2009

4. Birth event
5. Depot
To add an action to the particle diagram, you drag it to the event display from
the depot (the area at the bottom of the Particle View dialog). If you drag an
action 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 parameters 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 parameters to
affect particle behavior, as well as determine 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 can also easily enable and disable
actions and events, and determine the number of particles in each event. To
speed up checking particle activity at different times during the animation,
you can cache particle motion in memory. Using these tools, plus the ability
to create custom actions with scripting, you can create particle systems of a
level of sophistication previously unachievable.
The Life of a Particle
Another way of looking at Particle Flow is from the perspective of an individual
particle. Each particle first comes into existence, or is born, via the
Birth
operator
on page 2844, which lets you specify when to start and stop creating
particles, and how many to create.
The particles first appear at an object called an emitter. By default, the emitter
is the Particle Flow source icon using the
Position Icon operator on page 2850,
but you can alternatively use the
Position Object operator on page 2853 to specify
that particles should be born on the surface of or within any mesh object in
the scene.
After being born, particles can remain stationary 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 direction specified by various actions. These are
typically Speed operators, but other actions can also affect particle motion,
including
Spin on page 2863 and Find Target on page 2970. In addition, you can
use the
Force operator on page 2946 to affect their motion with outside forces.
2798 | Chapter 14 Space Warps and Particle Systems