2009

■ Prismatic constraint on page 3982
■ Rag Doll constraint on page 3948
Common Properties
The following properties are shared by all cooperative constraints:
Strength and Tau
These properties govern the impulses applied to the constraint's bodies in
order to maintain the constraint, and so how strongly the constraint works
to restrict their movement.
Strength The constraint applies an impulse to each attached body in order
to maintain the constraint, based on the relative velocities of the attached
bodies. The Strength parameter governs the percentage of this impulse the
constraint will apply to each object. If this is sufficient, then the constraint
is maintained.
Tau If the constraint drifts; that is, if the attached objects reach a state where
the constraint isn’t satisfied, then reactor applies a corrective force to rectify
this drift. An impulse is calculated to rectify the drift in a constraint system;
the Tau parameter governs the percentage of the corrective impulse the
constraint applies to each object.
NOTE Tau is unavailable in the Havok 3 engine.
Breakable Constraints
A breakable constraint stops working when a specified threshold is exceeded.
For example, you could use a breakable constraint to make a door that flies
off its hinges when kicked hard enough. You make a constraint breakable by
turning on its Breakable check box. It then ceases to exert impulses on its
constrained bodies if its limits are exceeded during the simulation.
3944 | Chapter 16 reactor