Soft Textured Shadow Volume

International audienceEfficiently computing robust soft shadows is a challenging and time consuming task. On the one hand, the quality of image-based shadows is inherently limited by the discrete property of their framework. On the other hand, object-based algorithms do not exhibit such discretization issues but they can only efficiently deal with triangles having a constant transmittance factor. This paper addresses this limitation. We propose a general algorithm for the computation of robust and accurate soft shadows for triangles with a spatially varying transmittance. We then show how this technique can be efficiently included into object-based soft shadow algorithms. This results in unified object-based frameworks for computing robust direct shadows for both standard and perforated triangles in fully animated scenes

Topology-Aware Neighborhoods for Point-Based Simulation and Reconstruction

International audienceParticle based simulations are widely used in computer graphics. In this field, several recent results have improved the simula- tion itself or improved the tension of the final fluid surface. In current particle based implementations, the particle neighborhood is computed by considering the Euclidean distance between fluid particles only. Thus particles from different fluid components interact, which generates both local incorrect behavior in the simulation and blending artifacts in the reconstructed fluid sur- face. Our method introduces a better neighborhood computation for both the physical simulation and surface reconstruction steps. We track and store the local fluid topology around each particle using a graph structure. In this graph, only particles within the same local fluid component are neighbors and other disconnected fluid particles are inserted only if they come into contact. The graph connectivity also takes into account the asymmetric behavior of particles when they merge and split, and the fluid surface is reconstructed accordingly, thus avoiding their blending at distance before a merge. In the simulation, this neighborhood information is exploited for better controlling the fluid density and the force interactions at the vicinity of its boundaries. For instance, it prevents the introduction of collision events when two distinct fluid components are crossing without contact, and it avoids fluid interactions through thin waterproof walls. This leads to an overall more consistent fluid simulation and reconstruction

Volume MLS Ray Casting

The method of Moving Least Squares (MLS) is a popular framework for reconstructing continuous functions from scattered data due to its rich mathematical properties and well-understood theoretical foundations. This paper applies MLS to volume rendering, providing a unified mathematical framework for ray casting of scalar data stored over regular as well as irregular grids. We use the MLS reconstruction to render smooth isosurfaces and to compute accurate derivatives for high-quality shading effects. We also present a novel, adaptive preintegration scheme to improve the efficiency of the ray casting algorithm by reducing the overall number of function evaluations, and an efficient implementation of our framework exploiting modern graphics hardware. The resulting system enables high-quality volume integration and shaded isosurface rendering for regular and irregular volume data.Engineering and Applied Science

Déformation de la peau d'un personnage avec prise en compte des contacts

National audienceLors de l'animation d'un maillage représentant la peau d'un personnage ou d'un animal par exemple, des techniques dites de skinning sont utilisées pour le déformer au niveau des articulations. Bien que très populaires dans l'industrie pour leur très faible coût d'évaluation, les techniques de skinning géométrique comme le LBS (Linear Blending Skinning) ou les dual quaternions, ne permettent pas d'imiter de façon crédible les déformations des membres. Pour mieux capturer le comportement de la peau, d'autres méthodes basées seulement sur le maillage, utilisent des calculs coûteux comme la détection de collisions ou la correction de volume. Toutefois ces approches restent seulement adaptées au rendu hors ligne. Nous présentons la première méthode temps réel produisant une déformation du maillage en prenant en compte le contact de la peau et, éventuellement, le gonflement des muscles. Nous proposons d'utiliser de façon conjointe le maillage et une représentation volumique. Le maillage est approximé avec une surface implicite qui nous permet de le déformer de façon plausible tout en traitant les collisions et en conservant les détails du maillage

