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Item A Survey on Reinforcement Learning Methods in Character Animation(The Eurographics Association and John Wiley & Sons Ltd., 2022) Kwiatkowski, Ariel; Alvarado, Eduardo; Kalogeiton, Vicky; Liu, C. Karen; Pettré, Julien; Panne, Michiel van de; Cani, Marie-Paule; Meneveaux, Daniel; Patanè, GiuseppeReinforcement Learning is an area of Machine Learning focused on how agents can be trained to make sequential decisions, and achieve a particular goal within an arbitrary environment. While learning, they repeatedly take actions based on their observation of the environment, and receive appropriate rewards which define the objective. This experience is then used to progressively improve the policy controlling the agent's behavior, typically represented by a neural network. This trained module can then be reused for similar problems, which makes this approach promising for the animation of autonomous, yet reactive characters in simulators, video games or virtual reality environments. This paper surveys the modern Deep Reinforcement Learning methods and discusses their possible applications in Character Animation, from skeletal control of a single, physically-based character to navigation controllers for individual agents and virtual crowds. It also describes the practical side of training DRL systems, comparing the different frameworks available to build such agents.Item PointCloudSlicer: Gesture-based Segmentation of Point Clouds(The Eurographics Association, 2023) Gowtham, Hari Hara; Parakkat, Amal Dev; Cani, Marie-Paule; Babaei, Vahid; Skouras, MelinaSegmentation is a fundamental problem in point-cloud processing, addressing points classification into consistent regions, the criteria for consistency being based on the application. In this paper, we introduce a simple, interactive framework enabling the user to quickly segment a point cloud in a few cutting gestures in a perceptually consistent way. As the user perceives the limit of a shape part, they draw a simple separation stroke over the current 2D view. The point cloud is then segmented without needing any intermediate meshing step. Technically, we find an optimal, perceptually consistent cutting plane constrained by user stroke and use it for segmentation while automatically restricting the extent of the cut to the closest shape part from the current viewpoint. This enables users to effortlessly segment complex point clouds from an arbitrary viewpoint with the possibility of handling self-occlusions.Item Reactive Gaze during Locomotion in Natural Environments(The Eurographics Association and John Wiley & Sons Ltd., 2024) Melgaré, Julia K.; Rohmer, Damien; Musse, Soraia R.; Cani, Marie-Paule; Skouras, Melina; Wang, HeAnimating gaze behavior is crucial for creating believable virtual characters, providing insights into their perception and interaction with the environment. In this paper, we present an efficient yet natural-looking gaze animation model applicable to real-time walking characters exploring natural environments. We address the challenge of dynamic gaze adaptation by combining findings from neuroscience with a data-driven saliency model. Specifically, our model determines gaze focus by considering the character's locomotion, environment stimuli, and terrain conditions. Our model is compatible with both automatic navigation through pre-defined character trajectories and user-guided interactive locomotion, and can be configured according to the desired degree of visual exploration of the environment. Our perceptual evaluation shows that our solution significantly improves the state-of-the-art saliency-based gaze animation with respect to the character's apparent awareness of the environment, the naturalness of the motion, and the elements to which it pays attention.Item Unerosion: Simulating Terrain Evolution Back in Time(The Eurographics Association and John Wiley & Sons Ltd., 2024) Yang, Zhanyu; Cordonnier, Guillaume; Cani, Marie-Paule; Perrenoud, Christian; Benes, Bedrich; Skouras, Melina; Wang, HeWhile the past of terrain cannot be known precisely because an effect can result from many different causes, exploring these possible pasts opens the way to numerous applications ranging from movies and games to paleogeography. We introduce unerosion, an attempt to recover plausible past topographies from an input terrain represented as a height field. Our solution relies on novel algorithms for the backward simulation of different processes: fluvial erosion, sedimentation, and thermal erosion. This is achieved by re-formulating the equations of erosion and sedimentation so that they can be simulated back in time. These algorithms can be combined to account for a succession of climate changes backward in time, while the possible ambiguities provide editing options to the user. Results show that our solution can approximately reverse different types of erosion while enabling users to explore a variety of alternative pasts. Using a chronology of climatic periods to inform us about the main erosion phenomena, we also went back in time using real measured terrain data. We checked the consistency with geological findings, namely the height of river beds hundreds of thousands of years ago.Item PropColor: Interactive Color Propagation for 2D Animations(The Eurographics Association, 2024) Gowtham, Hari Hara; Parakkat, Amal Dev; Cani, Marie-Paule; Linsen, Lars; Thies, JustusColoring is a fundamental yet time-consuming task in the 2D animation production pipeline. Traditional methods typically rely on frame-by-frame user interaction, leading to high user time and production costs. In this paper, we introduce PropColor, an interactive yet simple tool to propagate colors between adjacent frames of a hand-drawn animation. Starting with an initial frame colored by the user, our method propagates colors to neighboring frames based on the Delaunay triangulations computed from the sketch contours and the color hints. In addition to propagating colouring between frames, our method also associates a confidence score with each of them. This enables to identify the frames where user intervention is needed the most, either to validate the result or to provide additional color hints. Experiments show that our lightweight tool gives real-time feedback and significantly cuts down the animator's time.Item Driller: An Intuitive Interface for Designing Tangled and Nested Shapes(The Eurographics Association, 2024) Butler, Tara; Guehl, Pascal; Parakkat, Amal Dev; Cani, Marie-Paule; Hu, Ruizhen; Charalambous, PanayiotisThe