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Note: Whatever is chosen in the Show Particles As pop-up menu appears in your final
render. This can result in some interesting effects.
Point Size: This slider appears when Show Particles As is set to Points, and lets you adjust
how large the points are.
Random Seed: Although particle systems seem random, they’re deterministic. This means
that the variation in each particle system is created based on the number shown here.
Unless this seed number is changed, a particle system with the same parameter settings
always plays back with the same motion. If you don’t like the current random motion or
distribution of the particle system, you can change the seed number by typing a new
number or clicking Generate. This changes the random calculations performed for that
system for all randomness parameters.
For more information about the random nature of particle systems, see The Predictability
of Particle Systems.
Particle Source: In particle systems with more than one cell, an image well representing
each cell appears at the bottom of the Emitter Inspector. Each Particle Source well has a
checkbox you can use to enable or disable that cell.
Animating Objects in Particle Systems
You can add behaviors to a particle system’s emitter, or to the cells themselves, to 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 Inspector 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
generated at previous frames, creating a trail of particles.
Keyframing an emitter’s Emitter Inspector 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.
716 Chapter 14 Working with Particles