Computer Graphics
# 120 Rand Hall
# Ithaca, NY 14853
alias    tim_oconnor    [e-mail]

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

Ray/Triangle Intersection with Barycentric Coordinates
------------------------------------------------------
[sent to RT News and USENET]

    articles by Rod Bogart, Jeff Arenberg


From: hpfcla![e-mail] (Rod G. Bogart)

A while back, there was a posting concerning ray/triangle intersection.  The
goal was to determine if a ray intersects a triangle, and if so, what are the
barycentric coordinates.  For the uninitiated, barycentric coordinates are
three values (r,s,t) all in the range zero to one.  Also, the sum of the values
is one.  These values can be used as interpolation parameters for data which is
known at the triangle vertices (i.e. normals, colors, uv).

The algorithm presented previously involved a matrix inversion.  The math went
something like this: Since (r,s,t) are interpolation values, then the
intersection point (P) must be a combination of the triangle vertices scaled by
(r,s,t).

    [ x1 y1 z1 ] [ r ]   [ Px ]   [ r ]   [ Px ]
    [ x2 y2 z2 ] [ s ] = [ Py ]   [ s ] = [ Py ]  ~V
    [ x3 y3 z3 ] [ t ]   [ Pz ]   [ t ]   [ Pz ]

So, by inverting the vertex matrix (V -> ~V), and given any point in the plane
of the triangle, we can determine (r,s,t).  If they are in the range zero to
one, the point is in the triangle.

The only problem with this method is numerical instability.  If one vertex is
the origin, the matrix won't invert.  If the triangle lies in a coordinate
plane, the matrix won't invert.  In fact, for any triangle which lies in a
plane through the origin, the matrix won't invert.  (The vertex vectors don't
span R3.)  The reason this method is so unstable is because it tries to solve a
2D problem in 3D.  Once the ray/plane intersection point is known, the
barycentric coordinates solution is a 2D issue.

Another way to think of barycentric coordinates is by the relative areas of the
subtriangles defined by the intersection point and the triangle vertices.

        1         If the area of triangle 123 is A, then the area of
       /|\        P23 is rA.  Area 12P is sA and area 1P3 is tA.
      / | \       With this image, it is obvious that r+s+t must equal
     /  |  \      one.  If r, s, or t go outside the range zero to one,
    / t | s \     P will be outside the triangle.
   /  _-P-_  \
  / _-     -_ \
 /_-    r    -_\
3---------------2

By using the above are relationships, the following equations define r, s and
t.

    N = triangle normal = (vec(1 2) cross vec(1 3))
        (vec(1 P) cross vec(1 3)) dot N
    s = -------------------------------
            length N
        (vec(1 2) cross vec(1 P)) dot N
    t = -------------------------------
            length N
    r = 1 - (s + t)

In actual code, it is better to avoid the divide and the square root.  So, you
can set s equal to the numerator, and then test if s is less than zero or
greater than sqr(length N).  For added efficiency, preprocess the data and
store sqr( length N) in the triangle data structure.  Even for extremely long
thin triangles, this method is accurate and numerically stable.

RGB                         Living life in the fast lane, eight items or less.
({ihnp4,decvax}!utah-cs!bogart, [e-mail])


--------

From: [e-mail] (Jeff Arenberg)
Subject: Re: Ray/Triangle Intersection with Barycentric Coordinates
[from USENET]

Ok, here is how I handle this calculation in my ray tracing program.  I think
it is quite efficient.

Let a triangle be represented in the following manner :

           |\
           |  \
        p1 |    \
           |      \
  O ------------>  |________\
       p0              p2

where p0 is the vector from the origin to one vertex and p1, p2 are the vectors
from the first vertex to the other two vertices.

Let N =   p1 X p2  be the normal to the triangle.
          -------
    | p1 X p2 |

Construct the matrices

    b =  |  p1  | ,  bb = inv(b) = | bb[0] |
     |  p2  |                  | bb[1] |
     |  N   |                  | bb[2] |

and store away bb.

Let the intersecting ray be parameterizes as

    r = t * D + P

Now you can quickly intersect the ray with the triangle using the following
pseudo code. ( . means vector dot product)

    Den = D . bb[2]
    if (Den == 0) then ray parallel to triangle plane, so return

    Num = (p0 - P) . bb[2]

    t = Num / Den
    if (t <= 0) then on or behind triangle, so return

    p = t * D + P - p0

    a = p . bb[0]
    b = p . bb[1]

    if (a < 0.0 || b < 0.0 || a + b > 1.0) then not in triangle and return

    b1 = 1 - a - b     /* barycentric coordinates */
    b2 = a
    b3 = b


The idea here is that the matrix bb transforms to a coordinate frame where the
sides of the triangle form the X,Y axes and the normal the Z axis of the frame
and the sides have been scaled to unit length.  The variable Den represents the
dZ component of the ray in this frame.  If dZ is zero, then the ray must be
parallel to the X,Y plane.  Num is the Z location of the ray origin in the new
frame and t is simply the parameter in both frames required to intersect the
ray with the triangle's plane.  Once t is known, the intersection point is
found in the original frame, saved for latter use, and the X,Y coordinates of
this point are found in the triangle's frame.  A simple comparison is then made
to determine if the point is inside the triangle.  The barycenter coordinates
are also easily found.

I haven't seen this algorithm in any of the literature, but then I haven't
really looked either.  If anyone knows if this approach has been published
before, I'd really like to know about it.

Jeff Arenberg
-------------------------------------------------------------
UUCP : ( ucbvax, ihnp4, uscvax ) !trwrb!csed-pyramid!arenberg
GEnie: shifty
-------------------------------------------------------------

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

Letters and Replies
-------------------

From: David F. Rogers <hpfcla![e-mail]>
Subject:  Transforming normals

G'day Eric,

Was skimming the back issues of the RT News and your memo on transforming
normals caught my eye. Another way of looking at the problem is to recall
that a polygonal volume is made up of planes that divide space into two
parts. The columns of the volume matrix are formed from the coefficients of
the plane equations. Transforming a volume matrix requires that you
premultiply by the inverse of the manipulation matrix. The components of a
normal are the first three coefficients of the plane equation. Hence the
same idea should apply. (see PECG Sec. 4-3 on Robert's algorithm pp 211-213).
Surprising what you can learn from Roberts' algorithm yet most people
discount it.

