Interactive global illumination on the CPU

Computing realistic physically-based global illumination in real-time remains one of the major goals in the fields of rendering and visualisation; one that has not yet been achieved due to its inherent computational complexity. This thesis focuses on CPU-based interactive global illumination approaches with an aim to develop generalisable hardware-agnostic algorithms. Interactive ray tracing is reliant on spatial and cache coherency to achieve interactive rates which conflicts with needs of global illumination solutions which require a large number of incoherent secondary rays to be computed. Methods that reduce the total number of rays that need to be processed, such as Selective rendering, were investigated to determine how best they can be utilised. The impact that selective rendering has on interactive ray tracing was analysed and quantified and two novel global illumination algorithms were developed, with the structured methodology used presented as a framework. Adaptive Inter- leaved Sampling, is a generalisable approach that combines interleaved sampling with an adaptive approach, which uses efficient component-specific adaptive guidance methods to drive the computation. Results of up to 11 frames per second were demonstrated for multiple components including participating media. Temporal Instant Caching, is a caching scheme for accelerating the computation of diffuse interreflections to interactive rates. This approach achieved frame rates exceeding 9 frames per second for the majority of scenes. Validation of the results for both approaches showed little perceptual difference when comparing against a gold-standard path-traced image. Further research into caching led to the development of a new wait-free data access control mechanism for sharing the irradiance cache among multiple rendering threads on a shared memory parallel system. By not serialising accesses to the shared data structure the irradiance values were shared among all the threads without any overhead or contention, when reading and writing simultaneously. This new approach achieved efficiencies between 77% and 92% for 8 threads when calculating static images and animations. This work demonstrates that, due to the flexibility of the CPU, CPU-based algorithms remain a valid and competitive choice for achieving global illumination interactively, and an alternative to the generally brute-force GPU-centric algorithms

Otimização em GPU de bounding volume hierarchies para ray tracing

Orientador: Hélio PedriniDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de ComputaçãoResumo: Métodos de Ray Tracing são conhecidos por produzir imagens extremamente realistas ao custo de um alto esforço computacional. Pouco após terem surgido, percebeu-se que a maior parte do custo associado a estes métodos está relacionada a encontrar a intersecção entre o grande número de raios que precisam ser traçados e a geometria da cena. Estruturas de dados especiais que indexam e organizam a geometria foram propostas para acelerar estes cálculos, de forma que apenas um subconjunto da geometria precise ser verificado para encontrar as intersecções. Dentre elas, podemos destacar as Bounding Volume Hierarchies (BVH), que são estruturas usadas para agrupar objetos 3D hierarquicamente. Recentemente, uma grande quantidade de esforços foi aplicada para acelerar a construção destas estruturas e aumentar sua qualidade. Este trabalho apresenta um novo método para a construção de BVHs de alta qualidade em sistemas manycore. O método em questão é uma extensão do atual estado da arte na construção de BVHs em GPU, Treelet Restructuring Bounding Volume Hierarchy (TRBVH), e consiste em otimizar uma árvore já existente reorganizando subconjuntos de seus nós através de uma abordagem de agrupamento aglomerativo. A implementação deste método foi feita para a arquitetura Kepler utilizando CUDA e foi testada em dezesseis cenas que são comumente usadas para avaliar o desempenho de estruturas aceleradoras. É demonstrado que esta implementação é capaz de produzir árvores com qualidade comparável às geradas utilizando TRBVH para aquelas cenas, além de ser 30% mais rápidaAbstract: Ray tracing methods are well known for producing very realistic images at the expense of a high computational effort. Most of the cost associated with those methods comes from finding the intersection between the massive number of rays that need to be traced and the scene geometry. Special data structures were proposed to speed up those calculations by indexing and organizing the geometry so that only a subset of it has to be effectively checked for intersections. One such construct is the Bounding Volume Hierarchy (BVH), which is a tree-like structure used to group 3D objects hierarchically. Recently, a significant amount of effort has been put into accelerating the construction of those structures and increasing their quality. We present a new method for building high-quality BVHs on manycore systems. Our method is an extension of the current state-of-the-art on GPU BVH construction, Treelet Restructuring Bounding Volume Hierarchy (TRBVH), and consists of optimizing an already existing tree by rearranging subsets of its nodes using an agglomerative clustering approach. We implemented our solution for the NVIDIA Kepler architecture using CUDA and tested it on sixteen distinct scenes that are commonly used to evaluate the performance of acceleration structures. We show that our implementation is capable of producing trees whose quality is equivalent to the ones generated by TRBVH for those scenes, while being about 30% faster to do soMestradoCiência da ComputaçãoMestre em Ciência da Computaçã

