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Item Real-time Inextensible Hair with Volume and Shape(The Eurographics Association, 2015) Sánchez-Banderas, Rosa María; Barreiro, Héctor; García-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 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 Generating Coherent Ray Directions in Path Tracing(The Eurographics Association, 2012) Torres, Roberto; Martín, Pedro J.; Gavilanes, Antonio; Isabel Navazo and Gustavo PatowThe quality of the images produced by a global illumination rendering engine is highly connected to the number of paths that are randomly generated from the camera to the light sources. Graphics Processing Units (GPUs) have been used to implement renderers by typically binding each thread to a ray. Nevertheless, this purely random generation does not fit well on the architecture of current GPUs, due to their SIMD nature. We modify the way paths are extended in order to take the most of GPUs. The arrangement of rays is split into groups of contiguous rays. The hemisphere on each intersection point is divided into spherical patches, and the same patch is chosen for all the rays in the group. The next direction for each path will be randomly chosen on that patch. Thus, if the intersection points of a group are near, the new rays spawned will be similar. We have implemented different configurations of this idea on a path tracer in CUDA and they have been experimentally tested on usual scenes. In the same amount of time, most of our algorithms complete more paths and, therefore, they produce images of higher quality than those obtained by the purely random generation.Item Differential Ray Marching(The Eurographics Association, 2012) Muñoz, Adolfo; Isabel Navazo and Gustavo PatowSeveral participating media rendering algorithms are based on ray marching: they integrate the variations of radiance along the volume covered by the participating media by splitting the path of light into segments and sampling light contribution at each of those segments. This paper revisits the concept of ray marching not as an integration technique, but as the application of a numerical method to solve an initial value differential equation. We present how to apply different numerical methods as ray marching techniques, analyze a wide range of them and study their applicability under different scenarios. Furthermore, we show how each of them improves over traditional ray marching. Any participating media rendering algorithm that is based on ray marching will benefit from the application of our technique by reducing the number of needed samples (and therefore, rendering time) and/or increasing accuracy.Item An Interactive Algorithm for Virtual Patient Positioning(The Eurographics Association, 2015) Casafranca, Juan José; Sújar, Aaron; García, Marcos; Mateu Sbert and Jorge Lopez-MorenoIn the last years, Virtual Reality medical simulators are gaining importance, training new physicians in a safe environment. In order to improve the trainees' skills, these applications let them perform a specific medical procedure in different virtual patients with different anatomical variation. Typically, virtual patients are generated from medical imaging data sets, such as MRI (magnetic resonance imaging), CT (computed tomography) or US (ultra sound). Usually, these data are generally captured in specific subject position. This pose is different from the subjects' position required in the simulated specific medical procedure. This paper proposes a novel technique that allows adapting the virtual patient anatomy to any desired pose. Our algorithm follows a geometrically based approach with the intention of: (i) being independent of a proper mechanical description of the tissues which is rarely available and (ii) keeping our user interface running at interactive rates. We adapted the skeletal animation workflow to deal with internal anatomy models. Most of the stages of this workflow have been automated. The user intervention has been limited to the interactive pose selection process. Additionally, in order to refine the solutions provided by our geometric approach, we have designed an optimization phase to achieve more appealing results.Item More Stable SPH-based Fluid Simulation(The Eurographics Association, 2012) Perea, Juan J.; Cordero, Juan M.; Isabel Navazo and Gustavo PatowThe simulation of fluid is a field largely discussed, from the viewpoint of engineering, in the so-called computational fluid dynamics (CFD). A problem that occurs repeatedly in the literature of CFD is the stability of the simulation. One of the elements that introduce instability in any CFD model is the temporal integration method. Among the most commonly used CFD techniques, both in the field of engineering and in the computer graphics, is SPH, which is particularly relevant to its computational simplicity. However, this technique adds stability problems due to the treatment of viscous and pressure terms arising from the formulation of Navier'Stokes. SPH also introduces greater instability by the need to use interpolation functions appropriate to the phenomena that occur in fluid dynamics. We present solutions to these four problems of inestability mentioned: treatment of the terms of pressure and viscosity that appear in the Navier'Stokes, the formulation of the characteristic interpolation function of SPH and treatment of temporal integration.Item CAVAST: The Crows Animation, Visualization, and Simulation Testbed(The Eurographics Association, 2014) Beacco, Alejandro; Pelechano, Nuria; Adolfo Munoz and Pere-Pau VazquezSimulation, animation and rendering of crowds has become an important part of real-time applications such as videogames. Virtual environments achieve higher realism when being populated by virtual crowds as opposed to appearing uninhabited. There has been a large amount of research on simulation, animation and rendering of crowds, but in most cases they seem to be treated separately as if the limitations in one area did not affect the others. At the end of the day the goal is to populate environments with as many characters as possible in real time, and it is of little use if one can for instance render thousands of characters in real time, but you cannot move more than a hundred due to a simulation bottleneck. The goal of our work is to provide a framework that lets the researcher focus on each of these topics at a time (simulation, animation, or rendering) and be able to explore and push the boundaries on one topic without being strongly limited by the other related issues. This paper presents therefore a new prototyping testbed for crowds that lets the researcher focus on one of these areas of research at a time without loosing sight of the others. We offer default representations, animation and simulation controllers for real time crowd simulation, that can easily be replaced or extended. Fully configurable level-of-detail for both rendering and simulation is also available.Item A Survey on Development Tools for Mobile Augmented Reality(The Eurographics Association, 2012) Rovelo, Gustavo; Abad, Francisco; Camahort, Emilio; Isabel Navazo and Gustavo PatowAugmented Reality (AR) applications have become more popular beyond the research laboratory due to recent technological breakthroughs in computer hardware and mobile devices. Users are starting to interact with virtual content mixed with real environments at their offices, homes, and schools using their mobile phones. For this growing market, developers have first to decide the platform in which they will develop the application (e.g. Apple iOS or Android). Then they must decide whether start writing the application from scratch using only platform native tools, or using one of the available Software Development Kits (SDKs), or using high-level authoring tools for the chosen platform. Besides, developers have to face different AR related issues according to the application's requirements: markers, barcodes or general image tracking, geolocation, efficient rendering of 3D objects, and designing a robust GUI for the target devices. To help developers and researchers to start writing mobile AR applications, this survey identifies the main features of several freeware and commercial SDKs and authoring tools.