Dave Rogers

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

From: mcvax!ecn-nlerf.com![e-mail] (Jack van Wijk)
Subject: 2D box-test

An answer to the question of Jack Ritter, RT-News October 3, 1988,
    by Jack van Wijk

Jack Ritter proposes a method to improve the efficiency by testing the
ray-point against a 2-D box. This method has been published before:

Bronsvoort, W.F., J.J. van Wijk, and F.W. Jansen, "Two methods for Improving
the Efficiency of Ray Casting in Solid Modelling", Computer-Aided Design,
16(1), January 1984, pp. 51-55.

The method is used hierarchically here for CSG-defined models, in the spirit of
Roth. The gain of the method is significant, but not dramatically.  Probably in
our system the cost of the floating point intersection calculations was much
bigger than the box-test.

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

From: Jeff Goldsmith
Subject: Neutral File Format

   Yuk.  I don't think that the world needs another ugly scene description
language unless it does something special.  I haven't seen renderman, but other
people seem to like it, so maybe that'll be better.  Yours looks a lot like
Wavefront's, with the disadvantage that it doesn't support a binary
representation.

    I hate to say it, but I use my own (less, I feel, but still ugly) text
format that does have a binary format as well as an ascii numerical format.
You are welcome to it if you want, but I would doubt it.  It's different in
that algebraic expressions are possible in place of any constant, plus it
includes flow control, tests, some computer algebra-type primitives and macros.
Plus, a historyer, command line editing, etc.  It looks a lot like an
interactive F77 interpreter with massive numbers of bizarre graphics commands.

    Perhaps you can instigate an effort to create a sensible object description
language and (maybe) supply an interpreter and some compiled formats.  It would
be worthwhile.  Perhaps just setting up an effort to spec one out would be good
enough.  Whatever.

--------

Reply From: Eric Haines

    I guess I didn't make it clear - NFF has been in use about a year now.
It's the format that the SPD benchmarking package uses.  I should have written
a better preface, obviously: I wanted to get the point across that this is
supposed to be absolutely minimal, and that no one should be using it for
modeling, but only for transferring the final database to a renderer.  There
could indeed be an NFF++ language which would not be user hostile, like NFF is.
Essentially, I see NFF as incredibly stupid and brain damaged.  This makes it
accessible to almost anyone who simply wants to read in a scene database
without too much hassle (even now, though, I'm getting questions like "what's
hither?" from people on USENET).

    Anyway, I like your ideas for algebraic expressions - I could use it
right now in my other language, which is a tad more user friendly and is what I
use when I want to munge around by hand.

--------

Reply From: Jeff Goldsmith

    Hmmm.  If you are trying to find an interface that can be used by
professionals, then it is probably not the same interface that might be used by
USENET-types.  Both problems might be worth addressing, but I'd say (from gross
personal bias) that the high-end problem is worth doing more.  Simply so that I
can trade databases more easily.  Simply so that code can be shared more
easily.  I'm really not all that concerned about getting computer graphics
capabilities out to high schoolers and other randoms quite yet.  In fact, I
doubt that graphics will have that sort of distribution in its current
"modeler-renderer" form.  I suspect that Mac interface and high-quality
user-interfaces will be the medium for that type of technology dissemination.
Eventually, we'll have programs that are called "Graphics Processors" or some
other nonsense and will be transmitting reasonably complex graphics
capabilities to anyone who wants to do it.  Artists will be the primary users,
though managers and engineers will use them in both technical and non-
technical efforts.  Joe six-pack just doesn't have that much
use/interest/capacity for generating pictures out of thin air.

    It would be really nice if there were a standardish graphics language
kernel.  Since just about everybody has their own interpreter that does just
about the same set of very basic things, plus, of course, their set of
enhancements, why not create a spec that would still allow all the
enhancements, but cover the basics thoroughly.  It might stifle creativity a
bit, but I doubt it.

    For transmission between modelers and renders, why not use the same
language as input to modelers?  Remove some options (or don't) and keep the
files the same.  If you are worried about speed, then a binary complied version
is necessary in any event.  (Case in point: my current project is Hubble Space
Telescope.  The uncompiled model takes 17! minutes to read in.  The compiled
one takes about 35 seconds.)  It might also be worth considering that some
people out there do use Fortran and that some things are hard to parse (NFF,
for example) in Fortran.  In fact, it's hard to parse anything that isn't fixed
field formatted in Fortran.  (I've got an ugly version like that, too.  Really
ugly.  .7 Fixmans maybe even.)

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

From: Cary Scofield
Subject: RT and applications

K.R.Subramanian (UTexas at Austin) asks:

> On the RT news: I would like to see practical applications of ray tracing
> described here. What applications really require mirror reflections,
> refraction etc. Haven't seen applications where ray tracing was the way
> to go.

Applications for ray tracing (besides "realistic" image synthesis):

    MCAD (3D solids modeling)

    Material property calculations (mass, center of gravity,
        moments of inertia, etc.)

    Lens design (geometric optics)

    Toolpath planning for numerical-controlled milling

    Weapons research (ballistics analysis)

    Vulnerability assessments (collision detection between a
        projectile and an object)

    Nuclear reactors (determination of neutron distributions
        in reactor cores)

    Astrophysics (eg., diffusion of light through stellar
        atmospheres; penetration of light through planetary
        atmospheres)

IN SUMMARY: Just about anything that requires solving a linear (and non-linear
w/restrictions) particle transport problem is a candidate application for
ray-tracing/ray-casting algorithms.


Cary Scofield - Apollo Computer Inc. - Graphics Software R&D
UUCP: [decwrl!decvax,mit-eddie,attunix]!apollo!scofield
ARPA: [e-mail]
USMAIL: 270 Billerica Rd., Chelmsford, MA 01824  PHONE: [phone] x7744

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

From: [e-mail] (K.R.Subramanian.)
Subject: Re:  Goldsmith and eyes

on the automatic hierarchy scheme of Goldsmith and Salmon:

     Somewhere in the RT news you mentioned that the hierarchy is optimized
only for primary rays from the eye?

