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here are a handful of visual phenomena that are

devilishly difficult to simulate with a computer.

Fluids, hair, fur and cloth are notorious for

requiring complex and expensive software,

talented artistry and powerful computing. But these effects,

while feared by digital artists, are able to lend a sense of

realism to CG work not easily achieved by any other means.

While the topic of this tutorial is cloth, all of these effects

share a common trait: extreme complexity. You dont have to l ook

any further than your own shirt to witness the breadth of chaos

exhibited by a simple piece of cloth. The cascading folds of material

on a typical T-shirt would be enough to send any polygon modeller

screaming for help.

Fortunately, help isnt far away. This tutorial is meant to

introduce you to a typical workflow for animating cloth with

Maya Cloth. This is a powerful toolset which, in my opinion,

deserves some serious attention. Its not the easiest thing in the

world to use, but its reliable. Novice users are often confused by

its somewhat odd workflow, mistaking its steep learning curve

for a weakness. The truth is that Maya Cloth can be hard to learn,

but its difficulty is proportional to its flexibility. I want to mention

that many people prefer the SyFlexplug-in for serious cloth work.

In my experience, SyFlexhas definitely been somewhat easier to

work with and perhaps less prone to instability. The SyFlexsolver

seems to adaptively adjust itself where Maya Cloth requires a little

babysitting from time to time. The bottom line: if you have the

money, get SyFlex. However, Maya Cloth is still a capable solver.

This tutorial will provide an overview of a production-worthy

workflow for creating believable cloth animation. Well follow

the creation of a cloth garment for the Minx character from the

upcoming The Art of Rigging Vol iii. In the textbook, youll find

every detail of this fascinating topic, including the creation of our

characters hair/fur, cloth and much more.

Kiaran Ritchie is an author on The Art of Riggingseries from

CG Toolkit. Hes currently working on a number of PS3 projects

at Factor 5 in San Rafael, California

www.cgtoolkit.com

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FACTFILE

FOR

Maya Unlimited 7+

DIFFICULTY

Intermediate

TIME TAKEN

10-30 minutes

ON THE CD

Full-size screenshots

Mayascene files

Character turntable

movie

Playblast movies

ALSO REQUIRED

N/A

Creating realistic animated cloth is a notoriously difficult process, but this tailor-made tutorialshould help you get even the most misshapen characters clad with ease BY KIARAN RITCHIESackcloth and gashes

MAYAMAYA

TUTORIALS |Cloth simulation

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To model a garment with Maya Cloth, we must start

with a pattern. This pattern represents the various

pieces of cloth (panels) that will eventually be sewn

together to form the finished garment. A panel is constructed

from three or more planar NURBS curves that form a closed

loop. A typical garment may comprise several panels that are

sewn together to create a polygonal mesh.

Creating garment patterns is beyond the scope of

this tutorial, but you shouldnt have to look further

than your local fabric store for numerous examples

of various patterns for common garments. For the Minxs

robe, I constructed the panels without a set pattern, but for

a more humanoid character, it would be easier to use a pre-

made pattern. The Minxs robe uses 18 separate panels.

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STAGE ONE |Drawing the panels

Open stage01.mb from the CD. This scene file

contains the Minx character. Unlike most cloth

software, Maya Cloth provides a method of

both animating and modelling clothing. This is an often

misunderstood feature that, when used correctly, can create

excellently constructed garments with ease, using a real-

world pattern/panel/sewing paradigm.

01 02

Start by selecting each set of panel curves from the

Hypergraph. With a complete panel selected, choose

Cloth > Create Panel. This will create a shirt icon

in the middle of the panel. Go through the Hypergraph and

make a panel for each group of curves. Now were ready to

create the garment. Select a panel icon (the shirt) and chooseCloth > Create Garment. This creates a polygon mesh.

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To draw a panel, select the EP Curve Tool and trace

the pattern. Create a new curve for each segment

of the pattern. Use the [c] key to snap the start CV

of each new curve to the end CV of the last curve. Make sure

you create the curves in an orthographic viewport in order to

keep them planar. The size of a panel determines the surface

area of the resulting cloth.

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You can now group the panel curves and position

them around the character. This stage usually

involves lots of trial and error. The panels must be

sized to give the garment enough cloth so that it drapes

properly. You may find yourself returning to this step several

times to fine-tune the fit of the clothing. Remember, a larger

panel creates more cloth, which results in baggier clothing.

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Now open stage02.mb. This contains the finished

panel curves, ready to be sewn together into a

garment. This process involves three steps: first, we

must turn each set of panel curves into a panel. Second, we

create a garment from one of the panels. Finally, we sew the

neighbouring panels together, automatically creating the restof the garment as each new panel is sewn together.

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Cloth simulation| TUTORIALS

Now lets begin sewing everything together. Start

with the panel that was turned into a garment and

sew it to all of the neighbouring panels. To do this,

select two panel curves and execute Cloth > Create Seam.

This will add the new panel to the garment and extend the

polygon mesh into the new panel. Work your way through therest of the garment, sewing all the seams together.

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EXPERT TIP

Streamlined sewingThe process of creating panels,

sewing them together, draping,

fitting, adjusting and resizing can be

quite time consuming. To streamline

the process, we can create an

instanced duplicate of the cloth

curves to use for resizing, while

the sewn garment updates in real

time. To do this, create an instanced

duplicate of the panel curves before

turning them into panels. You now

need to create the garment from

the duplicates and sew it together.