Perceptually optimized real-time computer graphics

Perceptual optimization, the application of human visual perception models to remove imperceptible components in a graphics system, has been proven effective in achieving significant computational speedup. Previous implementations of this technique have focused on spatial level of detail reduction, which typically results in noticeable degradation of image quality. This thesis introduces refresh rate modulation (RRM), a novel perceptual optimization technique that produces better performance enhancement while more effectively preserving image quality and resolving static scene elements in full detail. In order to demonstrate the effectiveness of this technique, a graphics framework has been developed that interfaces with eye tracking hardware to take advantage of user fixation data in real-time. Central to the framework is a high-performance GPGPU ray-tracing engine written in OpenCL. RRM reduces the frequency with which pixels outside of the foveal region are updated by the ray-tracer. A persistent pixel buffer is maintained such that peripheral data from previous frames provides context for the foveal image in the current frame. Traditional optimization techniques have also been incorporated into the ray-tracer for improved performance. Applying the RRM technique to the ray-tracing engine results in a speedup of 2.27 (252 fps vs. 111 fps at 1080p) for the classic Whitted scene with reflection and transmission enabled. A speedup of 3.41 (140 fps vs. 41 fps at 1080p) is observed for a high-polygon scene that depicts the Stanford Bunny. A small pilot study indicates that RRM achieves these results with minimal impact to perceived image quality. A secondary investigation is conducted regarding the performance benefits of increasing physics engine error tolerance for bounding volume hierarchy based collision detection when the scene elements involved are in the user\u27s periphery. The open-source Bullet Physics Library was used to add accurate collision detection to the full resolution ray-tracing engine. For a scene with a static high-polygon model and 50 moving spheres, a speedup of 1.8 was observed for physics calculations. The development and integration of this subsystem demonstrates the extensibility of the graphics framework

Faster data structures and graphics hardware techniques for high performance rendering

Computer generated imagery is used in a wide range of disciplines, each with different requirements. As an example, real-time applications such as computer games have completely different restrictions and demands than offline rendering of feature films. A game has to render quickly using only limited resources, yet present visually adequate images. Film and visual effects rendering may not have strict time requirements but are still required to render efficiently utilizing huge render systems with hundreds or even thousands of CPU cores. In real-time rendering, with limited time and hardware resources, it is always important to produce as high rendering quality as possible given the constraints available. The first paper in this thesis presents an analytical hardware model together with a feed-back system that guarantees the highest level of image quality subject to a limited time budget. As graphics processing units grow more powerful, power consumption becomes a critical issue. Smaller handheld devices have only a limited source of energy, their battery, and both small devices and high-end hardware are required to minimize energy consumption not to overheat. The second paper presents experiments and analysis which consider power usage across a range of real-time rendering algorithms and shadow algorithms executed on high-end, integrated and handheld hardware. Computing accurate reflections and refractions effects has long been considered available only in offline rendering where time isn’t a constraint. The third paper presents a hybrid approach, utilizing the speed of real-time rendering algorithms and hardware with the quality of offline methods to render high quality reflections and refractions in real-time. The fourth and fifth paper present improvements in construction time and quality of Bounding Volume Hierarchies (BVH). Building BVHs faster reduces rendering time in offline rendering and brings ray tracing a step closer towards a feasible real-time approach. Bonsai, presented in the fourth paper, constructs BVHs on CPUs faster than contemporary competing algorithms and produces BVHs of a very high quality. Following Bonsai, the fifth paper presents an algorithm that refines BVH construction by allowing triangles to be split. Although splitting triangles increases construction time, it generally allows for higher quality BVHs. The fifth paper introduces a triangle splitting BVH construction approach that builds BVHs with quality on a par with an earlier high quality splitting algorithm. However, the method presented in paper five is several times faster in construction time

