Modern rendering systems require fast and efficient acceleration structures in order to compute visibility in real time. I present several novel data structures and algorithms for computing visibility with high performance. In particular, I present two algorithms for improving heuristic based acceleration structure build. These algorithms, when used in a demand driven way, have been shown to improve build performance by up to two orders of magnitude. Additionally, I introduce ray tracing in perspective transformed space. I demonstrate that ray tracing in this space can significantly improve visibility performance for near-common origin rays such as eye and shadow rays. I use these data structures and algorithms to support a key hypothesis of this dissertation: “There is no silver bullet for solving the visibility problem; many different acceleration structures will be required to achieve the highest performance.” Specialized acceleration structures provide significantly better performance than generic ones and building many specialized structures requires high performance build techniques. Additionally, I present an optimization-based taxonomy for classifying acceleration structures and algorithms in order to identify which optimizations provide the largest improvement in performance. This taxonomy also provides context for the algorithms I present. Finally, I present several novel cost metrics (and a correction to an existing cost metric) to improve visibility performance when using metric based acceleration structures. / text

A fundamental operation in computer graphics is to determine for a given point and direction in a scene, which geometric surface is nearest this point from this direction and thus visible. Conceptually, the point and direction define a "ray". Z-buffer hardware can compute surface visibility for a set of rays with a common origin (i.e. eye point) and a regular pattern of directions in real-time. However, this hardware is much less efficient at performing other visibility computations such as those required to accurately render shadows. A more flexible solution to the visible surface problem is needed. This work introduces the irregular Z-buffer algorithm, which efficiently solves the visible surface problem for rays with a common origin and arbitrary directions. In addition, we identify several changes to classical graphics architectures needed for hardware acceleration of this algorithm. Though these modifications are incremental in nature (i.e. no new functional units are introduced), we show that they enable significant new capability. In tandem with the irregular Z-buffer algorithm, a GPU with these changes has applications in: shadow rendering, indirect illumination, frameless rendering, adaptive anti-aliasing, adaptive textures, and jittered sampling. We explore the performance of hard and soft shadow rendering in particular, by way of a detailed hardware simulator. / text

Visualization of large scale time-varying volumetric datasets is an active topic of research. Technical limitations in terms of bandwidth and memory usage become a problem when visualizing these datasets on commodity computers at interactive frame rates. The overall objective is to overcome these limitations by adapting the methods of an existing Direct Volume Rendering pipeline. The objective is considered to be a proof of concept to assess the feasibility of visualizing large scale time-varying datasets using this pipeline. The pipeline consists of components from previous research, which make extensive use of graphics hardware to visualize large scale static data on commodity computers. This report presents a diploma work, which adapts the pipeline to visualize flow features concealed inside the large scale Computational Fluid Dynamics dataset. The work provides a foundation to address the technical limitations of the commodity computer to visualize time-varying datasets. The report describes the components making up the Direct Volume Rendering pipeline together with the adaptations. It also briefly describes the Computational Fluid Dynamics simulation, the flow features and an earlier visualization approach to show the system’s limitations when exploring the dataset.

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references and index.

This thesis explores efficient techniques for high quality real-time rendering of large architectural environments using affordable graphics hardware, as applied to illumination, including window reflections, shadows, and "bump mapping". For each of these fields, the thesis investigates existing methods and intends to provide adequate solutions. The focus lies on the use of new features found in current graphics hardware, making use of new OpenGL extensions and functionality found in Shader Model 3.0 vertex and pixel shaders and the OpenGL 2.0 core. The thesis strives to achieve maximum image quality, while maintaining acceptable performance at an affordable cost. The thesis shows the feasibility of using deferred shading on current hardware and applies high dynamic range rendering with the intent to increase realism. Furthermore, the thesis explains how to use environment mapping to simulate true planar reflections as well as incorporates relevant image post-processing effects. Finally, a shadow mapping solution is provided for the future integration of dynamic geometry.

The purpose of this thesis is to investigate performance aspects of layered displacement blending; a technique used to render realistic and transformable objects in real time rendering systems using the GPU. Layered displacement blending is done by blending layers of color maps and displacement maps together based on values stored in an influence map. In this thesis we construct a theoretical and practical model for layered displacement blending. The model is implemented in a test bed application to enable measuring of performance aspects. The implementation is fed input with variations in triangle count, number of subdivisions, texture size and number of layers. The execution time for these different combinations are recorded and analyzed. The recorded execution times reveal that the amount of layers associated with an object has no impact on performance. Further analysis reveals that layered displacement blending is heavily dependent on the triangle count in the input mesh. The results show that layered displacement blending is a viable option to representing transformable objects in real time applications with respect to performance. This thesis provides; a theoretical model for layered displacement blending, an implementation of the model using the GPU and measurements of that implementation.