From here, you can simply adjust theshape of the panel curves to quickly

tailor the garment.

i

STAGE TWO |Creating the garment


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Open stage03.mb to see the fully sewn garment.

Now select the garment and find the cpStitcher1

node in the Channel Box. Set the Base Resolution

attribute to a value of 600. This will create more polygons for

the solver to use when creating folds and collisions. Higher

resolutions yield more realistic folding, but at the cost of

longer simulation times.

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For a more accurate simulation (especially with

collisions), increment the Frame Samples attribute

until any interpenetrations or glitches are remedied.

The Relax Frame Length attribute is used to drape the

garment onto the character. It applies a rubbery material to

the cloth to help it pull together smoothly. Set this to 0 after

draping the garment.

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Open stage05.mb. Having seen how to create and

drape a garment, lets apply these principles to an

animation. This scene file contains a more refined

version of the garment thats draped onto the Minx. This

time, the character has been animated and so we need to set

up the simulation so that the cloth flops around as the Minxjumps up and down.

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Note that the scene file doesnt contain any curves,

panels or seams. This garment was created using

the same method described earlier, except that,

after draping, I duplicated the mesh to create the cloth

object. Theres no need to keep the construction history

(panels) for the cloth garment after its draped. Also note thatholes have been cut into the mesh at the base of the spikes.

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Run the simulation again and youll notice that the

garment now collides with the characters skin.

Unfortunately, it gets stuck on the spikes. We want

the collision to ignore the faces on the spikes. To do this,select all of the faces (use the Quick Select Set) and choose

Cloth > Collision Cloth Set > Create. Uncheck Enable Rigid

Collisions on the Cloth Set in the Attribute Editor.

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Open stage04.mb. Play back the scene (use Play

Every Frame) to run the simulation. At this point, the

garment crumples into a ball during the relaxation

phase (first five frames) and then falls due to gravity. Wewant it to hang from the character. To do this, select the

Minxs mesh and choose Cloth > Create Collision Object. Set

the Collision Depth and Collision Offset to a value of 0.1.

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Because Maya Clothuses a pseudo physically based

simulation engine, the scale of the solver must be

set in order to produce realistic results. This is

computed by taking the real-world size of the garment

(80cm) and dividing it by the scene size (8cm). Set the Solver

Scale attribute on the cpSolver node to a value of 10 (80/8).

Leave the rest of the solver attributes at their default values.

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Now we need to set up the cloth again. Select the

garment mesh and choose Cloth > Create Cloth

Object. On the solver node, set the Start Time to

-10 and the Solver Scale to 10. Because the garment is

already draped, set the Relax Frame Length to 0. Make the

Minxs mesh a collision object and set the Collision Offset andCollision Depth to 0.1.

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TUTORIALS | Cloth simulation

Run the simulation and you should now notice that

the garment passes right through the spikes. Well

cut holes in the garment, but for now we just want

the solver to ignore the spikes. Collision sets are useful forcheating the solver and can help you prevent glitches and

pinches in the cloth. This concludes the set-up of the cloth, so

lets take a look at simulation.

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STAGE THREE |Adjusting the Cloth solver and adding collisions

STAGE FOUR |Simulating the cloth


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Cloth simulation| TUTORIALS

You may notice that the cloth doesnt have any

thickness. Actually, it lacks any detail that would be

superfluous to its motion. Unhide the render cloth

layer to see a thickened version of the cloth. This copy has

been extruded and quadrangulated (for better smoothing),

and it will be wrap-deformed to the simulation garment, so

that it deforms along with that garment.

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Its rare that a cloth simulation will be perfect the

first time. This usually requires quite a bit of trial

and error, various adjustments and elbow grease.

Even if the simulation goes well, there are usually small

imperfections, popping vertices or interpenetrations. Its not

always easy (or even possible) to fix these by adjusting thesimulation. Sometimes you need to just dig in and manually

model the fixes. To do this, scrub to the offending frame and

model the correction. When youre happy with how it looks,

select the mesh and choose Simulation > Update Cloth State.

The cache file will be updated to include the new changes.

This kind of cheating is referred to as shot sculpting. Once

the animation is looking good, simply hide the simulationgarment, smooth the render garment and youre ready.

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STAGE FOUR (Continued) |Simulating the cloth

Now play the scene. You should notice that the

cloth begins to crumple and misbehave around

frames 3-5. This is when the Minx springs upwards

at the base of the jump. During extremely fast motion, its

not uncommon to have to tweak the solver to help it solve.

Increase the Frame Samples from 1 to 5.

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Rewind the scene and choose Simulation > Delete

Cache. Each time the simulation is run, Mayasaves

a cloth cache file (MCC). Subsequent playback will

read the cloth vertex positions from this cache data. In order

to resimulate the cloth, you must first delete the old cache.

If no cache is found for the current frame, the solver will

automatically recalculate it.

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With the cache deleted, replay the simulation. A

modest workstation may take several minutes to

compute the 50-frame cloth animation. When the

simulation is finished, you can scrub through the timeline

to view the animation stored in the cache file. If the cloth

encounters a problem, you can truncate the cache from the

problem frame, adjust some parameters and resimulate.

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STAGE FIVE |The finishing touches

Select the thick cloth, [Shift]-select the simulation

cloth and choose Deform > Create Wrap. Set the Max

Distance to 0.2 and Influence Type to Points. Now

the thick cloth is animated along with the simulation cloth.

The render garment can contain any extra details and should

be smoothed before being rendered. Also make sure to lay

out the UVs of the render garment before wrap-deforming it.

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