8

Particle Flow FAQ 119
How can I make all particles appear in the first
frame while giving them different ages?
Useanegativeframerangeinthe
Birth operator
(page 2–139)
.Forexample,togetaparticle-age
spread of 30 frames, set Emit Start to -29 and Emit
Stop to 0.
How can I specify the time frame in which
animated parameters are applied to pa rticles ?
You can animate many of the Particle Flow
parameter values with key framing. In most
actions, you can choose the time frame by which
to apply this animation to the particles from a
drop-down list labeled Sync By. You can apply
this animation to particles in the time frame of
the entire animation, or at a specific time of each
particle’s life (part icle age), or based on the length
of time the particle has b e en in the current event.
See the individual operator and test topics for
details.
How can I apply bubble motion to particles?
Although Particle Flow doesn’t have the
bubble
motion option (page 2–266)
found in PArray, you
can simulate the effect by following this procedure:
1. Add an object to ser ve as par ticle geometr y and
a
dummy helper object (page 2–15) .
2. Position the dummy away from the center of
theparticlegeometryobjectand
link (page
2–403)
your particle geometry to the dummy
so that the dummy is the parent object (that is,
drag f rom the geometry object to the dummy).
The distance between the
pivots (page 2–470)
of the two objects determines the radius of the
bubble motion.
3. In Particle View, add a
Shape Instance operator
(page 2–174)
and a Spin operator (page 2–150)
to the event in which the bubble motion is to
occur.
4. ClicktheShapeInstanceoperatorandspecify
the dummy object as the particle geometr y
object.
5. Click the Spin operator and set appropriate
values for Spin R ate and Variation. For Spin
Axis, keep the default setting of Random 3D.
Theresultisparticlemotioninwhichtheparticles
bob about while moving along their paths, similar
to bubble motion.
Events
How can I branch an event to several other
events?
Particle Flow includes several Split tests, w hich let
you send some particles to another event based
on quantity, selection, or source. You can use any
number of these in a single event to send parts of
the particle stream to different events, and then
use a
Send Out test (page 2–226) to redirect the
remaining p articles to another event. Keep in
mind that any tests subsequent to the first can
work only with particles remaining in the event,
not necessarily a l l part icles that begin in the event.
Does it matter which order I put actions in an
event?
It depends. If an event contains two or more
operators of the same type, such as Shape, the
last one overr ides the rest. If an event contains
two or more tests, they are evaluated and particles
redirected in the order in which the tests appear .
However, if two actions in an event control the
same properties, the interaction is more complex.
An act ion that works on a continuous basis will
typically prevail over one that affects particles
only when they first enter the event. For example,
both the
Find Target test (page 2–214) and Speed
operator (page 2–155)
can control particle speed
and direction, but the test works continuously,
while the operator ta kes effect only once. If an
event contains both, par ticle speed and direction