In computer graphics, lighting is an important area. To simulate shadows from area light sources, indirect lighting and shadows from indirect light, a class of algorithms commonly known as global illumination algorithms can be used. Ambient occlusion is an approximation to global illumination that can emulate shadows from area light sources and shadows from indirect light, giving very soft shadows. For real-time applications, ambient occlusion can be precomputed and stored in maps or per vertex. However, that can only be done with good results if the geometry is static. Therefore, a number of methods that can handle more or less dynamic scenes have been introduced in the recent years. In this thesis, a collection of ambient occlusion methods for dynamic objects and procedural environments will be described. The main contribution is the introduction of a novel method that handles ambient occlusion for procedural environments. Another contribution is a description of an implementation of Screen Space Ambient Occlusion (SSAO). SSAO is an algorithm that calculates approximate ambient occlusion in real-time by using the depths of surrounding pixels. It handles completely dynamic scenes with good performance. The method for procedural environments handles the scenario where a number of building blocks are procedurally assembled at run-time. The idea is to precompute an ambient occlusion map for each building block where the self-occlusion is stored. In addition, an ambient occlusion grid is precomputed for each block to accommodate the inter-block occlusion. At run-time, after the building blocks have been assembled, the ambient occlusion from the grids is blended with the ambient occlusion from the maps to generate new maps, valid for the procedural environment. Following that, the environment can be rendered with high quality ambient occlusion at almost no cost, in the same fashion as for a static environment where the ambient occlusion maps can be completely precomputed.

This thesis explores the balance between visual quality and the performance of a 3D object for computer games. Additionally, it aims to help new 3D artists to create assets that are both visually adequate and optimized for real-time rendering. It further investigates the differences in the judgement of the visual quality of thosethat know computer graphics, and thosenot familiar with it. Many explanations of 3D art optimization are often highly technical and challenging for graphic artists to grasp. Additionally, they regularly neglect the effects of optimization to the visual quality of the assets. By testing several 3D assets to measure their render time while using a survey to gather their visual assessments, it was discovered that 3D game art is very contextual. No definite or straightforward way was identified to find the balance between art quality and performance universally. Neither when it comes to performance nor visuals. However, some interesting findings regarding the judgment of visual quality were observed and presented. / Den här uppsatsen utforskar balansen mellan visuell kvalitéoch prestanda i 3D modeller för spel. Vidare eftersträvar den att utgöra ett stöd för nya 3D-modelleingskonstnärer för att skapa modeller som är både visuellt adekvata och optimerade för att renderas i realtid. Dessutom undersöks skillnaden mellan omdömet av den visuella kvalitén mellan de som är bekanta med 3D datorgrafik och de som inte är det. Många förklaringar gällande optimering av 3D grafik är högst tekniska och utgör en utmaning för grafiker att förståsig på och försummar dessutom ofta effekten av hur optimering påverkar resultatet rent visuallet. Genom att testa ett flertal 3D modeller, mäta tiden det tar för dem att renderas, samt omdömen gällande visuella intryck, drogs slutsatsen att bedömning av 3D modellering för spel är väldigt kontextuell. Inget definitivt och enkelt sätt att hitta balansen mellan visuella kvalitén upptäcktes. Varken gällande prestanda eller visuell kvalité. Däremot gjordes några intressanta upptäckter angående bedömningen av den visuella kvalitén som observerades och presenterades.

Computing complex lighting simulations such as global illumination is a computationally intensive task. Various real time solutions exist to approximate aspects of global illumination such as shadows, however, few of these methods offer single pass rendering solutions for soft shadows (self and other) and inter-reflections. In contrast, Precomputed Radiance Transfer (PRT) is a real-time computer graphics technique which pre-calculates an object's response to potential incident light. At run time, the actual incident light can be used to quickly illuminate the surface, rendering effects such as soft self-shadows and inter-reflections. In this thesis, we show that by calculating PRT lighting coefficients densely over a surface as texture data, additional surface detail can be encoded by integrating other computer graphics techniques, such as normal mapping. By calculating transfer coefficients densely over the surface of a mesh as texture data, greater fidelity can be achieved in lighting coarse meshes than simple interpolation can achieve. Furthermore, the lighting on low polygon objects can be enhanced by drawing surface normal and occlusion data from highly tessellated, detailed meshes. By applying such data to a decimated, simplified mesh, a more detailed and visually pleasing reconstruction can be displayed for a lower cost. In addition, this thesis introduces Hierarchical PRT, which extends some surface effects, such as soft shadows, between objects. Previous approaches to PRT used a more complex neighborhood transfer scheme in order to extend these lighting effects. Hierarchical PRT attempts to capture scene information in a tree data structure which represents coarse lighting relationships between objects. Potential occlusions can be found at run time by utilizing the same spherical harmonic representation used to represent surface lighting to instead store light "filters" between scene tree nodes. Such "filters" can be combined over a set of nodes in the scene to obtain the net shadowing of an object with good performance. We present both visually pleasing results on simplified meshes using normal mapping and textured PRT and initial results using Hierarchical PRT that captures low frequency lighting information for a small number of dynamic objects which shadow static scene objects with good results.

In the computer graphics production environment, artists often must tweak specific lighting and material parameters to match a mind's eye vision of the appearance of a 3D scene. However, the interaction between a material and a lighting environment is often too complex to cognitively predict without visualization. Therefore, artists operate in a design cycle, where they tweak the parameters, wait for a visualization, and repeat, seeking to obtain a desired look. We propose the use of appearance-driven material design. Here, artists directly design the appearance of reflected light for a specific view, surface point, and time. In this thesis, we discuss several methods for appearance-driven design with homogeneous materials, spatially-varying materials, and appearance-matching materials, where each uses a unique modeling and optimization paradigm. Moreover, we present a novel treatment of the illumination integral using sampling theory that can utilize the computational power of the graphics processing unit (GPU) to provide real-time visualization of the appearance of various materials illuminated by complex environment lighting. As a system, the modeling, optimization and rendering steps all operate on arbitrary geometry and in detailed lighting environments, while still providing instant feedback to the designer. Thus, our approach allows materials to play an active role in the process of set design and story-telling, a capability that was, until now, difficult to achieve due to the unavailability of interactive tools appropriate for artists.