The Iray Light Transport Simulation and Rendering System

While ray tracing has become increasingly common and path tracing is well understood by now, a major challenge lies in crafting an easy-to-use and efficient system implementing these technologies. Following a purely physically-based paradigm while still allowing for artistic workflows, the Iray light transport simulation and rendering system allows for rendering complex scenes by the push of a button and thus makes accurate light transport simulation widely available. In this document we discuss the challenges and implementation choices that follow from our primary design decisions, demonstrating that such a rendering system can be made a practical, scalable, and efficient real-world application that has been adopted by various companies across many fields and is in use by many industry professionals today

Bandwidth and memory efficiency in real-time ray tracing

Real time ray tracing has been given a lot of attention in recent years in the academic and research community. Several novel algorithms have appeared that parallelize different aspects of the ray tracing algorithm through the use of a GPU. Among these, the creation of Bounding Volume Hierarchies (BVHs). We believe that recent approaches have failed to consider the performance impact of memory accesses in GPU and how their cost affects the overall performance of the application. In this work we show that by reducing memory bandwidth and footprint we are able to achieve significant improvements in BVH traversal times. We do this by compressing the BVH and the triangle mesh in a parallel manner after its creation, in each frame, and then decompressing it as needed while traversing the BVH

Lichttransportsimulation auf Spezialhardware

It cannot be denied that the developments in computer hardware and in computer algorithms strongly influence each other, with new instructions added to help with video processing, encryption, and in many other areas. At the same time, the current cap on single threaded performance and wide availability of multi-threaded processors has increased the focus on parallel algorithms. Both influences are extremely prominent in computer graphics, where the gaming and movie industries always strive for the best possible performance on the current, as well as future, hardware. In this thesis we examine the hardware-algorithm synergies in the context of ray tracing and Monte-Carlo algorithms. First, we focus on the very basic element of all such algorithms - the casting of rays through a scene, and propose a dedicated hardware unit to accelerate this common operation. Then, we examine existing and novel implementations of many Monte-Carlo rendering algorithms on massively parallel hardware, as full hardware utilization is essential for peak performance. Lastly, we present an algorithm for tackling complex interreflections of glossy materials, which is designed to utilize both powerful processing units present in almost all current computers: the Centeral Processing Unit (CPU) and the Graphics Processing Unit (GPU). These three pieces combined show that it is always important to look at hardware-algorithm mapping on all levels of abstraction: instruction, processor, and machine.Zweifelsohne beeinflussen sich Computerhardware und Computeralgorithmen gegenseitig in ihrer Entwicklung: Prozessoren bekommen neue Instruktionen, um zum Beispiel Videoverarbeitung, Verschlüsselung oder andere Anwendungen zu beschleunigen. Gleichzeitig verstärkt sich der Fokus auf parallele Algorithmen, bedingt durch die limitierte Leistung von für einzelne Threads und die inzwischen breite Verfügbarkeit von multi-threaded Prozessoren. Beide Einflüsse sind im Grafikbereich besonders stark , wo es z.B. für die Spiele- und Filmindustrie wichtig ist, die bestmögliche Leistung zu erreichen, sowohl auf derzeitiger und zukünftiger Hardware. In Rahmen dieser Arbeit untersuchen wir die Synergie von Hardware und Algorithmen anhand von Ray-Tracing- und Monte-Carlo-Algorithmen. Zuerst betrachten wir einen grundlegenden Hardware-Bausteins für alle diese Algorithmen, die Strahlenverfolgung in einer Szene, und präsentieren eine spezielle Hardware-Einheit zur deren Beschleunigung. Anschließend untersuchen wir existierende und neue Implementierungen verschiedener MonteCarlo-Algorithmen auf massiv-paralleler Hardware, wobei die maximale Auslastung der Hardware im Fokus steht. Abschließend stellen wir dann einen Algorithmus zur Berechnung von komplexen Beleuchtungseffekten bei glänzenden Materialien vor, der versucht, die heute fast überall vorhandene Kombination aus Hauptprozessor (CPU) und Grafikprozessor (GPU) optimal auszunutzen. Zusammen zeigen diese drei Aspekte der Arbeit, wie wichtig es ist, Hardware und Algorithmen auf allen Ebenen gleichzeitig zu betrachten: Auf den Ebenen einzelner Instruktionen, eines Prozessors bzw. eines gesamten Systems

