Faking Dynamics of Cloth Animation for Animated Films

1
Faking Dynamics of Cloth Animation for Animated
Films

• Fabian Di Fiore
• Expertise Centre for Digital MediaHasselt
  University, Belgium
• fabian.difiore_at_uhasselt.be

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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

need for allowing animators to interactively
create visually pleasing animations of cloth
models while keeping them in full control of the
animation process
Introduction Related Work Contribution
Approach Results Conclusions motivation
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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
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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
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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
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Contribution
Introduction Related Work Contribution
Approach Results Conclusions
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Approach
Introduction Related Work Contribution
Approach Results Conclusions
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Cloth Modelling

• Representation
• cloths 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
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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
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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
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Cloth Modelling

• Surface Approximation (ctd)
• determine remaining points through subdivision
• through subdividing each triangle by creating
  catenary between highest vertex and triangles
  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
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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 edges
  end points, y through catenary between edges 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
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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
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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
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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
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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
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Results
Introduction Related Work Contribution
Approach Results Conclusions
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Results
Introduction Related Work Contribution
Approach Results Conclusions
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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