Apple Motion 4 - Manual (Page 651)

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In the Emitter or Particle Cell tab, Control-click a parameter, then choose a Parameter
behavior from the shortcut menu.
Using Particles Behaviors
The Particles category in the Library contains two behaviors specifically for use with the
cells or emitter in a particle system:
Scale Over Life
This behavior lets you grow or shrink the particles in a system over the duration of each
particle’s life. It has one main parameter, and three optional parameters that appear
depending on the selected Increment Type.
Parameters in the Inspector
Increment Type: Choose an option from this pop-up menu to determine which method
is used to resize particles over their lifetime. There are four options:
• Natural Scale: Specifies starting and ending scale percentages that are used to animate
each particle’s size over its lifetime. Natural Scale uses an exponential curve to allow
the animation to progress slowly when the scale values are small, and speed up when
the values are large. This creates the illusion that the scaling is occurring at a constant
speed. When Natural Scale is selected, the Scale At Birth and Scale At Death parameters
become available.
• Rate: Specifies a steady rate at which particles change size over their entire lifetimes.
When Rate is selected, the Scale Rate parameter becomes available.
• Birth and Death Values: Specifies starting and ending scale percentages that are used
to animate each particle’s size over its lifetime. The scale amount generated by this
option for a specific particle at a specific time is multiplied by the pre-existing particle
Scale (defined in the Cell Controls section of the Emitter tab). When this option is
selected, the Scale At Birth and Scale At Death parameters become available.
• Custom: This mini-curve editor allows you to customize the scale of the particles over
their lifetime. Click the disclosure triangle to display the mini-curve editor in the
Inspector. For more information on using mini-curve editors, see
Mini-Curve Editor .
Scale At Birth: Determines the initial size of particles when they are created. This parameter
appears when Natural Scale or Birth and Death Values is selected in the Increment Type
pop-up menu.
Scale At Death: Determines the size of each particle at the end of its lifetime. This
parameter appears when Natural Scale or Birth and Death Values is selected in the
Increment Type pop-up menu.
Scale Rate: Allows you to define how quickly each particle changes size. Positive values
grow particles over time, while negative values shrink particles over time. This parameter
appears when Rate is selected in the Increment Type pop-up menu.
651 Chapter 11 Working with Particles