Graphics Programs Reference
In-Depth Information
5. The emission is rather slow for hot
steam being pumped out as the loco-
motive drives the wheels, so change
the Speed setting for the emitter from
1 to 2.0, and change Speed Random
from 0 to 1. Doing so creates a ran-
dom speed range between 1 and 3 for
each particle. These two attributes are
found in the emitter's Attribute Editor
in the Basic Emission Speed Attri-
butes section.
6. So that all the steam doesn't emit
from the same point, keep the emit-
ter's Min Distance at 0 but set its Max Distance to 0.3. This creates a range of offset
between 0 and 0.3 units for the particle to emit from, as shown in Figure 12.28.
Figure 12.28
A range of offset
between 0 and 0.3
units creates a more
believable emission.
Setting nParticle Attributes
It's always good to get the particles moving as closely to what you need as possible before
you tend to their look. Now that you have the particles emitting properly from the steam
pump, you'll adjust the nParticle attributes. Start by setting a lifespan for them, and then
add rendering attributes:
1. Select the nParticle object, and open the Attribute Editor. In
the Lifespan section, set Lifespan Mode to Random Range. Set
Lifespan to 2 and Lifespan Random to 1. This creates a range of 1
to 3 for each particle's lifespan. (This is based on a lifespan of 3,
plus or minus a random value from 0 to 1.)
2. You can control the radius of the particles as they're emitted
from the pump. Under the Particle Size heading in the Attribute
Editor, set a Radius attribute of 0.50. Set the Radius Scale Ran-
domize attribute to 0.25. This allows you to have particles that
emit with a radius range between 0.25 and 0.75. Figure 12.29
shows the attributes.
3. If you play back the simulation, you see the particles are quite
large initially. Because steam expands as it travels, you need to
adjust the size (radius) of your nParticles to make them smaller
at birth; they will grow larger over their lifespan and produce a
good look for your steam.
Figure 12.29
The initial radius
settings for the
steam nParticles
