The implicit skinning is a geometric interactive skinning method, for skeleton-based animations, enabling plausible deformations at joints while resolving skin self-collisions. Even though requiring a few user interactions to be adequately parameterized, some efforts have to be spent on the edition of the shapes at jointsIn this research, we introduce a dedicated optimization framework for automatically adjusting the shape of the surfaces generating the deformations at joints when they are rotated during an animation. This approach directly fits in the implicit skinning pipeline and it has no impact on the algorithm performance during animation. Starting from the mesh partition of the mesh representing the animated character, we propose a dedicated hole filling algorithm based on a particle system and a power crust meshing. We then introduce a procedure optimizing the shape of the filled mesh when it rotates at the joint level. This automatically generates plausible skin deformation when joints are rotated without the need of extra user editing. (c) 2021 Elsevier Ltd. All rights reserved.

Most current methods for character skinning can be categorized into 1) geometric techniques, which are fast and easy to use but often lack physical realism, 2) data-driven approaches, which require a large set of examples that are tedious to edit, and 3) physics-based methods, which are highly realistic but slow and difficult to use. Recently introduced geometric Implicit Skinning methods can solve contact interactions and skin elasticity with results comparable to physics-based simulation in real-time. In this paper we introduce an animation method that adds anatomical plausibility while benefiting from the advantages of Implicit Skinning. We propose an efficient way to model muscle primitives with implicit surfaces. Volumetric extrusions of individual muscles are attached to muscle center lines simulated with a fast, low-dimensional physics-based approach (Position Based Dynamics of one-dimensional line segments). This combination of physics-based simulation with implicit modeling allows us to elegantly resolve muscle-muscle and muscle-bone collisions and add dynamic effects such as flesh jiggling while guaranteeing volume preservation (which is a property of real biological muscles) and producing visually plausible skin-skin contact behavior. Our method runs at interactive frame-rates and features intuitive modeling parameters which allow animators to quickly explore a variety of designs and physics-based effects. (C) 2018 Elsevier Ltd. All rights reserved.

Particle based simulations are widely used in computer graphics. In this field, several recent results have improved the simulation 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 surface. 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.

Recent advances in implicit surface modeling now provide highly controllable blending effects. These effects rely on the field functions of R 3 → R in which the implicit surfaces are defined. In these fields, there is an outside part in which blending is defined and an inside part. The implicit surface is the interface between these two parts. As recent operators often focus on blending, most efforts have been made on the outer part of field functions and little attention has been paid on the inner part. Yet, the inner fields are important as soon as difference and intersection operators are used. This makes its quality as crucial as the quality of the outside. In this paper, we analyze these shortcomings, and deduce new constraints on field functions such that differences and intersections can be seamlessly applied without introducing discontinuities or field distortions. In particular, we show how to adapt state of the art gradient-based union and blending operators to our new constraints. Our approach enables a precise control of the shape of both the inner or outer field boundaries. We also introduce a new set of asymmetric operators tailored for the modeling of fine details while preserving the integrity of the resulting fields.