Apple Motion 5.1.1 - Manual (Page 550)

Chapter 14 Particles 550
m Select the cell to display animated parameters such as Birth Rate or Angle (in the Particle Cell
Inspector).
Note: To manually send an animated parameter to the Keyframe Editor, choose Show In
Keyframe Editor from the parameter’s Animation menu.
The parameter is displayed in the Keyframe Editor in a new, untitled curve set.
Use masks with particle systems
As shown in the following images, you can apply masks to the cell source of a particle emitter.
The effect of the mask on the cell source is carried through to the emitted particles.
Original source layer Bezier mask applied
to source layer
Resulting particle system
You can also apply masks to the emitter object itself.
Rectangle mask (inverted) applied
to the emitter object
67% resize factor