Fishes
, the superclass Pisces, are an important species of
animals that exhibit elaborate behaviors both as individuals and in
groups. Most people find them fascinating to watch. Their behavioral
complexity is generally higher than that of most insects, but lower
than that of most mammals. Since realistic, automatic animation of
the locomotion of humans and other advanced animals remains elusive, a
visually convincing virtual marine world presents an excellent choice
for validating our approach to animating natural ecosystems.
Imagine a virtual marine world inhabited by a variety of realistic fishes. In the presence of underwater currents, the fishes employ their muscles and fins to swim gracefully around static obstacles and among moving aquatic plants and other fishes. They autonomously explore their dynamic world in search of food. Large, hungry predator fishes stalk smaller prey fishes in the deceptively peaceful habitat. Prey fishes swim around contentedly until the sight of predators compels them to take evasive action. When a dangerous predator appears in the distance, similar species of prey form schools to improve their chances of survival. As the predator nears a school, the fishes scatter in terror. A chase ensues in which the predator selects victims and consumes them until satiated. Some species of fishes seem untroubled by predators. They find comfortable niches and feed on floating plankton when they get hungry. Driven by healthy libidos, they perform elaborate courtship rituals to secure mates.
We have successfully applied the basic methodology outlined in the previous section to develop an animation framework within whose scope fall all of the above complex patterns of behavior, and many more, without any keyframing. We aim to make the colorfully textured denizens of the fish world as realistic as the ``Jurassic Park'' dinosaurs. Yet, unlike the dinosaurs, each fish in this community exists as an independent, self-governing virtual agent. None of the actions is keyframed or scripted in advance, but is instead driven by the individual perceptions and internal desires of the artificial fishes. Each fish attends to a hierarchy of needs, with its brain considering the urgency of each situation. When the animation program is initiated, the operator specifies only which fish are present and their initial conditions. Upon starting the artificial life simulation, the creatures proceed to act of their own accord.
The visual results of this work are illustrated by two animations.
Our 1993 animation ``Go Fish!'' [Tu, Terzopoulos and Fiume1993] shows a colorful
variety of artificial fishes foraging in translucent water. A sharp
hook on a line descends towards the hungry fishes and attracts them.
A hapless fish, the first to bite the bait, is caught and drawn to the
surface. The color plates show stills from our 1994 animation ``The
Undersea World of Jack Cousto'' [Tu, Grzeszczuk and Terzopoulos1995].
Fig. 
shows a variety of animated artificial
fishes. The reddish fish are engaged in a mating ritual, the large,
dark colored fish is a predator hunting for small prey, the remaining
fishes are feeding on plankton (white dots). Dynamic seaweeds grow
from the ocean bed and sway in the current. In
Fig. , the large male in the foreground is
courtship dancing with the female (top). The prey fish in the
background are engaging in schooling behavior, a common subterfuge for
avoiding predators. Fig. shows a shark stalking the
school. The detailed motions of the artificial fishes emulate the
complexity and unpredictability of movement of their natural
counterparts, and this enhances the visual beauty of the animations.
Figure: Artificial fishes in their physics-based world.
Figure: Mating behavior. Female (top) is courted by larger male.
Figure: Predator shark stalking school of prey fish.
| Xiaoyuan Tu | January 1996 |