Fundamentals of Computer Graphics, 3rd Edition

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17

Michael Ashikhmin

Computer Animation

Animation is derived from the Latin anima and means the act, process, or result

of imparting life, interest, spirit, motion, or activity. Motion is a defining property

of life and much of the true art of animation is about how to tell a story, show

emotion, or even express subtle details of human character through motion. A

computer is a secondary tool for achieving these goals—it is a tool which a skillful

animator can use to help get the result he wants faster and without concentrating

on technicalities in which he is not interested. Animation without computers,

which is now often called “traditional” animation, has a long and rich history of

its own which is continuously being written by hundreds of people still active in

this art. As in any established field, some time-tested rules have been crystallized

which give general high-level guidance to how certain things should be done and

what should be avoided. These principles of traditional animation apply equally

to computer animation, and we will discuss some of them below.

The computer, however, is more than just a tool. In addition to making the

animator’s main task less tedious, computers also add some truly unique abil-

ities that were simply not available or were extremely difficult to obtain be-

fore. Modern modeling tools allow the relatively easy creation of detailed three-

dimensional models, rendering algorithms can produce an impressive range of

appearances, from fully photorealistic to highly stylized, powerful numerical sim-

ulation algorithms can help to produce desired physics-based motion for partic-

ularly hard to animate objects, and motion capture systems give the ability to

record and use real-life motion. These developments led to an exploding use

of computer animation techniques in motion pictures and commercials, automo-

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414 17. Computer Animation

tive design and architecture, medicine and scientific research among many other

areas. Completely new domains and applications have also appeared including

fully computer-animated feature films, virtual/augmented reality systems and, of

course, computer games.

Other chapters of this book cover many of the developments mentioned above

(for example, geometric modeling and rendering) more directly. Here, we will

provide an overview only of techniques and algorithms directly used to create and

manipulate motion. In particular, we will loosely distinguish and briefly describe

four main computer animation approaches:

• Keyframing gives the most direct control to the animator who provides nec-

essary data at some moments in time and the computer fills in the rest.

• Procedural animation involves specially designed, often empirical, mathe-

matical functions and procedures whose output resembles some particular

motion.

• Physics-based techniques solve differential equation of motion.

• Motion capture uses special equipment or techniques to record real-world

motion and then transfers this motion into that of computer models.

We do not touch upon the artistic side of the field at all here. In general, we can

not possibly do more here than just scratch the surface of the fascinating subject

of creating motion with a computer. We hope that readers truly interested in the

subject will continue their journey well beyond the material of this chapter.

17.1 Principles of Animation

In his seminal 1987 SIGGRAPH paper (Lasseter, 1987), John Lasseter brought

key principles developed as early as the 1930’s by traditional animators of Walt

Disney studios to the attention of the then-fledgling computer animation com-

munity. Twelve principles were mentioned: squash and stretch; timing; antic-

ipation; follow through and overlapping action; slow-in and slow-out; staging;

arcs; secondary action; straight-ahead and pose-to-pose action; exaggeration;

solid drawing skill; appeal. Almost two decades later, these time-tested rules,

which can make a difference between a natural and entertaining animation and a

mechanistic-looking and boring one, are as important as ever. For computer ani-

mation, in addition, it is very important to balance control and flexibility given to

the animator with the full advantage of the computer’s abilities. Although these

principles are widely known, many factors affect how much attention is being