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Tests
The basic function of a test in Particle Flow is to determine whether particles
satisfy one or more conditions, and if so, make them available for sending to
another event. When a particle passes a test, it is said to “test True.” To send
eligible particles to another event, you must wire the test to that event. Particles
that don't pass the test (“test False”) remain in the event and are repeatedly
subjected to its operators and tests. Or, if the test isn't wired to another event,
all particles remain in the event. You can use several tests in an event; the
first test checks all particles in the event, and each test after the first checks
only particles that remain in the event.
One test, Spawn, doesn't actually perform a test, but simply creates new
particles from existing ones, and sets the new particles' test result to True so
they're automatically eligible for redirection to another event. And the Send
Out test simply sends all particles to the next event by default.
Some tests can also serve as operators, in that they contain parameters that
modify particle behavior. If you don't wire a test to another event, it functions
only as an operator; the test aspect doesn't affect particle flow.
TIP Always place a test at the end of its event, unless you have specific reasons
for placing it elsewhere. That way, all preceding actions can take effect during
each integration step before the test is evaluated.
All the tests are grouped together in the Particle View depot, and are listed in
alphabetical order. All test icons are the same: a yellow diamond containing
a simplified diagram of an electrical switch.
2956 | Chapter 14 Space Warps and Particle Systems