    In their paper, they mention that the probability of hitting a bounding
volume is proportional to the solid angle of the bounding volume presented at
the eye and if the eye is sufficiently far away, then this can be approximated
by the surface area of the bounding volume of the object(s).

    Is this the reason that the hierarchy is not the best for secondary
rays?  If that is so, what if the eye is somewhere within the scene?  In this
case, the assumption is again violated.


K.R.Subramanian
Department of Computer Sciences
The University of Texas at Austin
Austin, Tx-78712.
[e-mail]
{uunet}!cs.utexas.edu!subramn

--------

Reply From: Eric Haines

    Jeff Goldsmith and I were discussing in the latest RT News whether the
eye location might be used to help out the hierarchy made by the Goldsmith/
Salmon algorithm.  Essentially, Jeff finds that since so many of his rays are
eye rays, he might want to try to test intersection of the objects closer to
the eye first.  In other words, after the G-S hierarchy is created, go through
and sort the sons of each bounding volume by the additional criterion of
distance to the eye.  This is an added fillip to the G-S algorithm: normally
(i.e. in the original article) they do not pay attention to the order of the
sons of a bounding volume.  The idea is that if you test the closer object
first and hit it, you can often quickly reject the further object when it is
tested (since you now have a maximum bound on the distance the ray is shot).
For example, say you have a list: polygon, sphere.  The closest approach (or
the center, or whatever criterion you decide to use) of the sphere is closer
than that of the polygon, so you reorder the son list: sphere, polygon.  If you
now test a ray against this list you get four possibilities:

    1) Sphere missed, polygon missed - no savings is accrued by sorting.
    2) Sphere missed, polygon hit - no savings is accrued by sorting.
    3) Sphere hit, polygon missed - by hitting the sphere, we now have
       a maximum bound on the ray's (really the line segment's) length.
       Now when the polygon is tested it might be quickly rejected. Say
       we hit the polygon plane beyond the maximum distance.  In this
       case, we can stop testing the polygon without doing the inside-
       outside testing.  If we had intersected in the order "polygon,
       sphere", we would have had to do this inside-outside test, then
       gone on to test the sphere - extra work we could have avoided.
    4) Sphere hit, polygon hit - Pretty much the same as case (3), except
       even more so:  in this case time is saved by (a) not having to
       to do the inside-outside test, (b) not having to store information
       about the intersected polygon, and (c) it is all the more likely
       that a polygon beyond the sphere which is actually hit has the
       intersection distance beyond the sphere's intersection distance
       (vs. a missed polygon, where the intersection distance is somewhere
       on an infinite plane which could easily be in front of the sphere).

    My idea for ordering the son lists was simply object size: within a son
list, sort from largest to smallest area, on the theory that larger objects
will tend to get hit more often and so get you an intersection point quickly.
The savings are based more on probability of hits, but the idea makes for G-S
hierarchy trees that are not eye-dependent (I use item buffering, so eye rays
are minimized).  Another idea is to order the lists by difficulty of
calculation: test spheres before splines, test triangles before 100-sided
polygons, etc.

    The idea of ordering lists by either size or difficulty is valid for
other efficiency schemes, too.  Octree lists and SEADS might benefit from
ordering the lists in a sensible fashion.  Has anyone else out there tried such
schemes?

--------

Reply From: [e-mail] (K.R.Subramanian.)

Yes, I understood these discussions and they are all valid.  Somehow just
trying to optimize the eye rays doesn't impress me very much because you
yourself have mentioned the item buffer for eye rays and the light buffer for
doing shadow rays from the first level intersections.  It is not very clear to
me if the above schemes you mention will bear a great improvement.  Anyhow, I
am really interested in secondary rays since that's what ray tracing is all
about. In very complex scenes like the Cornell rings or Cornell mountain
databases (SPD data bases) its the secondary rays that are dominant.

My real question was trying to figure out if Jeff's approximation in using the
surface area of the bounding volumes to figure out the conditional
probabilities was valid for all rays, primary and secondary.  There he said
something like 'if you are far away, you can approximate ........'. Does this
refer to the ray length ?


K.R.Subramanian
Department of Computer Sciences
The University of Texas at Austin
Austin, Tx-78712.
[e-mail]
{uunet}!cs.utexas.edu!subramn

--------

Reply From: Eric Haines

    Indeed, Jeff's optimization for eye rays doesn't thrill me.  But how do
you feel about optimizing on size or on intersection complexity (or both)?
Seems like this has a good chance of validity for secondary rays, too.

    I will pass on your comments to Jeff and see how he responds.  You
might just want to write him directly at:

alias    jeff_goldsmith    [e-mail]


    I should clear up an important point: the SPD databases are in no way
connected with Cornell.  I designed them in August 1987, more than a year and a
half after leaving Cornell.  I hope that nowhere in the document I imply that
Cornell is associated with these.  Why the fuss?  Partly because Don Greenberg,
my president (at 3D/Eye Inc) is very firm about separating work done at 3D/Eye
and work done at the Cornell graphics lab (which he also runs).  Another reason
is that Cornell doesn't "endorse" these databases - Don would be pretty bugged
at me if it was said that they did.  So, please just refer to the SPD
databases, or the 3D/Eye SPD databases.  'Nuff said, and thanks.

--------

Reply From: KR Subramanian

>          Indeed, Jeff's optimization for eye rays doesn't thrill me.  But
>    how do you feel about optimizing on size or on intersection complexity
>    (or both)? Seems like this has a good chance of validity for
>    secondary rays, too.

    You are right. Using size or intersection cost in ordering your
intersections will do good, especially in shadow ray computation. As far as the
pixel or reflection rays are concerned, this depends on the method used. I have
a modified version of the BSP tree where the search goes very close to the path
of the ray and only on collection of unordered objects can we take advantage of
the above 2 facts.

    Also, this is basically a hack (well, I wouldn't go quite that far).
But size as presented to a ray depends on the direction of the ray, since
projected area on to a ray varies.  A polygon could present its entire area to
a ray orthogonal to it or almost nothing if its parallel to it.

