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164 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 Par t icle View.
5. In the Surface Geometry group, click Add, and
then select the cyl inder.
6. Play the animation again, and then stop.
Theparticlesstillmovedownward.
7. Go to f r ame 15, so you can see the particles,
and then slowly move the cylinder downward
alongtheZaxis,whilewatchingtheparticles
in the Perspective and Front view por ts. Stop
when the emitter is above the cylinder.
As the bottom of the c ylinder passes below the
emitter, more and more particles start moving
on the XY plane rather than perpendicular
to it. That’s because they eventually become
closertooneoftheverticalsidesofthecylinder,
rather than t he bottom, at which p oint they
move perpendicular to the vertical sides. When
the top becomes the closest side, the part icles
again move vertically, but upward instead of
downward.
8. Move the cylinder back up until the emitter
is at its vertical center. Then, on the Modify
panel, click the lower part of the Sides spinner
to decrease the number of s ides, one at a time.
Each time you 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 O ut Of Surface, and then move the
cylinder up and down.
The overall behavior doesn’t change much. Out
Of Surface becomes more useful when you use
the Control Speed Continuously option, as
you’ll observe shortly .
10. In the Speed By Surface parameters, change
DirectiontoParallelToSurface,andthenmove
the cylinder up and down.
Now the pa rticle behavior is effectively opposite
of that with the other two opt ions. When
the part icles are closer to the top or bottom,
they move along the XY plane, and when
they’re closer to the ver tical 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 p arameters, 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 direc tion to make it travel parallel to
that side. You can affect the size of the part icles’
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 t he n
press F3 to set it to Wireframe view.
13. In Part icle View, click the Speed 01 operator
and set Direction to Random 3D.