Animating Objects in Particle Systems

You can add behaviors to a particle system’s emitter, or to the cells themselves, to quickly 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 tab 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 that were generated at previous frames, which creates a trail of particles.

Keyframing an emitter’s Emitter tab 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.

For an example of a keyframed emitter object in a particle system, see Example 2: Creating Animated Pixie Dust. For more information on keyframing parameters in the Curve Editor, see Keyframes and Curves.

Applying Behaviors to Emitters

Applying behaviors to emitters is a quick and easy way to move emitters in your project. Attaching the Motion Path and Snap Alignment to Motion behaviors to an emitter affects the position of the source of all new generated particles. Throw and Spin affect the position and rotation, respectively, of the emitted particles, unless Affect Subobjects is deselected.

With all Basic Motion behaviors, once individual particles emerge, they’re unaffected by changes to the position of the emitter. This means that moving the emitter around the screen using behaviors results in the creation of a trail of particles that behave according to their particle cell parameters.

Note: This effect can be overridden by increasing a cell’s Attach to Emitter parameter value.

To apply a behavior to an emitter
  • Drag a behavior from the Library onto an emitter in the Canvas, Layers tab, or Timeline.

    The behavior is applied to the emitter, which begins to move according to the parameters of the behavior.

Note: Not all behaviors instantly activate an object when applied. For example, when a Throw behavior is applied to an object, the Throw Velocity parameter must be adjusted before the object moves.

Applying Behaviors to Cells

Simulation behaviors that are applied directly to cells are in turn applied to each individual particle generated from that cell. This can result in some extremely complex animations as dozens of particles move according to the behaviors you’ve defined. Behaviors applied to cells have no effect on the position of the emitter. Parameter behaviors on a cell only affect particles when they are created.

To apply a behavior to a cell
  • Drag a behavior from the Library to a cell in the Layers tab or Timeline.

    The behavior is applied to the cell, and all particles generated from that cell begin to move according to the parameters of the behavior.

    Tip: If you do not see your expected result when applying behaviors to particle cells, try turning the Affect Subobjects parameter on or off or selecting a different option from the Affect pop-up menu in the HUD or Behaviors tab of the Inspector. These parameters determine whether the entire object (such as the particle emitter) or its components (such as the particle cells) are affected by the behavior and how an object interacts with surrounding objects, respectively.

    Note: The Affect Subobjects checkbox only appears in the Behaviors tab when the Throw and Spin behaviors are applied to a group that contains multiple objects, such as a group, particle emitter, or text.

Applying Parameter Behaviors to Emitter or Cell Parameters

As with all objects in Motion, you can apply Parameter behaviors to the parameters in the Emitter or Particle Cell tab.

To apply a parameter behavior to an emitter or cell parameter
Do one of the following:
  • Drag a behavior from the Library onto an emitter or cell in the Layers tab or Timeline. In the Apply To section of the Behaviors tab or HUD, choose an option from the Go pop-up menu.

  • Select an emitter or cell in the Layers tab or Timeline, click Add Behavior, and choose a Parameter behavior. In the Apply To section of the Behaviors tab or HUD, choose an option from the Go pop-up menu.

  • 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
  • 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.
  • Custom Scale: This group of parameters appears when Increment Type is set to Custom. Use this mini-curve editor for more precise control over the Scale of particles in your particle system.
    • Custom Scale: Use this slider to adjust the value of the selected keyframe in the mini-curve editor. This parameter appears when Custom is selected in the Increment Type pop-up menu.
    • Over Life: Use this slider to adjust the position of the selected keyframe in the life of the particle. This parameter appears when Custom is selected in the Increment Type pop-up menu.
HUD Controls

The HUD contains the Increment Type pop-up menu, and the Scale Rate, Scale At Birth, and Scale At Death parameters.

Spin Over Life

This behavior lets you spin 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
  • Spin Rate: Allows you to define how quickly each particle spins and the direction of the spin. Positive values spin particles faster over time and in a counterclockwise direction; negative values spin particles slower over time and in a clockwise direction.
  • Spin At Birth: Determines the initial spin of the particles when they are created.
  • Spin At Death: Determines the spin of the particles at the end of their lifetime.
  • Custom Spin: This group of parameters appears when Increment Type is set to Custom. Use this mini-curve editor for more precise control over the Spin of particles in your particle system.
    • Custom Spin: Use this control to adjust the value of the selected keyframe in the mini-curve editor. This parameter appears when Custom is selected in the Increment Type pop-up menu.
    • Over Life: Use this slider to adjust the position of the selected keyframe in the life of the particle. This parameter appears when Custom is selected in the Increment Type pop-up menu.
HUD Controls

The HUD contains the Increment Type pop-up menu, and the Spin Rate, Spin At Birth, and Spin At Death parameters.