8

106 Chapter 11: Space Warps and Particle Systems
1. Event display
2. Particle diagram
3. Global event
4. Birth event
5. De pot
Toaddanactiontothe particle diagram ,youdrag
it to the
event display from the depot (the area at
the bottom of t he Particle View dialog). If you drag
an act ion to an event, you can add it to the event
or replace an existing action, depending on where
you drop it. If you drop it in an empty area, it
creates a new event. Then, to customize the action,
you click its event entry, and then edit its settings
in the par ameters panel at the side of Particle View.
To add complexity to the particle system, you can
add a test to an event, and then wire the test to
another event. You can adjust the test p a rameters
toaffectparticlebehavior,aswellasdetermine
whether specific conditions exist. When particles
meet these conditions, they become eligible for
redirection to the next event.
Particle Flow provides a number of tools for
determining where in the system particles
currently reside, including the ability to change
particle color and shape on an event-by-event
basis. You c an also easily enable and disable
actions and events, and determine the number
of part icles in each event. To speed up checking
particle activ ity at different times during the
animation, you c an cache particle motion in
memory. Using these tools, plus the ability to
create custom actions with scripting, you can
create part icle systems of a level of sophistication
previously unachievable.
The Life of a Par ticle
Another way of looking at Particle Flow is from
the perspective o f an individual particle. Each
particle first comes into existence, or is
born ,via
the
Birth operator (p age 2–139) ,whichletsyou
specify when to start and stop creating particles,
and how many to create.
The particles first appear at an object called an
emitter. By defau lt, the emitter is the Particle
Flow source icon using the
P osition Icon operator
(page 2–143)
,butyoucanalternativelyusethe
Position Object operator (page 2–144) to specify
thatparticlesshouldbebornonthesurfaceofor
within any mesh object in the scene.
After being born, particles can remain stationar y
at the emission point, or start moving in two
different ways. First, they can move, physically,
within the scene at a speed and in a direct ion
specified by various actions. These are typically
Speed operators, but other actions can also affect
particle motion, including
Spin (page 2–150) and
Find Target (page 2–214) . In addition, you can
use the
Force operator (page 2–200) to affect their
motion with outside forces.