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

Multi-Modal Perception for Selective Rendering

A major challenge in generating high-fidelity virtual environments (VEs) is to be able to provide realism at interactive rates. The high-fidelity simulation of light and sound is still unachievable in real-time as such physical accuracy is very computationally demanding. Only recently has visual perception been used in high-fidelity rendering to improve performance by a series of novel exploitations; to render parts of the scene that are not currently being attended to by the viewer at a much lower quality without the difference being perceived. This paper investigates the effect spatialised directional sound has on the visual attention of a user towards rendered images. These perceptual artefacts are utilised in selective rendering pipelines via the use of multi-modal maps. The multi-modal maps are tested through psychophysical experiments to examine their applicability to selective rendering algorithms, with a series of fixed cost rendering functions, and are found to perform significantly better than only using image saliency maps that are naively applied to multi-modal virtual environments

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

Ray Tracing Gems

This book is a must-have for anyone serious about rendering in real time. With the announcement of new ray tracing APIs and hardware to support them, developers can easily create real-time applications with ray tracing as a core component. As ray tracing on the GPU becomes faster, it will play a more central role in real-time rendering. Ray Tracing Gems provides key building blocks for developers of games, architectural applications, visualizations, and more. Experts in rendering share their knowledge by explaining everything from nitty-gritty techniques that will improve any ray tracer to mastery of the new capabilities of current and future hardware. What you'll learn: The latest ray tracing techniques for developing real-time applications in multiple domains Guidance, advice, and best practices for rendering applications with Microsoft DirectX Raytracing (DXR) How to implement high-performance graphics for interactive visualizations, games, simulations, and more Who this book is for: Developers who are looking to leverage the latest APIs and GPU technology for real-time rendering and ray tracing Students looking to learn about best practices in these areas Enthusiasts who want to understand and experiment with their new GPU

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

Generating renderers

Most production renderers developed for the film industry are huge pieces of software that are able to render extremely complex scenes. Unfortunately, they are implemented using the currently available programming models that are not well suited to modern computing hardware like CPUs with vector units or GPUs. Thus, they have to deal with the added complexity of expressing parallelism and using hardware features in those models. Since compilers cannot alone optimize and generate efficient programs for any type of hardware, because of the large optimization spaces and the complexity of the underlying compiler problems, programmers have to rely on compiler-specific hardware intrinsics or write non-portable code. The consequence of these limitations is that programmers resort to writing the same code twice when they need to port their algorithm on a different architecture, and that the code itself becomes difficult to maintain, as algorithmic details are buried under hardware details. Thankfully, there are solutions to this problem, taking the form of Domain-Specific Lan- guages. As their name suggests, these languages are tailored for one domain, and compilers can therefore use domain-specific knowledge to optimize algorithms and choose the best execution policy for a given target hardware. In this thesis, we opt for another way of encoding domain- specific knowledge: We implement a generic, high-level, and declarative rendering and traversal library in a functional language, and later refine it for a target machine by providing partial evaluation annotations. The partial evaluator then specializes the entire renderer according to the available knowledge of the scene: Shaders are specialized when their inputs are known, and in general, all redundant computations are eliminated. Our results show that the generated renderers are faster and more portable than renderers written with state-of-the-art competing libraries, and that in comparison, our rendering library requires less implementation effort.Die meisten in der Filmindustrie zum Einsatz kommenden Renderer sind riesige Softwaresysteme, die in der Lage sind, extrem aufwendige Szenen zu rendern. Leider sind diese mit den aktuell verfügbaren Programmiermodellen implementiert, welche nicht gut geeignet sind für moderne Rechenhardware wie CPUs mit Vektoreinheiten oder GPUs. Deshalb müssen Entwickler sich mit der zusätzlichen Komplexität auseinandersetzen, Parallelismus und Hardwarefunktionen in diesen Programmiermodellen auszudrücken. Da Compiler nicht selbständig optimieren und effiziente Programme für jeglichen Typ Hardware generieren können, wegen des großen Optimierungsraumes und der Komplexität des unterliegenden Kompilierungsproblems, müssen Programmierer auf Compiler-spezifische Hardware-“Intrinsics” zurückgreifen, oder nicht portierbaren Code schreiben. Die Konsequenzen dieser Limitierungen sind, dass Programmierer darauf zurückgreifen den gleichen Code zweimal zu schreiben, wenn sie ihre Algorithmen für eine andere Architektur portieren müssen, und dass der Code selbst schwer zu warten wird, da algorithmische Details unter Hardwaredetails verloren gehen. Glücklicherweise gibt es Lösungen für dieses Problem, in der Form von DSLs. Diese Sprachen sind maßgeschneidert für eine Domäne und Compiler können deshalb Domänenspezifisches Wissen nutzen, um Algorithmen zu optimieren und die beste Ausführungsstrategie für eine gegebene Zielhardware zu wählen. In dieser Dissertation wählen wir einen anderen Weg, Domänenspezifisches Wissen zu enkodieren: Wir implementieren eine generische, high-level und deklarative Rendering- und Traversierungsbibliothek in einer funktionalen Programmiersprache, und verfeinern sie später für eine Zielmaschine durch Bereitstellung von Annotationen für die partielle Auswertung. Der “Partial Evaluator” spezialisiert dann den kompletten Renderer, basierend auf dem verfügbaren Wissen über die Szene: Shader werden spezialisiert, wenn ihre Eingaben bekannt sind, und generell werden alle redundanten Berechnungen eliminiert. Unsere Ergebnisse zeigen, dass die generierten Renderer schneller und portierbarer sind, als Renderer geschrieben mit den aktuellen Techniken konkurrierender Bibliotheken und dass, im Vergleich, unsere Rendering Bibliothek weniger Implementierungsaufwand erfordert.This work was supported by the Federal Ministry of Education and Research (BMBF) as part of the Metacca and ProThOS projects as well as by the Intel Visual Computing Institute (IVCI) and Cluster of Excellence on Multimodal Computing and Interaction (MMCI) at Saarland University. Parts of it were also co-funded by the European Union(EU), as part of the Dreamspace project

