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Item Cosserat Rod with rh-Adaptive Discretization(The Eurographics Association and John Wiley & Sons Ltd., 2020) Wen, Jiahao; Chen, Jiong; Nobuyuki, Umetani; Bao, Hujun; Huang, Jin; Eisemann, Elmar and Jacobson, Alec and Zhang, Fang-LueRod-like one-dimensional elastic objects often exhibit complex behaviors which pose great challenges to the discretization method for pursuing a faithful simulation. By only moving a small portion of material points, the Eulerian-on-Lagrangian (EoL) method already shows great adaptivity to handle sharp contact, but it is still far from enough to reproduce rich and complex geometry details arising in simulations. In this paper, we extend the discrete configuration space by unifying all Lagrangian and EoL nodes in representation for even more adaptivity with every sample being assigned with a dynamic material coordinate. However, this great extension will immediately bring in much more redundancy in the dynamic system. Therefore, we propose additional energy to control the spatial distribution of all material points, seeking to equally space them with respect to a curvature-based density field as a monitor. This flexible approach can effectively constrain the motion of material points to resolve numerical degeneracy, while simultaneously enables them to notably slide inside the parametric domain to account for the shape parameterization. Besides, to accurately respond to sharp contact, our method can also insert or remove nodes online and adjust the energy stiffness to suppress possible jittering artifacts that could be excited in a stiff system. As a result of this hybrid rh-adaption, our proposed method is capable of reproducing many realistic rod dynamics, such as excessive bending, twisting and knotting while only using a limited number of elements.Item Automatic Band-Limited Approximation of Shaders Using Mean-Variance Statistics in Clamped Domain(The Eurographics Association and John Wiley & Sons Ltd., 2020) Li, Shi; Wang, Rui; Huo, Yuchi; Zheng, Wenting; Hua, Wei; Bao, Hujun; Eisemann, Elmar and Jacobson, Alec and Zhang, Fang-LueIn this paper, we present a new shader smoothing method to improve the quality and generality of band-limiting shader programs. Previous work [YB18] treats intermediate values in the program as random variables, and utilizes mean and variance statistics to smooth shader programs. In this work, we extend such a band-limiting framework by exploring the observation that one intermediate value in the program is usually computed by a complex composition of functions, where the domain and range of composited functions heavily impact the statistics of smoothed programs. Accordingly, we propose three new shader smoothing rules for specific composition of functions by considering the domain and range, enabling better mean and variance statistics of approximations. Aside from continuous functions, the texture, such as color texture or normal map, is treated as a discrete function with limited domain and range, thereby can be processed similarly in the newly proposed framework. Experiments show that compared with previous work, our method is capable of generating better smoothness of shader programs as well as handling a broader set of shader programs.Item Wake Synthesis For Shallow Water Equation(The Eurographics Association and Blackwell Publishing Ltd., 2012) Pan, Zherong; Huang, Jin; Tong, Yiying; Bao, Hujun; C. Bregler, P. Sander, and M. WimmerIn fluid animation, wake is one of the most important phenomena usually seen when an object is moving relative to the flow. However, in current shallow water simulation for interactive applications, this effect is greatly smeared out. In this paper, we present a method to efficiently synthesize these wakes. We adopt a generalized SPH method for shallow water simulation and two way solid fluid coupling. In addition, a 2D discrete vortex method is used to capture the detailed wake motions behind an obstacle, enriching the motion of SWE simulation. Our method is highly efficient since only 2D simulation is required. Moreover, by using a physically inspired procedural approach for particle seeding, DVM particles are only created in the wake region. Therefore, very few particles are required while still generating realistic wake patterns. When coupled with SWE, we show that these patterns can be seen using our method with marginal overhead.Item Semi-supervised Mesh Segmentation and Labeling(The Eurographics Association and Blackwell Publishing Ltd., 2012) Lv, Jiajun; Chen, Xinlei; Huang, Jin; Bao, Hujun; C. Bregler, P. Sander, and M. WimmerRecently, approaches have been put forward that focus on the recognition of mesh semantic meanings. These methods usually need prior knowledge learned from training dataset, but when the size of the training dataset is small, or the meshes are too complex, the segmentation performance will be greatly effected. This paper introduces an approach to the semantic mesh segmentation