Physics-Based Animation

Yijing Li, Jernej Barbič

Self-intersecting, or nearly self-intersecting, meshes are commonly found in 2D and 3D computer graphics practice. Self-intersections occur, for example, in the process of artist manual work, as a by-product of procedural methods for mesh generation, or due to modeling errors introduced by scanning equipment. If the space bounded by such inputs is meshed naively, the resulting mesh joins (“glues”) self-overlapping parts, precluding efficient further modeling and animation of the underlying geometry. Similarly, near self-intersections force the simulation algorithm to employ an unnecessarily detailed mesh to separate the nearly self-intersecting regions. Our work addresses both of these challenges, by giving an algorithm to generate an “un-glued” simulation mesh, of arbitrary user-chosen resolution, that properly accounts for self-intersections and near self-intersections. In order to achieve this result, we study the mathematical concept of immersion, and give a deterministic and constructive algorithm to determine if the input self-intersecting triangle mesh is the boundary of an immersion. For near self-intersections, we give a robust algorithm to properly duplicate mesh elements and correctly embed the underlying geometry into the mesh element copies. Both the self-intersections and near self-intersections are combined into one algorithm that permits successful meshing at arbitrary resolution. Applications of our work include volumetric shape editing, physically based simulation and animation, and volumetric weight and geodesic distance computation on self-intersecting inputs.

Immersion of Self-Intersecting Solids and Surfaces

FEPR: Fast Energy Projection for Real-Time Simulation of Deformable Objects

Yue Peng, Bailin Deng, Juyong Zhang, Fanyu Geng, Wenjie Qin, Ligang liu

Anderson Acceleration for Geometry Optimization and Physics Simulation

Martin Komaritzan, Mario Botsch

We present a novel approach for physics-based character skinning. While maintaining real-time performance it overcomes the well-known artifacts of commonly used geometric skinning approaches, it enables dynamic effects, and it resolves local self-collisions. Our method is based on a two-layer model consisting of rigid bones and an elastic soft tissue layer. This volumetric model is easily and efficiently computed from an input surface mesh of the character and its underlying skeleton. In particular, our method neither requires skinning weights, which are often expensive to compute or tedious to hand-tune, nor a complex volumetric tessellation, which fails for many real-world input meshes due to self-intersections.

Projective Skinning

Dan Casas, Miguel Otaduy

We present a novel method to enrich existing vertex-based human body models by adding soft-tissue dynamics. Our model learns to predict per-vertex 3D offsets, referred to as dynamic blendshapes, that reproduce nonlinear mesh deformation effects as a function of pose information. This enables the synthesis of realistic 3D mesh animations, including soft-tissue effects, using just skeletal motion. At the core of our method there is a neural network regressor trained on high-quality 4D scans from which we extract pose, shape and soft-tissue information. Our regressor uses a novel nonlinear subspace, which we build using an autoencoder, to efficiently compact soft-tissue dynamics information. Once trained, our method can be plugged to existing vertex-based skinning methods with little computational overhead (<10ms), enabling real-time nonlinear dynamics. We qualitatively and quantitatively evaluate our method, and show compelling animations with soft-tissue effects, created using publicly available motion capture datasets

Learning Nonlinear Soft-Tissue Dynamics for Interactive Avatars