FROM THE back of a speeding truck a dachshund stretches out a paw to help his
friend Woody the cowboy, chasing behind in a radio controlled car. Suddenly the
truck surges forward and the dog鈥檚 body, made from a 鈥淪linky鈥� wire coil,
stretches to its limits. Woody loses his grip, and SlinkyDog鈥檚 spring-like body
recoils with a snap.
The scene is from Disney鈥檚 latest blockbuster movie Toy Story, which
opened in Britain last month. It is a film virtually untouched by human hand.
The behaviour of SlinkyDog鈥檚 body as it stretches and ripples was not drawn by
an artist with a pencil, but by mathematical models. Toy Story, which
tells how two lost toys try to find their way home, is the first full-length
film made entirely inside a computer. All the characters, sets, lighting and
action were brought to life in silicon.
Previous films hailed as 鈥渓andmarks鈥� in computer animation, such as
Tron and Who Framed Roger Rabbit, used computer graphics to show
off the latest special effects and make the audience gasp at the power of the
technology. What sets Toy Story apart from these is that the director,
John Lasseter, set out to make the animation more like the quirky realism of
traditional hand-drawn cartoons. That slightly lopsided, asymmetrical feel of
cartoons where wooden gates are gnarled, dogs slink and their owners lope had
never been created on computer in such detail and at such length.
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In touch with reality
To achieve this 鈥渉eightened reality鈥�, Lasseter called on all the resources of
his employer, the computer graphics company Pixar, which used to be a part of
Lucasfilm. By the time Toy Story had its first preview, the director
and his company had created a variety of new programs, and put together a
formidable array of computers for storing and processing the digital images.
Pixar claims that it dedicated the equivalent of 30 Cray supercomputers to
producing the film鈥攎ore power than for any previous Hollywood
computer-generated animation.
For Lasseter and Bill Reeves, his long-time colleague and chief computer
scientist, one of the most difficult tasks was giving the characters the spark
of life. 鈥淲oody may only be a toy, but he had to be our main emotional guide,鈥�
says Reeves. 鈥淗e had to have facial expressions as seemingly human as a
live-action actor. And he had to demonstrate every emotion under the Sun. It
isn鈥檛 enough just to give the character anatomy. You鈥檝e got to give it acting
power.鈥� This meant having precise control over the characters鈥檓ovements.
The main characters started life as clay models which Reeves鈥檚 team converted
into a digitised form. To do this they dragged a pen-shaped device know as a
鈥渟pace digitiser position sensor鈥� across the surface of each clay model. The
sensor emits a radio signal which is picked up by three receivers around the
model and converted by computer into a series of three-dimensional
coordinates.
A program called Marionette then uses these coordinates to recreate a digital
image shaped like the original model.
Next the animators drew in a skeleton to show how joints and limbs should
move. SlinkyDog鈥檚 skeleton was a coil. Pixar鈥檚 programmers translated the
animators鈥� ideas of how the coil should stretch and contract into a series of
mathematical equations which included fictional values for properties such as
mass and elasticity. These formed the heart of a set of 鈥渁rticulation controls鈥�.
With these software controls stored in a computer, the animators could place
SlinkyDog in any position and they made the body respond appropriately.
Puppet on a string
Reeves describes these controls as the computerised equivalent of a
puppeteer鈥檚 strings. But the creators of Toy Story wanted their
characters to have fluid, believable movements, not the jerky movements of a
marionette. This meant each character needed a huge number of strings. Woody,
for example, had 200 programs written to control his face. These described the
surface of his skin and simulated muscles so that the character appeared to
talk, gasp and smile in a lifelike way. A further 500 articulation controls
animated his body. Woody is 50 000 lines of computer code.
Many of the programs used in making Toy Story were extensions of
software that already existed. But the program that produced a seamless paint
job for the characters is entirely new. 鈥淯nwrap鈥� enables an artist to strip off
the surface of a three-dimensional model and flatten it out, much like a
Mercator projection of the Earth鈥檚 surface. The artist then digitally paints the
flat surface before wrapping it back onto the model.
While the animators constructed the characters, other artists built digital
sets. One of the shortcomings of computer graphics has been that, because they
are the product of mathematics, they produce unrealistically precise and clean
images. 鈥淐omputers still deal best with stiff, shiny objects,鈥� says Lasseter.