Software-Based Ray Tracing for Mobile Devices

Ray tracing is a way to produce realistic images of three dimensional virtual scenes. It scales more to the number of pixels in the image than to the amount of details in the scene. This makes it an interesting application for mobile systems, which in general have smaller screens. Modern high-performance ray tracing depends on special acceleration data structures such as bounding volume hierarchies. Compressing the size of the bounding volume hierarchy leads to smaller memory bandwidth usage. This should be especially beneficial for mobile systems, which in general have smaller memory bandwidth. Compression also reduces cache misses and memory usage. Unfortunately, compression reduces the quality of the data structure, leading the ray traversal into unnecessary computations. In addition, compression increases the amount of work which needs to be carried out in the performance critical inner loop. The previous work on bounding volume hierarchy compression concentrates on inferring some of the coordinates from other coordinates or using different integer precisions. This thesis concentrates on using half-precision floating-point numbers, which have potential due to their greater dynamic range. If the halfs are too inaccurate for use as plain world coordinates, they can be used with hierarchical encoding. This restores the quality of the data structure back to original, but it requires even more work in the inner loop. Halfs reduce the whole memory usage by 7% and cache misses by 16%. Furthermore, they reduce power usage by 1.7%. The halfs’ effect on the performance is heavily dependent on the targeted hardware’s support for them. If decompression of the halfs is too slow, they will have a negative impact. Compared to integers, halfs have better performance in the so-called teapot-in-a-stadium problem

Mobile ray-tracing

Dissertação de mestrado em Computer ScienceThe technological advances and the massification of information technologies have allowed a huge and positive proliferation of the number of libraries and APIs. This large offer has made life easier for programmers in general, because they easily find a library, free or commercial, that helps them solve the daily challenges they have at hand. One area of information technology where libraries are critical is in Computer Graphics, due to the wide range of rendering techniques it offers. One of these techniques is ray tracing. Ray tracing allows to simulate natural electromagnetic phenomena such as the path of light and mechanical phenomena such as the propagation of sound. Similarly, it also allows to simulate technologies developed by men, like Wi-Fi networks. These simulations can have a spectacular realism and accuracy, at the expense of a very high computational cost. The constant evolution of technology allowed to leverage and massify new areas, such as mobile devices. Devices today are increasingly faster, replacing and often complementing tasks that were previously performed only on computers or on dedicated hardware. However, the number of image rendering libraries available for mobile devices is still very scarce, and no ray tracing based image rendering library has been able to assert itself on these devices. This dissertation aims to explore the possibilities and limitations of using mobile devices to execute rendering algorithms that use ray tracing, such as progressive path tracing. Its main goal is to provide a rendering library for mobile devices based on ray tracing.Os avanços tecnológicos e a massificação das tecnologias de informação permitiu uma enorme e positiva proliferação do número de bibliotecas e APIs. Esta maior oferta permitiu facilitar a vida dos programadores em geral, porque facilmente encontram uma biblioteca, gratuita ou comercial, que os ajudam a resolver os desafios diários que têm em mãos. Uma área das tecnologias de informação onde as bibliotecas são fundamentais é na Computação Gráfica, devido à panóplia de métodos de renderização que oferece. Um destes métodos é o ray tracing. O ray tracing permite simular fenómenos eletromagnéticos naturais como os percursos da luz e fenómenos mecânicos como a propagação do som. Da mesma forma também permite simular tecnologias desenvolvidas pelo homem, como por exemplo redes Wi-Fi. Estas simulações podem ter um realismo e precisão impressionantes, porém têm um custo computacional muito elevado. A constante evolução da tecnologia permitiu alavancar e massificar novas áreas, como os dispositivos móveis. Os dispositivos são hoje cada vez mais rápidos e cada vez mais substituem e/ou complementam tarefas que anteriormente eram apenas realizadas em computadores ou em hardware dedicado. Porém, o número de bibliotecas para renderização de imagens disponíveis para dispositivos móveis é ainda muito reduzido e nenhuma biblioteca de renderização de imagens baseada em ray tracing conseguiu afirmar-se nestes dispositivos. Esta dissertação tem como objetivo explorar possibilidades e limitações da utilização de dispositivos móveis para a execução de algoritmos de renderização que utilizem ray tracing, como por exemplo, o path tracing progressivo. O objetivo principal é disponibilizar uma biblioteca de renderização para dispositivos móveis baseada em ray tracing