Vertex-Tracing - Interaktives Ray-Tracing durch adaptiv progressives Refinement im Objektraum

Abstract This dissertation presents an approach for interactive, physically exact simulation of specular reflections and specular refractions in virtual environments. The introduced approach is called Vertex Tracing and allows a hybrid rendering to add global illumination effects in traditional hardware rendering systems. The core of the Vertex Tracing is an adaptive progressive ray tracing. In contrast to standard ray tracing we use image coherence to compute only pixels (samples) that are essential for the final image reconstruction. The step by step adaption towards the final image is performed by geometry refinement of chosen polyhedra. These are scene objects with visual characteristics as specular reflections or refractions and should be handled particularly for Vertex Tracing. The object vertices are the starting point of computation. First, primary rays are shot from the eye point to the object vertices and after that, like in classical ray tracing approaches, a recursive ray shooting is performed from each vertex. If needed new vertices are inserted and consequently a step by step refinement of the object geometry is done. The reconstruction of the final image is performed by bilinear interpolation via graphics hardware. Beside the possibility of a combined rendering with OpenGL-objects, the use of graphics hardware additionally allows an efficient handling of textures. In this context, we introduce a defered texture lookup to prevent a costly sampling of high frequent textures. In addition, this thesis considers aspects of a distributed and parallel computation to speed up Vertex Tracing. In detail we implemented a distributed Vertex Tracing for a heterogenous network as well as a parallel approach for shared memory machines. Despite the adaptive progressive characteristic of the Vertex Tracing both techniques show that a significant speed-up can be achieved.Die vorliegende Dissertation beschreibt ein Verfahren zur interaktiv physikalisch exakten Simulation spekularer Reflexionen sowie spekularer Brechungen in virtuellen Umgebungen. Unter dem Begriff Vertex-Tracing wird in dieser Arbeit ein Ansatz vorgestellt, der es durch hybrides Rendering erlaubt, traditionelles Hardware-Rendering mit globalen Beleuchtungsphänomenen zu ergänzen. Kern des Verfahrens Vertex-Tracing bildet ein adaptiv progressives Ray-Tracing. Im Gegensatz zum Standard-Ray-Tracing besteht das Ziel darin, vorhandene Bildkohärenzen auszunutzen, indem nur diejenigen Pixel (Samples) berechnet werden, die für die Rekonstruktion des Finalbildes erforderlich sind. Die schrittweise Annäherung an das gewünschte Finalbild erfolgt durch Verfeinerung (Refinement) der Geometrie ausgewählter Polyeder. Diese sind Szenenobjekte, die aufgrund ihrer visuellen Charakteristik in Form spekularer Reflexionen oder Brechungen einem Vertex-Tracing unterzogen werden sollen. Ausgangspunkt der Berechnung dieser Objekte stellen ihre Objekt-Vertices dar. Sie bilden jeweils den Aufpunkt eines geschossenen Primärstrahles vom Betrachter und sind zugleich Startpunkt für eine weitere rekursive Strahlenverfolgung im Sinne des klassischen Ray-Tracing. Je nach Bedarf erfolgt das Einfügen neuer Vertices, dass eine schrittweise Verfeinerung der Objektgeometrie nach sich zieht. Die Rekonstruktion des Finalbildes erfolgt durch bilineare Interpolation mit Hilfe von Graphik-Hardware. Ihre Nutzung gestattet nicht nur ein kombiniertes Rendering mit herkömmlichen OpenGL-Objekten, sondern erlaubt darüber hinaus eine effiziente Behandlung von Texturen im Vertex-Tracing. In diesem Zusammenhang wird ein verzögerter Textur-Lookup vorgestellt. Er verhindert ein vollständiges Sampling von Texturen, das vor allem bei hochfrequenten Texturen einen erheblichen Mehraufwand bedeuten würde. Im Hinblick auf die Beschleunigung des Verfahrens werden ferner Aspekte einer verteilt, parallelen Berechnung untersucht beziehungsweise umgesetzt. Im Vordergrund steht dabei die Verteilung des Vertex-Tracings im Rechner-Cluster sowie eine Parallelisierung des Algorithmus auf Shared-Memory-Maschinen. Beide Ansätze zeigen, dass trotz des adaptiv progressiven Charakters des Verfahrens Vertex-Tracing ein signifikanter Speed-Up erzielbar ist

