Faking Dynamics of Cloth Animation for Animated Films Fabian Di Fiore Expertise Centre for Digital Media Hasselt University, Belgium

AMDO2010 July, /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

AMDO2010 July, /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, /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, /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, /19 Contribution Introduction Related Work Contribution Approach Results Conclusions

AMDO2010 July, /19 Approach Introduction Related Work Contribution Approach Results Conclusions

AMDO2010 July, /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, /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, /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, /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, /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, /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, /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, /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, /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, /19 Results Introduction Related Work Contribution Approach Results Conclusions

AMDO2010 July, /19 Results Introduction Related Work Contribution Approach Results Conclusions

AMDO2010 July, /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