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Item Extracting Microfacet-based BRDF Parameters from Arbitrary Materials with Power Iterations(The Eurographics Association and John Wiley & Sons Ltd., 2015) Dupuy, Jonathan; Heitz, Eric; Iehl, Jean-Claude; Poulin, Pierre; Ostromoukhov, Victor; Jaakko Lehtinen and Derek NowrouzezahraiWe introduce a novel fitting procedure that takes as input an arbitrary material, possibly anisotropic, and automatically converts it to a microfacet BRDF. Our algorithm is based on the property that the distribution of microfacets may be retrieved by solving an eigenvector problem that is built solely from backscattering samples. We show that the eigenvector associated to the largest eigenvalue is always the only solution to this problem, and compute it using the power iteration method. This approach is straightforward to implement, much faster to compute, and considerably more robust than solutions based on nonlinear optimizations. In addition, we provide simple conversion procedures of our fits into both Beckmann and GGX roughness parameters, and discuss the advantages of microfacet slope space to make our fits editable. We apply our method to measured materials from two large databases that include anisotropic materials, and demonstrate the benefits of spatially varying roughness on texture mapped geometric models.Item Environment-aware Real-Time Crowd Control(The Eurographics Association, 2012) Henry, Joseph; Shum, Hubert P. H.; Komura, Taku; Jehee Lee and Paul KryReal-time crowd control has become an important research topic due to the recent advancement in console game quality and hardware processing capability. The degrees of freedom of a crowd is much higher than that provided by a standard user input device. As a result most crowd control systems require the user to design the crowd move- ments through multiple passes, such as first specifying the crowd's start and goal points, then providing the agent trajectories with streamlines. Such a multi-pass control would spoil the responsiveness and excitement of real- time games. In this paper, we propose a new, single-pass algorithm to control crowds using a deformable mesh. When controlling crowds, we observe that most of the low level details are related to passive interactions between the crowd and the environment, such as obstacle avoidance and diverging/merging at cross points. Therefore, we simplify the crowd control problem by representing the crowd with a deformable mesh that passively reacts to the environment. As a result, the user can focus on high level control that is more important for context delivery. Our algorithm provides an efficient crowd control framework while maintaining the quality of the simulation, which is useful for real-time applications such as strategy games.Item Real-time Inextensible Hair with Volume and Shape(The Eurographics Association, 2015) Sánchez-Banderas, Rosa MarÃa; Barreiro, Héctor; GarcÃa-Fernández, Ignacio; Pérez, Mariano; Mateu Sbert and Jorge Lopez-MorenoHair simulation is a common topic extensively studied in computer graphics. One of the many challenges in this field is simulating realistic hair in a real-time environment. In this paper, we propose a unified simulation scheme to consider three of the key features in hair simulation; inextensibility, shape preservation and hair-hair interaction. We use an extension to the Dynamic Follow the Leader (DFTL) method to include shape preservation. Our implementation is also coupled with a Lagrangian approach to address the hair-hair interaction dynamics. A GPU-friendly scheme is proposed that is able to exploit the massive parallelism these devices offer, being able to simulate thousands of strands in real-time. The method has been integrated in a game development platform with a shading model for rendering and several test applications have been developed using this implementation.Item Virtual Spherical Gaussian Lights for Real-time Glossy Indirect Illumination(The Eurographics Association and John Wiley & Sons Ltd., 2015) Tokuyoshi, Yusuke; Stam, Jos and Mitra, Niloy J. and Xu, KunVirtual point lights (VPLs) are well established for real-time global illumination. However, this method suffers from spiky artifacts and flickering caused by singularities of VPLs, highly glossy materials, high-frequency textures, and discontinuous geometries. To avoid these artifacts, this paper introduces a virtual spherical Gaussian light (VSGL) which roughly represents a set of VPLs. For a VSGL, the total radiant intensity and positional distribution of VPLs are approximated using spherical Gaussians and a Gaussian distribution, respectively. Since this approximation can be computed using summations of VPL parameters, VSGLs can be dynamically generated using mipmapped reflective shadow maps. Our VSGL generation is simple and independent from any scene geometries. In addition, reflected radiance for a VSGL is calculated using an analytic formula. Hence, we are able to render one-bounce glossy interreflections at real-time frame rates with smaller artifacts.Item Example-based Interpolation and Synthesis of Bidirectional Texture Functions(The Eurographics Association and Blackwell Publishing Ltd., 2013) Ruiters, Roland; Schwartz, Christopher; Klein, Reinhard; I. Navazo, P. PoulinBidirectional Texture Functions (BTF) have proven to be a well-suited representation for the reproduction of measured real-world surface appearance and provide a high degree of realism. We present an approach for designing novel materials by interpolating between several measured BTFs. For this purpose, we transfer concepts from existing texture interpolation methods to the much more complex case of material interpolation. We employ a separation of the BTF into a heightmap and a parallax compensated BTF to cope with problems induced by parallax, masking and shadowing within the material. By working only on the factorized representation of the parallax compensated BTF