8

Particle Generation Rollout 257
Use R ate—
Specifies a fixed number of particles
emitted per frame. 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 frames, is specified by
theLifespinnerintheParticleTiminggroup,
described later in this topic.
Tip: Generally, U se Rate is best for a continuous
flow of particles, like a trail of pixie dust, while Use
Total is better for bursts of particles ov er a short
period of t ime.
Particle Motion group
These spinners control the initial particle velocity,
which is directed along the sur face, edge, or vertex
norma ls (interpolated for each emitter point).
Speed—The velocity of the particle at birth, along
the normal, in units traveled per frame.
Variation—Applies a percentage of variation to the
speed of emission for each p art icle.
Divergence—Applies an angular degree of
variation by which each p art icle’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.
Par ticle Timing group
These options specify when particle emission
starts and stops, and the lifespa n of the individual
particles.
Emit Start—Sets the frame at which par ticles begi n
to exist in the scene.
Emit Stop—Sets the last frame at which particles
are emitted. This setting has no effect if you choose
the Object Fragments par ticle t ype.
Display Until—Specifies the frame at w hich all
particles will disappear, regardless of other
settings.
Life—Sets the lifespan in number of frames of each
particle from the frame of creation.
Variation—Specifies the number of frames by
which the life of each particle can vary from the
norm.
Subframe Sampling—Tur ning on any of the thre e
check boxes below helps avoid particle "puffing"
by sampling particles at a much higher subframe
resolution, instead of the relatively coarse frame
resolution. D epending on your needs, you can
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 especially noticeable when
the emitter is animated.
•
Cr e a tio n Tim 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 Fragments part icle type.
Default=on.
•
Emitter Translati on—If the object-based emitter
is mo ving 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, tur n
this on to a void puffing and produce smooth
spiral effects. Default=off.
Impor tant: Each additional subframe sampling
check box that you turn on progressively increases
the necessary computation. In addition, the methods
are listed in order of least amount of computation