Scale Operator

The Scale operator lets you set and animate particle size during an event, with optional random variation. Options for how scaling and animation are applied give this operator a great deal of flexibility.

Particle View > Click a Scale operator in an event or add a Scale operator to the particle system and then select it.

Procedures

Example: To animate particle scale:

This procedure gives an overview of animating particles to grow for 30 frames, remain at full size for the next 30 frames, and then shrink for 30 frames. It also gives an option for having the particles pulsate in size during the middle period. To follow this procedure, you should be familiar with the basic usage of Particle Flow and Track View.

Set up a default Particle Flow system. Set the Shape operator to Sphere, and set the Display operator to Geometry.
Add a Send Out test to Event 01.
Add a new Scale operator to the event display, creating a new event. Set the new event's Display operator to Geometry, and make sure it's a different color than the one in Event 01.
Wire the Send Out test in Event 01 to Event 02.
In the Event 02 Scale operator, set Type to Absolute, and animate the Scale Factor values from 10 to 100 over frames 0 to 30. In the Animation Offset Keying group, set Sync By to Event Duration.
Add an Age Test to Event 02. Set it to Event Age, set Test Value to 30, and Variation to 0.
In this event, particles grow from 10 percent of their original size to full size over the first 30 frames of their existence, which is the same as their duration in the event. At that point, they'll be eligible to move to the next event.
Use a new Scale operator to create a new event, Event 03. Set the new event's Display operator to Geometry, and make sure it's a different color than the others.
Wire the Age Test in Event 02 to Event 03.
In the Event 03 Scale operator, Set Type to Absolute, and in the Animation Offset Keying group, set Sync By to Event Duration.
Copy and paste the Age Test as an instance from Event 02 to Event 03.
Particles in Event 03 remain at full scale for 30 frames, and then move on to the next event.
Use a new Scale operator to create a new event: Event 04. Set the new event's Display operator to Geometry, and make sure it's a different color than the others.
Wire the Age Test in Event 03 to Event 04.
In the Event 04 Scale operator, set Type to Absolute, and animate the Scale Factor values from 100 to 10 over frames 0 to 30. In the Animation Offset Keying group, set Sync By to Event Duration.
Copy and paste the Age Test as an instance from Event 03 to Event 04.
In this event, particles shrink from full size to 10 percent of their original size over 30 frames.
Play the animation.
Next, you'll use a Noise controller to cause the particles in Event 03 to pulsate in size.
Add a second Scale operator to Event 03, below the existing Scale operator. Set it to Relative Successive, and set Sync By to Event Duration.
The name of this operator should be Scale 04.
In Particle view, right-click the Scale Factor X % parameter field on the Scale 04 rollout, and choose Show In Track View.
The Curve Editor opens with the X Scale Factor parameter highlighted.
Right-click the X Scale Factor item and choose Assign Controller from the menu.
In the Assign Float Controller dialog, double-click Noise Float.
The Noise Controller dialog opens.
Set Strength to 200, and to the right of Strength, turn on the >0 checkbox.
Copy this controller, and then paste it as instances to Y Scale Factor and Z Scale Factor.
Although the Scale operator defaults to constraining all scale factors to the same value, thus scaling particles uniformly, changing controllers in Track View works on a per-parameter basis.
Play the animation.
This time, the particles grow in size for 30 frames, then pulsate in size for the next 30 frames, and then shrink from the size at the end of Event 03 to 10 percent of that over the next 30 frames.

Interface

The user interface appears in the parameters panel, on the right side of the Particle View dialog.

Type

The scaling Type setting includes options that let you scale particles once in an event or repeatedly, and apply scaling as an absolute or relative factor.

