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Part X: Dynamic Animation
FIGURE 43.10
Animating these falling donuts, simulated as soft body objects, was easy with reactor.

Constraining Objects
Constraints are ways to limit the amount of motion that an object can do. Using constraints can help con-
trol objects in the scene as they interact with other objects. Perhaps the simplest constraint isn’t a constraint
at all. If you enable the Unyielding option in the Property Editor, the rigid body is set so that it won’t move
and is a good option for the ground plane. It also allows hand-keyed animated objects to interact with rigid
body objects instead of relying on the dynamics engine.
Other constraints are found in the Animation ➪ reactor ➪ Create Objects menu and consist of Constraint
Solver, Rag Doll Constraint, Hinge Constraint, Point-Point Constraint, Prismatic Constraint, Car-Wheel
Constraint, and Point-Path Constraint, as listed in Table 43.4.

After a Constraint object is added to the scene, you can select the objects that will be included as child and
parent objects using the buttons in the Properties rollout. The Properties rollout also includes buttons to
align the constraint to the Child Body, Parent Body, Child Space, or Parent Space. For each constraint, you
can set the Strength and Tau of the connection. This determines how strong the link is and how easily bro-
ken. In addition to the Strength and Tau values, you can set Limits and allow the hinge to be Breakable
under a defined Linear or Angular force value. The Threshold value defines the breakability of the con-
straint. Higher Threshold values make it less likely to break. The Threshold value works only with reactor
version 3.

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