This is the sort of imagery he wanted to avoid. So again the programmers were
called in to write software that would make the room belonging to Sid鈥攖he
film鈥檚 bad guy鈥攍ook like 鈥渢oy hell鈥�. The room needed what Lasseter
describes as 鈥渁n ominous atmosphere of abuse and neglect鈥� to fit in with Sid鈥檚
image as the neighbour who takes perverse pleasure in pulling apart toys and
reassembling them as mutant playthings.
To achieve this effect, the programmers wrote 鈥渟haders鈥�, programs that
specify the colour, reflectivity and bumpiness of surfaces. For Sid鈥檚 window
ledge, the shader consisted of five layers of programs that reproduced the wood
grain, a hand-painted undercoat, a topcoat, software that specified where and to
what depth these were chipped, and a coat of dirt, stains and scratches. 鈥淭he
process of creating a realistic shader mimics the process of time,鈥� says Reeves.
鈥淚t creates, it grows, it ages objects.鈥�
With the characters and sets ready, Lasseter and Reeves started shooting. The
story line and art direction were plotted in minute detail on 25 000
storyboards, including sketches of what a scene should look like and what the
actors would say. 鈥淚n effect we edited the film before we started the
animation,鈥� says Lasseter. Then the actors were called in to do the voice-overs.
Tom Hanks played Woody and the comic Tim Allen played Buzz Lightyear, a toy
astronaut.
This dialogue became the animators鈥� inspiration and guide. The 200 programs
that simulated movement in Woody鈥檚 face enabled him to express a range of
complex emotions. Even though the programmers could mimic a flesh-and-blood
face, Lasseter urged them to aim for a stylised reality. 鈥淚 said it was not
essential to get the mouth shape exactly right. It鈥檚 the acting and the lip
synch that counts,鈥� he says. Despite this compromise, it took up to a week to
animate 8 seconds of dialogue.
The eyes to the right
Lasseter enhanced the feeling of reality by using nonverbal cues such as
posture, gesture and facial expressions to back up what the characters said.
鈥淭he eyes more than anything else give life to a toy,鈥� says Lasseter. 鈥淭he angle
of a blink, how far the pupils go off to the side when a character is trying to
peek at something without being noticed, convey a sense of presence better than
any other element.鈥�
Once the animated characters had played their parts on a blank computer
screen, it was time to put them on the 3D sets, which were downloaded from disc.
The main tasks here were to decide on the lighting and camera angle. Because the
lights and cameras were all virtual, the director had all the advantages of a
real-life sound stage without the grips, gofers and truckloads of equipment. The
virtual camera can view the set from any angle鈥攃lose up or zoom鈥攁nd
it can move between shots to enhance the sequence of action. Every position is
represented as a chunk of computer code.
The lighting team used up to 100 virtual lights for each scene. Again, these
existed only as lines of code specifying the position of each lamp, the
intensity and colour of its light, and how that light spread. In one scene, for
example, virtual sunlight shines through two windows and reflects off numerous
surfaces, including the furniture and Buzz鈥檚 helmet. To intensify the effects,
the lighting crew often cheated. 鈥淭hroughout the lighting process, the challenge
is to make the scenes look real but with the visual richness that is not
necessarily limited by realism,鈥� says Reeves.
Finally, all the characters, scenery and lighting were combined. This
process, known as rendering, melds the data from the articulation, graphics,
lighting and camera programs. For example, it takes the lighting details in
conjunction with information about the objects and characters in a
scene鈥攖heir colours, surface reflectivity and so on鈥攁nd uses it to
work out how the final images should look, including how an object will cast a
shadow. The entire scene is viewed from the angle specified by the camera
program.
Although rendering is well established in computer animation, this posed some
of the greatest problems. The 77-minute movie needed 110 000 frames, each of
which took between 2 and 15 hours to render. On one machine the task would have
taken more than 40 years. So Pixar put together 117 Sun work stations containing
about 300 processors which ran 24 hours a day, seven days a week, during
production.
High-resolution digital images produce huge files. A single rendered frame
consumes 5 megabytes of disc space. To store the digital version of the film,
Pixar built a 鈥渄isc farm鈥� of 50 machines with a total memory capacity of 260
gigabytes. Pixar developed its own software, called Ringmaster, to coordinate
these machines. Ringmaster calculates the most efficient way to distribute the
processing across all the work stations.
The entire film is stored on hard discs at Pixar鈥檚 California offices. The
digital images had to be transferred to film before Toy Story could go
on general release. This, of course, doesn鈥檛 mean that Pixar has abandoned its
digital archive. Toy Story, the director鈥檚 cut, the CD-ROM and the Web
site are only a few hundred lines of computer code away.