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Chapter 6
Particle Dynamics
W
shi focus now and cover an aspect of Maya that can be used
to simulate particle dynamics. Maya has engines that can simulate two dierent
aspects of real-world physics. e rst involves the emission of particles, their semirandom
behavior, and their interaction with each other and with objects in a scene. e second
involves the physics of colliding objects, which we will look at in Chapter 11.
Particle dynamics are useful for situations where a large number of small objects are
needed to properly construct a scene. In short, particle dynamics can scale to many
hundreds or thousands of individual particles. is capability can be used to model
smoke, re, rain, and water. Particle dynamics can be used to make realistic cloth as
well. Particles can be used to create eects where each particle is visually distinct or
where the particles seem to form an organic mass where the boundaries of each particle
cannot be identied visually. When we use particle dynamics, we tend to call the model
a “special eect.”
e general idea is to create an object, oen called an “emitter,” which will generate
many geometrically identical objects. Typically, we also include a random factor that
causes individual particles to have semi-independent movements and visual qualities, as
we are oen trying to model a chaotic eect.
We can program the emitter to incrementally produce particles over the course of some
number of frames; this is how we might produce rain. But when modeling an ocean, we
might want to generate all the particles but not render them or their movement until the
complete body of water has been made.
USE EMITTERS SPARINGLY
ere are some complications that occur when using particle dynamics in an animated
project. Perhaps the most signicant is that particle dynamics can radically increase render
times. Imagine an ocean scene created with an emitter. Water scenes are oen impressive
visually; the surface can be alive with whitecaps, ripples, and waves. But this means that
the position and appearance (how it reacts to light) of every single particle could poten-
tially change in every single frame. For many of us who are creating animated scenes on
200 ◾ 3D Animation for the Raw Beginner Using Maya
desktop or notebook computers, rendering massive particle eects can be intractable. A
minute-long water eect could take many hours or days to render.
In Maya, some particle eects can be rendered using the Maya soware renderer or
mental ray. ere are also particles that are rendered with the hardware renderer, which
pushes most of the job of rendering to the graphics card, thus making the process some-
what faster. Sometimes this makes the dierence between an undoable and a doable eect.
SAVING RENDER TIME
In Maya, you can render a scene in layers, just as we saw earlier that you can choose to only
display certain layers at a given time. By using render layers, you could render a particle
eect once and not have to rerender it every time you rerender other objects in the scene.
Layers also allow you to use dierent renderers for dierent parts of a scene.
You can create render layers in a scene by clicking on the icon on the far upper right of
the Main Window, and then choosing the Render tab at the bottom of the right-hand side
of the window. Of course, you need to compose the rendered layers into a single video, and
this is done outside of Maya.
When doing one frame test renders, you can choose to rerender only a piece of a frame,
by using the second icon in from the le at the top of the Render View. It has a red box
around it. is is particularly useful when rendering particles.
In addition to the Display and Render tabs, there is one called Anim, which is for layer-
ing animation. is is a complex task and is not covered in this book.
ROCKET POLLUTION AND HARDWARE PARTICLES
In Maya, there are two dierent settings on the Main Menu Selector for creating a particle
eect. Dynamics has been in Maya for a long time and nDynamics is somewhat newer.
First, we will use Dynamics, and later we will look at nDynamics. ese two dynamics
systems overlap signicantly in their capabilities, with nDynamics being in many cases
more powerful and easier to tailor. It is oen easier to produce visually impressive results
with nDynamics.
We are using a cylinder to host our emitter. A NURBS cylinder was chosen because it
consists of three pieces: two disks and a tube. is way, the bottom disk can be selected and
Maya will default the placement of the emitter to the center of the disk. We can imagine
that our cylinder is a rocket, but we will only concern ourselves with the disk at the bottom
of it.
