8

Object Motion Inheritance Rollout 265
Spin Axis Controls group
These options determine the spin axis for the
particles, and provide a partial method of apply ing
motion blur to the particles.
Random—Thespinaxisforeachoftheparticles
is random.
Direction of Travel/Mblur—(Not available with the
Blizzard particle system.) Rotates the particles
about a vector formed by the direction in which
they’re moving. This option also lets you apply
aformofmotionblurtotheparticlesbyusing
the Stretch spinner. For f urther information, see
Achieving Part icle Motion Blur (page 2–236) .
Stretch—When greater than 0, the particles stretch
along the travel axis, depending on their speed.
Specifically, the Stretch value specifies the percent
of their leng th per each unit of the Speed setting
(in the Part icle Motion group). Thus, if you set
Stretch to 2 w hile Speed is set at 10, the p articles
are stretched 20 percent longer than their original
size along the axis of their travel. This spinner
is available only when you choose Direction of
Travel/Mblur.
Note: For best results when using Stretch, you
should also assign the Particle MBlur map as
an opacity map of the material assigned to the
particle system.
User Def ined—Uses a vector defined in the three X,
Y, and Z axis spinners.
X/Y /Z Axis—Specifies the spin vector of the X, Y, or
Z axis, respectively. These spinners are available
only w hen User Defined is chosen.
Variation—The amount, in degrees, by which
thespinaxisofeachparticlemayvaryfromthe
specified X Axis, Y Axis, and Z Axis settings. This
spinner is available only when you choose User
Defined.
Interpar ticle Collisions group
These options enable collisions between particles,
and control how the collisions occur. Note that this
involves intensive calculation, par ticularly when
large numbers of particles are involved.
Enable—Enablesinter-particlecollisionsinthe
calculation of the particle movements.
Calc Intervals Per Frame—The number of
intervalsperrenderinginterval,duringwhich
an int er-particle collision test is conducted. The
higher the va lue, the more accurate the simulation,
but the slower the simulation will run.
Bounce—The degree to which speed is recovered
after a collision.
Variation—Thepercentageofrandomvariationof
theBouncevalue,appliedtotheparticles.
Object M otion I nheri tance R ol lout
Create pa nel > Geometry button > Choose Particle
Systems from the drop-down list. > O bject Type rollout
> SuperSpray/Blizzard/Parray/PCloud > Object Motion
Inheritance rollout
Select a SuperSpray/Blizzard/Parray/PCloud emitter. >
Modify panel > Object Motion Inheritance rollout
Each particle’s position and direction of movement
are determined by the position and orientation of
the emitter at the time the particle is created. If the
emitter is moving through the scene, particles are
scattered along the emitter’s path.
Use these options to affect the motion of the
particles b y the motion of the emitter.
Procedure
Ex ample: To obser ve object motion inher ita nce:
1.
Create a Super Spray particle system.
2. Animate the emitter moving sideways
(perpendicular to the direction of the particle
stream) between frames 1 and 15.