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580 Chapter 8: Modifiers
The Simulation
Once all of your parameters are set and you’re
ready to go, it’s time to simulate. In many cases,
you will first perform a local simulation to fit your
fabric to your character. Once your fabric is in
place, you can simulate over time.
Ru nning a simulation in Cloth is very freeform.
You are able to make many changes and edits to a
simulation, ma k ing it more of a work in progress
than a click and a “hope for the best” scenario.
Constraints
You can constrain fabric in various ways to create
different fabric effects during simulations. Cloth
can constrain cloth to have extra drag as it flies
through the air, or can cause it to b e affected by
a space warp in the scene. Linking a p ortion
of the fabric to an animated object or attaching
to a surface are other common constraints. If
you wanted to create a pair of pants you would
constrain the top portion of the pants to the waist
of the character or a curtain can be constrained
to a rod. Constraints are a very important and
robust part of Cloth. Cloth has the ability to make
multiple groups of constrained vertices for great
flexibility. You can constrain many different parts
of a piece of clothing to different nodes’ surfaces or
other cloth objects.
You build constraints in Cloth at the modifier’s
Group sub-object level (page 1–589).Atthislevel,
you can see vertices of a ll selected objects, both
cloth and collision. You can then select these and
place them in groups. Once a group is defined,
you can then attach or "constrain" the selection
set to another object, or have it affected by some
external force.
Pr ocedur es
Example: To use the K eep Shape option:
If your cloth object starts out with 3D shape that
you’d like to retain during the simulation, you
can use the Keep Shape option and setting to
preserve this shape, or even reverse it. This simple
procedure provides an example of how to use Keep
Shape.
1. IntheToporPerspectiveviewport,addaPlane
primitive object of about 90 x 90 units, with 20
x20segments.
2. Apply a Bend modifier , set Angle to 250.0,and
set Bend Axis to X.
This produces the initial tubular shape.
3. Copy the bent plane twice so you have three
planes in a row. Rename the planes as follows:
• don’t keep s h ape
• keep sh ap e
• reverse shape
4. Select all three planes and apply the Cloth
modifier.
5. On the Simulation Parameters rollout, turn off
Gravity and set cm/unit to 0.5.
Turn ing off Gravity keeps the cloth objects
from falling during the simulation, so they
stay in view, and lowering the cm/unit setting
compensates for the planes’ relatively large size.
6. On the Object rollout, click Object Prop erties.
This opens the Object Properties dialog.
7. In the Objects In Simulation list, highlight all
three planes (by dragging), and then, above the