GPU-Based Global Illumination Using Lightcuts

Global Illumination aims to generate high quality images. But due to its highrequirements, it is usually quite slow. Research documented in this thesis wasintended to offer a hardware and software combined acceleration solution toglobal illumination. The GPU (using CUDA) was the hardware part of the wholemethod that applied parallelism to increase performance; the “Lightcuts”algorithm proposed by Walter (2005) at SIGGRAPH 2005 acted as the softwaremethod. As the results demonstrated in this thesis, this combined method offersa satisfactory performance boost effect for relatively complex scenes

Efficient Many-Light Rendering of Scenes with Participating Media

We present several approaches based on virtual lights that aim at capturing the light transport without compromising quality, and while preserving the elegance and efficiency of many-light rendering. By reformulating the integration scheme, we obtain two numerically efficient techniques; one tailored specifically for interactive, high-quality lighting on surfaces, and one for handling scenes with participating media

Using a Full Spectral Raytracer for Calculating Light Microclimate in Functional-Structural Plant Modelling

Raytracers that allow the spatially explicit calculation of the fate of light beams in a 3D scene allow the consideration of shading, reflected and transmitted light in functional-structural plant models (FSPM). However, the spectrum of visible light also has an effect on cellular and growth processes. This recently created the interest to extend this modelling paradigm allowing the representation of detailed spectra instead of monochromatic or white light and to extend existing FSPM platforms accordingly. In this study a raytracer is presented which supports the full spectrum of light and which can be used to compute spectra from arbitrary light sources and their transformation at the organ level by absorption, reflection and transmission in a virtual canopy. The raytracer was implemented as an extension of the FSPM platform GroIMP

Efficient representations of large radiosity matrices

The radiosity equation can be expressed as a linear system, where light interactions between patches of the scene are considered. Its resolution has been one of the main subjects in computer graphics, which has lead to the development of methods focused on different goals. For instance, in inverse lighting problems, it is convenient to solve the radiosity equation thousands of times for static geometries. Also, this calculation needs to consider many (or infinite) light bounces to achieve accurate global illumination results. Several methods have been developed to solve the linear system by finding approximations or other representations of the radiosity matrix, because the full storage of this matrix is memory demanding. Some examples are hierarchical radiosity, progressive refinement approaches, or wavelet radiosity. Even though these methods are memory efficient, they may become slow for many light bounces, due to their iterative nature. Recently, efficient methods have been developed for the direct resolution of the radiosity equation. In this case, the challenge is to reduce the memory requirements of the radiosity matrix, and its inverse. The main objective of this thesis is exploiting the properties of specific problems to reduce the memory requirements of the radiosity problem. Hereby, two types of problems are analyzed. The first problem is to solve radiosity for scenes with a high spatial coherence, such as it happens to some architectural models. The second involves scenes with a high occlusion factor between patches. For the high spatial coherence case, a novel and efficient error-bounded factorization method is presented. It is based on the use of multiple singular value decompositions along with a space filling curve, which allows to exploit spatial coherence. This technique accelerates the factorization of in-core matrices, and allows to work with out-of-core matrices passing only one time over them. In the experimental analysis, the presented method is applied to scenes up to 163K patches. After a precomputation stage, it is used to solve the radiosity equation for fixed geometries and infinite bounces, at interactive times. For the high occlusion problem, city models are used. In this case, the sparsity of the radiosity matrix is exploited. An approach for radiative exchange computation is proposed, where the inverse of the radiosity matrix is approximated. In this calculation, near-zero elements are removed, leading to a highly sparse result. This technique is applied to simulate daylight in urban environments composed by up to 140k patches.La ecuación de radiosidad tiene por objetivo el cálculo de la interacción de la luz con los elementos de la escena. Esta se puede expresar como un sistema lineal, cuya resolución ha derivado en el desarrollo de diversos métodos gráficos para satisfacer propósitos específicos. Por ejemplo, en problemas inversos de iluminación para geometrías estáticas, se debe resolver la ecuación de radiosidad miles de veces. Además, este cálculo debe considerar muchos (infinitos) rebotes de luz, si se quieren obtener resultados precisos de iluminación global. Entre los métodos desarrollados, se destacan aquellos que generan aproximaciones u otras representaciones de la matriz de radiosidad, debido a que su almacenamiento requiere grandes cantidades de memoria. Algunos ejemplos de estas técnicas son la radiosidad jerárquica, el refinamiento progresivo y la radiosidad basada en wavelets. Si bien estos métodos son eficientes en cuanto a memoria, pueden ser lentos cuando se requiere el cálculo de muchos rebotes de luz, debido a su naturaleza iterativa. Recientemente se han desarrollado métodos eficientes para la resolución directa de la ecuación de radiosidad, basados en el pre-cómputo de la inversa de la matriz de radiosidad. En estos casos, el desafío consiste en reducir los requerimientos de memoria y tiempo de ejecución para el cálculo de la matriz y de su inversa. El principal objetivo de la tesis consiste en explotar propiedades específicas de ciertos problemas de iluminación para reducir los requerimientos de memoria de la ecuación de radiosidad. En este contexto, se analizan dos casos diferentes. El primero consiste en hallar la radiosidad para escenas con alta coherencia espacial, tal como ocurre en algunos modelos arquitectónicos. El segundo involucra escenas con un elevado factor de oclusión entre parches. Para el caso de alta coherencia espacial, se presenta un nuevo método de factorización de matrices que es computacionalmente eficiente y que genera aproximaciones cuyo error es configurable. Está basado en el uso de múltiples descomposiciones en valores singulares (SVD) junto a una curva de recubrimiento espacial, lo que permite explotar la coherencia espacial. Esta técnica acelera la factorización de matrices que entran en memoria, y permite trabajar con matrices que no entran en memoria, recorriéndolas una única vez. En el análisis experimental, el método presentado es aplicado a escenas de hasta 163 mil parches. Luego de una etapa de precómputo, se logra resolver la ecuación de radiosidad en tiempos interactivos, para geométricas estáticas e infinitos rebotes. Para el problema de alta oclusión, se utilizan modelos de ciudades. En este caso, se aprovecha la baja densidad de la matriz de radiosidad, y se propone una técnica para el cálculo aproximado de su inversa. En este cálculo, los elementos cercanos a cero son eliminados. La técnica es aplicada a la simulación de la luz natural en ambientes urbanos compuestos por hasta 140 mil parches

