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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 Large Scale Terrain Generation from Tectonic Uplift and Fluvial Erosion(The Eurographics Association and John Wiley & Sons Ltd., 2016) Cordonnier, Guillaume; Braun, Jean; Cani, Marie-Paule; Benes, Bedrich; Galin, Éric; Peytavie, Adrien; Guérin, Éric; Joaquim Jorge and Ming LinAt large scale, landscapes result from the combination of two major processes: tectonics which generate the main relief through crust uplift, and weather which accounts for erosion. This paper presents the first method in computer graphics that combines uplift and hydraulic erosion to generate visually plausible terrains. Given a user-painted uplift map, we generate a stream graph over the entire domain embedding elevation information and stream flow. Our approach relies on the stream power equation introduced in geology for hydraulic erosion. By combining crust uplift and stream power erosion we generate large realistic terrains at a low computational cost. Finally, we convert this graph into a digital elevation model by blending landform feature kernels whose parameters are derived from the information in the graph. Our method gives high-level control over the large scale dendritic structures of the resulting river networks, watersheds, and mountains ridges.Item A Review of Digital Terrain Modeling(The Eurographics Association and John Wiley & Sons Ltd., 2019) Galin, Eric; Guérin, Eric; Peytavie, Adrien; Cordonnier, Guillaume; Cani, Marie-Paule; Benes, Bedrich; Gain, James; Giachetti, Andrea and Rushmeyer, HollyTerrains are a crucial component of three-dimensional scenes and are present in many Computer Graphics applications. Terrain modeling methods focus on capturing landforms in all their intricate detail, including eroded valleys arising from the interplay of varied phenomena, dendritic mountain ranges, and complex river networks. Set against this visual complexity is the need for user control over terrain features, without which designers are unable to adequately express their artistic intent. This article provides an overview of current terrain modeling and authoring techniques, organized according to three categories: procedural modeling, physically-based simulation of erosion and land formation processes, and example-based methods driven by scanned terrain data. We compare and contrast these techniques according to several criteria, specifically: the variety of achievable landforms; realism from both a perceptual and geomorphological perspective; issues of scale in terms of terrain extent and sampling precision; the different interaction metaphors and attendant forms of user-control, and computation and memory performance. We conclude with an in-depth discussion of possible research directions and outstanding technical and scientific challenges.Item Interactive Flat Coloring of Minimalist Neat Sketches(The Eurographics Association, 2020) Parakkat, Amal Dev; Madipally, Prudhviraj; Gowtham, Hari Hara; Cani, Marie-Paule; Wilkie, Alexander and Banterle, FrancescoWe introduce a simple Delaunay-triangulation based algorithm for the interactive coloring of neat line-art minimalist sketches, ie. vector sketches that may include open contours. The main objective is to minimize user intervention and make interaction as natural as with the flood-fill algorithm while extending coloring to regions with open contours. In particular, we want to save the user from worrying about parameters such as stroke weight and size. Our solution works in two steps, 1) a segmentation step in which the input sketch is automatically divided into regions based on the underlying Delaunay structure and 2) the interactive grouping of neighboring regions based on user input. More precisely, a region adjacency graph is computed from the segmentation result, and is interactively partitioned based on user input to generate the final colored sketch. Results show that our method is as natural as a bucket fill tool and powerful enough to color minimalist sketches.Item Pair Correlation Functions with Free-Form Boundaries for Distribution Inpainting and Decomposition(The Eurographics Association, 2020) Nicolet, Baptiste; Ecormier-Nocca, Pierre; Memari, Pooran; Cani, Marie-Paule; Wilkie, Alexander and Banterle, FrancescoPair Correlation Functions (PCF) have been recently spreading as a reliable representation for distributions, enabling the efficient synthesis of point-sets, vector textures and object placement from examples. In this work we introduce a triangulationbased local filtering method to extend PCF-based analysis to exemplars with free-form boundaries. This makes PCF applicable to new problems such as the inpainting of missing parts in an input distribution, or the decomposition of complex, non-homogeneous distributions into a set of coherent classes, in which each category of points can be studied together with their intra and inter-class correlations.Item Generation of Folded Terrains from Simple Vector Maps(The Eurographics Association, 2015) Michel, Elie; Emilien, Arnaud; Cani, Marie-Paule; B. Bickel and T. RitschelWhile several terrain generation methods focused on plausible watersheds, the fact that most mountains should not be isolated but rather be part of wider scale mountain ranges was seldom considered. In this work, we present the first procedural method that generates folded terrains from simple user input, in the form of some sparse peak distribution on a vector map. The key idea is to infer possible continental plates from this distribution and to use simplified plate tectonics to generate relevant terrain folds. The resulting terrain with large-scale folds, computed in real-time, can be further refined using standard erosion simulation. This leads to detailed terrains with plausible mountain ranges that match the peak distributions and main rivers specified on simple vector maps.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 Sketch-based Modeling(The Eurographics Association, 2016) Cordier, Frederic; Singh, Karan; Etem, Even; Cani, Marie-Paule; Gingold, Yotam; Augusto Sousa and Kadi BouatouchSketching is one of the most natural ways to exchange ideas. It has been used by human beings since prehistory. Research has shown that human beings have an inherent ability to understand sketches. This is why sketch-based interfaces for 3D modeling are so appealing; creating and animating 3D shapes could become as simple as drawing with a tablet and a digital pen. The purpose of this tutorial is to explore the most important aspects of sketch-based modeling, from the preprocessing of sketch strokes to the problem of 3D reconstruction. We will first explain some aspects of how humans interpret sketches. The second part of the tutorial will be dedicated to the problem of filtering and processing strokes. Other parts of the tutorial will focus on the sketch-based modeling of curves and surfaces using multi-view and single-view sketches. Sketch-based modeling using prior-knowledge will be also discussed; this class of methods is particularly well adapted to the 3D reconstruction of complex shapes. The last part of the tutorial addresses sketch-based interfaces for editing 3D shapes.Item Towards Developable Products from a Sketch(The Eurographics Association, 2017) Fondevilla, Amélie; Bousseau, Adrien; Rohmer, Damien; Hahmann, Stefanie; Cani, Marie-Paule; Pierre Benard and Daniel SykoraDevelopable surfaces are surfaces that can be unfolded onto a plane, without distortion, and are widely used in industry. We propose an end-to-end system for the interactive modeling of developable objects from a single annotated photo, restricted to the case of symmetrical objects made by assemblies of planes and generalized cylinders.