Overwrite Once (The default.) Sets the scale one time only as an absolute percentage value, disregarding any previous scaling.
To produce a range of different birth sizes, and specify the scaling explicitly, use Overwrite Once with animated scale factors.
Inherit Once Sets the scale one time only as a percentage of existing scaling. The existing scaling should be specified with a previous Scale operator, the Scale setting in the Shape operator, or a Shape Instance operator.
For instance, if you previously used Scale with Overwrite Once to scale particles' birth size within a range, and then want to scale them to half their previous size, use Inherit Once and set Scale Factor to 50%.
Absolute Sets the scale continuously, while the particle is in the event, as an absolute percentage value, disregarding any previous scaling.
Use Absolute if you want to animate the particles' scale explicitly.
Relative First Sets the scale continuously, while the particle is in the event, as a percentage of existing scaling. The existing scaling should be specified with a previous Scale operator, or a Shape Instance.
Use Relative First when you want to scale the particles relative to the scaling at which they enter the event, and optionally animate the scaling, or before a Relative Successive operator.
Relative Successive Scales the particles continuously, relative to scaling set earlier in the same event.
Note: Always precede Relative Successive in the same event with an operator that modifies the scale channel all the time, such as a Scale operator set to Absolute or Relative First, or a Shape Instance operator with the Scale checkbox turned on (it's on by default).

Scale Factor group

The operator performs scaling on each particle's local axes. It can scale particles on a single axis or on any combination of axes.

X/Y/Z: Sets the scaling as a percentage of the particle's current size. To scale uniformly, turn on Constrain Proportions, and then change any axis setting. Range=0 to 10000000. Default=100.
Constrain Proportions: When on, retains the current ratio of scale factor settings, so that changing any axis setting changes all of them. Default=on.

Scale Variation group

X/Y/Z

Sets the scaling variation as a percentage of the particle's previous size. To scale uniformly, turn on Constrain Proportions, and then change any axis setting. Range=0 to 100. Default=0.

Constrain Proportions

When on, retains the current ratio of scale variation settings, so that changing any axis setting changes all of them. Default=on.

Bias

Lets you choose how to distribute the scaling variation within the specified range or ranges. Default=None.

None No bias; scaling variation is distributed equally through the range.
Centered Scaling variation is concentrated near the middle of the range; that is, at 0.0%.
With this choice, scaling will occur more frequently with low percentage values than with ones near the values you set. In other words, most scaling variants will be close to the specified scaling value.
Towards Minimum Scaling variation is concentrated near the lower end of the range (base-variation); that is, most scaling variants will be smaller than the scaling value.
Towards Maximum Scaling variation is concentrated near the upper end of the range (base+variation); that is, most scaling variants will be larger than the scaling value.

Animation Offset Keying group

If you animate the Scale Factor or the Scale Variation settings or both, Particle Flow can begin applying this animation to all particles as of the start frame of the animation or the first frame of the current event, or to each particle based on its age. For instance, if you set Sync By to Particle Age, and set Scale Factor keys at frames 0 and 30, then Particle Flow will animate the scaling factor for each particle between its birth and its 30th frame of existence, if the particle is in the scaling event or a prior event. Following this example, any particle that has already reached its 30th frame of existence before reaching the event will enter the event fully scaled. That is, Particle Flow will apply the Scale Factor value that you set at frame 30 to each particle aged 30 or above at the moment it enters the scaling event. However, any particle that leaves the scaling event before reaching age 30 will stop scaling as of its exit frame. In other words, with respect to particles in other events, animation of action parameters is retroactive, but not post-active.

Alternatively, if you set Sync By to Absolute Time, the scaling is animated from frame 0 to frame 30 of the animation, regardless of particle age, and even if no particles are in the event at that time. Or, if you set Sync By to Event Duration, the scaling animation is applied to each particle as of the time that it enters the event.

Note: With the Overwrite Once and Inherit Once scaling types, scaling always occurs with respect to the entire animation; that is, in Absolute Time mode. Thus, when either of those scaling types is in effect, the Sync By setting is unavailable. Also, if you animate Scale Factor or Scale Variation when using Overwrite Once or Inherit Once, it doesn't cause scaling animation in the particles, but rather applies one-time scaling to particles born during that period. For instance, if you animate Scale Factor on all three axes from 100% to 200% over frames 0 to 30, particles born at frame 0 are normal size, particles born at frame 15 are one-and-one-half times normal size, and particles born at frame 30 (and thereafter) are twice normal size.

Sync By

Choose the time frame for applying animated parameters:

Absolute Time Any keys set for parameters are applied at the actual frames for which they're set.
Particle Age Any keys set for parameters are applied at the corresponding frames of each particle's existence.
Event Duration Any keys set for parameters are applied to each particle starting when it first enters the event.

Uniqueness group

The Uniqueness setting affects the randomization of scale variation.

Seed: Specifies a randomization value.
New: Calculates a new seed using a randomization formula.