Path manipulation strategies for rendering dynamic environments.

The current work introduces path manipulation as a tool that extends bidirectional path tracing to reuse paths in the temporal domain. Defined as an apparatus of sampling and reuse strategies, path manipulation reconstructs the subpaths that compose the light transport paths and addresses the restriction of static geometry commonly associated with Monte Carlo light transport simulations. By reconstructing and reusing subpaths, the path manipulation algorithm obviates the regeneration of the entire path collection, reduces the computational load of the original algorithm and supports scene dynamism. Bidirectional path tracing relies on local path sampling techniques to generate the paths of light in a synthetic environment. By using the information localized at path vertices, like the probability distribution, the sampling techniques construct paths progressively with distinct probability densities. Each probability density corresponds to a particular sampling technique, which accounts for specific illumination effects. Bidirectional path tracing uses multiple importance sampling to combine paths sampled with different techniques in low-variance estimators. The path sampling techniques and multiple importance sampling are the keys to the efficacy of bidirectional path tracing. However, the sampling techniques gained little attention beyond the generation and evaluation of paths. Bidirectional path tracing was designed for static scenes and thus it discards the generated paths immediately after the evaluation of their contributions. Limiting the lifespan of paths to a generation-evaluation cycle imposes a static use of paths and of sampling techniques. The path manipulation algorithm harnesses the potential of the sampling techniques to supplant the static manipulation of paths with a generation-evaluation-reuse cycle. An intra-subpath connectivity strategy was devised to reconnect the segregated chains of the subpaths invalidated by the scene alterations. Successful intra-subpath connections generate subpaths in multiple pieces by reusing subpath chains from prior frames. Subpaths are reconstructed generically, regardless of the subpath or scene dynamism type and without the need for predefined animation paths. The result is the extension of bidirectional path tracing to the temporal domain

