2009

1. Particle immediately after creation, with no speed.
2. The Speed operator sets the particle in motion.
3. The particle continues moving until acted upon by another action.
The second way that particles move is logically, from event to event through
the particle diagram, as constructed in Particle View on page 2811. Each event
can contain any number of operators that can affect, in addition to motion,
a particle's surface appearance, its shape and size, and others.
The particles start out in the birth event, which typically is the first event after
the global event. During a particle's residence in an event, Particle Flow
evaluates each of the event's actions from top to bottom, once per integration
step, and makes any applicable changes to the particle. If the event contains
a test, Particle Flow determines whether the particle tests True for the test's
parameters, such as whether it has collided with an object in the scene. If it
does, and if the test is wired to another event, Particle Flow sends the particle
to the next event. If it doesn't, the particle remains in the current event, and
may be further acted upon by its operators and tests. Thus, each particle exists
in only one event at a time.
An action in an event can change the particle shape (1), or the particle spin (2), or
spawn new particles (3).
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