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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 Visual Language Generalization for Procedural Modeling of Buildings(The Eurographics Association, 2012) Barroso, Santiago; Patow, Gustavo; Isabel Navazo and Gustavo PatowProcedural modeling has become the accepted standard for the creation of detailed large scenes, in particular urban landscapes. With the introduction of visual languages there has been a huge leap forward in terms of usability, but there is still need of more sophisticated tools to simplify the development process. In this paper we present extensions to the visual modeling of procedural buildings, which adapt concepts from general purpose programming languages, with the objective of providing higher descriptive power. In particular, we present the concepts of visual modules, parameter linking and the possibility to seamlessly add abstract parameter templates to the designer visual toolbox. We base our demonstrations on a new visual language created for volume-based models like historic architectonic structures (aqueducts, churches, cathedrals, etc.), which cannot be modeled as 2D facades because of the intrinsic volumetric structure of these construction (e.g. vaults or arches).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 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 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 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 Characterisation of Position Based Dynamics for Elastic Materials(The Eurographics Association, 2016) Rodero, Cristóbal; Real, Pablo; Zuñeda, Pedro; Monteagudo, Carlos; Lozano, Miguel; García-Fernández, Ignacio; Alejandro Garcia-Alonso and Belen MasiaPosition Based Dynamics (PBD) methodology is a widely used approach for simulation of deformable bodies in the context of video games. Its main advantages over force based methods are its unconditional stability and its constraint based approach. However, it does not involve physically inspired parameters and its behaviour depends on time step size. This makes it difficult to reproduce a given elastic behaviour. In this work we perform an analysis of the mechanical properties in a PBD elastic system, and compare it to the Finite Element Method (FEM). We propose a methodology to fit the parameters of PBD to simulate a particular Young's modulus and Poisson's ratio.Item A Procedural Modeling System for the Creation of Huge Models(The Eurographics Association, 2012) Cubero, Francisco; Mas, Albert; Patow, Gustavo; Isabel Navazo and Gustavo PatowThis paper presents a new general purpose procedural geometrical modeling system. It is focused on providing flexibility, modularity and scalability. Furthermore, it is taylored to manage huge geometric models, with millions of polygons. An out-of-core memory management system assures that any scene size can be generated during the modeling evolution. This generation is performed by a set of rules and operations on geometrical objects, organized as a directed acyclic graph.