Cloth Animation

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Outline

Overview (this class)Cloth Modeling (this class) Integrating ODE of cloth (next class)Collision detection and handling (next class)

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Why cloth simulation?

High demands fromCharacter animationGame industryFashion industryTextile industry

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Challenges of Cloth Simulation

Realistic cloth Interactive cloth Stable clothComplex clothCollision detection/handling

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Cloth Modeling

Textile Engineeringmeasuring mechanical propertiesCAD/CAM and industrial applications

Computer GraphicsSimulating the complex shapes and deformations

of fabric and clothingGeometric approachesPhysically-based approaches

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The Drapemeter (1950)Used to quantify draping behavior

Drape factorNumber of folds

DA R2

2

R12 R2

2

cloth

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Kawabata System (1973)

Measure the mechanical properties of clothBending, shearing, tensile, compression, etc.

Volino and Magnenat-Thalmann, “Virtual Clothing”

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CG Cloth Modeling

Geometric approachesWeil (1986)

Continuum approachesFeynman (1986) - minimize strain energyTerzopoulos et al. (1987) - elasticity-based

forcesThalmanns (1990 on) –virtual clothing

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CG Cloth Modeling (cont.)

Particle-based approachesHaumann (1987) - Mass-spring modelBreen et al. (1991-94) - Particle-based model

Misc.Eberhardt et al. (1995 on) - Modeling knitsBaraff & Witkin (1998) - Implicit integrationDesbrun et al. (2000) - Interactive “cloth”Ko & Choi (2002) –Buckling model

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Continuum Approaches

Modeling cloth with continuum physicsDiscretize objectCalculate forces Integrate forcesBased on elasticity theoryBased on finite-element method

Not commonly used in practice

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Feynman (1986) Predicts cloth deformation by minimizing

Strain energyBending energy

Very “stretchy”cloth

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Terzopoulos et al. (1987) Based on elasticity theory & differential geometry

Simplified dynamicsElastic deformation Inelastic deformationFracture

21

22duduBBGG oo

distance & angle curvature

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Terzopoulos et al. Results

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Terzopoulos et al. Results

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Thalmann (1990 - Present)

Extend Terzopoulos model Enhanced computational techniques

Collision detection and response

Designing a complete set of clothingUser interfaceData structures

Focused on clothing virtual actors

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Thalmann et al. Results

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Thalmann et al. Results (1995)

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Thalmann et al. Results (2005)

La Haute Couture Mise en Equations

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Particle-based Approaches Breen, House, Getto, Wozny, 1992-1994 Macroscopic behavior arises from modeling

microscopic structure Particles based on thread-level interactions

Breen et al. “A physically-based particle model of woven cloth,”1992

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Breen (1994) Energy-based model

Compute final draping configuration byminimizing the total energy in the cloth

iiiii trellisbendstretchrepeltotal UUUUU

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Breen (1994) Tries to make the drape more realistic by

measuring from the reality (Kawabata system) Fit functions to the measured data

No dynamics involvedBending Tester

Shearing Tester

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Breen et al. Results

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Breen et al. Results

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Extend to include dynamics

Add cloth springs to model Stretch Shearing Bending

separation spring(nonlinear forces)

trellising spring(nonlinear torques)

bending spring(nonlinear torques)

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Mass-spring Model

A simple spring-damper system due to Provot(1995)

Courtesy of Chris Twigg

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Baraff and Witkin (1998)

Rapid cloth simulation with implicitintegration

Larger time steps and faster simulations Triangle-based representation Exploit sparseness of JacobianUsed in Maya ClothWe will introduce this approach in next class

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Baraff and Witkin Results

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Ko, Choi (2002)Cloth property

Weak resistance to bendingStrong resistance to tension

Problem in spring-mass modelStiff system for non-stretchNeed large compression forces for out-of-plane

motion

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Ko, Choi (2002)Use column buckling as their basic modelReplace bend and compression forces with a

single nonlinear model

ideal bucking curve

approximated

bucking load

column bucking

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Ko and Choi results

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Eberhardt et al. (1995 - Present)

Focus on knits, instead of woven cloth Particle system with measured energiesVolumetric approach to rendering knits

Represent microstructureSweep density distributions along yarns

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Eberhardt et al. Results