Graphics Reference
In-Depth Information
vior that can be mimicked by using a fixed set of criteria to determine the direction and speed of each entity's
movements at each point in time.
In the Physics properties for boids, you can control the maximum and minimum air speed for the boids, the
maximum and minimum acceleration values, the average amount of personal space each boid gets, all for both
flying and land travel cases, as well as the smoothness of landing, in cases where boids both fly and travel on
land.
By default, boids behavior occurs in 3D, as in the case of birds, fish, and flying insects. To simulate ants or
other swarmlike behaviors that occur over a surface, you can select the Allow Land option.
In a boids system in Blender 2.6, there are two general rules that can be prioritized on the Boid Brain tab.
These are Separate and Flock, which determine the boids' overall desire to move away from each other and
their overall desire to stay close to one another.
Boids have been around since Craig Reynolds first implemented a boids system in 1986 and coined the
term. The idea behind boids was to use a minimal set of parameters and weighted constraints on the motion
of entities in a group to simulate the way living things behave when moving in groups. When these simple
rules are applied to individual boid entities' motion, a complex pattern emerges. Craig Reynolds's boids
page is an excellent resource for learning more about boids and similar emergent behaviors. You can find
that page at
www.red3d.com/cwr/boids
.
Setting Up the Boids System
Setting up a basic boids system is simple. As with other particle systems, it is necessary to create an emitter
(boids themselves can be of either Emitter or Reactor particle types). Set the Emit From value to Random and
choose Boids from the drop-down menu on the Physics tab. That is all there is to it to create a simple swarm of
particles.
As you can see if you press Alt+A with this setup, the boids emanate outward from the emitter object in
indirect, wigglytrajectories. Ateachstep,theirvelocity isrecalculated toenable theboidstocontinue theircur-
rent course, subject to the default constraints. Because the Crowd constraint makes it a priority for the boids to
avoidcolliding witheachother,andtherearenogoals,predators,ordeflection objects toinfluence theirtraject-
ories, they tend to move farther and farther away from each other.
Working with Goals and Predators
Goals and predators are created by placing an object on the same layer as the boids system with a Spherical
force field. A negative value in the force field means the object is a goal, and a positive value in the force field
means the object is a predator. When a goal force is present, the boids head straight toward the goal after being
emitted from the emitter mesh. After they reach the goal, they circle back and pass through it again and again
as long as they continue to be alive. When a predator is set up, the boids make a wide arc around the predator
object and circle back to meet the goal object.
Predators andgoal objects can bemoved and animated, andthe boids respond inreal time, making their way
around one side and then the other as the predator passes. Both predators and goals can be animated, resulting
in the expected boids' behavior. If you've ever been chased by a swarm of bees, you already know something
about how boids behave when pursuing a moving goal.