        For shadow rays, if you have a mix of complex objects (patches, splines
etc) and simple objects like polygons, spheres you better do this in the order
of their complexity. That will definitely save a lot of work especially when
there are multiple light sources and lots of spawned rays.

--------

Reply From: Jeff Goldsmith

Ok.  Optimizations.

    1) The only reason that I suggest ordering from the eye is that there are
eye rays in all scenes.  Not true for secondary.  Besides, most secondary rays
get other kludges.  More importantly, they are somewhat random, so it's tough
to optimize for them.

    2) What he is confusing with the above is the heuristic for "probability"
determination.  That is not based on eye rays, but assumes a uniform
distribution of ray directions throughout the scene.  This is not the case, but
we haven't dealt with more complicated heuristics other than to decide that
they are a bit more tricky than they might seem.

    3) There is a factor in the tree combination heuristic (the one that adds
up the node costs into a tree cost) that is biased for primary rays.  I call
the tree cost the sum of the node costs.  This isn't strictly true for
secondary rays, because they emanate from a leaf node, thereby adding some
additional cost to the big nodes.  We tried accounting for this by using a
formulation that takes internal emanation costs into account.  Yes, it was more
accurate.  Not by enough to bother with.  I think the difference was on the
order of a few percent.  It was definitely well under the noise level.  We
don't use it anymore for no particular reason.  Don't bother to code it, except
as an intellectual exercise.  (Not a bad one at that.)

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

From: hpfcla![e-mail] (Rod G. Bogart)
Subject: Wood Textures

As for the wood textures, there really isn't a lot to say.  They were scanned
with a Vicom frame grabber.  The data is 512x512 bytes.  The book they were
taken from is Textures by Brodatz.  We do not have permission from the author
or the publisher, so thats why we haven't made the whole set available.  Yes,
we did scan the whole book (over 100 images) but without permission, I dare not
let out more than a handful.  So, the images are on cs.utah.edu, and they are
wood[1234].img.  As for mailing them (UUCP), I'd rather not.  A quarter meg
uuencoded is a long mail message.  If you really really can't get them from a
friend with ftp access, then ask nice.

RGB

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

From: [e-mail] ( Steven Stadnicki,212 Reynolds,2684079,5186432664)
Subject: Shadows, mirrors, and "virtual lighting"
[from USENET]

     I am currently working on a simple raytracer (VERY simple--so far it only
models triangles) and have a major problem.  For shadow calculations I need to
know if there are any light sources which could shine on a point.  The problem?
With mirrors in the scene, it's possible to have reflected light illuminate
some section that would normally be in shadow, e. g.:

Light-> O                               |                               O'
         \------                        |                        ------/
                \------                 |                 ------/
                       \------          |          ------/
                              \------   | M ------/
             +-----+                 \-\| i
             |     |                 /-/| r
             |object          /------   | r
             |     |   /------          | o
             |     | SSSS               | r
----------------------------------------|

Then the area covered by the S's would not be in shadow, even though it isn't
directly illuminated by the light O.  I know how to solve the problem using
"virtual" lights; that is, a light that you would obtain if you reflected the
Light at O in the mirror above; it would appear at O'.  Multiple reflections
can be handled by re-reflecting virtual lights, etc.  So what's my problem?
Simple: if you have M mirrors and reflections can go up to depth K, you need
O(M^K) virtual lights for each "real" light.  Is there any way I might be able
to eliminate, for a given point, some combinations of reflections without
having to do much testing?

                                            Steven Stadnicki
                                            [e-mail]

P.S.  The "virtual lights" idea came from a wonderful book: "A Companion
to Concrete Analysis", by Melzak.

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

From: [e-mail] (David Jevans)
Subject: Re: Basics of raytracing
[from USENET]

If anyone is looking for the analysis of a regular subdivision
ray tracing method, see:

 journal:  Visual Computer July 1988
 title:    Analysis of an Algorithm for Fast Ray Tracing Using
           Uniform Space Subdivision
 authors:  Cleary, J and Wyvill, G

What the paper does is to describe the voxel traversal algorithm that Cleary
developed and that I use in my ray tracer, and then a theoretical analysis is
presented.  It is a convincing argument for using regular voxel subdivision
(although my method - submitted to CGI '89 in UK - works better for scenes
where polygons are not evenly distributed throughout a scene).

Visual Computer is published by Springer Verlag.  Unfortunately it doesn't
enjoy the circulation of CG&A or TOG so it is pretty (outrageously?) expensive
(like $160 US for 6 issues!).

The design of our Mesh Machine is in:
  journal:  Proc CIPS Graphics Interface '83, 33-34, Edmonton, Alberta, May
  title:    Design and Analysis of a Parallel Ray Tracing Computer
  authors:  John Cleary and Brian Wyvill and Graham Birtwistle and Reddy Vatti

--------(second article appended)

In article <[e-mail]>, [e-mail] (Mr Booga (detonate)) writes:
>   I have a request similar to Randy Ray's (Raytracing introduction).  I am
> starting a project in parallel raytracing using a Sequent Balance 8000 and
> a couple of color Sun 3's running X.  I have virtually exhausted the
> local resources on raytracing and am in need of basic ray tracing algorithms
> and simple optimization algorithms.

Our university (the U. of Calgary) has significant experience in parallel ray
tracing.  Professors Cleary and Wyvill developed a mesh machine for raytracing
several years ago.  Graduate student (now working at Alias) Andrew Pearce
implemented a parallel raytracer for the mesh machine that also ran on a
network of Corvus'.

I implemented a parallel ray tracing algorithm for polygons and implicit
surfaces earlier in the year on a BBN Butterfly.  I used regular spatial
subdivision combined with adaptive (octree) subdivision to converge on the
surfaces.  Up to 10 nodes I got almost linear speedup, and on a 70 node system
I was still getting 50% from each new node added.

If anyone else is interested in references on parallel raytracing (the mesh
machine articles, Pearces Masters thesis, or others such as Dippe in Siggraph
86 etc) you can send me mail and I can send a list or copies of some of t

"behind these eyes that say I still exist..."

