9

810 Chapter 13: reactor
details, see World rollout > Fracture Penetrations
group (page 2–773).
Simulation group
These controls are available only with the Havok 3
engine.
The first lets you choose how reactor computes the
simulation:
•
Discrete—reactor checks for collisions only at
the beginning and end of each simulation step .
This is faster but less accurate.
•
Continuous—reactor checks for collisions
constantly, throughout each step. This is the
default choice, and results in slower but highly
accurate simulations. This option significantly
reduces the chances of m issed collisions.
M a x L in ea r V el . —The assumed maximum linear
velocity for all bodies.
This does not set objects’ linear velocity. If, later
on, a rigid body’s velocity significantly exceeds
this value, it might tunnel through other objects
even if its Qualit y property is set to Critical.
Thedefaultvalueis200meters/second. This
value is used during continuous simulations by
the collision solver to optimize the simulation, so
if it can assume a maximum linear velocity it can
discard several cases and get a solution faster.
Stiffness—The hardness of the constraints in the
scene.
Use this parameter to configure the dynamics
solver. When constraints used in the scene are
very hard or stiff, set this to Hard; the S of t or
Medium setting works most other cases. Setting
Stiffness to Soft can lead to unstable solutions if
the constraints are too stiff.
Tip: Another way to reduce the stiffness of the
simulation is by lowering t he Strength value of
constraints, thus relaxing the constraints.
Collisions R ollout
Utility panel > reactor > Collisions rollout
These sett ings let you store collision details f rom
your scene, and enable and disable collision
detection for specific pairs of objects . Pairs of
objectswithcollisionsdisabledpassthrougheach
other during the simulation. Disabling collisions
canbeusefulwhenyouhaveobjectsthatare
attached together, such as the wheels of a car and
its chassis. This means reactor doesn’t check for
every small collision b etween the objects, which
can slow down the simulation.
Interfa ce
Collisions rollout
Store Collisions—See Storing and Accessing
Collisions (page 2–774).