IPAM Studios
Research in Industrial Projects for Students
Summer Session 2003
Secret Agent : The Lava Lamp of Doom
Quang-Thu (Victoria) Huynh, University of Houston
Kang-Yu Ni, University of California, Santa Barbara
Nemanja Spasojevic, Massachusetts Institute of Technology
Jan Sýkora, Charles University
Dr. Doug Enright, Faculty Mentor/R+D Technical Director
Dr. John Anderson, Industry Mentor/Special Effects Supervisor
1
The Company[CGIMag.com, Cinefex 64, Cinefex 76, Cinefex 81]
Pixar Animation Studios is the industry leader in the creation of original stories in the medium of
computer animation. Pixar has combined creative and technical artistry to create five of the most
successful animated films of all time: Academy Award-winning Toy Story (1995), A Bug’s Life
(1998), Golden-Globe-winner Toy Story 2 (1999), Monsters, Inc. (2001), and this summer’s
animation hit Finding Nemo (2003). Previous to Finding Nemo, Pixar’s four films have earned
more than $1.7 billion at the worldwide box office to date. Pixar is a publicly traded company
(NASDAQ: PIXR) with a current market capitalization of $2.8 billion.
Pixar Animation Studios was founded in 1986 after Steve Jobs purchased the computer graphics
division of Lucasfilm, Ltd. from George Lucas for $10 million. Ed Catmull was named cofounder and chief technology officer. Ed Catmull is now the president of Pixar. Pixar premiered
its first animated short film, Luxo Jr., at the annual SIGGRAPH computer graphics conference.
Luxo Jr., Pixar
For the next nine years Pixar focused on developing the technologies necessary to produce the
first completely computer animated feature film. Pixar released several award winning short
films including Red’s Dream, Tin Toy, and Knick Knack. Pixar continues to use short films to
perfect new technologies. Also during this period of time Pixar produced several computer
animated television commercials. In 1989 Pixar launched its RenderMan product, which has
become the industry standard renderer to produce stunningly realistic imagery. In 1993 the
Academy of Motion Picture Arts and Sciences bestowed a Scientific & Technical Award to the
developers of RenderMan (Loren Carpenter, Rob Cook, Ed Catmull, Tom Porter, Pat Hanrahan,
Tony Apodaca, and Darwyn Peachy). In addition the Board of Governors of the Academy of
Motion Pictures Arts and Sciences honored Ed Catmull, Loren Carpenter, and Rob Cook with an
Academy Award of Merit (Oscar) in 2001 “for significant advancements to the field of
motion picture rendering as exemplified by Pixar’s RenderMan.”
1995 was a monumental year for Pixar. Pixar went public with an initial public offering of 6.9
million shares at $22 per share. The IPO raised $140 million for Pixar and was the largest IPO
of the year, beating out Netscape Communications. Toy Story was released Thanksgiving Day
weekend, marking a milestone in the movie industry as the first fully computer animated feature
film. Toy Story became the highest grossing film of 1995, making over $358 million in
worldwide box office receipts. With the release of Toy Story, the feature film industry was
forever changed, demonstrating the near limitless possibilities of computer animation. The 77
minute movie had 1561 individual shots, all of which progressed down the production pipeline
2
from storyboards to modeling to layout to animation to shading and finally to lighting. Toy Story
generated one terabyte of data and required 800,000 machine hours to render. To deal with the
shear complexity of managing the entire production pipeline, three core proprietary software
systems were developed: Marionette, an animation software system for modeling, animating
and lighting; Ringmaster, a production management software system for scheduling,
coordinating and tracking a computer animation project; and an enhanced version of RenderMan
for high-quality, photo-realistic image synthesis (rendering). Walt Disney Studios distributed Toy
Story as according to their 1991 three feature film distribution agreement with Pixar. John
Lasseter, a former Disney animator and currently creative executive vice president of Pixar,
directed and co-wrote Toy Story. He won an Academy Award for Special Achievement for his
“inspired leadership of the Pixar Toy Story team resulting in the first feature-length computer
animated film.”
In 1997 Pixar released another short film, Geri’s Game, demonstrating Pixar’s ability to produce
realistic skin and cloth effects. Also, Pixar and Walt Disney Studios superseded their previous
feature film agreement, agreeing to produce five original computer-animated feature-length
theatrical motion pictures for distribution by Disney. In addition, Disney and Pixar agreed to cofinance, co-own, co-brand, and share equally in the profits from these films.
