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Item From 3D Models to 3D Prints: An Overview of the Processing Pipeline(The Eurographics Association and John Wiley & Sons Ltd., 2017) Livesu, Marco; Ellero, Stefano; MartÃnez, Jonà s; Lefebvre, Sylvain; Attene, Marco; Victor Ostromoukov and Matthias ZwickerDue to the wide diffusion of 3D printing technologies, geometric algorithms for Additive Manufacturing are being invented at an impressive speed. Each single step along the processing pipeline that prepares the 3D model for fabrication can now count on dozens of methods, that analyse and optimize geometry and machine instructions for various objectives. This report provides a classification of this huge state of the art, and elicits the relation between each single algorithm and a list of desirable objectives during model preparation - a process globally refereed to as Process Planning. The objectives themselves are listed and discussed, along with possible needs for tradeoffs. Additive Manufacturing technologies are broadly categorized to explicitly relate classes of devices and supported features. Finally, this report offers an analysis of the state of the art while discussing open and challenging problems from both an academic and an industrial perspective.Item StarDEM: Efficient Discrete Element Method for Star-shaped Particles(The Eurographics Association, 2024) Schreck, Camille; Lefebvre, Sylvain; Jourdan, David; MartÃnez, Jonà s; Hu, Ruizhen; Charalambous, PanayiotisGranular materials composed of particles with complex shapes are challenging to simulate due to the high number of collisions between the particles. In this context, star shapes are promising: they cover a wide range of geometries from convex to concave and have interesting geometric properties. We propose an efficient method to simulate a large number of identical star-shaped particles. Our method relies on an effective approximation of the contacts between particles that can handle complex shapes, including highly non-convex ones. We demonstrate our method by implementing it in a 2D simulation using the Discrete Element Method, both on the CPU and GPU.Item Rethinking Texture Mapping(The Eurographics Association and John Wiley & Sons Ltd., 2019) Yuksel, Cem; Lefebvre, Sylvain; Tarini, Marco; Giachetti, Andrea and Rushmeyer, HollyThe intrinsic problems of texture mapping, regarding its difficulties in content creation and the visual artifacts it causes in rendering, are well-known, but often considered unavoidable. In this state of the art report, we discuss various radically different ways to rethink texture mapping that have been proposed over the decades, each offering different advantages and trade-offs. We provide a brief description of each alternative texturing method along with an evaluation of its strengths and weaknesses in terms of applicability, usability, filtering quality, performance, and potential implementation related challenges.Item Clean Color: Improving Multi-filament 3D Prints(The Eurographics Association and John Wiley and Sons Ltd., 2014) Hergel, Jean; Lefebvre, Sylvain; B. Levy and J. KautzFused Filament Fabrication is an additive manufacturing process by which a 3D object is created from plastic filament. The filament is pushed through a hot nozzle where it melts. The nozzle deposits plastic layer after layer to create the final object. This process has been popularized by the RepRap community. Several printers feature multiple extruders, allowing objects to be formed from multiple materials or colors. The extruders are mounted side by side on the printer carriage. However, the print quality suffers when objects with color patterns are printed a disappointment for designers interested in 3D printing their colored digital models. The most severe issue is the oozing of plastic from the idle extruders: Plastics of different colors bleed onto each other giving the surface a smudged aspect, excess strings oozing from the extruder deposit on the surface, and holes appear due to this missing plastic. Fixing this issue is difficult: increasing the printing speed reduces oozing but also degrades surface quality on large prints the required speed level become impractical. Adding a physical mechanism increases cost and print time as extruders travel to a cleaning station. Instead, we rely on software and exploit degrees of freedom of the printing process. We introduce three techniques that complement each other in improving the print quality significantly. We first reduce the impact of oozing plastic by choosing a better azimuth angle for the printed part. We build a disposable rampart in close proximity of the part, giving the extruders the opportunity to wipe oozing strings and refill with hot plastic. We finally introduce a toolpath planner avoiding and hiding most of the defects due to oozing, and seamlessly integrating the rampart. We demonstrate our technique on several challenging multiple color prints, and show that our tool path planner improves the surface finish of single color prints as well.Item Interactive Modeling of Support-free Shapes for Fabrication(The Eurographics Association, 2016) Reiner, Tim; Lefebvre, Sylvain; T. Bashford-Rogers and L. P. SantosWe introduce an interactive sculpting approach that enables modeling of support-free objects: objects which do not require any support structures during 3D printing. We propose three operators - trim, preserve, grow - to maintain the support-free property during interactive modeling. These operators let us define brushes that perform either in an unconstrained manner (adapting the shape to the brush effect), or selectively discard changes inside the brush volume. Our technique can be applied to many modeling operations and we demonstrate it on brushes for adding or removing