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Item Elasticity-based Clustering for Haptic Interaction with Heterogeneous Deformable Objects(The Eurographics Association, 2017) Gouis, Benoît Le; Marchal, Maud; Lécuyer, Anatole; Arnaldi, Bruno; Fabrice Jaillet and Florence ZaraPhysically-based simulation of heterogeneous objects remains computationally-demanding for many applications, especially when involving haptic interaction with virtual environments. In this paper, we introduce a novel multiresolution approach for haptic interaction with heterogeneous deformable objects. Our method called "Elasticity-based Clustering" is based on the clustering and aggregation of elasticity inside an object, in order to create large homogeneous volumes preserving important features of the initial distribution. The design of such large and homogeneous volumes improves the attribution of elasticity to the elements of the coarser geometry. We could successfully implement and test our approach within a complete and real-time haptic interaction pipeline compatible with consumer-grade haptic devices. We evaluated the performance of our approach on a large set of elasticity configurations using a perception-based quality criterion. Our results show that for 90% of studied cases our method can achieve a 6 times speedup in the simulation time with no theoretical perceptual difference.Item C++ Compile Time Polymorphism for Ray Tracing(The Eurographics Association, 2017) Zellmann, Stefan; Lang, Ulrich; Matthias Hullin and Reinhard Klein and Thomas Schultz and Angela YaoReducing the amount of conditional branching instructions in innermost loops is crucial for high performance code on contemporary hardware architectures. In the context of ray tracing algorithms, typical examples for branching in inner loops are the decisions what type of primitive a ray should be tested against for intersection, or which BRDF implementation should be evaluated at a point of intersection. Runtime polymorphism, which is often used in those cases, can lead to highly expressive but poorly performing code. Optimization strategies often involve reduced feature sets (e.g. by simply supporting only a single geometric primitive type), or an upstream sorting step followed by multiple ray tracing kernel executions, which effectively places the branching instruction outside the inner loop. In this paper we propose C++ compile time polymorphism as an alternative optimization strategy that does on its own not reduce branching, but that can be used to write highly expressive code without sacrificing optimization potential such as early binding or inlining of tiny functions. We present an implementation with modern C++ that we integrate into a ray tracing template library. We evaluate our approach on CPU and GPU architectures.Item Evaluating the Effects of Hand-gesture-based Interaction with Virtual Content in a 360° Movie(The Eurographics Association, 2017) Khan, Humayun; Lee, Gun A.; Hoermann, Simon; Clifford, Rory M. S.; Billinghurst, Mark; Lindeman, Robert W.; Robert W. Lindeman and Gerd Bruder and Daisuke IwaiHead-mounted displays are becoming increasingly popular as home entertainment devices for viewing 360° movies. This paper explores the effects of adding gesture interaction with virtual content and two different hand-visualisation modes for 360° movie watching experience. The system in the study comprises of a Leap Motion sensor to track the user's hand and finger motions, in combination with a SoftKinetic RGB-D camera to capture the texture of the hands and arms. A 360° panoramic movie with embedded virtual objects was used as content. Four conditions, displaying either a point-cloud of the real hand or a rigged computer-generated hand, with and without interaction, were evaluated. Presence, agency, embodiment, and ownership, as well as the overall participant preference were measured. Results showed that participants had a strong preference for the conditions with interactive virtual content, and they felt stronger embodiment and ownership. The comparison of the two hand visualisations showed that the display of the real hand elicited stronger ownership. There was no overall difference for presence between the four conditions. These findings suggest that adding interaction with virtual content could be beneficial to the overall user experience, and that interaction should be performed using the real hand visualisation instead of the virtual hand if higher ownership is desired.Item Sketching for Real-time Control of Crowd Simulations(The Eurographics Association, 2017) Gonzalez, Luis Rene Montana; Maddock, Steve; Tao Ruan Wan and Franck VidalCrowd simulations are used in various fields such as entertainment, training systems and city planning. However, controlling the behaviour of the pedestrians typically involves tuning of the system parameters through trial and error, a time-consuming process relying on knowledge of a potentially complex parameter set. This paper presents an interactive graphical approach to control the simulation by sketching in the simulation environment. The user is able to sketch obstacles to block pedestrians and lines to force pedestrians to follow a specific path, as well as define spawn and exit locations for pedestrians. The obstacles and lines modify the underlying navigation representation and pedestrian trajectories are recalculated in real time. The FLAMEGPU framework is used for the simulation and the game engine Unreal is used for visualisation. We demonstrate the effectiveness of the approach using a range of scenarios, producing interactive editing and frame rates for tens of thousands of pedestrians. A comparison with the commercial software MassMotion is also given.Item Downsampling and Storage of Pre-Computed Gradients for Volume Rendering(The Eurographics Association, 2017) DÃaz-GarcÃa, Jesús; Brunet, Pere; Navazo, Isabel; Vázquez, Pere-Pau; Fco. Javier Melero and Nuria PelechanoThe way in which gradients are computed in volume datasets influences both the quality of the shading and the performance obtained in rendering algorithms. In particular, the visualization of coarse datasets in multi-resolution representations is affected when gradients are evaluated on-the-fly in the shader code by accessing neighbouring positions. This