The following two years saw Pixar release two new feature films, A Bug’s Life (1998) and Toy
Story 2 (1999). A Bug’s Life had a worldwide box office of $362 million, while Toy Story 2
grossed $483 million worldwide. Toy Story 2 was the first film in history to be entirely created,
mastered, and exhibited digitally. Some of the technological breakthroughs seen in A Bug’s Life
included: a subdivision surface modeling technology; new illumination models for translucent
effects – a critical component in achieving the proper lighting effects seen in the “small” world
inhabited by bugs as compared to the world we inhabit; a proprietary crowd system for
animating hundreds of ants seen in the ant colony; new fire and rain simulators based upon
particle systems; and a state-of-the-art digital editing system.
Toy Story 2 leveraged many of the technologies developed for A Bug’s Life. These technologies
allowed the models of the original Toy Story characters to take on a softer look and were shaded
better as compared to the “plastic” look of the original Toy Story. Also, more controls were
added to the characters to assist the animators. In addition more human characters, including the
chief villain, toy collector Al McWhiggin, are prominently featured in Toy Story 2. As noted by
John Lasseter, “We put a lot of focus and R&D into the creation of humans on this film. Humans
are, by far, the most difficult thing for us to do; and though they worked well in Toy Story, we
wanted them to be better.”[Cinefex 81, p. 34] New skin and hair models and facial articulation
controls with more than 150 fine-tune controls for just Al’s head alone were developed.
Advanced draping and cloth models were used to clothe the characters with loose-fitting
clothing, instead of skin-tight outfits seen in the original Toy Story. Finally a “special effects
team” was formed to deal with effects that didn’t fit within the modeling, animation, and
rendering pipeline. This team generated imaginative solutions for a range of problems including
modeling rocket exhaust, starfields, laser blasts, and reentry shockwaves. The combination of
these technical advances helped Toy Story 2 to become the first animated sequel to outperform
the original at the box office and win a Golden Globe award for Best Picture, Musical, or
Comedy.
3
Pixar released Monsters, Inc. in 2001. The movie became the highest grossing animated film
worldwide and the second highest grossing animated film ever, earning over $100 million at the
domestic box office is just nine days. Monsters, Inc. featured many new technologies, including
a highly advanced hair animation system on the monster Sullivan. Sullivan, who is one of the
main characters in the movie, is also an extremely furry blue and purple monster. The only parts
of Sullivan not covered in fur were the soles of his feet and the palms of his hands. Overall,
more than 2 million hairs needed to be simulated on Sullivan’s body. The fur on Sullivan also
was long, thick fur, in order to provide a more realistic look to Sullivan while he walked. After
extensive R+D work, a specialized ‘keyhair’ control system was implemented which allow the
animators a degree of control over Sullivan’s hair while at the same time reducing the overall
number of hairs to be animated to a reasonable number. Also, a completely new cloth simulation
system was created to animate the T-shirt of Boo, a small girl who befriends the monsters of
Monster’s Inc.
The newest member of the Pixar family of movies, Finding Nemo, opens on May 30, 2003. The
movies welcomes a new host of characters from the young adventurous clownfish Nemo; his
fretful father, Marlin, who goes looking for his lost son; Dory, a forgetful but relentlessly
optimistic Regal Blue Tang; Nigel a peculiar old brown pelican; to Bruce a great white shark.
The movie features the voice talents of Albert Brooks, Ellen DeGeneres, Geoffrey Rush, Barry
Humphries, and others. Pixar is currently in production on The Incredibles (holiday 2004) and
Cars (holiday 2005).
Overall, Pixar Animation Studios and its employees have received more than 100 awards and
nominations for its animated films, commercials and technical contributions. Pixar’s relentless
pursuit of creative technical solutions to the needs of the underlying story have made Pixar’s
films a unique mixture of cutting-edge visual special effects and good old fashion story telling
and have placed them in a special place in film history.
The Industrial Mentor/Special Effects Supervisor
Dr. John Anderson is currently a Senior Scientist at Pixar Animation Studios. Before joining the
special effects industry, John was a professor of atmospheric and oceanic sciences and founding
chair of the computational sciences program at the University of Wisconsin-Madison. In 1998
John joined Industrial Light + Magic as a resident scientist in the areas of procedural effects and
simulations. While at ILM, John created visual special effects for the productions of Jurassic
Park III, Mission to Mars, The Mummy, The Mummy Returns, Pearl Harbor, Star Wars: Episode
I – The Phantom Menace, Star Wars: Episode II – Attack of the Clones, and The Perfect Storm.