matter. We describe an efficient implementation of a voxel-based modeling tool that produces only support-free shapes, and show example shapes modeled within minutes.Item Procedural Bridges-and-pillars Support Generation(The Eurographics Association, 2022) Freire, Marco; Hornus, Samuel; Perchy, Salim; Lefebvre, Sylvain; Pelechano, Nuria; Vanderhaeghe, DavidAdditive manufacturing requires support structures to fabricate parts with overhangs. In this paper, we revisit a known support structure based on bridges-and-pillars (see Figure 1). The support structures are made of vertical pillars supporting horizontal bridges. Their scaffolding structure makes them stable and reliable to print. However, the algorithm heuristic search does not scale well and is prone to produce contacts with the parts, leaving scars after removal. We propose a novel algorithm for this type of supports, focusing on avoiding unnecessary contacts with the part as much as possible. Our approach builds upon example-based model synthesis to enable early detection of collision-free passages as well as non-reachable regions.Item Iterative Carving for Self-supporting 3D Printed Cavities(The Eurographics Association, 2018) Hornus, Samuel; Lefebvre, Sylvain; Diamanti, Olga and Vaxman, AmirAdditive manufacturing technologies fabricate objects layer by layer, adding material on top of already solidified layers. A key challenge is to ensure that there is always material below, for otherwise added material simply falls under the effect of gravity. This is a critical issue with most technologies, and with fused filament in particular. In this work we investigate how to compute as large as possible empty cavities which boundaries are self-supporting. Our technique is based on an iterated carving algorithm, that is fast to compute and produces nested sets of inner walls. The walls have exactly the minimal printable thickness of the manufacturing process everywhere. Remarkably, our technique is out-of-core, sweeping through the model from the top down. Using our approach, we can print large objects using as little as a single filament thickness for the boundary, providing one order of magnitude reduction in print time and material use while guaranteeing printability.Item Topology Optimization for Computational Fabrication(The Eurographics Association, 2017) Wu, Jun; Aage, Niels; Lefebvre, Sylvain; Wang, Charlie; Adrien Bousseau and Diego GutierrezAdditive manufacturing (AM) and topology optimization (TO) form a pair of complementary techniques in transforming digital models into physical replicas: AM enables a cost-effective fabrication of geometrically complex shapes, while TO provides a powerful design methodology for generating optimized models, which are typically complex from a geometric perspective. The potential of both techniques has recently been explored in graphics, resulting in fantastic applications especially regarding structural and aesthetic properties of fabricated models. In this tutorial, we start from the fundamentals of AM and TO, and proceed to advanced TO techniques which steer the optimization process, i.e., taking into account the manufacturing as well as aesthetic appearance.Item Double QuickCurve: revisiting 3-axis non-planar 3D printing(The Eurographics Association, 2025) Ottonello, Emilio; Hugron, Pierre-Alexandre; Parmiggiani, Alberto; Lefebvre, Sylvain; Ceylan, Duygu; Li, Tzu-MaoAdditive manufacturing builds physical objects by accumulating layers of solidified material. This is typically done with planar layers. Fused filament printers however have the capability to extrude material along 3D curves, leading to the idea of depositing in a non-planar fashion. In this paper we introduce a novel algorithm for this purpose, targeting simplicity, robustness and efficiency. Our method interpolates curved slicing surfaces between two top and bottom slicing surfaces, optimized to align with the object curvatures. These slicing surfaces are intersected with the input model to extract non-planar layers and curved deposition trajectories. We further orient trajectories according to the object's curvatures, improving deposition.Item Game Level Layout from Design Specification(The Eurographics Association and John Wiley and Sons Ltd., 2014) Ma, Chongyang; Vining, Nicholas; Lefebvre, Sylvain; Sheffer, Alla; B. Levy and J. KautzThe design of video game environments, or levels, aims to control gameplay by steering the player through a sequence of designer-controlled steps, while simultaneously providing a visually engaging experience. Traditionally these levels are painstakingly designed by hand, often from pre-existing building blocks, or space templates. In this paper, we propose an algorithmic approach for automatically laying out game levels from user-specified blocks. Our method allows designers to retain control of the gameplay flow via user-specified level connectivity graphs, while relieving them from the tedious task of manually assembling the building blocks into a valid, plausible layout. Our method produces sequences of diverse layouts for the same input connectivity, allowing for repeated replay of a given level within a visually different, new environment. We support complex graph connectivities and various building block shapes, and are able to compute complex layouts in seconds. The two key components of our algorithm are the use of configuration spaces defining feasible relative positions of building blocks within a layout and a graph-decomposition based layout strategy that leverages graph connectivity to speed up convergence and avoid local minima. Together these two tools quickly steer the solution toward feasible layouts. We demonstrate our method on a variety of real-life inputs, and generate appealing layouts conforming to user specifications