and labeling which incorporates knowledge imparted by both segmented, labeled meshes, and unsegmented, unlabeled meshes. A Conditional Random Fields (CRF) based objective function measuring the consistency of labels and faces, labels of neighbouring faces is proposed. To implant the information from the unlabeled meshes, we add an unlabeled conditional entropy into the objective function. With the entropy, the objective function is not convex and hard to optimize, so we modify the Virtual Evidence Boosting (VEB) to solve the semi-supervised problem efficiently. Our approach yields better results than those methods which only use limited labeled meshes, especially when many unlabeled meshes exist. The approach reduces the overall system cost as well as the human labelling cost required during training. We also show that combining knowledge from labeled and unlabeled meshes outperforms using either type of meshes alone.Item Real-Time Linear BRDF MIP-Mapping(The Eurographics Association and John Wiley & Sons Ltd., 2017) Xu, Chao; Wang, Rui; Zhao, Shuang; Bao, Hujun; Zwicker, Matthias and Sander, PedroWe present a new technique to jointly MIP-map BRDF and normal maps. Starting with generating an instant BRDF map, our technique builds its MIP-mapped versions based on a highly efficient algorithm that interpolates von Mises-Fisher (vMF) distributions. In our BRDF MIP-maps, each pixel stores a vMF mixture approximating the average of all BRDF lobes from the finest level. Our method is capable of jointly MIP-mapping BRDF and normal maps, even with high-frequency variations, at real-time while preserving high-quality reflectance details. Further, it is very fast, easy to implement, and requires no precomputation.Item Symmetry and Orbit Detection via Lie-Algebra Voting(The Eurographics Association and John Wiley & Sons Ltd., 2016) Shi, Zeyun; Alliez, Pierre; Desbrun, Mathieu; Bao, Hujun; Huang, Jin; Maks Ovsjanikov and Daniele PanozzoIn this paper, we formulate an automatic approach to the detection of partial, local, and global symmetries and orbits in arbitrary 3D datasets. We improve upon existing voting-based symmetry detection techniques by leveraging the Lie group structure of geometric transformations. In particular, we introduce a logarithmic mapping that ensures that orbits are mapped to linear subspaces, hence unifying and extending many existing mappings in a single Lie-algebra voting formulation. Compared to previous work, our resulting method offers significantly improved robustness as it guarantees that our symmetry detection of an input model is frame, scale, and reflection invariant. As a consequence, we demonstrate that our approach efficiently and reliably discovers symmetries and orbits of geometric datasets without requiring heavy parameter tuning.Item Efficient and Stable Simulation of Inextensible Cosserat Rods by a Compact Representation(The Eurographics Association and John Wiley & Sons Ltd., 2022) Zhao, Chongyao; Lin, Jinkeng; Wang, Tianyu; Bao, Hujun; Huang, Jin; Umetani, Nobuyuki; Wojtan, Chris; Vouga, EtiennePiecewise linear inextensible Cosserat rods are usually represented by Cartesian coordinates of vertices and quaternions on the segments. Such representations use excessive degrees of freedom (DOFs), and need many additional constraints, which causes unnecessary numerical difficulties and computational burden for simulation. We propose a simple yet compact representation that exactly matches the intrinsic DOFs and naturally satisfies all such constraints. Specifically, viewing a rod as a chain of rigid segments, we encode its shape as the Cartesian coordinates of its root vertex, and use axis-angle representation for the material frame on each segment. Under our representation, the Hessian of the implicit time-stepping has special non-zero patterns. Exploiting such specialties, we can solve the associated linear equations in nearly linear complexity. Furthermore, we carefully designed a preconditioner, which is proved to be always symmetric positive-definite and accelerates the PCG solver in one or two orders of magnitude compared with the widely used block-diagonal one. Compared with other technical choices including Super-Helices, a specially designed compact representation for inextensible Cosserat rods, our method achieves better performance and stability, and can simulate an inextensible Cosserat rod with hundreds of vertices and tens of collisions in real time under relatively large time steps.Item MINERVAS: Massive INterior EnviRonments VirtuAl Synthesis(The Eurographics Association and John Wiley & Sons Ltd., 2022) Ren, Haocheng; Zhang, Hao; Zheng, Jia; Zheng, Jiaxiang; Tang, Rui; Huo, Yuchi; Bao, Hujun; Wang, Rui; Umetani, Nobuyuki; Wojtan, Chris; Vouga, EtienneWith the rapid development of data-driven techniques, data has played an essential role in various computer vision tasks. Many realistic and synthetic datasets have been proposed to address different problems. However, there are lots of unresolved challenges: (1) the