David Jevans, U of Calgary Computer Science, Calgary AB  T2N 1N4  Canada
uucp: ...{ubc-cs,utai,alberta}!calgary!jevans

--------

From: [e-mail] (Subrata Dasgupta)
Subject: Re: Basics of raytracing
[from USENET]

In article <[e-mail]> [e-mail] (David Jevans) writes:
>
>Our university (the U. of Calgary) has significant experience in parallel
>ray tracing.  Professors Cleary and Wyvill developed a mesh machine for
>raytracing several years ago.  Graduate student (now working at Alias)
>Andrew Pearce implemented a parallel raytracer for the mesh machine
>that also ran on a network of Corvus'.

    This all sounds very interesting! A few articles back a person inquired
about a paper on an algorithm analysis by Profs. Wyvill and Cleary. I am trying
to track that paper down but the reason for sending you this letter is to
request some info. on the mesh machine for ray- tracing developed at your univ.
If you can refer me to a recent paper on this machine it will be great. At Duke
we are developing what has come to be known as the Raycasting machine which
computes intersection of an array of parallel rays with primitives and then
uses constructive solid geometry to compute the shape, volume and other
parameters of an arbitrary object. Thus I would be very much interested in any
work in this area.

>If anyone else is interested in references on parallel raytracing
>(the mesh machine articles, Pearces Masters thesis, or others
>such as Dippe in Siggraph 86 etc) you can send me mail and I can send
>a list or copies of some of t

Any other info. in this area would be very much appreciated. Thanks!

Subrata Dasgupta

Department of Computer Science, Duke University, Durham, NC 27706
ARPA:     [e-mail]
CSNET:     sdg@duke
UUCP:     decvax!duke!sdg

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

From: [e-mail] (Steve Upstill)
Subject: Re: What is Renderman Standard?
Organization: Pixar -- Marin County, California
[from USENET]

    I'm writing the RenderMan book, so I guess I'm qualified to clear up
    a couple of things from this posting:

In article <[e-mail]> [e-mail] (Keith Fish) writes:
>
>I'm sure PIXAR is more than willing to send you a spec of Renderman ...
>just ask them.  Also, there may be something available through the
>Siggraph 88 proceedings.

    There's nothing in the SIGGRAPH 88 proceedings about RenderMan.  You can
    get a copy of the spec by sending $15 (yes, I know it's a pain, but we've
    sent out ~1000 specs so far, and it got kind of expensive; this is the
    real cost) to
    Pixar
    3240 Kerner Blvd.
    San Rafael, Ca. 94901

>
><<< The following is MY understanding of Renderman >>>
>
>Renderman is an attempt by PIXAR to force a de facto standard interface in the
>Graphics Rendering/Imaging arena.  My understanding is that this interface
>is based on tools/routines that they have developed throughout the years for
>use on their hardware.  Because it was not designed for general/varying
>graphics architectures, many companies wonder if it will only work well on
>their systems -- hence, making their hardware also the de facto standard.

    RenderMan is based on about six years' research at Pixar and Lucasfilm on
    how to get quasi-photographic realism into computer graphics.  The effort
    has encompassed algorithms, software and hardware, and much of what is in
    the standard has been proven to work by actually implementing it;  so in
    some sense the above is a correct statement.  However, there is an
    implication here that RenderMan is some in-house methodology that Pixar is
    trying to foist off on the rest of the industry.  That is definitely
    untrue.  Pat Hanrahan and Tom Porter spent about six months talking to
    other companies in the industry, trying to establish a consensus and
    ensure that the standard is technically sound.  The best evidence I
    have of how much it changed as a result is the amount of work I had
    to put into changing my book between Versions 2 and 3 of the spec.

    As for the standard being specific to some particular hardware or
    software configuration, you just have to look at the standard itself.
    From the geometric standpoint, it is a simple protocol for describing
    scenes, as generic as can be, and deliberately so.  It is essentially
    a superset of PHIGS+, with two differences: there is no provision for
    changing model descriptions once defined (you have to respecify scenes
    from one frame to another), and there are extensions for realism like
    the shading language, motion blur and depth-of-field.  The hardware-
    specificity is a canard, pure and simple.  The current (incomplete)
    version of our software runs on Sun, Silicon Graphics and '386-based
    Compaq machines, as well as on Transputer-based hardware accelerators
    in all three.

    More specifically, I can tell you that Pat went to a lot of trouble to
    make the interface standard independent of even the basic rendering
    algorithm.  That is, RenderMan is consistent with scanline-based methods
    as well as ray tracing; standard shading models as well as radiosity
    techniques.  That wasn't easy.

>More importantly, PIXAR already has the software written for this "standard"
>so if this becomes a standard, any competitor of PIXAR would have to make the
>$$$ investment to write this software -- a good way to limit your competition.

    Sorry.  I'm working closely with the software group in trying to
    generate pictures and example programs for my book, and I can testify
    that the software, while quite far along, is not "already written",
    largely because of extensions to the standard that came out of
    discussions with other companies.  True enough, we probably have a
    head start on others, but the standard has been out there for five
    months now, and will probably have been around for close to a year
    before Pixar has its stuff on the market.

    Besides, the standard specifies nine capabilities which are optional for
    any particular implementation.  No renderer should have any trouble
    meeting the RenderMan standard if it supports PHIGS primitives and
    performs such quality calculations as anti-aliasing and gamma correction.

>PIXAR made a big push for Renderman at Siggraph 88.  Although a few companies
>agreed to endorse this package (SUN, of course ... they'd endorse anything to
>get their name in lights ;-), many took a more intelligent approach and said
>that they would evaluate it.  PIXAR basically used a lot of marketing hype
>to get support initially and even listed supporters who, when you would
>walk up to their booth at Siggraph and ask them, said they did not support it.

    This comment is borderline offensive to me, partly because it is admittedly
    based on speculation and partly because I was around during the process
    I mentioned above, and I know what a painful and elaborate job Pat had
    to get the proposal into shape to win the support of the companies he did.
    There is a difference between endorsement and support.  Endorsement means
    "we have evaluated this; it is sound and we believe this is the way the
    industry should go".  Support means "we have hardware and/or software
    which implements this standard".  You would expect the latter to be a
    subset of the former.

