GRAPHIC GEMS II Edited by DAVID KIRK
i
GRAPHIC GEMS II Edited by DAVID KIRK
This is a volume in
The Graphics Gems Series
A Collection of Practical Techniques
for the Computer Graphics Programmer
Series Editor
Andrew S. Glassner
Xerox Palo Alto Research Center
Palo Alto, Califomia
ii
GRAPHIC GEMS II Edited by DAVID KIRK
G
RAPHICS
III
edited by
DAVID KIRK
California Institute of Technology
Computer Graphics Laboratory
Computer Graphics Laboratory
Pasadena, California
Pasadena, California
AP PROFESSIONAL
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iii
RAPHICS
G
EMS
EMS
III
EMS
California Institute of Technology
Computer Graphics Laboratory
Copyright (c) 1995 by Academic Press, Inc.
GRAPHICS GEMS copyright (c) 1990 by Academic Press, Inc.
GRAPHICS GEMS II copyright (c) 1991 by Academic Press, Inc.
GRAPHICS GEMS III copyright (c) 1992 by Academic Press, Inc.
QUICK REFERENCE TO COMPUTER GRAPHICS TERMS
copyright (c) 1993 by Academic Press, Inc.
RADIOSITY AND REALISTIC IMAGE SYNTHESIS
copyright (c) 1993 by Academic Press Inc.
VIRTUAL REALITY APPLICATIONS AND EXPLORATIONS
copyright (c) 1993 by Academic Press Inc.
All rights reserved.
No part of this product may be reproduced or transmitted in any form or by any
means, electronic or mechanical, including input into or storage in any information
system, other than for uses specified in the License Agreement, without permission
in writing from the publisher.
Except where credited to another source, the C and C++ Code may be used freely to
modify or create programs that are for personal use or commercial distribution.
Produced in the United States of America
ISBN 0-12-059756-X
GRAPHIC GEMS II Edited by DAVID KIRK
About the Cover
1992 The VALIS Group, RenderMan
Ò
image created by The VALIS Group,
reprinted from Graphics Gems III, edited by David Kirk, copyright
Ó
Ó
1992 Academic Press, Inc. All
, shaders literally endow everything in the image with their own characteristic
appearances, from the lights and the objects to the atmosphere. The shaders themselves are
procedural descriptions of a material or other phenomenon written in the RenderMan
Ò
Shading
Language. We did not use any scanned textures or 2-D paint retouching software to produce
this picture.
Where appropriate, we used existing shaders on the surfaces of objects in this picture, taken from
our commercially available VG Shaders
TM
+ VG Looks
TM
libraries. For example,we used Hewn Stone
Masonry (Volume 3) to create the temple wall and well; Stone Aggregate (Volume 3) for the
jungle-floor, and polished metal (Volume 2) for the gold dish. In addition to these and other existing
shaders, several new shaders were created for this image. The custom shaders include those for the
banana leaves, the steamy jungle atmosphere, the well vapor, and the forest canopy dappled lighting
effect.
Shaders also allowed us to do more with the surfaces than merely effect the way they are colored.
In RenderMan
Ò
, shaders can transform simple surfaces into more complex forms by moving the
surface geometry to add dimension and realistic detail. Using shaders we turned a cylinder into a
stone well, spheres into boulders and rocks, and a flat horizontal plane into a jungle floor made up of
stones and pebbles.
Similarly, we altered the surface opacity to create holes in surfaces. In this instance, we produced
the ragged edges of the banana leaves and the well vapor by applying our custom RenderMan
Ò
,
shaders to flat pieces of geometry before rendering with PhotoRealistic RenderMan
Ò
.
Initially, this image was composed at a screen resolution of 450
600 pixels on a MacIIfx using
Showplace. Rendering was done transparently over the network on a Unix
Ò
workstation using Pixar’s
NetRenderMan
TM
. This configuration afforded us the convenience and flexibility of using a Mac for
design and a workstation for quick rendering and preview during the picture-making process.
Once the design was complete, the final version of the image was rendered at 2250
´
3000 pixel
resolution. The final rendering of this image was done on a 486 PC/DOS machine with Truevision’s
RenderPak
TM
and Horizon860
TM
card containing 32 MBytes of RAM.
During the rendering process, RenderMan
´
Ò
separates shadows into a temporary file called a
2k shadow map for this image was rendered in less than an hour. However,
using shaders to alter the surface geometry increases rendering time and memory requirements
dramatically. As a result, we had to divide the image into 64 separate pieces and render each one
individually. The total rendering time for all 64 pieces was 41.7 hours. Once these were computed,
´
v
Cover image copyright
rights reserved.
This cover image evolved out of a team effort between The VALIS Group, Andrew Glassner,
Academic Press, and the generous cooperation and sponsorship of the folks at Pixar. Special thanks
go to Tony Apodaca at Pixar for post-processing the gems in this picture using advanced Render-
Man
Ò
techniques. The entire cover image was created using RenderMan
Ò
from Pixar.
We saw the
Graphics Gems III
cover as both an aesthetic challenge and an opportunity to
demonstrate the kind of images that can be rendered with VALIS’ products and Pixar ’s RenderMan
Ò
.
Given the time constraints, all of the geometry had to be kept as simple as possible so as not to
require any complex and lengthy modeling efforts. Since RenderMan
Ò
works best when the geometric
entities used in a 3-D scene are described by high order surfaces, most of the objects consisted of
surfaces made up of quadric primitives and bicubic patches. Andrew’s gem data and the Archimedean
solids from the VALIS Prime RIB
TM
library are-the only polygonal objects in the picture.
Once all of the objects were defined, we used Pixar’s Showplace
TM
, a 3-D scene arranging
application on the Mac, to position the objects and compose the scene. Showplace also allowed us to
position the camera and the standard light sources as well as attach shaders to the objects
In RenderMan
Ò
shadow map. The 2k
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