4

Animating Objects in 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. You can animate any emitter
using Basic Motion, Parameter, or Simulation behaviors. Emitter parameters and cell
parameters can also be animated via keyframes. 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.
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’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.
Particles also have their own category of behaviors. The Particles behaviors include Scale
Over Life and Spin Over Life, which allow you to modify and animate the rotation and
size of the particles over their lifetime.
Using the Motion Tracking behaviors, you can apply existing tracking data to an emitter
or track an emitter to a clip. For more information on using the Motion Tracking behaviors,
see Motion Tracking.
For an example of a keyframed emitter object in a particle system, see Example 2: Creating
Animated Pixie Dust. For more information on keyframing parameters in the Curve Editor,
see Keyframes and Curves.
Applying Behaviors to Emitters
Applying behaviors to emitters is a quick and easy way to move emitters in your project.
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 Subobjects is deselected.
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 increasing a cell’s Attach to Emitter parameter
value.
649Chapter 11 Working with Particles