Shadows have captivated humanity since the dawn of time; with the current age being no exception – shadows are core to realism and ambience, be it to invoke a classic Baroque interplay of lights, darks and colours as the case in Rembrandt van Rijn’s Militia Company of Captain Frans Banning Cocq or to create a sense of mystery as found in film noir and expressionist cinematography. Shadows, in this traditional sense, are regions of blocked light – the combined effect of placing an object between a light source and surface. This dissertation focuses on real-time shadow generation as a subset of 3D computer graphics. Its main focus is the critical analysis of numerous real-time shadow rendering algorithms and the construction of an empirically derived system for the high-speed rendering of shadows. This critical analysis allows us to assess the relationship between shadow rendering quality and performance. It also allows for the isolation of key algorithmic weaknesses and possible bottleneck areas. Focusing on these bottleneck areas, we investigate several possibilities of improving the performance and quality of shadow rendering; both on a hardware and software level. Primary performance benefits are seen through effective culling, clipping, the use of hardware extensions and by managing the polygonal complexity and silhouette detection of shadow casting meshes. Additional performance gains are achieved by combining the depth-fail stencil shadow volume algorithm with dynamic spatial subdivision. Using this performance data gathered during the analysis of various shadow rendering algorithms, we are able to define a fuzzy logic-based expert system to control the real-time selection of shadow rendering algorithms based on environmental conditions. This system ensures the following: nearby shadows are always of high-quality, distant shadows are, under certain conditions, rendered at a lower quality and the frames per second rendering performance is always maximised. / Dissertation (MSc)--University of Pretoria, 2009. / Computer Science / unrestricted

[pt] O mapeamento de sombras é uma técnica de renderização amplamente utilizada para a geração de sombras de superfícies arbitrárias em tempo real. No entanto, devido a sua natureza amostrada, apresenta dois problemas de difícil resolução: o aspecto chamuscado de objetos e a aparência serrilhada das bordas das sombras. Em particular, o sombreamento de modelos CAD (Computer-Aided Design) apresenta desafios ainda maiores, devido à existência de objetos estreitos com silhuetas complexas e o elevado grau de complexidade em profundidade. Neste trabalho, fazemos uma análise detalhada dos problemas de chamuscamento e serrilhamento, revisando e completando trabalhos de diferentes autores. Apresentamos ainda algumas propostas para melhoria de algoritmos existentes: o alinhamento de amostras independente de programas de vértice, um parâmetro generalizado para o LiSPSM (Light- Space Perspective Shadow Map), e um esquema de particionamento adaptativo em profundidade. Em seguida, investigamos a eficácia de diferentes algoritmos quando aplicados a modelos CAD, avaliando-os em critérios como facilidade de implementação, qualidade visual e eficiência computacional. / [en] Shadow mapping is a widely used rendering technique for shadow generation on arbitrary surfaces. However, because of the limited resolution available for sampling the scene, the algorithm presents two difficult problems to be solved: the incorrect self-shadowing of objects and the jagged appearance of shadow borders, also known as aliasing. Generating shadows for CAD (Computer-Aided Design) models presents additional challenges, due to the existence of many thin complex-silhouette objects and the high depth complexity. In this work, we present a detailed analysis of self-shadowing and aliasing by reviewing and building on works from different authors. We also propose some impromevents to existing algorithms: sample alignment without vertex shaders, a generalized parameter for the LiSPSM (Light-Space Perspective Shadow Map) algorithm, and an adaptive z- partitioning scheme. Finally, we investigate the effectiveness of different algorithms when applied to CAD models, considering ease of implementation, visual quality and computational efficiency.

Rendering in computer graphics is the process of converting a three dimensional scene description into a two dimensional image. In this work we focus on high quality rendering, which has numerous applications in entertainment and visualization. Many films today are created either entirely or in concert with computationally generated imagery and serve as a vivid example of the benefits of high quality rendering. This dissertation consists of two parts, each presenting novel work in the field of high quality, high performance rendering. The first part proposes the use of volumetric occluders, or a collection of axis-aligned boxes placed within a polygonal model, to accelerate the rendering of shadows cast by the model while producing images identical to the unaccelerated baseline. We show that our approach performs well on single object scenes and extend our approach for use with scenes from a professional open source movie. Although the technique has not yet proven itself on these multi-object scenes, we identify the scene characteristics which are hampering the approach and show that in some cases it is still possible to achieve an improvement in performance. The second part of the dissertation presents a new way to determine micropolygon tessellation rate within a Reyes style renderer. Our new scheme, called final approach tessellation, evaluates the tessellation rate close to a Reyes surface rather than upon entry into its bounding box. Our determination of the tessellation rate is more aggressive than previous approaches, producing a more compact tessellation which in turn is faster to compute and requires less memory. Our evaluation shows that although final approach tessellation is promising in theory, it ultimately fails to improve performance on actual test scenes. / text