Faking Dynamics of Cloth Animation for Animated Films

Fabian Di Fiore

Expertise Centre for Digital MediaHasselt University, Belgium

fabian.difiore@uhasselt.be

AMDO2010

July, 8 2010

2/19

Introduction

Visually pleasing animations of cloth models are an important feature of many of today's movies and games, and of the professional clothing industry (fashion, textile)

Existing animation and simulation techniques depend on real dynamics simulation

prohibitive in terms of computational cost prohibitive in terms of user control

Introduction • Related Work • Contribution • Approach • Results • Conclusions

motivation

need for allowing animators to interactively create visually pleasing animations of cloth models while keeping them in full control of the animation process

need for allowing animators to interactively create visually pleasing animations of cloth models while keeping them in full control of the animation process

AMDO2010

July, 8 2010

3/19

Related Work

Magic Carpet in Aladdin (1992, Disney) initially, full CGI model

texturally ok, but dynamics too ‘computerish’

hybrid solution (2D + 3D) animation entirely drawn on paper

(i.e. traditional 2D) 3D model artist laid out computer model over

the drawn carpet, frame by frame corner tassels were manually drawn

afterwards

Introduction • Related Work • Contribution • Approach • Results • Conclusions

AMDO2010

July, 8 2010

4/19

Related Work

Faking dynamics of Ropes and Springs

(1997, Ronen Barzel) Toy Story movies simple method for modelling 1D flexible linear

bodies such as ropes and springs default natural rest shape controls that perform gross modification and

deformations of the rest shape over time

no dynamic simulation limited to 1D

Introduction • Related Work • Contribution • Approach • Results • Conclusions

AMDO2010

July, 8 2010

5/19

Contribution

Fake dynamics for cloth animation in animated films distinguish between a modelling phase and a separate animation

phase

cloth is modelled hanging from arbitrary constraint points

interactively create and control the animation by adjusting the shape of models over time

using intuitive deformation tools and keyframe animation techniques

Introduction • Related Work • Contribution • Approach • Results • Conclusions

AMDO2010

July, 8 2010

6/19

Contribution

Introduction • Related Work • Contribution • Approach • Results • Conclusions

AMDO2010

July, 8 2010

7/19

Approach

Introduction • Related Work • Contribution • Approach • Results • Conclusions

AMDO2010

July, 8 2010

8/19

Cloth Modelling

Representation cloth’s surface = quadrilateral mesh initially a 2D grid consisting of 3D coordinates user specifies density, dimensions and constraint points

Introduction • Related Work • Contribution • Approach • Results • Conclusions

cloth modelling

AMDO2010

July, 8 2010

9/19

Cloth Modelling

Surface Approximation positions of constraint points known determine inner points between each pair of constraint points

using catenaries

Introduction • Related Work • Contribution • Approach • Results • Conclusions

cloth modelling

AMDO2010

July, 8 2010

10/19

Cloth Modelling

Surface Approximation (ctd) beware of crossings

different 3D position according to employed catenary remove lowest catenary as points can only be lifted during the

following relaxation step

Introduction • Related Work • Contribution • Approach • Results • Conclusions

cloth modelling

AMDO2010

July, 8 2010

11/19

Cloth Modelling

Surface Approximation (ctd) determine remaining points through subdivision

through subdividing each triangle by creating catenary between highest vertex and triangle’s centroid; repeat recursively

points along each new catenary can be calculated, however, severe approximation errors are induced

instead,show 3D catenaries and let user adjust constraint points

Introduction • Related Work • Contribution • Approach • Results • Conclusions

cloth modelling

AMDO2010

July, 8 2010

12/19

Cloth Modelling

Surface Approximation (ctd) determine remaining points at once

for each point P straight lines are drawn between the vertices and P we compute 3D positions for the intersections V; x and z coords by

interpolating between edge’s end points, y through catenary between edge’s end points

construct catenaries between vertices and intersection points V: x and z coords by interpolation, y through the highest located catenary

Introduction • Related Work • Contribution • Approach • Results • Conclusions

cloth modelling

AMDO2010

July, 8 2010

13/19

Cloth Modelling

Relaxation intended for fine-tuning the surface involves displacing the grid points until some constraints are

obeyed for each point, its placement is at a certain distance d from its

neighbours (d is influenced by the point's position on the catenary and the elasticity parameter)

for each point the angle formed with consecutive neighbours is related to the stiffness parameter

Introduction • Related Work • Contribution • Approach • Results • Conclusions

cloth modelling

AMDO2010

July, 8 2010

14/19

Cloth Dynamics

Sway Deformation swing back and forth or to and fro due to external force (e.g., wind) by means of a displacement vector for each point adjustable parameters indicate the magnitude, direction and speed

of swaying

Introduction • Related Work • Contribution • Approach • Results • Conclusions

cloth dynamics

AMDO2010

July, 8 2010

15/19

Cloth Dynamics

Wave Deformation defined by the parameters magnitude, frequency, and phase other parameters are time (t) and speed (v) to shift waves in time

and attenuation (a) to cause a larger waving effect in the centre of the cloth and a fall off near the constraint points

Introduction • Related Work • Contribution • Approach • Results • Conclusions

cloth dynamics

AMDO2010

July, 8 2010

16/19

Cloth Animation

Key frame animation system allows animators to easily adjust and edit pose and timing with

per-frame accuracy

key frames are easily created by building rest shapes

dynamic motions are incorporated in the timeline by superimposing them on the key and in-between frames

layered approach: multiple instances of deformations can be used together

Introduction • Related Work • Contribution • Approach • Results • Conclusions

cloth animation

AMDO2010

July, 8 2010

17/19

Results

Introduction • Related Work • Contribution • Approach • Results • Conclusions

AMDO2010

July, 8 2010

18/19

Results

Introduction • Related Work • Contribution • Approach • Results • Conclusions

AMDO2010

July, 8 2010

19/19

Conclusions

Concept of fake dynamics for cloth animation in animated films

Cloth is hanging from arbitrary constraint points

Existing animation and simulation techniques are often prohibitive in terms of user control

Our system allows the user to interactively model and animate cloth models over time using intuitive deformation tools and keyframe animation techniques

Introduction • Related Work • Contribution • Approach • Results • Conclusions