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Now showing 1 - 9 of 9
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    Voxel DAGs and Multiresolution Hierarchies: From Large-Scale Scenes to Pre-computed Shadows
    (The Eurographics Association, 2018) Assarsson, Ulf; Billeter, Markus; Dolonius, Dan; Eisemann, Elmar; Jaspe, Alberto; Scandolo, Leonardo; Sintorn, Erik; Ritschel, Tobias and Telea, Alexandru
    In this tutorial, we discuss voxel DAGs and multiresolution hierarchies, which are representations that can encode large volumes of data very efficiently. Despite a significant compression ration, an advantage of these structures is that their content can be efficiently accessed in real-time. This property enables various applications. We begin the tutorial by introducing the concepts of sparsity and of coherency in voxel structures, and explain how a directed acyclic graph (DAG) can be used to represent voxel geometry in a form that exploits both aspects, while remaining usable in its compressed from for e.g. ray casting. In this context, we also discuss extensions that cover the time domain or consider an advanced encoding strategies exploiting symmetries and entropy. We then move on to voxel attributes, such as colors, and explain how to integrate such information with the voxel DAGs. We will provide implementation details and present methods for efficiently constructing the DAGs and also cover how to efficiently access the data structures with e.g. GPU-based ray tracers. The course will be rounded of with a segment on applications. We highlight a few examples and show their results. Pre-computed shadows are a special application, which will be covered in detail. In this context, we also explain how some of previous ideas contribute to multi-resolution hierarchies, which gives an outlook on the potential generality of the presented solutions.
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    Area Lights in Signed Distance Function Scenes
    (The Eurographics Association, 2019) Bán, Róbert; Bálint, Csaba; Valasek, Gábor; Cignoni, Paolo and Miguel, Eder
    This paper presents two algorithms to incorporate spherical and general area lights into scenes defined by signed distance functions. The first algorithm employs an efficient approximation to the contribution of spherical lights to direct illumination and renders them at real-time rates. The second algorithm is of superior quality at a higher computational cost which is better suited for interactive rates. Our results are compared to both real-time soft shadow algorithms and a ground truth obtained by Monte Carlo integration. We show in these comparisons that our real-time solution computes more accurate shadows while the more demanding variant outperforms Monte Carlo integration at the expense of accuracy.
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    Adaptive Frameless Rendering with NVIDIA OptiX
    (The Eurographics Association, 2019) Hsiao, Chung-Che; Watson, Benjamin; Fusiello, Andrea and Bimber, Oliver
    We implement adaptive frameless rendering (AFR) on NVIDIA OptiX, a real-time ray tracing API taking advantage of NVIDIA GPUs including their latest RTX functionality. OptiX is a parallel system that sits on top of NVIDIA's better-known CUDA API. AFR has sampling and reconstruction processes that use information distributed across both space and time, aiming to generate low-latency updates. Previous AFR implementations were sequential prototypes. Our parallel prototype is allowing us to confront several unique challenges, including closed loop control of both sampling and reconstruction, and load balancing between CPU and GPU.
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    On the Pedagogy of Teaching Introductory Computer Graphics without Rendering APIs
    (The Eurographics Association, 2018) Chen, Minsi; Xu, Zhijie; Rippin, Wayne; Post, Frits and Žára, Jirí
    Teaching modern computer graphics programming has become increasingly challenging due to the advancement in the granularity of application programming interfaces (APIs). In this paper, we put forward a discussion on the pedagogical value of implementing a software rasteriser prior to tackling the issues of learning modern graphics APIs and shader programming. An API-free approach to teaching introductory computer graphics along with its assessment strategy are presented. Our observation found that students were more effective and confident in learning and using modern rendering APIs when subsequently studying advanced real-time graphics.
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    Monte Carlo Methods for Volumetric Light Transport Simulation
    (The Eurographics Association and John Wiley & Sons Ltd., 2018) Novák, Jan; Georgiev, Iliyan; Hanika, Johannes; Jarosz, Wojciech; Hildebrandt, Klaus and Theobalt, Christian
    The wide adoption of path-tracing algorithms in high-end realistic rendering has stimulated many diverse research initiatives. In this paper we present a coherent survey of methods that utilize Monte Carlo integration for estimating light transport in scenes containing participating media. Our work complements the volume-rendering state-of-the-art report by Cerezo et al. [CPP 05]; we review publications accumulated since its publication over a decade ago, and include earlier methods that are key for building light transport paths in a stochastic manner. We begin by describing analog and non-analog procedures for freepath sampling and discuss various expected-value, collision, and track-length estimators for computing transmittance. We then review the various rendering algorithms that employ these as building blocks for path sampling. Special attention is devoted to null-collision methods that utilize fictitious matter to handle spatially varying densities; we import two ''next-flight'' estimators originally developed in nuclear sciences. Whenever possible, we draw connections between image-synthesis techniques and methods from particle physics and neutron transport to provide the reader with a broader context.