Implicit Skinning: Real-Time Skin Deformation with Contact Modeling

SIGGRAPH 2013 Conference ProceedingsInternational audienceGeometric skinning techniques, such as smooth blending or dualquaternions, are very popular in the industry for their high performances, but fail to mimic realistic deformations. Other methods make use of physical simulation or control volume to better capture the skin behavior, yet they cannot deliver real-time feedback. In this paper, we present the first purely geometric method handling skin contact effects and muscular bulges in real-time. The insight is to exploit the advanced composition mechanism of volumetric, implicit representations for correcting the results of geometric skinning techniques. The mesh is first approximated by a set of implicit surfaces. At each animation step, these surfaces are combined in real-time and used to adjust the position of mesh vertices, starting from their smooth skinning position. This deformation step is done without any loss of detail and seamlessly handles contacts between skin parts. As it acts as a post-process, our method fits well into the standard animation pipeline. Moreover, it requires no intensive computation step such as collision detection, and therefore provides real-time performances

Robust iso-surface tracking for interactive character skinning

International audienceWe present a novel approach to interactive character skinning, which is robust to extreme character movements, handles skin contacts and produces the effect of skin elasticity (sliding). Our approach builds on the idea of implicit skinning in which the character is approximated by a 3D scalar field and mesh-vertices are appropriately re-projected. Instead of being bound by an initial skinning solution used to initialize the shape at each time step, we use the skin mesh to directly track iso-surfaces of the field over time. Technical problems are two-fold: firstly, all contact surfaces generated between skin parts should be captured as iso-surfaces of the implicit field; secondly, the tracking method should capture elastic skin effects when the joints bend, and as the character returns to its rest shape, so the skin must follow. Our solutions include: new composition operators enabling blending effects and local self-contact between implicit surfaces, as well as a tangential relaxation scheme derived from the as-rigid-as possible energy to solve the tracking problem

Monte Carlo simulations of random non-commutative geometries

Random non-commutative geometries are introduced by integrating over the space of Dirac operators that form a spectral triple with a fixed algebra and Hilbert space. The cases with the simplest types of Clifford algebra are investigated using Monte Carlo simulations to compute the integrals. Various qualitatively different types of behaviour of these random Dirac operators are exhibited. Some features are explained in terms of the theory of random matrices but other phenomena remain mysterious. Some of the models with a quartic action of symmetry-breaking type display a phase transition. Close to the phase transition the spectrum of a typical Dirac operator shows manifold-like behaviour for the eigenvalues below a cut-off scale

Faster Geometric Algorithms via Dynamic Determinant Computation

The computation of determinants or their signs is the core procedure in many important geometric algorithms, such as convex hull, volume and point location. As the dimension of the computation space grows, a higher percentage of the total computation time is consumed by these computations. In this paper we study the sequences of determinants that appear in geometric algorithms. The computation of a single determinant is accelerated by using the information from the previous computations in that sequence. We propose two dynamic determinant algorithms with quadratic arithmetic complexity when employed in convex hull and volume computations, and with linear arithmetic complexity when used in point location problems. We implement the proposed algorithms and perform an extensive experimental analysis. On one hand, our analysis serves as a performance study of state-of-the-art determinant algorithms and implementations. On the other hand, we demonstrate the supremacy of our methods over state-of-the-art implementations of determinant and geometric algorithms. Our experimental results include a 20 and 78 times speed-up in volume and point location computations in dimension 6 and 11 respectively.Comment: 29 pages, 8 figures, 3 table

Empreinte carbone des heures de calculs : limites et paradoxes

National audienceAvec la prise de conscience croissante de l'urgence climatique nous pouvons observer une frénésie à la quantification carbone de la moindre action individuel. Le domaine du calcul intensif n'échappe pas à ce constat, que ce soit pour quantifier les impacts liés à une publication, un projet, un laboratoire, ou autre. Au travers cet exposé nous commencerons par décortiquer la fabrication de ces indicateurs pour mieux comprendre ce qu'ils nous révèlent de la réalité et au contraire ce qu'ils cachent. Cet analyse nous permettra de mettre en lumière de mauvaises interprétations fréquemment réalisées dont certaines conduisent à des situations paradoxales, voire même à des actions contre productives. Enfin, je partagerais quelques pistes pour ce prémunir de ces biais

