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168 Chapter 11: Space Warps and Particle Systems
world origin (X/Y/Z=0), and set the icon’s
Length and Width values both to 30.
2. Add a Cylinder primitive to the scene. Position
it above the source icon: X/Y=0 and Z=30.Set
Radius=20 and Height=40.
3. Play the animation, and then stop.
The particles move downward, using the
default starting setup.
4. Open Particle View and add a Speed By Surface
operator to the end of Event 01. Click the
operator in the event to display its parameters
panel in Particle View.
5. In the Surface Geometry group, click Add, and
then select the cylinder.
6. Play the animation again, and then stop.
Theparticlesstillmovedownward.
7. Go to frame 15, so you can see t he par ticles,
and then slowly m ove the cylinder downward
alongtheZaxis,whilewatchingtheparticles
in the Perspective and Front viewpor ts. Stop
when the emitter is above t he cylinder.
As the bottom of the cylinder passes below the
emitter, more and more particles start moving
on the XY plane r ather than perpendicular
to it. That’s because they e ventually b e come
closertooneoftheverticalsidesofthecylinder,
rather than the bottom, at which point they
move perpendicular to the vertical sides. When
the top be comes the closest side, the p articles
again move vertically, but upward instead of
down ward.
8. Move the c ylinder back up until the emitter
is at its vert ical center. Then, on the Modify
panel, click the lower part of the Sides spinner
to decrease the number of sides, one at a time.
Each time y o u click, the particle streams
traveling outward change, to move
perpendicular to the vertical sides as they
change position. You might also try rotating
thecylinder,andnotethattheparticlestreams
also rotate, like the spokes of a wheel.
9. In the Speed By Surface parameters, change
Direction to Out Of Surface, and then move t he
cylinder up and down.
The overall behavior doesn’t change much. Out
Of Surface becomes more useful w hen you use
the Control Speed Continuously option, as
you’ll observe shortly.
10. In the Speed By Surface p arameters, change
DirectiontoParallelToSurface,andthenmove
the cylinder up and down.
Now the particle behavior is effectively opposite
of that with the other two options. When
the particles are closer to the top or b ottom,
they move along the XY plane, and when
they’re closer to the vertical sides, they move
downward. If you want them to move upward
instead, set Speed to a negative va lue.
Next, you’ll discover how the Control Speed
Continuously option alters particle behavior.
11. In the Speed By Surface parameters, choose
Control Speed Continuously, and then drag the
time slider.
The particles spread out from the emitter, and
then start orbiting the cylinder in a roughly
cylindrical overall formation. The software
continually checks to see which side of the
cylinder a particle is closest to, and, if necessary,
changes its direct ion to make it travel parallel to
that side. You can affect the size of the particles’
orbits by changing their speed.
Lastly, you’ll see how to contain particle motion
within the cylinder.
12. Make the cylinder considerably larger:
Radius=60 and Height=90.Activatethe
Perspective viewport, if necessary, and then
press
F3 tosetittoWireframeview.
13. In Particle View, click the Speed 01 operator
and set Direction to Random 3D.