    Nineteen companies endorsed the RenderMan standard at rollout.  The main
    holdouts at this point are Silicon Graphics and Wavefront.  My personal
    suspicion (not to be taken as the views of Pixar) is that Wavefront
    perceives RenderMan as a threat to their rendering market because
    it supports features which would be difficult or impossible to
    implement using their rendering algorithm.  And Wavefront software
    runs on SGI machines.

>Many (most ?) of the companies who looked at Renderman have decided that it
>still needs a lot of work before it can be considered as even a base to start
>the development of a standard in the rendering/imaging arena.

    Who are these "many companies"??  What is this "lot of work"??  We would
    love to hear about.  There is a RenderMan Advisory Council made up of
    industry representatives whose job it is to hear complaints like that.

    I don't expect to hear too many of them, however.  As I said before,
    RenderMan is basically a simple-minded extension of PHIGS (read: EXTENSION.
    Meaning "If PHIGS is good enough for you, so should be RenderMan")
    adding constructs for supporting realistic graphics.  It has gone
    through the mill of two major rewrites as a result of consultations
    with "many companies".

>There are
>several problems in the area of getting Renderman to mesh with other current
>standard graphics environments (eg. phigs, cgi, ...) so that it becomes a
>natural extension to the less-interesting/fancy graphics people do today.

    What are these problems??  Can you be more specific??

>Even for the niche market of image-rendering, Renderman does not include
>many (any ?) ideas from the companies that have been in this business for
>years ...  Wavefront, Alias Research, Neo-Visuals, Disney, etc.

    What are these ideas??  Come to think of it, what ideas has Disney
    contributed to image rendering?

>Keith Fish
>
>PS. I'm not cutting down PIXAR -- I think that the work they do is
>    fantastic (literally)!  I just don't like marketing ploys to degrade
>    what should be good technology, and this is what the Renderman-hype
>    seems to be.

    I appreciate your appreciation, but I wish I knew where these
    impressions of yours came from.

>    I think that the industry can develop a good imaging
>    interface standard if everyone (animation software companies,
>    universities, graphics hardware companies, etc.) gets to contribute.

    Again, I thought that's exactly what we did.

    If anyone on the net is interested in more information on RenderMan
    without investing $15 in a spec, the current issue of Unix Review
    includes an article I wrote discussing the major aspects of the
    standard.  Also, the November issue of Dr. Dobb's Journal has a
    cover story on the shading language, which is RenderMan's doorway
    for extensibility.

Steve Upstill

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

Free On-Line Computer Graphics References
-----------------------------------------

[incidentally, the latest version of the Ray Tracing Bibliography by Paul
Heckbert (and updated by myself) is available from Mark Vandewettering's
anonymous ftp site, drizzle.cs.uoregon.edu. --EAH]

From: [e-mail] (Eugene Miya)
Subject: A little announcement (part 1 of 3)
Organization: NASA Ames Research Center, Calif.
[from USENET]

For a long time now, a lot of people have been asking simple information
queries in places like comp.graphics.  This resulted in the inevitable
repeating of topics, flood of inane news messages (many of which are wrong),
and a repeating cycle which bring disillusionment.

Computer graphics, unlike a lot of disciplines, has an overseer of the
literature.  If you open up an ACM/SIGGRAPH proceedings you will notice a
reference to "References" to Baldev Singh (currently at MCC).  Baldev has has
published significant references in the Computer Graphics Quarterly for a
couple of years (and is preparing for another shortly).  These bibliographies:

%A Baldev Singh
%T Computer Grap[hics Literature for 1986: A Bibliography
%J Computer Graphics
%V 21
%N 3
%D June 1987
%P 189-208

and

%A Baldev Singh
%A Gunther Schrack
%T Computer Grap[hics Literature for 1985: A Bibliography
%J Computer Graphics
%V 20
%N 3
%D July 1986
%P 85-145

Coverage in the field (for graphics) is quite good.  I know, I am trying to
maintain a comprehensive study of another field (see postings in comp.arch or
comp.parallel).  The problem is searching for literature on a paper database is
difficult (I won't get into details, take my word).  Frequently entries are
also wrong (not as bad as the net however).

A machine readable form however, solves many of these problems.  You can update
a machine readable form.  The problem becomes then of distribution and search,
surprise! something computers are good for!  It is with this back ground that
we in the Bay Area Association for Computing Machinery's Special Interest Group
on Computer Graphics announce the availability of Singh's ACM/SIGGRAPH
bibliography in a machine readable form.

While Baldev will oversee the collection and quality of entries, we with a
generous donation of cycles and disk space from the Digital Equipment
Corporation (DEC) will help oversee the redistribution of the computer graphics
bibliography.

This first article will describe how hosts on the Internet can retrieve the
computer graphics bibliography.  Two other optional means for those not on the
Internet will be presented over the next two days (but clearly Internet is the
superior way to do this).

THERE ARE TWO DANGERS inherent in all of these means.  The bibliography is kind
of big.  It's not a megabyte, but it's getting there.  IF YOU ARE at an
Internet site with lots of users, it's kind of dumb if you ALL made personal
copies (n megabytes ;-).  So before you copy, agree who at your site will
oversee obtaining it.  One copy per site please.

The second danger is everybody copying at the same time.  The information which
follows will illustrate the problem.  The DEC host which you be copying from is
DEC's gateway to the Internet.  It will be a tragedy to abuse this gateway if
every site tried to copy at once.  I know, we provide the 9600 baud IMP port to
DEC.  So let's not abuse this, let's be patient and take our turns. 1) copy the
computer graphics bibliography only during the weekends or evenings Pacific
Daylight or Standard time. 2) copy on a randomly determined evening of the
week.  How?  Flip a coin 3 times (say HTH, make Head == 0, Tails == 1, this
translates to 010 binary or 2 base 10). Using Sunday as 1, make Monday 2, copy
Monday evening P[SD]T.  (HHH or 000, retry).  If this is confusing, wait for
the weekend. AGAIN copy only in the evenings.