In Figure6.1, we see a particle emitter being created. In the dropdown, we see two
choices for creating an emitter. One is to make a stand-alone emitter not attached to any
other object in the scene, and the other is to create an emitter and plant it on the surface of
an object. Since we are trying to make a rocket take o, we will create a surface emitter. To
do this, we must rst select an object in the scene.
So, we select the bottom disk of our rocket, and then, choose:
Dynamics Main Menu → Particles → Emit from Object
Particle Dynamics ◾ 201
In Figure6.2, we see that Maya creates a small icon and places it where the emitter is
attached to the object.
The Attributes of the Emitter and the Particles
In Figure6.3, we are adjusting the attributes
of the emitter. We will focus on three basic
attributes for now. e rst is the Direction
Y setting. Notice that it is set to a negative
one: we want our particles to fall down-
ward, toward the earth. at is because our
rocket trail needs to come out of the rocket’s
bottom. e second is the type of emitter.
Our setting is Directional. Other choices
for settings include Omni (all directions)
and Surface (generating particles from the
entirety of some surface). e particle rate is
the nal attribute we will look at here; 100 is
fairly low, but it was chosen to decrease ren-
dering time.
In Figure6.4, we see that each particle
has attributes as well. One fundamental set-
ting is Particle Render Type, which happens
to be set to Points. Particle Render Type
denes the geometry of the particles and
how they are rendered. Points are rendered
with the hardware renderer. Some of the
choices include “s/w” in their names; these
are rendered with soware. Particles that
FIGURE 6.1 Emitter menu. FIGURE 6.2 Emitter on the rocket.
FIGURE 6.3 Emitter attributes.
202 ◾ 3D Animation for the Raw Beginner Using Maya
are rendered by hardware have no geometric existence. ey are points in the (x, y, z)
grid that are, in a sense, innitely small. Hardware particles only possess properties that
tell them how they should visually react to light and how they should move.
Next, we want to give our particles some color. So we go the Hypershade and create a
Blinn material and choose black for its color. en, in the Main Window, we use the Playback
controls to run about a hundred frames. Particles are emitted, as shown in Figure6.5. As
in Figure6.6, we select the particles and go to the Hypershade, right click on the Blinn and
assign it to the particles. ey will now render black.
It is not necessary to select all the particles to do this—you can generate just a small
number and then assign the material. All particles emitted later will have the same
material.
Figure6.7 is a rendering of the particles. ese are hardware particles, so we must render
them with the renderer called Maya Hardware. We can see the large particulate pollution
spewing from our rocket. If we had wanted our rocket to emit soware particles that had
true geometry and could be rendered with the Maya Soware renderer or mental ray, we
would have had to choose a particle type with “s/w” next to it.
USING SOFTWARE PARTICLES IN nDYNAMICS TO CREATE TRIX
Now, we will look at using soware-rendered particles. We will create particles that have
actual geometry. us, we will be using 3D geometry to specify the appearance of each
particle, but their movement will be dened by the same mathematics of particle dynamics
we would use for hardware-rendered particles.
FIGURE 6.4 Particle attributes.
FIGURE 6.5 e hard-
ware particles.
Particle Dynamics ◾ 203
nDynamics in Maya
e n in nDynamics stands for Nucleus, and you can access it by selecting
nDynamics in the Main Menu Selector. is is an alternative dynamics
system in Maya, and to distinguish it, the Maya interface uses the terms
nParticles, nCloth (which we will look at momentarily), and so on.
In the Dynamics system, a particle does not modify its behavior in
response to the movement of other particles. In particular, they cannot
collide. But in nDynamics, the movements of particles can be dynami-
cally aected by each other, and in particular, two particles can collide.
Particles can even be set to react if they come within a specic distance
from each other.
Particle Dynamics Engines and Solvers
Applications like Maya include complex systems that contain math-
ematical subsystems that simulate the physics of the real world.
FIGURE 6.6 Assigning a black Blinn to the particles.
FIGURE 6.7 e
hardware rendered
particles.
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