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    Analysis of Sample Correlations for Monte Carlo Rendering
    (The Eurographics Association and John Wiley & Sons Ltd., 2019) Singh, Gurprit; Öztireli, Cengiz; Ahmed, Abdalla G. M.; Coeurjolly, David; Subr, Kartic; Deussen, Oliver; Ostromoukhov, Victor; Ramamoorthi, Ravi; Jarosz, Wojciech; Giachetti, Andrea and Rushmeyer, Holly
    Modern physically based rendering techniques critically depend on approximating integrals of high dimensional functions representing radiant light energy. Monte Carlo based integrators are the choice for complex scenes and effects. These integrators work by sampling the integrand at sample point locations. The distribution of these sample points determines convergence rates and noise in the final renderings. The characteristics of such distributions can be uniquely represented in terms of correlations of sampling point locations. Hence, it is essential to study these correlations to understand and adapt sample distributions for low error in integral approximation. In this work, we aim at providing a comprehensive and accessible overview of the techniques developed over the last decades to analyze such correlations, relate them to error in integrators, and understand when and how to use existing sampling algorithms for effective rendering workflows.
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    Adaptive Quantization Visibility Caching
    (The Eurographics Association and Blackwell Publishing Ltd., 2013) Popov, Stefan; Georgiev, Iliyan; Slusallek, Philipp; Dachsbacher, Carsten; I. Navazo, P. Poulin
    Ray tracing has become a viable alternative to rasterization for interactive applications and also forms the basis of most global illumination methods. However, even today's fastest ray-tracers offer only a tight budget of rays per pixel per frame. Rendering performance can be improved by increasing this budget, or by developing methods that use it more efficiently. In this paper we propose a global visibility caching algorithm that reduces the number of shadow rays required for shading to a fraction of less than 2% in some cases. We quantize the visibility function's domain while ensuring a minimal degradation of the final image quality. To control the introduced error, we adapt the quantization locally, accounting for variations in geometry, sampling densities on both endpoints of the visibility queries, and the light signal itself. Compared to previous approaches for approximating visibility, e.g. shadow mapping, our method has several advantages: (1) it allows caching of arbitrary visibility queries between surface points and is thus applicable to all ray tracing based methods; (2) the approximation error is uniform over the entire image and can be bounded by a user-specified parameter; (3) the cache is created on-the-fly and does not waste any resources on queries that will never be used. We demonstrate the benefits of our method on Whitted-style ray tracing combined with instant radiosity, as well as an integration with bidirectional path tracing.
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    A Survey on Gradient-Domain Rendering
    (The Eurographics Association and John Wiley & Sons Ltd., 2019) Hua, Binh-Son; Gruson, Adrien; Petitjean, Victor; Zwicker, Matthias; Nowrouzezahrai, Derek; Eisemann, Elmar; Hachisuka, Toshiya; Giachetti, Andrea and Rushmeyer, Holly
    Monte Carlo methods for physically-based light transport simulation are broadly adopted in the feature film production, animation and visual effects industries. These methods, however, often result in noisy images and have slow convergence. As such, improving the convergence of Monte Carlo rendering remains an important open problem. Gradient-domain light transport is a recent family of techniques that can accelerate Monte Carlo rendering by up to an order of magnitude, leveraging a gradient-based estimation and a reformulation of the rendering problem as an image reconstruction. This state of the art report comprehensively frames the fundamentals of gradient-domain rendering, as well as the pragmatic details behind practical gradient-domain uniand bidirectional path tracing and photon density estimation algorithms. Moreover, we discuss the various image reconstruction schemes that are crucial to accurate and stable gradient-domain rendering. Finally, we benchmark various gradient-domain techniques against the state-of-the-art in denoising methods before discussing open problems.
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    Accelerating Sphere Tracing
    (The Eurographics Association, 2018) Bálint, Csaba; Valasek, Gábor; Diamanti, Olga and Vaxman, Amir
    This paper presents two performance improvements on sphere tracing. First, a sphere tracing variant designed to take optimal step sizes near planar surfaces is proposed. We demonstrate how relaxation is used to make this method applicable to sphere tracing arbitrary geometries and compare its performance to classical (by Hart) and relaxed (Keinert et al.) sphere tracing in rendering various scenes. The method is also general in the sense that it can be applied in any scenario that requires the computation of ray-surface intersections. Our second contribution is a multi-resolution rendering strategy that can be used with any sphere tracing variant. By starting from a lower resolution and gradually increasing it, render times can be reduced.