and the heightmap, it is possible to efficiently perform the material interpolation. By this novel method to mix existing BTFs, we are able to design plausible and realistic intermediate materials for a large range of different opaque material classes. Furthermore, it allows for the synthesis of tileable and seamless BTFs and finally even the generation of gradually changing materials following user specified material distribution maps.Item Multi-Domain Real-time Planning in Dynamic Environments(ACM SIGGRAPH / Eurographics Association, 2013) Kapadia, Mubbasir; Beacco, Alejandro; Garcia, Francisco; Reddy, Vivek; Pelechano, Nuria; Badler, Norman I.; Theodore Kim and Robert SumnerThis paper presents a real-time planning framework for multicharacter navigation that enables the use of multiple heterogeneous problem domains of differing complexities for navigation in large, complex, dynamic virtual environments. The original navigation problem is decomposed into a set of smaller problems that are distributed across planning tasks working in these different domains. An anytime dynamic planner is used to efficiently compute and repair plans for each of these tasks, while using plans in one domain to focus and accelerate searches in more complex domains. We demonstrate the benefits of our framework by solving many challenging multi-agent scenarios in complex dynamic environments requiring space-time precision and explicit coordination between interacting agents, by accounting for dynamic information at all stages of the decision-making process.Item Improving SIMD Efficiency for Parallel Monte Carlo Light Transport on the GPU(ACM, 2011) Antwerpen, Dietger van; Carsten Dachsbacher and William Mark and Jacopo PantaleoniMonte Carlo Light Transport algorithms such as Path Tracing (PT), Bi-Directional Path Tracing (BDPT) and Metropolis Light Transport (MLT) make use of random walks to sample light transport paths. When parallelizing these algorithms on the GPU the stochastic termination of random walks results in an uneven workload between samples, which reduces SIMD efficiency. In this paper we propose to combine stream compaction and sample regeneration to keep SIMD efficiency high during random walk construction, in spite of stochastic termination. Furthermore, for BDPT and MLT, we propose to evaluate all bidirectional connections of a sample in parallel in order to balance the workload between GPU threads and improve SIMD efficiency during sample evaluation. We present efficient parallel GPU-only implementations for PT, BDPT, and MLT in CUDA.We show that our GPU implementations outperform similarCPU implementations by an order of magnitude.Item Perceptually Motivated Real-Time Compression of Motion Data Enhanced by Incremental Encoding and Parameter Tuning(The Eurographics Association, 2013) Firouzmanesh, Amirhossein; Cheng, Irene; Basu, Anup; M.- A. Otaduy and O. SorkineWe address the problem of efficient real-time motion data compression considering human perception. Using incremental encoding plus a database of motion primitives for each key point, our method achieves a higher or competitive compression rate with less online overhead. Trade-off between visual quality and bandwidth usage can be tuned by varying a single threshold value. A user study was performed to measure the sensitivity of human subjects to reconstruction errors in key rotation angles. Based on these evaluations we are able to perform lossy compression on the motion data without noticeable degradation in rendered qualities. While achieving real-time performance, our technique outperforms other methods in our experiments by achieving a compression ratio exceeding 50 : 1 on regular sequences.Item High Resolution Medical 3D Data Sets on Mobile Devices and WebGL(The Eurographics Association, 2012) Jimenez, Juan-Roberto; Noguera, Jose Maria; Isabel Navazo and Gustavo PatowNowadays, mobile devices and the web are being used to deliver 3D graphics to mass users. However, applications such as visualization of high resolution medical models are still impossible to handle in such platforms due to texture limitations, mainly the lack of 3D texture support. In this paper we propose a software architecture and a novel texture storage technique that overcome these limitations. In addition, our proposal allows us to adapt existing direct volume rendering techniques based on 3D textures to mobile devices and WebGL. Our experiments demonstrate the feasibility and validity of our proposal to render high resolution volumetric models on both platforms.Item Anatomy-Guided Multi-Level Exploration of Blood Flow in Cerebral Aneurysms(The Eurographics Association and Blackwell Publishing Ltd., 2011) Neugebauer, Mathias; Janiga, Gabor; Beuing, Oliver; Skalej, Martin; Preim, Bernhard; H. Hauser, H. Pfister, and J. J. van WijkFor cerebral aneurysms, the ostium, the area of inflow, is an important anatomic landmark, since it separates the pathological vessel deformation from the healthy parent vessel. A better understanding of the inflow characteristics, the flow inside the aneurysm and the overall change of pre- and post-aneurysm flow in the parent vessel provide insights for medical research and the development of new risk-reduced treatment options. We present an approach for a qualitative, visual flow exploration that incorporates the ostium and derived anatomical landmarks. It is divided into three scopes: a global scope for exploration of the in- and outflow, an ostium scope that provides characteristics of the flow profile close to the ostium and a local scope for a detailed exploration of the flow in the parent vessel and the aneurysm. The approach was applied to five representative datasets, including measured and simulated blood flow. Informal interviews with two board-certified radiologists confirmed the usefulness of the provided exploration tools and delivered input for the integration of the ostium-based flow analysis into the overall exploration workflow.