John’s work on The Perfect Storm set a new standard in the computer animation of fluids. He
developed a variety of CFD sim tools, allowing for the creation of 100 foot waves and incredibly
stormy seas which were three dimensional in nature.[sgi Feature Archive] In addition to his
ground breaking water effects work, John received a Technical Achievement Award from the
Academy of Motion Pictures, Arts and Sciences for his role in the development of the ILM
Creature Dynamics System, which has been used extensively on a variety of ILM productions
including Star Wars: Epsiode II – Attack of the Clones. In 2001, John left ILM and joined Pixar
to work on a variety of projects including the newest Pixar film, Finding Nemo.
4
Goal
Pixar Animation Studios is producing a short film, Secret Agent : The Lava Lamp of Doom,
featuring Buzz and Woody with a new character, Secret Agent , in a plot to stop the evil Dr.
Goo. Dr. Goo has created a gigantic lava lamp which once fully operational, will cause the toys
in Andy’s room to be cast into an unbreakable hypnotic trance. Consequently, they will be
unable to play with Andy ever again. The fate of the toys in Andy’s room depends upon the
combined abilities of Buzz, Woody and Secret Agent  to stop Dr. Goo’s diabolical plan. In a
key moment in the short, Dr. Goo dreams about his lava lamp fully functioning, to the terror of
the inhabitants of Andy’s room. Since Pixar wishes to explore the possibility of incorporating a
new three dimensional, multiphase liquid sim engine with heating into their production pipeline,
we have been tasked with setting up a stripped down version of the production pipeline to pull
off this shot.
Objectives
We will need to set up a stripped down version of the production pipeline. Part of our work will
involve the modeling, shading and lighting of a lava lamp with and without the waxy “lava”.
Since the accurate calculation of the transport of light through the scene is important in order to
achieve the look we are seeking, we will use a sophisticated free-ware ray tracer.
The
Persistence of Vision Raytracer (POV-Ray) [PoV web site] is able to perform photon-mapping,
which allows the ray tracer to accurately render refractive and reflective caustics in a
photorealistic manner. Photon-mapping for ray tracing was pioneered by Henrik Wann Jensen
[Jensen 2001].
Example of Reflective Caustics (PoV-Ray website)
In order to complete the lava lamp, we will need to animate the motion of the waxy “lava” within
the lamp. To achieve a believable look, we will enhance a pre-existing three dimensional
multiphase liquid sim engine. The sim engine currently solves the three dimensional NavierStokes equations describing the motion of the liquid:
5


   ( v )  0
t





v
   ( v v )  p    [  (v  v T )]  g ,
t

where v  (u, v, w) , is the liquid velocity field; p is the pressure;  is the density;  is the

viscosity; and g is the local gravity field. Note that since we are modeling a multiphase (two
immiscible liquids) flow, the density and viscosity depends upon both space and time. We will
track the movement of the interface through the use of an implicit function, , denoting the
signed distance to the interface, e.g. regions which contain the waxy lava would have <0 while
the surrounding clear liquid would be indicated by >0. The exact location of the interface is be
given by =0. Since the interface moves with the underlying fluid velocity, the evolution
equation for  is given by
 
 v    0.
t
An implicit function (level set) representation of the interface naturally allows for topological
changes to the interface, facilitating the animation of the pinching off and merging together of
blobs of lava commonly seen in a lava lamp.[Osher and Fedkiw 2002] A complete description
of the numerical methods that are used in solving the above equations for engineering style
applications can be found in [Kang et al. 2000, Liu et al. 2000]. Slightly different numerical
techniques are used to solve the above equations in an animation environment, namely faster first
order methods are used to advance the equations in time and a semi-Lagrangian treatment of the
advection terms are used. Also, on the coarse computational grids commonly used in computer
animation, excessive amounts of numerical diffusion in the level set function needs to be
controlled. This can be achieved by using a hybrid particle-level set method to track the motion
of the interface. Further information concerning the use of these methods can be found in [Stam
1999, Foster and Fedkiw 2001, Enright et al. 2002(1), Enright et al. 2002(2)]. The result of
utilizing all of these numerical techniques on a related free surface liquid model can be seen
below, where water is being poured into a glass.
