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@uhasselt.be

2. 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

3. 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

4. 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

5. 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

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

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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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

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

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

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