9

142 Chapter 11: Space Warps and Particle Systems
Tests
Most tests in Particle Flow function only as tests.
At each integration step, they check each par ticle
for the specified conditions, and then return the
test result: True or False. So, as tests, they work
on a continuous basis. For example, Age Test
checks each particle’s age at every integration step,
because par ticles might not reach the specified age
until remaining in the event for a wh i le, and a lso
because another action in the event might change
or reset particle age.
The principal exceptions to this are the Split tests,
whichtesteachparticleonlywhenitfirstenters
the event. That is, a Split test splits the particle
stream only once for each particle that enters the
event. Any par ticles that remain in the event are
not subject again to being split off from the stream
bythesametest.Also,theSendOuttestperforms
no test, but simply moves p articles along to the
next event.
Sometestsalsofunctionasoperators,inthatthey
directly affect particle behavior. These are the ones
listed here, and the specified time fr ame is related
to the operator functionality, not the test.
Test
Time Frame
Collision Spawn
Continuous
Find Target
Continuous
Go To Rotation Continuous
Script Test
Depends on script
Spawn Continuous, except once
with Once
Oper ator s
Theoperatoristhebasicelementoftheparticle
system; you combine operators into events to
specify the particles’ characteristics over a given
period of time. Operators let you describe particle
speed and direction, shape, appearance, and more.
The operators reside in two groups in the Particle
View depot, and within each group appear in
alphabetical order . Each operator’s icon has a blue
background, except for the Birth operators, which
have a green background. The first group contains
operators that directly affect particle b ehavior,
such as transformation.
The second group, found at the end of the depot
listing, contains four operators that serve more
of a utility function: Cache, for optimizing
particle-system playback; Display, for determining
how particles appear in the viewports; Notes, for
adding comments; and Render, for specifying
render-time characteristics.
TheParticleFlowoperatorsintheParticleViewdepot
The primary operators in Part icle Flow are:
Birth Operator (page 2–143)
Birth Script Operator (page 2–145)
Delete Operator (page 2–146)
Force Operator (page 2–204)
Keep Apart Operator (page 2–172)
Mapping O perator (page 2–195)
Material Dy namic Operator (page 2–191)