Anatomy of a Particle System
Every particle system is made up of an emitter and one or more particle cells. Each cell
appears as a sublayer underneath the emitter in the Layers list and the Timeline (click
the disclosure triangle beside the emitter layer to hide or reveal its sublayers).
Emitter
Original object (disabled)
Cell (with behaviors
applied)
The emitter and cells have separate sets of parameters that control the particle system’s
behavior. If you imagine that a garden hose is a particle system, the nozzle acts as the
emitter, while the water represents the flow of particles. Changing the parameters of the
emitter changes the shape from which the particles are emitted and their direction, while
changing the cell’s parameters affects each particle.
By changing a few parameters, it’s possible to create different effects using the same cell.
Note: In a particle system, cells and particles are not the same thing. A cell is a layer (in
the Layers list) that acts as the “mold” for the particles (the multiple objects generated
in the Canvas). The cell itself is a copy of a source object (cell source) that appears dimmed
(disabled) in the Layers list, and therefore is by default not visible in the Canvas.
As with any effect in Motion, particle system parameters can be keyframed to change a
particle effect’s dynamics over time. For example, you can create a path of bubbles that
follows an object onscreen by keyframing the emitter’s Position parameter. For more
information on keyframing, see
Keyframes and Curves
.
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Chapter 14
Working with Particles
You can also track an emitter to a moving object in a clip, or apply existing tracking data
in your project to an emitter. For more information on using the Motion Tracking behaviors,
see
Motion Tracking
.
In addition, you can add behaviors to each cell or to the emitter to create even more
varied effects (simulation behaviors can be especially effective). Any behavior that you
apply to a cell is in turn applied to each particle it generates. This lets you achieve almost
limitless variation. Adding behaviors to cells in addition to the particle system’s own
parameters is an easy way to create complex, organic motion that would be impossible
to accomplish any other way. You can also apply a behavior to another object in your
project (an object that is not part of the particle system), such as Repel, and have the
particles weave around that object. For more information about behaviors, see
Using
Behaviors
.