Apple Motion 4 - Manual (Page 915)

Once an emitter is added to the project, the Emitter object is selected In the Layers tab,
the generator object (the Soft Gradient) becomes an emitter source for the new particle
cells, and the original reference object (the Soft Gradient) is disabled.
In the Canvas, the emitter bounding box appears, which can be transformed using the
onscreen controls or the Inspector. The particle appears in the Canvas in the same location
as the original object. Although it appears as if the particle is selected, it is actually the
bounding box for the emitter.
5 Play the project (press Space bar).
Soft gradient particles are emitted.
You can change the particle color, emitter shape, scale, emission angle, birth rate, and
so on in the Emitter controls. For more information on working with particles, see
Working
with Particles .
Modified particles using the
Soft Gradient generator as a
particle cell source
915 Chapter 15 Working with Generators