Utilising path-vertex data to improve Monte Carlo global illumination.

Efficient techniques for photo-realistic rendering are in high demand across a wide array of industries. Notable applications include visual effects for film, entertainment and virtual reality. Less direct applications such as visualisation for architecture, lighting design and product development also rely on the synthesis of realistic and physically based illumination. Such applications assert ever increasing demands on light transport algorithms, requiring the computation of photo-realistic effects while handling complex geometry, light scattering models and illumination. Techniques based on Monte Carlo integration handle such scenarios elegantly and robustly, but despite seeing decades of focused research and wide commercial support, these methods and their derivatives still exhibit undesirable side effects that are yet to be resolved. In this thesis, Monte Carlo path tracing techniques are improved upon by utilizing path vertex data and intermediate radiance contributions readily available during rendering. This permits the development of novel progressive algorithms that render low noise global illumination while striving to maintain the desirable accuracy and convergence properties of unbiased methods. The thesis starts by presenting a discussion into optical phenomenon, physically based rendering and achieving photo realistic image synthesis. This is followed by in-depth discussion of the published theoretical and practical research in this field, with a focus on stochastic methods and modem rendering methodologies. This provides insight into the issues surrounding Monte Carlo integration both in the general and rendering specific contexts, along with an appreciation for the complexities of solving global light transport. Alternative methods that aim to address these issues are discussed, providing an insight into modem rendering paradigms and their characteristics. Thus, an understanding of the key aspects is obtained, that is necessary to build up and discuss the novel research and contributions to the field developed throughout this thesis. First, a path space filtering strategy is proposed that allows the path-based space of light transport to be classified into distinct subsets. This permits the novel combination of robust path tracing and recent progressive photon mapping algorithms to handle each subset based on the characteristics of the light transport in that space. This produces a hybrid progressive rendering technique that utilises the strengths of existing state of the art Monte Carlo and photon mapping methods to provide efficient and consistent rendering of complex scenes with vanishing bias. The second original contribution is a probabilistic image-based filtering and sample clustering framework that provides high quality previews of global illumination whilst remaining aware of high frequency detail and features in geometry, materials and the incident illumination. As will be seen, the challenges of edge-aware noise reduction are numerous and long standing, particularly when identifying high frequency features in noisy illumination signals. Discontinuities such as hard shadows and glossy reflections are commonly overlooked by progressive filtering techniques, however by dividing path space into multiple layers, once again based on utilising path vertex data, the overlapping illumination of varying intensities, colours and frequencies is more effectively handled. Thus noise is removed from each layer independent of features present in the remaining path space, effectively preserving such features