Représentation hybride pour la modélisation géométrique interactive

De nos jours, les objets virtuels sont devenus omniprésents. On les trouve dans de nombreux domaines comme le divertissement (cinéma, jeux vidéo, etc.), la conception assistée par ordinateur ou encore la réalité virtuelle. Nous nous intéressons en particulier à la modélisation d'objets 3D dans le domaine de la création artistique. Ici, la création d'images riches nécessite de faire appel à des modèles très détaillés et donc extrêmement complexes. Les surfaces de subdivision, traditionnellement utilisées dans ces domaines, voient leur complexité croître rapidement lorsqu'on ajoute des détails, et la gestion de la connectivité du maillage de contrôle devient trop contraignante. Une approche standard pour gérer la complexité de tels modèles est d'utiliser des représentations différentes pour la forme générale de la surface et les détails. Cependant, ces détails sont représentés par des cartes matricielles qui ne possèdent pas la plupart des avantages des représentations vectorielles, et cela complexifie certaines tâches, comme par exemple l'animation. Dans cette thèse, nous proposons deux nouvelles représentations vectorielles, la première pour les surfaces de base, la deuxième pour les détails. Nous utilisons pour cette dernière une représentation vectorielle appelée images de diffusion permettant de créer des variations lisses à l'aide d'un ensemble réduit de contraintes. Cela nous permet de représenter aussi bien la géométrie que la couleur ou d'autres paramètres nécessaires au rendu de façon purement vectoriel, en conservant des contrôles de haut niveau.Notre première contribution est une représentation de surfaces, baptisée LS3, issue de la combinaison entre surfaces de subdivision et -point set surfaces. Cette approche réduit notablement les artefacts des surfaces de subdivision aux alentours de sommets dits extraordinaires, qui sont connus pour poser problème. Nous présentons une analyse numérique des propriétés de ces surfaces, qui tend à montrer que du point de vue de la continuité elles se comportent au moins aussi bien que les schémas de subdivision linéaires traditionnels. Notre deuxième contribution est un solveur pour les images de diffusion dont le principal avantage est de produire en sortie une autre représentation vectorielle légère et très rapide à évaluer. Nous illustrons la force de note solveur sur de nombreux exemples difficiles ou impossibles à réaliser avec les méthodes précédentes. Pour conclure, nous montrons comment combiner nos deux contributions pour obtenir une représentation de surface entièrement vectorielle capable de représenter des détails sans avoir à manipuler la connectivité d'un maillage.Nowadays, virtual objects have become omnipresent. We can find them in various domains such as entertainment (movies, video games, etc.), computer-aided design or virtual reality. Our main focus in this document is the modeling of 3D objects in the domain of artistic creation, where rich images creation requires highly detailed and complex models.Subdivision surfaces, the most used surface representation in this domain, quickly become very dense as the user add details, and manual handling of the connectivity becomes too cumbersome. A standard approach to handle the complexity of such models is to separate the overall shape of the surface and the details. Although, these detail maps are often stored in bitmap images that does not provide the advantages of vectorial representation, which complicate some tasks, like animation.In this document, we present two new vectorial representations: the first one for the base surface, the second one for the detail maps. For the later, we use a vectorial representation called diffusion images that allow to create smooth or sharp variations from a small set of constraints. This enables us to represent geometry as well as color or any other parameter required for rendering, while keeping high-level controls.Our first contribution is a surface representation, called LS3, based on the combination of subdivision surfaces and point set surfaces. This approach reduces notably artifacts that subdivision surfaces produce around so called extraordinary vertices. We also present a numerical analysis of the mathematical properties of these surfaces, that show that they behave at least as well as classical subdivision schemes.Our second contribution is a solver for diffusion images that has the particularity to produce as output a denser vectorial representation which is light and fast to evaluate. We show the advantages of this approach on several examples that would be hard or impossible to produce with former methods.To conclude, we show how these two contributions can be used together to obtain a fully vectorial surface representation able to produce detailed surfaces without needing to deal with complex connectivity.BORDEAUX1-Bib.electronique (335229901) / SudocSudocFranceF