ability to represent not only isolated shapes but also shapes that interact is essential in various fields, from design to biology or anatomy. In this paper, we propose an intuitive interface to control and edit complex shape arrangements. Using a set of pre-defined shapes that may intersect, our ''Driller'' interface allows users to trigger their local deformation so that they rest on each other, become tangled, or even nest within each other. Driller provides an intuitive way to specify the relative depth of different shapes beneath user-selected points of interest by setting their local depth ordering perpendicularly to the camera's viewpoint. Deformations are then automatically generated by locally propagating these ordering constraints. In addition to being part of the final arrangement, some of the shapes can be used as deformers, which can be later deleted to help sculpt the target shapes. We implemented this solution within a sketch-based modeling system designed for novice users.Item Bio-Sketch: A New Medium for Interactive Storytelling Illustrated by the Phenomenon of Infection(The Eurographics Association, 2023) Olivier, Pauline; Chabrier, Renaud; Memari, Pooran; Coll, Jean-Luc; Cani, Marie-Paule; Hansen, Christian; Procter, James; Renata G. Raidou; Jönsson, Daniel; Höllt, ThomasIn the field of biology, digital illustrations play a crucial role in conveying complex phenomena, allowing for idealized shapes and motion, in contrast to data visualization. In the absence of suitable media, scientists often rely on oversimplified 2D figures or have to call in professional artists to create better illustrations, which can be limiting. We introduce Bio-Sketch, a novel progressive sketching system designed to ease the creation of animated illustrations, as exemplified here in the context of the infection phenomenon. Our solution relies on a new progressive sketching paradigm that seamlessly combines 3D modeling and pattern-based shape distribution to create background volume and temporal animation control. The elements created can be assembled into a complex scenario, enabling narrative design experiments for educational applications in biology. Our results and first feedback from experts in illustration and biology demonstrate the potential of Bio-Sketch to assist communication on the infection phenomenon, helping to bridge the gap between expert and non-expert audiences.Item Inferring the Routes of Prehistoric Humans(The Eurographics Association, 2023) Rahary, Adrien Ramanana; Lorre-Guidt, Mylène; Grégoire, Sophie; Cani, Marie-Paule; Bucciero, Alberto; Fanini, Bruno; Graf, Holger; Pescarin, Sofia; Rizvic, SelmaPrehistoric research is in high demand for 3D simulation to help validate hypotheses and enrich knowledge. While previous multidisciplinary studies focused on the reconstruction of ecosystems around excavation sites, this work takes up a new issue: deducing and visualizing the routes and the time taken by the hominids to reach the places where they harvested their resources, based on field data about raw material sources, the paleoclimate, and the surrounding ecosystem. We rely on the energy consumption of a simplified version of a walking character to compute the most likely locomotion speed and the best routes between input sites of interest, while taking into account local slopes, ground types and the presence of vegetation along the way. We show that this approach allows to evaluate the duration of the typical journeys of Homo heidelbergensis staying at the Caune de l'Arago (France) to collect lithic raw materials and to hunt - allowing archaeologists to deepen their knowledge of economic and territorial practices to the Lower Paleolithic and the Acheulean culture, 500,000 years ago.Item Generating Upper-Body Motion for Real-Time Characters Making their Way through Dynamic Environments(The Eurographics Association and John Wiley & Sons Ltd., 2022) Alvarado, Eduardo; Rohmer, Damien; Cani, Marie-Paule; Dominik L. Michels; Soeren PirkReal-time character animation in dynamic environments requires the generation of plausible upper-body movements regardless of the nature of the environment, including non-rigid obstacles such as vegetation. We propose a flexible model for upper-body interactions, based on the anticipation of the character's surroundings, and on antagonistic controllers to adapt the amount of muscular stiffness and response time to better deal with obstacles. Our solution relies on a hybrid method for character animation that couples a keyframe sequence with kinematic constraints and lightweight physics. The dynamic response of the character's upper-limbs leverages antagonistic controllers, allowing us to tune tension/relaxation in the upper-body without diverging from the reference keyframe motion. A new sight model, controlled by procedural rules, enables high-level authoring of the way the character generates interactions by adapting its stiffness and reaction time. As results show, our real-time method offers precise and explicit control over the character's behavior and style, while seamlessly adapting to new situations. Our model is therefore well suited for gaming applications.Item Volcanic Skies: Coupling Explosive Eruptions with Atmospheric Simulation to Create Consistent Skyscapes(The Eurographics Association and John Wiley & Sons Ltd., 2024) Pretorius, Pieter C.; Gain, James; Lastic, Maud; Cordonnier, Guillaume; Chen, Jiong; Rohmer, Damien; Cani, Marie-Paule; Bermano, Amit H.; Kalogerakis, EvangelosExplosive volcanic eruptions rank among the most terrifying natural phenomena, and are thus frequently depicted in films, games, and other media, usually with a bespoke once-off solution. In this paper, we introduce the first general-purpose model for bi-directional interaction between the atmosphere and a volcano plume. In line with recent interactive volcano models, we approximate the plume dynamics with Lagrangian disks and spheres and the atmosphere with sparse layers of 2D Eulerian grids, enabling us to focus on the transfer of physical quantities such as temperature, ash, moisture, and wind velocity between these sub-models. We subsequently generate volumetric animations by noise-based procedural upsampling keyed to aspects of advection, convection, moisture, and ash content to generate a fully-realized volcanic skyscape. Our model captures most of the visually salient features emerging from volcano-sky interaction, such as windswept plumes, enmeshed cap, bell and skirt clouds, shockwave effects, ash rain, and sheathes of lightning visible in the dark.