An implicit formulation for precise contact modeling between flexible solids

Published under the name Marie-Paule GascuelInternational audienceThis paper presents an implicit deformable model, based on isosurfaces of potential fields generated by skeletons, that provides elegant and unified formulations for both geometric parameters such as shape or deformation and physical properties such as rigidity. The model is especially designed to improve collision and contact processing for non-rigid objects. In particular, it generates and maintains exact contact surfaces during interactions

A Vortex Method for Bi-phasic Fluids Interacting with Rigid Bodies

We present an accurate Lagrangian method based on vortex particles, level-sets, and immersed boundary methods, for animating the interplay between two fluids and rigid solids. We show that a vortex method is a good choice for simulating bi-phase flow, such as liquid and gas, with a good level of realism. Vortex particles are localized at the interfaces between the two fluids and within the regions of high turbulence. We gain local precision and efficiency from the stable advection permitted by the vorticity formulation. Moreover, our numerical method straightforwardly solves the two-way coupling problem between the fluids and animated rigid solids. This new approach is validated through numerical comparisons with reference experiments from the computational fluid community. We also show that the visually appealing results obtained in the CG community can be reproduced with increased efficiency and an easier implementation

The Line of Action: an Intuitive Interface for Expressive Character Posing

International audienceThe line of action is a conceptual tool often used by cartoonists and illustrators to help make their figures more consistent and more dramatic. We often see the expression of characters--may it be the dynamism of a super hero, or the elegance of a fashion model--well captured and amplified by a single aesthetic line. Usually this line is laid down in early stages of the drawing and used to describe the body's principal shape. By focusing on this simple abstraction, the person drawing can quickly adjust and refine the overall pose of his or her character from a given viewpoint. In this paper, we propose a mathematical definition of the line of action (LOA), which allows us to automatically align a 3D virtual character to a user specified LOA by solving an optimization problem. We generalize this framework to other types of lines found in the drawing literature, such as secondary lines used to place arms. Finally, we show a wide range of poses and animations that were rapidly created using our system

N-ary implicit blends with topology control

International audienceConstructive implicit surfaces are attractive for modeling and animation because they seamlessly handle shapes with complex and dynamic topology. However, the way they merge shapes is difficult to control. This paper introduces a solution: an improved blend operator that provides control over how topology changes are handled. It is based on a correction applied to the standard blending operator: the sum. Building on summation preserves the n-ary nature of the blend, providing the simplicity of arbitrary (e.g. flat) construction trees and segmentation invariance. The correction is based on projection to a reference case in the variation-space defined by the field and the norm of its gradient. It provides a single parameter, allowing for tuning behavior to achieve effects ranging from avoiding topological combination, through merging only during overlap, to merging at a distance. Dynamic adjustment of the parameter allows for context-dependent effects. Applications range from skeleton-based modeling, where shapes keep the topology of their skeleton, to objects that change topology during animation, with controllable merging. We illustrate the latter with Manga-style hair, where merging depends on the angle between hair wisps

Generation of Folded Terrains from Simple Vector Maps

International audienceWhile several terrain generation methods focused on plausible watersheds, the fact that most mountains should not be isolated but rather be part of wider scale mountain ranges was seldom considered. In this work, we present the first procedural method that generates folded terrains from simple user input, in the form of some sparse peak distribution on a vector map. The key idea is to infer possible continental plates from this distribution and to use simplified plate tectonics to generate relevant terrain folds. The resulting terrain with large-scale folds, computed in real-time, can be further refined using standard erosion simulation. This leads to detailed terrains with plausible mountain ranges that match the peak distributions and main rivers specified on simple vector maps

Ajout de détails dynamiques à une animation temps-réel de personnage

National audienceReal-time animation of characters often relies on a geometric technique called skinning which enables the skin and clothes to follow the skeleton motion. However, dynamic effects - non-rigid tissues vibrations, dynamic wrinkles of skin and clothes - can not be generated by it. However such deformations are of primary importance for the realism of the generated animation. In this paper, we propose two intuitive methods which address those specific problems with little increase in computational cost of the animation. Our tools can be combined together on an existing animation sequence to enhance its realism, with no need to change the original animation, no mechanics precomputation and no modification of the model. We illustrate our results with several characters and animals animations.L'animation temps-réel de personnages repose généralement sur une technique d'habillage, appelée skinning en anglais, permettant à la peau et aux vêtements de suivre les mouvements du squelette. Cette technique n'engendre malheureusement aucun des effets dynamiques - vibrations des tissus non-rigides, plissement variable de la peau et des vêtements - pourtant cruciaux pour le réalisme. Dans cet article, nous présentons deux techniques complémentaires pour ajouter ces effets de manière intuitive, tout en limitant au maximum les sur-coûts lors du calcul de l'animation. Combinables entre eux et rapides à mettre en place, nos outils améliorent le réalisme visuel du mouvement sans nécessiter de modification de la séquence d'animation de départ, de précalcul mécanique ni de modification des modèles. Nous illustrons nos résultats sur des animations variées de personnages et d'animaux

Active Implicit Surface for Animation

Published under the name Marie-Paule Cani-GascuelInternational audienceThis paper introduces a new model of deformable surfaces designed for animation, which we call active implicit surfaces. The underlying idea is to animate a potential field defined by discrete values stored in a grid, rather than directly animating a surface. This surface, defined as an iso-potential of the field, has the ability to follow a given object using a snake-like strategy. Surface tension and other characteristics such as constant surface area or constant volume may be added to this model. The implicit formulation allows the surface to easily experience topology changes during simulation. We present an optimized implementation: computations are restricted to a close neighborhood around the surface. Applications range from the coating of deformablematerials simulated by particle systems (the surface hides the granularity of the underlying model) to the generation of metamorphosis between shapes that may not have the same topology.Nous présentons dans ce papier un nouveau modèle de surface déformable pour l'animation en Synthèse d'Images, appelé surface implicite active. Cette surface est définie comme une isopotentielle d'un champ discret, dont on modifie les valeurs afin d'animer la surface en retour. Le comportement de la surface permet de suivre le contour d'un objet à la manière des snakes en vision, tout en simulant une tension de surface et/ou un volume constant. La formulation implicite permet tout changement de topologie. Nous proposons une implémentation optimisée, où les calculs sont restreints à un voisinage proche de la surface. Les applications peuvent s'étendre de l'enrobage de systèmes de particules, où la surface permet de dissimuler la granularité de la simulation, à la création de métamorphoses automatiques entre objets de topologie quelconque

Un modeleur interactif d'objets définis par des surfaces implicites

Published under the name Marie-Paule GascuelNational audienceThis article presents a modeling tool for interactive design of objects defined by implicit surfaces. Based on a new sampling, it offers to complementary real-time visualizing modes and allows the user to control the defined objects in a very simple way, by interactively manipulating their skeletons and the associated field functions.Cet article présente un outil de modélisation interactive d'objets définis par des surfaces implicites engendrées par des squelettes. Basé sur une nouvelle technique de discrétisation adaptative, il offre deux modes complémentaires de visualisation temps réel, et permet un contrôle simple des objets via la manipulation interactive de leur squelettes et des fonctions potentiel associées

Virtual Clay for Direct Hand Manipulation

International audienceIn order to make virtual modeling as easy as real clay manipulation, we describe a realtime virtual clay model, specially designed for direct hand manipulation. We build on a previous layered model for clay, extending it to handle local properties such as colour or fluidity, to deal with an arbitrary number of tools, and to capture twist effects due to rotating tools. The resulting clay model is the first step towards a more long term goal, namely direct interaction through video tracking of the user's hands