Técnicas de altas prestaciones para métodos de iluminación global

[Resumen] El gran interés en los métodos de iluminación global se debe a sus múltiples aplicaciones y al realismo de sus imágenes resultantes. La investigación presentada en esta memoria se centra en mejorar computacionalmente el algoritmo de radiosidad, planteando estrategias tanto para métodos determinísticos como estocásticos. Respecto de los métodos determinísticos, se expondrán nuestras implementaciones en un sistema distribuido del algoritmo de radiosidad progresiva, utilizando el paradigma de paso de mensajes. Estas implementaciones están basadas en la división de la escena de una manera uniforme o no uniforme. Además, se usa la técnica de las máscaras de visibilidad para el cálculo de visibilidad entre elementos de distintos subescenas. También se demuestra que estas metodologías pueden reducir el tiempo de ejecución secuencial. Relativo a las soluciones estocásticas, presentamos dos implementaciones del método de relajación estocástica de Monte Carlo para radiosidad: en un sistema distribuido y en una Graphics Processing Unit (GPU). La primera se basa en tres técnicas: partición de la escena, empaquetamiento de rayos y determinación distribuida del fin de iteración. En la implementación GPU, además de la partición de la escena se empleó la simplificación de la malla de elementos y una organización eficiente de la ejecución de las tareas.[Resumo] O grande interese nos métodos de iluminación global débese ás súas múltiples aplicacións e ao realismo das súas imaxes resultantes. A investigación presentada nesta memoria céntrase en mellorar computacionalmente o algoritmo de radiosidade, formulando estratexias tanto para métodos determinísticos como estocásticos. Respecto dos métodos determinísticos, exporanse as nosas implementacións nun sistema distribuído do algoritmo de radiosidade progresiva, utilizando o paradigma de paso de mensaxes. Estas implementacións están baseadas na división da escena dunha maneira uniforme ou non uniforme. Ademais, úsase a técnica das máscaras de visibilidade para o cálculo de visibilidade entre elementos de distintas subescenas. Tamén se demostra que estas metodoloxías poden reducir o tempo de execución secuencial. Relativo as solucións estocásticas, presentamos dúas implementacións do método de relaxación estocástica de Monte Carlo para radiosidade: nun sistema distribuído e nunha Graphics Processing Unit (GPU). A primeira baséase en tres técnicas: partición da escena, empaquetamento de raios e determinación distribuída do fin de iteración. Na implementación GPU, ademais da partición da escena empregouse a simplificación da malla de elementos e unha organización eficiente da execución das tarefas.[Abstract] The great interest in global illumination methods is due to their multiple applications and the realism of the resulting images. The research presented in the present thesis focuses on computationally improving the radiosity algorithm, proposing strategies for both deterministic and stochastic approaches. For deterministic approaches, our implementations of the progressive radiosity algorithm will be demonstrated in a distributed system , using the message passing paradigm. These implementations are based on the partitioning of the scene in a uniform or non uniform manner. Furthermore, the technique of visibility masks is employed to calculate the visibility between elements in different subscenes. It is also shown that these methods are capable of reducing the sequential execution time. With regard to stochastic solutions, we present two implementations of the stochastic relaxation method for Monte Carlo radiosity: in a distributed system and in a Graphics Processing Unit (GPU). The first is based on three techniques: partition of the scene, ray packing strategy and distributed testing of the end of each iteration. In the GPU implementation, as well as the partition of the scene a simplified mesh of the elements was used along with an efficient thread scheduling

Generating Radiosity Maps on the GPU

Global illumination algorithms are used to render photorealistic images of 3D scenes taking into account both direct lighting from the light source and light reflected from other surfaces in the scene. Algorithms based on computing radiosity were among the first to be used to calculate indirect lighting, although they make assumptions that work only for diffusely reflecting surfaces. The classic radiosity approach divides a scene into multiple patches and generates a linear system of equations which, when solved, gives the values for the radiosity leaving each patch. This process can require extensive calculations and is therefore very slow. An alternative to solving a large system of equations is to use a Monte Carlo method of random sampling. In this approach, a large number of rays are shot from each patch into its surroundings and the irradiance values obtained from these rays are averaged to obtain a close approximation to the real value. This thesis proposes the use of a Monte Carlo method to generate radiosity texture maps on graphics hardware. By storing the radiosity values in textures, they are immediately available for rendering, making this algorithm useful for interactive implementations. We have built a framework to run this algorithm and using current graphics cards (NV6800 or higher) it is possible to execute it almost interactively for simple scenes and within relatively low times for more complex scenes

