9

Cooperative Constraints 735
Cooper a tiv e Cons tr ai nts
Cooperativeconstraintsaremorestablethan
simple constraints (page 2–727),butcanbe
more computationally expensive to simulate.
Foracooperativeconstrainttotakepartinthe
simulation, you first need to add it to a Constraint
Solver (page 2–736). The s olver acts as a container
for the cooperative constraint in a particular Rigid
Body Collection, and performs all the calculations
necessary for the constraints to work together.
The following constrain t types are cooperative
constraints:
• Hinge (page 2–747)
• Point-Point constraint (page 2–750)
• Point-Path constraint (page 2–762)
• Car-Wheel constraint (page 2–757)
• Prismatic constraint (page 2–754)
• Rag Doll constraint (page 2–737)
Common Pr oper ti es
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 b o dy in order to maintain the
constraint, based on the relative velocities of the
attached bodies. The Strength parameter governs
thepercentageofthisimpulsetheconstraintwill
apply to e ach 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.
Break able 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.
Youmakeaconstraintbreakablebyturningon
its Breakable check b ox. It then ceases to exert
impulses on its constrained bodies if its limits are
exceeded during the simulation.
B r ea kab l e—Tur n on to m ake the constr aint
breakable.
TheLinearandAngularparametersapplyonlyto
Havok 1, and the Theshold p arameter applies only
to Havok 3.
Linear—The maximum linear impulse the
breakable constrai nt can apply before it breaks.
Available in Havok 1 only.
Angular—The m aximum angular impulse the
breakable constrai nt can apply before it breaks.
Available in Havok 1 only.
Threshold—A generic impulse parameter that
governs t he overall breakability of the constraint.
Larger values make the constraint harder to break.
Available in Havok 3 only.