Abstract Muscle‐based control is transforming the field of physics‐based character animation through the integration of knowledge from neuroscience, biomechanics and robotics, which enhance motion realism. Since any physics‐based animation system can be extended to a muscle‐actuated system, the possibilities of growth are tremendous. However, modelling muscles and their control remains a difficult challenge. We present an organized review of over a decade of research in muscle‐based control for character animation, its fundamental concepts and future directions for development. The core of this review contains a classification of control methods, tables summarizing their key aspects and popular neuromuscular functions used within these controllers, all with the purpose of providing the reader with an overview of the field.

Abstract In the current paper, we present a bio‐inspired solution for the control of overactuated models in animation, such as musculoskeletal models. This solution consists in the extraction of muscle synergies from human experiments, followed by a control method consisting of a series of optimizations to adapt muscle parameters and synergies to match experimental data. We apply the framework on throwing motions, and the results show that these motions can be accurately reproduced on a character with a simplified muscular structure, while preserving important characteristics in the original synergies or control signals.

In the current paper, we present a control method based on muscle synergy extraction and adaptation to drive a human arm in a direct dynamics simulation of an overhead throwing motion. The experimental protocol for synergy extraction and model are first presented, followed by a control method consisting of a series of optimizations to adapt muscle parameters and synergies to match experimental data. Results show that the motion can be accurately reproduced thanks to the muscle synergy extraction and adaptation to the model.

In complex scenes with many objects, collision detection plays a key role in the simulation performance. This is particularly true in fracture simulation for two main reasons. One is that fracture fragments tend to exhibit very intensive contact, and the other is that collision detection data structures for new fragments need to be computed on the fly. In this paper, we present novel collision detection algorithms and data structures for real-time simulation of fracturing rigid bodies. We build on a combination of well-known efficient data structures, namely, distance fields and sphere trees, making our algorithm easy to integrate on existing simulation engines. We propose novel methods to construct these data structures, such that they can be efficiently updated upon fracture events and integrated in a simple yet effective self-adapting contact selection algorithm. Altogether, we drastically reduce the cost of both collision detection and collision response. We have evaluated our global solution for collision detection on challenging scenarios, achieving high frame rates suited for hard real-time applications such as video games or haptics. Our solution opens promising perspectives for complex fracture simulations involving many dynamically created rigid objects.

Nowadays the process of workstation design tends to include assessment steps in a virtual environment (VE) to evaluate the ergonomic features. These approaches are cost-effective and convenient since working directly on the digital mock-up in a VE is preferable to constructing a real physical mock-up in a real environment (RE). This study aimed at understanding the ability of a VR-based assembly tasks simulator to evaluate physical risk factors in ergonomics. Sixteen subjects performed simplified assembly tasks in RE and VE. Motion of the upper body and five muscle electromyographic activities were recorded to compute normalized and averaged objective indicators of discomfort, that is, rapid upper limb assessment score, averaged muscle activations, and total task time. Rated perceived exertion (RPE) and a questionnaire were used as subjective indicators of discomfort. The timing regime and complexity of the assembly tasks were investigated as within-subject factors. The results revealed significant differences between measured indicators in RE and VE. While objective measures indicated lower activity and exposure in VE, the subjects experienced more discomfort than in RE. Fairly good correlation levels were found between RE and VE for six of the objective indicators. This study clearly demonstrates that ergonomic studies of assembly tasks using VR are still challenging. Indeed, objective and subjective measurements of discomfort that are usually used in ergonomics to minimize the risks of work-related musculoskeletal disorders development exhibit opposite trends in RE and VE. Nevertheless, the high level of correlation found during this study indicates that the VR-based simulator can be used for such assessments.

We present a novel physically based approach for simulating realistic brittle fracture of impacting bodies in real time. Our method is mainly composed of two novel parts: 1) a fracture initiation method based on modal analysis, and 2) a fast energy-based fracture propagation algorithm. We propose a way to compute the contact durations and the contact forces between stiff bodies to simulate the damped deformation wave that is responsible for fracture initiation. As a consequence, our method naturally takes into account the damping properties of the bodies as well as the contact properties to simulate the fracture. To obtain a complete fracture pipeline, we present an efficient way to generate the fragments and their geometric surfaces. These surfaces are sampled on the edges of the physical mesh, to visually represent the actual fracture surface computed. As shown in our results, the computation time performances and realism of our method are well suited for physically based interactive applications.

Abstract A common weathering effect is the appearance of cracks due to material fractures. Previous exemplar‐based aging and weathering methods have either reused images or sought to replicate observed patterns exactly. We introduce a new approach to exemplar‐based modeling that creates weathered patterns on synthetic objects by matching thestatisticsof fracture patterns in a photograph. We present a user study to determine which statistics are correlated to visual similarity and how they are perceived by the user. We then describe a revised physically‐based fracture model capable of producing a wide range of crack patterns at interactive rates. We demonstrate how a Bayesian optimization method can determine the parameters of this model so it can produce a pattern with the same key statistics as an exemplar. Finally, we present results using our approach and various exemplars to produce a variety of fracture effects in synthetic renderings of complex environments. The speed of the fracture simulation allows interactive previews of the fractured results and its application on large scale environments.

This paper aims at proposing a framework for animating virtual humans that can efficiently interact with real users in virtual reality (VR). If the user's order can be modeled as targets and commands, the system searches a database for the most convenient behavior. In order to avoid using a huge database that can deal with any kind of situation, we propose to associate this searching process to an adaptation module. Hence, even if the selected motion is not perfectly suited with the situation, it can be adapted in order to reach accurately the target specified by the user. This framework is illustrated with a kung-fu fighter example. Two people are involved in this example: the user and the supervisor. The user is displacing in the real environment while the position of his head is tracked in real-time thanks to reflective markers. The virtual opponent follows the displacement of the user to stay close to him. At any time, the supervisor can ask the virtual character to kick or punch the user. Our system automatically searches for the convenient motion in an average-size database (75 motions compared to hundreds of motions required for motion graphs) and adapts it to the current situation.

International audience

We propose a multi-resolution data structure for interactive manipulation of huge mockups in virtual reality. It is based on a partitioning of the input mesh into several sub-meshes that can be treated independently in the VR scene. The dual graph of the partition ensures easy multi-resolution handling on the whole model and easy out-of-core management of the sub-meshes, thus providing a relevant and efficient mesh inspection tool to the user.