While the previously described sim engine can physically model the motion of a constant density
waxy lava suspended in a liquid of different density, it is unable to capture the hypnotic effect of
the lava lamp, namely the up and down motion of the blobs of lava. If one observes an actual
lava lamp in action, the upwards motion of the lava is due to the heating of the lava from below
by a hot light. As the lava rises, it cools off and descends back towards the bottom of the lamp
6
and the cycle is repeated. Physically, the waxy substance making up the lava has a temperature
dependent density. When heated, the density of the wax is slightly less than the surrounding
liquid, causing it move upwards due to buoyancy. Once the wax cools off, its density is greater
than the surrounding liquid, causing it to fall. So to capture this hypnotic effect, we will need to
add a temperature dependent wax density to our model. We will also need model how the
temperature throughout the lamp changes. Our model should allow for the convective transport,
and diffusion of the temperature through the two immiscible liquids. We will also make the
assumption (the Boussinesq approximation) that the density of each liquid phase is constant in all
terms of the Navier-Stokes equations except for the wax buoyancy term, g , and all other fluid
properties are constant. Taking these assumptions into account we obtain the following equation
for the time evolution of the temperature field,
T 
 v  T  T ,
t
where  is the coefficient of thermal diffusivity. We will take a linear relationship between the
temperature and density for the waxy lava, i.e. the buoyancy term in the Navier-Stokes equations
becomes

 wax (1   (T  Twax )) g ,
where  wax is the constant reference density for the wax at Twax and  is the coefficient of
thermal expansion for the wax.
We will numerically approximate the above temperature transport equation using some of the
technology that has already been used to solve the Navier-Stokes equations. We will get used to
the pre-existing Navier-Stokes solver by simulating boiling water in a box. The data produced
will allow us to set up our rendering pipeline. While getting accustomed to how the sim works,
we will work on creating the algorithms necessary to simulate our lava lamp. We will then test
out our algorithms in two dimensions first to ensure that everything is working to our satisfaction
before proceeding to a three dimensional implementation. Once the 3D sim is working, we will
output frames from the simulation to our rendering pipeline in order to obtain a realistic look for
the lava. From the rendered frames, we will produce an animation. We will use daily animation
review sessions in order to perfect the lava lamp simulation and ultimately produce the best
looking animation possible.
References
[CGIMag.com] Brooker, Darren, “Men in white coats.” Computer Generated Imaging – The
Technology of Entertainment. March 2002. <http://www.cgimag.com/technology/
randd_march02.shtml>
[Cinefex 64] Street, Rita, “Toys Will Be Toys.” Cinefex v. 64 (1995) : 76-91.
[Cinefex 76] Vaz, Mark Cotta, “A Bug’s Life: An Entomological Epic.” Cinefex v. 76 (1999) :
41-44, 49-50, 133-134, 139-140.
[Cinefex 81, p. 34] Shay, Estelle, “Beyond Andy’s Room.” Cinefex v. 81 (2000) : 31-34, 39-40,
127-130.
[sgi Feature Archive] “SGI at ILM: Bringing The Perfect Storm to Life”, September 2000.
< http://www.sgi.com/features/2000/sept/perfect_storm/>
7
[Enright et al. 2002(1)] “Animation and Rendering of Complex Water Surfaces”, ACM
SIGGRAPH 2002, 736-744 (2002).
[Enright et al. 2002(2)] “A Hybrid Particle Level Set Method for Improved Interface Capturing”,
J. Comput. Phys. 183, 83-116 (2002).
[Foster and Fedkiw 2001] “Practical Animation of Liquids”, ACM SIGGRAPH 2001, 15-22
(2001).
[Jensen 2001] Jensen, Henrik Wann, “Realistic Image Synthesis Using Photon Mapping”, AK
Peters (2001).
[Kang et al. 2000] Kang, M., Fedkiw, R., and Liu, X.-D., “A Boundary Condition Capturing
Method for Multiphase Incompressible Flow”, J. Sci. Comput. 15, 323-360 (2000).
[Liu et al. 2000] Liu, X.-D., Fedkiw, R., and Kang, M., “A Boundary Condition Capturing
Method for Poisson’s Equation on Irregular Domain”, J. Comput. Phys. 160, 151-178 (2000).
[Osher and Fedkiw 2002] Osher, S. and Fedkiw, R., “Level Set Methods and Dynamic Implicit
Surfaces”, Springer-Verlag 2002.
[PoV website] <http://www.povray.org>
[Stam 1999] Stam, J., “Stable Fluids”, ACM SIGGRAPH 99, 121-128 (1999).
8