Apple Motion 2 - Manual (Page 610)

610 Chapter 8 Working With Particles
Animating Objects in Particle Systems
You can animate any emitter or cell parameter in a particle system by using Parameter
behaviors or by keyframing them. If you animate emitter-specific parameters such as
Emission Angle or Emission Range, the position and distribution of new particles
generated by that emitter are animated. All animation occurs relative to the duration of
the emitter. This works the same way for cell parameters and emitter parameters. If the
parameters are animated, then it only affects how particles are created. It does not
affect existing particles.
Animating an emitter’s Properties tab parameters is useful for altering the position and
geometric distribution of a particle system over time. Keyframing an emitter object’s
Position parameter moves the source of newly emitted particles without affecting any
particles that were generated at previous frames, which creates a trail of particles.
Keyframing an emitter’s Emitter tab parameters is a good way to modify the particle
system’s overall characteristics over time, such as increasing or decreasing the size,
speed, or lifetime of newly generated particles.
For an example of a keyframed emitter object in a particle system, see “ Example 2:
Creating Animated Pixie Dust ” on page 615. For more information on keyframing
parameters in the Curve Editor, see “ Keyframes and Curves ” on page 401.
Using Behaviors With Particle Systems
You can add behaviors to a particle system’s emitter, or to the cells themselves, to
quickly achieve sophisticated, organic effects with very little effort.
Applying Behaviors to Emitters
Attaching the Motion Path and Snap Alignment to Motion behaviors to an emitter
affects the position of the source of all new generated particles. Throw and Spin affect
the position and rotation, respectively, of the emitted particles, unless Affect Objects is
turned off.
With all Basic Motion Behaviors, once individual particles emerge, they’re unaffected by
changes to the position of the emitter. This means that moving the emitter around the
screen using behaviors results in the creation of a trail of particles that behave
according to their particle cell parameters.
Note: This effect can be overridden by turning on a cell’s Attach to Emitter parameter.
To apply a behavior to an emitter:
m Drag a behavior from the Library onto an emitter in the Canvas, Layers tab, or Timeline.
The behavior is applied to the emitter, which begins to move according to the
parameters of the behavior.
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