Now the questions you have all been patiently waiting for and I have been
rambling: where do I get, and how do I get it.  The Internet host is the
machine gatekeeper.dec.com [128.45.9.52].  Please respect this machine (hacker
ethic) for the assistance DEC is providing.  We don't wish to yank the
bibliography from this machine.  Don't try to break in, please.

Old time ARPAnet hackers will know where to go from here.  The "how" is a
process called anonymous FTP (File Transfer Protocol or Program, hasn't changed
since 1973 ;-)] Don't all do this at once.  Below is a sample session with
annotation as to how this works.  Catch the names of the subdirectories and
files below.  A lot of people aren't familiar with distributed systems other
than Email, so we've made the language oversimplistic, if you have problems
consult your local network guru.

Note the bibliographies exist in a data compressed binary form.  Use the Unix
uncompress(1) command to decode them.  Not on a Unix system?  Tough for the
time being.  Try to find one.  The further format of individual entries is Unix
refer format (a sample, see the two references above).  This is how Singh has
them, and also how my bibliography is stored.  Refer has lots of advantages
over other systems: free-format, widely available on Unix systems, uses a
minimum of space, ASCII, fully machine and human readable (it separates the
binary data from the text), fairly easy to learn, easily converted to other
formats (like [bib]TeX, Scribe, etc.)

Start script
  eos % ftp gatekeeper.dec.com
        ^^^^^^^^^^^^^^^^^^^^^^ issue this command, after some time you get:
  Connected to gatekeeper.dec.com.
  220 gatekeeper.dec.com FTP server (Version 4.28
  Name (gatekeeper.dec.com:######): anonymous
                                    ^^^^^^^^^ use this name
  331 Guest login ok, send ident as password.
  Password:
           ^^^^^^^^ does not echo, I typed "guest," doesn't matter
  230 Guest login ok, access restrictions apply.
  ftp> cd pub/graf-bib
       ^^^^^^^^^^^^^^^ change directory to pub/graf-bib
  200 CWD command okay.
  ftp> binary
       ^^^^^^  very important, you are getting compressed binary files
  200 Type set to I.
  ftp> ls
       ^^ optional  just to should you what you are getting ('dir' is okay, too)
  200 PORT command okay.
  150 Opening data connection for /bin/ls (128.102.21.2,1118) (0 bytes).
  bib85.Z
  bib86.Z
  226 Transfer complete.
  ^^^^^^^ those two filenames are what you want!
  18 bytes received in 0.2 seconds (0.09 Kbytes/s)
  ftp> mget *
       ^^^^^^ asks for all (star) files
  mget bib85.Z?
  mget bib86.Z?
                ^ you type "y <cr>" or "n <cr>" if you want them.
                NOTE: THIS WILL TAKE SOME TIME.
  ftp> quit
       ^^^^  done
  221 Goodbye.
  eos % # Now you can uncompress bib85.Z, etc.
end script

If you don't have a network guru, send mail to siggraph, not the poster of this
note below.  (Illiterates will type "reply" or "follow-up" to news.  Sorry, I'm
very tired of this. That's why I'm doing this.)  Big thanks are due to Brian
Reid and Jamie Painter (at DEC for this work).  Rick Beach okay'ed ACM
copyrights.  This is not for profit.  Please ACK the above people and
organizations (in particular, Baldev) when citing.  As I hope you can tell, we
are really trying to advance the state of the art in computer graphics.  This
should benefit experts as well as students alike.  It also shows the use of
technologies other than graphics to our (graphics) benefit.

--------

Subject: A little announcement (part 2 of 3)

I described the advantages of searching and reformatting.  I described
anonymous FTP.  This is the way to go if you are a major Internet site like
most universities.  The problem is: what about more casual users, poor people
with small disks?  Well, the files reside of DEC's disk.  Just LEAVE THEM
THERE.  Let Bay Area ACM/SIGGRAPH and Singh maintain them.  Then how do you
access it?  By electronic mail.

A similar system exists at the Argonne National Labs (and AT&T Bell Labs):
netlib numerical software distribution [CACM ref. if you need it].  A similar
set up for benchmarks exists at the NBS (See latest IEEE Computer).  Why not do
this for graphics references?

With a generous donation of cycles and disk space from the Digital Equipment
Corporation (DEC) and some software from CSIL at Stanford we have done just
this.

THERE ARE TWO DANGERS inherent: The bibliography is kind of big.  The second
danger is everybody copying at the same time.

The DEC host which you be copying from is DEC's gateway to the Internet.  It
will be a tragedy to abuse this gateway if every site tried to copy at once.
So let's not abuse this, let's be patient and take our turns.

1) retrieve references only during the weekends or evenings Pacific Daylight or
Standard time.

2) copy on a randomly determined evening of the week.  How?  Flip a coin 3
times (say THT make Head == 0, Tails == 1, this translates to 101 binary or 5
base 10). Using Sunday as 1, make Thursday 5, copy Thursday evening P[SD]T.
(HHH or 000, retry).  If this is confusing, wait for the weekend. AGAIN copy
only in the evenings.

Where, okay here goes the dangerous information:
    send mail to:
    [e-mail]
This can also be
    {your favorite UUCP path}!decwrl!graf-bib-server
or if you work for DEC and have ENET access:
    DECWRL::graf-bib-server

Your mailer should ask for a "Subject:" field.  This is important.  If your
mailer doesn't (and lots don't) ask your system folk about mailrc file or
mh_profiles or how to invoke this field.  Because you should place the keywords
in that subject field.  One special keyword is "help."  You get a short little
description.  Make the first alphanumeric (don't give "years").  Additional
keywords are conjective (and's) causing a smaller and smaller search.  The
contents aren't perfect, but give us time.

Your mail is answered by the server daemon.  It searches and tries to find
relevant cited keywords (up to 6 significant first characters.  Choose
carefully.  Don't ask for all references with "computer graphics."  Hope you
understand why.  Just try "help" as your first keyword unless you know what you
are looking for.  The information comes back in the aforementioned (yesterday)
refer format.

