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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 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 Natural Phenomena as Metaphors for Visualization of Trend Data in Interactive Software Maps(The Eurographics Association, 2015) Würfel, Hannes; Trapp, Matthias; Limberger, Daniel; Döllner, Jürgen; Rita Borgo and Cagatay TurkaySoftware maps are a commonly used tool for code quality monitoring in software-development projects and decision making processes. While providing an important visualization technique for the hierarchical system structure of a single software revision, they lack capabilities with respect to the visualization of changes over multiple revisions. This paper presents a novel technique for visualizing the evolution of the software system structure based on software metric trends. These trend maps extend software maps by using real-time rendering techniques for natural phenomena yielding additional visual variables that can be effectively used for the communication of changes. Therefore, trend data is automatically computed by hierarchically aggregating software metrics. We demonstrate and discuss the presented technique using two real world data sets of complex software systems.Item A Simple Surface Tracking Method for Physically-Based 3D Water Simulations(The Eurographics Association, 2021) Amador, G.; Gomes, A.; Silva, F. and Gutierrez, D. and RodrÃguez, J. and Figueiredo, M.Water simulation, and more generically fluid simulation, is an important research topic in computer graphics. In 3D Eulerian Navier-Stokes-based water simulations, surface tracking and rendering are two delicate problems. The existing solutions to these problems (i.e., implicit surfaces-based approaches, height-fields, ray-tracing), are either to computationally intensive for real-time scenarios, or present bulge water surfaces (i.e., blobby water surfaces). In this paper, we propose a novel tracking algorithm for rendering water surfaces. Instead of tracking the flow of water using either level sets or height-fields, each cell of an 3D grid density value is directly measured in order to determine if it is either water, air, or water-air contact surface. The information in each cell is later used for the water surface splat rendering, using OpenGL vertex buffer objects.Item Bidirectional Rendering of Polarized Light Transport(The Eurographics Association, 2016) Jarabo, Adrian; Gutierrez, Diego; Alejandro Garcia-Alonso and Belen MasiaOn the foundations of many rendering algorithm is the symmetry between the path traversed by light and its adjoint from the camera. However, several effects, including polarization or fluorescence, break that symmetry and are defined only on the direction of light. This complicates the applicability of bidirectional methods, that exploit the symmetry for effective rendering light transport. In this work we focus on how to include polarization within a bidirectional rendering algorithm. For that, we generalize the path integral to support the constraints imposed by non-symmetric light transport. Based on this theoretical framework, we propose modifications on two bidirectional methods, namely bidirectional path tracing and photon mapping, extending them to support polarization.Item Procedural Modeling of Suspension Bridges(The Eurographics Association, 2021) Patow, Gustavo; Silva, F. and Gutierrez, D. and RodrÃguez, J. and Figueiredo, M.In this paper we introduce a method for designing a class of engineering structures, namely suspension bridges. These bridges are ubiquitous in the industrialized countries, often appearing in known city landscapes, yet they are complex enough that hand-based modeling is tedious and time consuming. We present a method that finds the right proportions for such a structure through an optimization method that tries to distribute the tower positions while maintaining cable width to be a finite number. By simultaneously optimizing the span and sag of the cables of a bridge, we optimize the geometry and soundness of the structure. We present the details of our technique together with examples illustrating its use, including comparisons with real structures.Item Crossmodal Perception in Immersive Environments(The Eurographics Association, 2016) Allue, Marcos; Serrano, Ana; Bedia, Manuel G.; Masia, Belen; Alejandro Garcia-Alonso and Belen MasiaWith the proliferation of low-cost, consumer level, head-mounted displays (HMDs) such as Oculus VR or Sony's Morpheus, we are witnessing a reappearance of virtual reality. However, there are still important stumbling blocks that hinder the development of applications and reduce the visual quality of the results. Knowledge of human perception in virtual environments can help overcome these limitations. In this paper, within the much-studied area of perception in virtual environments, we chose to look into the less explored area of crossmodal perception, that is, the interaction of different senses when perceiving the environment. In particular, we looked at the influence of sound on visual motion perception in a virtual reality scenario. We first replicated a well-known crossmodal perception experiment, carried out on a conventional 2D display, and then extended it to a 3D headmounted display (HMD). Next, we performed an additional experiment in which we increased the complexity of the stimuli of the previous experiment, to test whether the effects observed would hold in more realistic scenes. We found that the trend which was previously observed in 2D displays is maintained in HMDs, but with an observed reduction of the crossmodal effect. With more complex stimuli the trend holds, and the crossmodal effect is further reduced, possibly due to the presence of additional visual cues.Item Real-Time Modelling and Rendering of Sprayed Concrete(The Eurographics Association, 2021) Vélez, G.; Matey, L.; Amundarain, A.; Ordás, F.; MarÃn, J.A.; Silva, F. and Gutierrez, D. and RodrÃguez, J. and Figueiredo, M.This paper presents a new real-time method to model and render how sprayed concrete is spread on a surface. The method not only models and renders deposits sprayed from any angle, any distance and with any concrete flow, but it is also able to compute the amount of deposited volume taking into account the percentage of material that rebounds. The proposed method has been developed for a real-time training simulator for concrete spraying machinery, where most of the algorithm is parallelised and computed in the GPU, leaving the CPU free for other computations. In this research, the method has been validated for its use on plain surfaces and tunnel walls, but it can be extended to other types of surfaces.Item Efficient Propagation of Light Field Edits(The Eurographics Association, 2021) Jarabo, Adrian; Masia, Belen; Gutierrez, Diego; Silva, F. and Gutierrez, D. and RodrÃguez, J. and Figueiredo, M.Light field editing is a complex task, due to the large amount of data and the need to keep consistency between views. This has hampered the creation of efficient edit propagation methods, similar to those existing for single images. We propose a framework to edit light fields at interactive rates, by propagating some sparse user edits in the full light field. This propagation is guided by a novel affinity function, which forces similar pixels (defined by our affinity space) to receive similar edits, thus ensuring consistency. To manage the light field's large amount of data, we propose a novel multi-dimensional downsampling technique: we first cluster pixels with high affinity, and then perform edit propagation over the downsampled data. We finally upsample back to the original full resolution, maintaining visual fidelity and view consistency between views.