A Gathering and Shooting Progressive Refinement Radiosity Method

This paper presents a gathering and shooting progressive refinement radiosity method. Our method integrates the iterative process of light energy gathering used in the standard full matrix method and the iterative process of light energy shooting used in the conventional progressive refinement method. As usual, in each iteration, the algorithm first selects the patch which holds the maximum unprocessed light energy in the environment as the shooting patch. But before the shooting process is activated, a light energy gathering process takes place. In this gathering process, the amount of the unprocessed light energy which is supposed to be shot to the current shooting patch from the rest of the environment in later iterations is pre-accumulated. In general, this extra amount of gathered light energy is far from trivial since it comes from every patch in the environment from which the current shooting patch can be seen. However, with the reciprocity relationship for form-factors, still only one hemi-cube of the form-factors is needed in each iteration step. Based on a concise record of the history of the unprocessed light energy distribution in the environment, a new progressive refinement algorithm with revised gathering and shooting procedures is then proposed. With little additional computation and memory usage compared to the conventional progressive refinement radiosity method, a solid convergence speedup is achieved. This gathering and shooting approach extends the capability of the radiosity method in accurate and efficient simulation of the global illuminations of complex environments

Hardware Acceleration of Progressive Refinement Radiosity using Nvidia RTX

A vital component of photo-realistic image synthesis is the simulation of indirect diffuse reflections, which still remain a quintessential hurdle that modern rendering engines struggle to overcome. Real-time applications typically pre-generate diffuse lighting information offline using radiosity to avoid performing costly computations at run-time. In this thesis we present a variant of progressive refinement radiosity that utilizes Nvidia's novel RTX technology to accelerate the process of form-factor computation without compromising on visual fidelity. Through a modern implementation built on DirectX 12 we demonstrate that offloading radiosity's visibility component to RT cores significantly improves the lightmap generation process and potentially propels it into the domain of real-time.Comment: 114 page

Master of Science

thesisVirtual point lights (VPLs) provide an effective solution to global illumination computation by converting the indirect illumination into direct illumination from many virtual light sources. This approach results in a less noisy image compare to Monte Carlo methods. In addition, the number of VPLs to generate can be specified in advance; therefore, it can be adjusted depending on the scene, desired quality, time budget, and the available computational power. In this thesis, we investigate a new technique that carefully places VPLs for providing improved rendering quality for computing global illumination using VPLs. Our method consists of three different passes. In the first pass, we randomly generate a large number of VPLs in the scene starting from the camera to place them in positions that can contribute to the final rendered image. Then, we remove a considerable number of these VPLs using a Poisson disk sample elimination method to get a subset of VPLs that are uniformly distributed over the part of the scene that is indirectly visible to the camera. The second pass is to estimate the radiant intensity of these VPLs by performing light tracing starting from the original light sources in the scene and scatter the radiance of light rays at a hit-point to the VPLs close to that point. The final pass is rendering the scene, which consists of shading all points in the scene visible to the camera using the original light sources and VPLs

Serious Games in Cultural Heritage

Although the widespread use of gaming for leisure purposes has been well documented, the use of games to support cultural heritage purposes, such as historical teaching and learning, or for enhancing museum visits, has been less well considered. The state-of-the-art in serious game technology is identical to that of the state-of-the-art in entertainment games technology. As a result the field of serious heritage games concerns itself with recent advances in computer games, real-time computer graphics, virtual and augmented reality and artificial intelligence. On the other hand, the main strengths of serious gaming applications may be generalised as being in the areas of communication, visual expression of information, collaboration mechanisms, interactivity and entertainment. In this report, we will focus on the state-of-the-art with respect to the theories, methods and technologies used in serious heritage games. We provide an overview of existing literature of relevance to the domain, discuss the strengths and weaknesses of the described methods and point out unsolved problems and challenges. In addition, several case studies illustrating the application of methods and technologies used in cultural heritage are presented

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

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

Developing serious games for cultural heritage: a state-of-the-art review

Although the widespread use of gaming for leisure purposes has been well documented, the use of games to support cultural heritage purposes, such as historical teaching and learning, or for enhancing museum visits, has been less well considered. The state-of-the-art in serious game technology is identical to that of the state-of-the-art in entertainment games technology. As a result, the field of serious heritage games concerns itself with recent advances in computer games, real-time computer graphics, virtual and augmented reality and artificial intelligence. On the other hand, the main strengths of serious gaming applications may be generalised as being in the areas of communication, visual expression of information, collaboration mechanisms, interactivity and entertainment. In this report, we will focus on the state-of-the-art with respect to the theories, methods and technologies used in serious heritage games. We provide an overview of existing literature of relevance to the domain, discuss the strengths and weaknesses of the described methods and point out unsolved problems and challenges. In addition, several case studies illustrating the application of methods and technologies used in cultural heritage are presented