Artistic Path Space Editing of Physically Based Light Transport

Die Erzeugung realistischer Bilder ist ein wichtiges Ziel der Computergrafik, mit Anwendungen u.a. in der Spielfilmindustrie, Architektur und Medizin. Die physikalisch basierte Bildsynthese, welche in letzter Zeit anwendungsübergreifend weiten Anklang findet, bedient sich der numerischen Simulation des Lichttransports entlang durch die geometrische Optik vorgegebener Ausbreitungspfade; ein Modell, welches für übliche Szenen ausreicht, Photorealismus zu erzielen. Insgesamt gesehen ist heute das computergestützte Verfassen von Bildern und Animationen mit wohlgestalteter und theoretisch fundierter Schattierung stark vereinfacht. Allerdings ist bei der praktischen Umsetzung auch die Rücksichtnahme auf Details wie die Struktur des Ausgabegeräts wichtig und z.B. das Teilproblem der effizienten physikalisch basierten Bildsynthese in partizipierenden Medien ist noch weit davon entfernt, als gelöst zu gelten. Weiterhin ist die Bildsynthese als Teil eines weiteren Kontextes zu sehen: der effektiven Kommunikation von Ideen und Informationen. Seien es nun Form und Funktion eines Gebäudes, die medizinische Visualisierung einer Computertomografie oder aber die Stimmung einer Filmsequenz -- Botschaften in Form digitaler Bilder sind heutzutage omnipräsent. Leider hat die Verbreitung der -- auf Simulation ausgelegten -- Methodik der physikalisch basierten Bildsynthese generell zu einem Verlust intuitiver, feingestalteter und lokaler künstlerischer Kontrolle des finalen Bildinhalts geführt, welche in vorherigen, weniger strikten Paradigmen vorhanden war. Die Beiträge dieser Dissertation decken unterschiedliche Aspekte der Bildsynthese ab. Dies sind zunächst einmal die grundlegende Subpixel-Bildsynthese sowie effiziente Bildsyntheseverfahren für partizipierende Medien. Im Mittelpunkt der Arbeit stehen jedoch Ansätze zum effektiven visuellen Verständnis der Lichtausbreitung, die eine lokale künstlerische Einflussnahme ermöglichen und gleichzeitig auf globaler Ebene konsistente und glaubwürdige Ergebnisse erzielen. Hierbei ist die Kernidee, Visualisierung und Bearbeitung des Lichts direkt im alle möglichen Lichtpfade einschließenden "Pfadraum" durchzuführen. Dies steht im Gegensatz zu Verfahren nach Stand der Forschung, die entweder im Bildraum arbeiten oder auf bestimmte, isolierte Beleuchtungseffekte wie perfekte Spiegelungen, Schatten oder Kaustiken zugeschnitten sind. Die Erprobung der vorgestellten Verfahren hat gezeigt, dass mit ihnen real existierende Probleme der Bilderzeugung für Filmproduktionen gelöst werden können

Efficient Rendering of Scenes with Dynamic Lighting Using a Photons Queue and Incremental Update Algorithm

Photon mapping is a popular extension to the classic ray tracing algorithm in the field of realistic image synthesis. Moreover, it benefits from the massive parallelism computational power brought by recent developments in graphics processor hardwareand programming models. However rendering the scenes with dynamic lights stillgreatly limits the performance due to the re-construction at each rendered frame ofa kd-tree for the photons. We developed a novel approach based on the idea that storing the photons data along with the kd-tree leaf nodes data and implemented new incremental update scheme to improve the performance for dynamic lighting. The implementation is GPU-based and fully parallelized. A series of benchmarks with the prevalent existing GPU photon mapping technique is carried out to evaluate our approach. Our new technique is shown to be faster when handling scenes with dynamic lights than the existing technique while having the same image quality

Exploring heterogeneous computing with advanced path tracing algorithms

The CG research community has a renewed interest on rendering algorithms based on path space integration, mainly due to new approaches to discover, generate and exploit relevant light paths while keeping the numerical integrator unbiased or, at the very least, consistent. Simultaneously, the current trend towards massive parallelism and heterogeneous environments, based on a mix of conventional computing units with accelerators, is playing a major role both in HPC and embedded platforms. To efficiently use the available resources in these and future systems, algorithms and software packages are being revisited and reevaluated to assess their adequateness to these environments. This paper assesses the performance and scalability of three different path based algorithms running on homogeneous servers (dual multicore Xeons) and heterogeneous systems (those multicore plus manycore Xeon and NVidia Kepler GPU devices). These algorithms include path tracing (PT), its bidirectional counterpart (BPT) and the more recent Vertex Connect and Merge (VCM). Experimental results with two conventional scenes (one mainly diffuse, the other exhibiting specular-diffuse-specular paths) show that all algorithms scale well across the different platforms, the actual scalability depending on whether shared data structures are accessed or not (PT vs. BPT vs. VCM).This work was supported by COMPETE: POCI-01-0145FEDER-007043 and FCT (Fundação para a Ciência e Tecnologia) within Project Scope (UID/CEC/00319/2013), by the Cooperation Program with the University of Texas at Austin and co-funded by the North Portugal Regional Operational Programme (ON.2 - O Novo Norte), under the National Strategic Reference Framework, through the European Regional Development Fund