is not only a costly computation that compromises the performance of the visualization process, but also one that provides gradients of low quality that do not resemble the originals as much as desired because of the new topology of downsampled datasets. An obvious solution is to pre-compute the gradients and store them. Unfortunately, this originates two problems: First, the downsampling process, that is also prone to generate artifacts. Second, the limited bit size of storage itself causes the gradients to loss precision. In order to solve these issues, we propose a downsampling filter for pre-computed gradients that provides improved gradients that better match the originals such that the aforementioned artifacts disappear. Secondly, to address the storage problem, we present a method for the efficient storage of gradient directions that is able to minimize the minimum angle achieved among all representable vectors in a space of 3 bytes. We also provide several examples that show the advantages of the proposed approaches.Item k-d Tree Construction Designed for Motion Blur(The Eurographics Association, 2017) Yang, Xin; Liu, Qi; Yin, Baocai; Zhang, Qiang; Zhou, Dongsheng; Wei, Xiaopeng; Matthias Zwicker and Pedro SanderWe present a k-d tree construction algorithm designed to accelerate rendering of scenes with motion blur, in application scenarios where a k-d tree is either required or desired. Our associated data structure focuses on capturing incoherent motion within the nodes of a k-d tree and improves both data structure quality and efficiency over previous methods. At build-time stage, we tracks primitives with motion that is significantly distinct from other primitives within the node, guarantee valid node references and the correctness of the data structure via primitive duplication heuristic and propagation rules. Our experiments with this hierarchy show artifact-free motion-blur rendering using a k-d tree, and demonstrate improvements against a traditional BVH with interpolation and a MSBVH structure designed to handle moving primitives, particularly in render time.Item Variable k-buffer using Importance Maps(The Eurographics Association, 2017) Vasilakis, Andreas-Alexandros; Vardis, Konstantinos; Papaioannou, Georgios; Moustakas, Konstantinos; Adrien Peytavie and Carles BoschSuccessfully predicting visual attention can significantly improve many aspects of computer graphics and games. Despite the thorough investigation in this area, selective rendering has not addressed so far fragment visibility determination problems. To this end, we present the first ''selective multi-fragment rendering'' solution that alters the classic k-buffer construction procedure from a fixed-k to a variable-k per-pixel fragment allocation guided by an importance-driven model. Given a fixed memory budget, the idea is to allocate more fragment layers in parts of the image that need them most or contribute more significantly to the visual result. An importance map, dynamically estimated per frame based on several criteria, is used for the distribution of the fragment layers across the image. We illustrate the effectiveness and quality superiority of our approach in comparison to previous methods when performing order-independent transparency rendering in various, high depth-complexity, scenarios.Item Image-based Remapping of Material Appearance(The Eurographics Association, 2017) Sztrajman, Alejandro; Krivánek, Jaroslav; Wilkie, Alexander; Weyrich, Tim; Reinhard Klein and Holly RushmeierDigital 3D content creation requires the ability to exchange assets across multiple software applications. For many 3D asset types, standard formats and interchange conventions are available. For material definitions, however, inter-application exchange is still hampered by different software packages supporting different BRDF models. To make matters worse, even if nominally identical BRDF models are supported, these often differ in their implementation, due to optimisations and safeguards in individual renderers. To facilitate appearance-preserving translation between different BRDF models whose precise implementation is not known (arguably the standard case with commercial systems), we propose a robust translation scheme which leaves BRDF evaluation to the targeted rendering system, and which expresses BRDF similarity in image space. As we will show, even naïve applications of a nonlinear fit which uses such an image space residual metric work well in some cases; however, it does suffer from instabilities for certain material parameters. We propose strategies to mitigate these instabilities and perform reliable parameter remappings between differing BRDF definitions. We report on experiences with this remapping scheme, both with respect to robustness and visual differences of the fits.Item Interactive Paper Tearing(The Eurographics Association and John Wiley & Sons Ltd., 2017) Schreck, Camille; Rohmer, Damien; Hahmann, Stefanie; Loic Barthe and Bedrich BenesWe propose an efficient method to model paper tearing in the context of interactive modeling. The method uses geometrical information to automatically detect potential starting points of tears. We further introduce a new hybrid geometrical and physical-based method to compute the trajectory of tears while procedurally synthesizing high resolution details of the tearing path using a texture based approach. The results obtained are compared with real paper and with previous studies on the expected geometric paths of paper that tears.Item Appearance of Interfaced Lambertian Microfacets, using STD Distribution(The Eurographics Association, 2017) Ribardière, M.; Meneveaux, D.; Bringier, B.; Simonot, L.; Reinhard Klein and Holly RushmeierThis paper presents the use of Student’s T-Distribution (STD) with interfaced Lambertian (IL) microfacets. The resulting model increases the range of materials while providing a very accurate adjustment of appearance. STD has been recently proposed as a generalized distribution of microfacets which includes Beckmann and GGX widely used in computer graphics; IL corresponds to a physical representation of a Lambertian substrate covered with a flat Fresnel interface. We illustrate the appearance variations that can be observed, and discuss the advantages of using such a combination.