If you don't have a network guru, send mail to siggraph, not the poster of this
note below.  (Illiterates will type "reply" or "follow-up" to news.  Sorry, I'm
very tired of this. That's why I'm doing this.)  Big thanks are due to Brian
Reid and Jamie Painter (at DEC for this work).  Rick Beach okay'ed ACM
copyrights.  This is not for profit.  Please ACK the above people and
organizations (in particular, Baldev) when citing.  As I hope you can tell, we
are really trying to advance the state of the art in computer graphics.  This
should benefit experts as well as students alike.  It also shows the use of
technologies other than graphics to our (graphics) benefit.

Our last note will concern one more way of getting references: just asking for
a floppy (low tech).  We in the Bay Area ACM/SIGGRAPH local group will be
adding to these.  Reference contributions and corrections are welcome.  It's
only possible if we work together to see this through.

--------

From: [e-mail] (Eugene Miya)
Subject: Re: bib notation question

In article <[e-mail]> [e-mail] (Ping Kang Hsiung) writes:
>I got Eugene Miya's bib files over the weekend. There are some
>notations used in the files that I don't understand:
>
>1. Some \(em or (em  in the %J field. What these mean?
>(and why they don't have the closing ")".)
>
>2. In the key field, there are some numbers:
>    %K I3m educational computing
>    %K I3m mechanical engineering computing
>    %K I35 modeling systems
>How do I interpret/use these I3m, I35 numbers?
>
>3. Some acronyms: CGF, CAMP, ISATA. They are not defined in the files.

Oops!  Sorry. I got other mail on this.  I forgot all about them.  The
BACKSLASH macros are troff-isms.  There are tools like deroff to take them out
or r2bib to convert things into bibTeX.  These macros are 4 characters in size
\(em is a slightly longer dash.  They aren't a significant problem, write sed
filter.

The I fields are ACM Classification codes.  You can either get them from ACM
Computing Reviews (blue and white things, that most don't get) or you can get
the hardcopy versions of these bibliographies (they have the CR classification
scheme for graphics).

The acronyms are unfortunately a long term problems.  We can get a table to use
use U. AZ's bib program to fill them out.

I hope you are all finding some use of this stuff.  We NEED people around the
country to help us update this.  There are earlier years.  Also new papers are
being written all the time.  They have to get entered (even finding them is
hard).  I don't deserve the credit, I'm only pissed off that I have to read
queries over and over.  The credit belongs to the crew of Bay Area ACM/SIGGRAPH
working on this project. (other volunteers are welcome: especially key entry
help)

Another gross generalization from

--eugene miya, NASA Ames Research Center, [e-mail]
  ex-Lame-duck Prez. Bay Area ACM/SIGGRAPH
  resident cynic at the Rock of Ages Home for Retired Hackers:
  "Mailers?! HA!", "If my mail does not reach you, please accept my apology."
  {uunet,hplabs,ncar,decwrl,allegra,tektronix}!ames!aurora!eugene
  "Send mail, avoid follow-ups.  If enough, I'll summarize."

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Here is the short form of the present mailing list, showing just email paths
from an ARPA node.  If you want the full list, which includes additional info
and snail mail addresses, drop me a note - Eric Haines

alias    jim_arvo        apollo![e-mail]
alias    al_barr            [e-mail]
alias    brian_barsky        [e-mail]
alias    daniel_bass        [e-mail]
alias    rod_bogart        [e-mail]
alias    wim_bronsvoort        dutrun![e-mail]
alias    at_campbell         [e-mail]
alias    john_chapman        fornax!sfu-cmpt![e-mail]
alias    chuan_chee        [e-mail]
alias    michael_cohen        [e-mail]
alias    jim_ferwerda        [e-mail]
alias    fred_fisher        [e-mail]
alias    john_francis        apollo![e-mail]
alias    phil_getto        [e-mail]
alias    andrew_glassner        [e-mail]
alias    jeff_goldsmith        [e-mail]
alias    chuck_grant        [e-mail]
alias    paul_haeberli        sgi![e-mail]
alias    eric_haines        hpfcla!hpfcrs!eye![e-mail]
alias    roy_hall        [e-mail]
alias    pat_hanrahan        pixar![e-mail]
alias    paul_heckbert        [e-mail]
alias    michael_hohmeyer    [e-mail]
alias    jeff_hultquist        [e-mail]
alias    erik_jansen        dutio![e-mail]
alias    ken_joy            [e-mail]
alias    mike_kaplan        dana![e-mail]
alias    tim_kay            [e-mail]
alias    dave_kirk        [e-mail]
alias    roman_kuchkuda        megatek![e-mail]
alias    george_kyriazis        [e-mail]
alias    david_lister        [e-mail]
alias    pete_litwinowicz    [e-mail]
alias    gray_lorig        [e-mail]
alias    wayne_lytle        [e-mail]
alias    tom_malley        esunix![e-mail]
alias    don_marsh        [e-mail]
alias    michael_natkin        [e-mail]
alias    tim_oconnor        [e-mail]
alias    masataka_ohta        [e-mail]
alias    tom_palmer        [e-mail]
alias    darwyn_peachey        pixar![e-mail]
alias    john_peterson        [e-mail]
alias    frits_post        dutrun![e-mail]
alias    pierre_poulin        [e-mail]
alias    thierry_priol        inria!irisa![e-mail]
alias    panu_rekola        [e-mail]
alias    david_rogers        [e-mail]
alias    linda_roy        [e-mail]
alias    cary_scofield        apollo![e-mail]
alias    pete_segal        [e-mail]
alias    scott_senften        apctrc!bigmac![e-mail]
alias    cliff_shaffer        [e-mail]
alias    susan_spach        [e-mail]
alias    rick_speer        [e-mail]
alias    stephen_spencer        [e-mail]
alias    steve_stepoway        [e-mail]
alias    mike_stevens        apctrc![e-mail]
alias    paul_strauss        [e-mail]
alias    kr_subramanian        [e-mail]
alias    kelvin_thompson        [e-mail]
alias    russ_tuck        [e-mail]
alias    greg_turk        [e-mail]
alias    ben_trumbore        [e-mail]
alias    mark_vandewettering    [e-mail]
alias    jack_van_wijk        ecn![e-mail]
alias    greg_ward        [e-mail]
alias    bob_webber        [e-mail]
alias    lee_westover        [e-mail]
alias    andrew_woo         [e-mail]
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END OF RTNEWS