creation of dataset is usually a tedious process with manual annotations, (2) most datasets are only designed for a single specific task, (3) the modification or randomization of the 3D scene is difficult, and (4) the release of commercial 3D data may encounter copyright issue. This paper presents MINERVAS, a Massive INterior EnviRonments VirtuAl Synthesis system, to facilitate the 3D scene modification and the 2D image synthesis for various vision tasks. In particular, we design a programmable pipeline with Domain-Specific Language, allowing users to select scenes from the commercial indoor scene database, synthesize scenes for different tasks with customized rules, and render various types of imagery data, such as color images, geometric structures, semantic labels. Our system eases the difficulty of customizing massive scenes for different tasks and relieves users from manipulating fine-grained scene configurations by providing user-controllable randomness using multilevel samplers. Most importantly, it empowers users to access commercial scene databases with millions of indoor scenes and protects the copyright of core data assets, e.g., 3D CAD models. We demonstrate the validity and flexibility of our system by using our synthesized data to improve the performance on different kinds of computer vision tasks. The project page is at https://coohom.github.io/MINERVAS.Item Runtime Shader Simplification via Instant Search in Reduced Optimization Space(The Eurographics Association and John Wiley & Sons Ltd., 2018) Yuan, Yazhen; Wang, Rui; Hu, Tianlei; Bao, Hujun; Jakob, Wenzel and Hachisuka, ToshiyaTraditional automatic shader simplification simplifies shaders in an offline process, which is typically carried out in a contextoblivious manner or with the use of some example contexts, e.g., certain hardware platforms, scenes, and uniform parameters, etc. As a result, these pre-simplified shaders may fail at adapting to runtime changes of the rendering context that were not considered in the simplification process. In this paper, we propose a new automatic shader simplification technique, which explores two key aspects of a runtime simplification framework: the optimization space and the instant search for optimal simplified shaders with runtime context. The proposed technique still requires a preprocess stage to process the original shader. However, instead of directly computing optimal simplified shaders, the proposed preprocess generates a reduced shader optimization space. In particular, two heuristic estimates of the quality and performance of simplified shaders are presented to group similar variants into representative ones, which serve as basic graph nodes of the simplification dependency graph (SDG), a new representation of the optimization space. At the runtime simplification stage, a parallel discrete optimization algorithm is employed to instantly search in the SDG for optimal simplified shaders. New data-driven cost models are proposed to predict the runtime quality and performance of simplified shaders on the basis of data collected during runtime. Results show that the selected simplifications of complex shaders achieve 1.6 to 2.5 times speedup and still retain high rendering quality.Item Economic Upper Bound Estimation in Hausdorff Distance Computation for Triangle Meshes(© 2022 Eurographics ‐ The European Association for Computer Graphics and John Wiley & Sons Ltd, 2022) Zheng, Yicun; Sun, Haoran; Liu, Xinguo; Bao, Hujun; Huang, Jin; Hauser, Helwig and Alliez, PierreThe Hausdorff distance is one of the most fundamental metrics for comparing 3D shapes. To compute the Hausdorff distance efficiently from a triangular mesh to another triangular mesh , one needs to cull the unnecessary triangles on quickly. These triangles have no chance to improve the Hausdorff distance estimation, that is the parts with local upper bound smaller than the global lower bound. The local upper bound estimation should be tight, use fast distance computation, and involve a small number of triangles in during the reduction phase for efficiency. In this paper, we propose to use point‐triangle distance, and only involve at most four triangles in in the reduction phase. Comparing with the state‐of‐the‐art proposed by Tang et al. in 2009, which uses more costly triangle‐triangle distance and may involve a large number of triangles in reduction phase, our local upper bound estimation is faster, and with only a small impact on the tightness of the bound on error estimation. Such a more economic strategy boosts the overall performance significantly. Experiments on the Thingi10K dataset show that our method can achieve several (even over 20) times speedup on average. On a few models with different placements and resolutions, we show that close placement and large difference in resolution bring big challenges to Hausdorff distance computation, and explain why our method can achieve more significant speedup on challenging cases.
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