9

Particle Generation Rollout 261
Use R ate—
Specifies a fixed number of particles
emitted per fr ame. Use the spinner to set the
number of particles formed per frame.
Use Total—Specifies a total number of particles
formed over the life of the system. Use the spinner
to set the number of particles formed per frame.
The life of the system, in fr ames, is specified by
theLifespinnerintheParticleTiminggroup,
described later in th is topic.
Tip: Generally, Use Rate is best for a continuous
flow of particles, like a trail of pixie dust, while Use
Total is better for bursts of particles over a short
period of t ime.
Particle Motio n group
These spinners control the initial particle velocity,
which is directed a long the surface, edge, or vertex
norma ls (interpolated for each emitter point).
Speed—The velocity of the particle at birth, along
the n orma l, in units traveled per frame.
Variation—Applies a percentage of variation to the
speed of emission for each particle.
Divergence—Applies an angular degree of
variation by which each particle’s velocity can vary
from the emitter normal.
Note: The initial direction for a fragment cluster is
the normal of t he cluster’s seed face. Clusters are
created by choosing a single face (the seed face),
and then creating a cluster outward from that face,
depending on the method chosen in the Object
Fragment Controls group on the Particle Type
rollout.
Particle Tim ing group
These options specify when particle emission
starts and stops, and the lifespan of the individual
particles.
Emit S tart—Sets the f rame at which particles begin
to exist in the scene.
Emit S top—Sets the last frame at which p articles
are emitted. This setting has no effect if you choose
the Object Fragments particle type.
Display Until—Specifies the frame at which all
particles will disappear, regardless of other
settings.
Life—Sets the lifespan in number of fra mes of e ach
particle from the frame of creation.
Variation—Specifies the number of f rames by
which the life of each particle can vary from the
norm.
Subframe S ampling—Turning on any of the th ree
check boxes below helps avoid particle "puffing"
by sampling p a rticles at a much higher subframe
resolution, instead of the relatively coars e frame
resolution. Depending on your needs, you ca n
do this over time, over motion, or over rotation.
"Puffing" is the effect of emitting separate "puffs"
or clusters of particles, rather than a continuous
stream. This effect is e specially noticeable when
the emitter is animated.
•
Cr e a ti on Ti m e —Enables the addition of a
time offset to the equations of motion that
prevents puffing in time. This setting has no
effect with the Object Frag ments particle type.
Default=on.
•
Emitter Translation—If the object-based emitter
is moving in space, particles are created at
integral times at positions along the geometry’s
path between renderable positions. This
prevents puffing in space. This setting has no
effect if Object Fragment particle type is on .
Default=on.
•
Emitter R otation—If the emitter is rotating, turn
this on to avoid puffing and produce smooth
spiral effects. Defaul t=off.
Impor tant: Each a dditi onal subframe sampling
check box that you turn on progressively increases
the necessar y computation. In addition, the methods
are listed in order of least amount of computation