Visibility Computations for Real-Time Rendering in General 3D Environments
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Visibility computations are essential operations in computer graphics, which are required for rendering acceleration in the form of visibility culling, as well as for computing realistic lighting. Visibility culling, which is the main focus of this thesis, aims to provide output sensitivity by sending only visible primitives to the hardware. Regardless of the rapid development of graphics hardware, it is of crucial importance for many applications like game development or architectural design, as the demands on the hardware regarding scene complexity increase accordingly. Solving the visibility problem has been an important research topic for many years, and countless methods have been proposed. Interestingly, there are still open research problems up to this day, and many algorithms are either impractical or only usable for specific scene configurations, preventing their widespread use. Visibility culling algorithms can be separated into algorithms for visibility preprocessing and online occlusion culling. Visibility computations are also required to solve complex lighting interactions in the scene, ranging from soft and hard shadows to ambient occlusion and full fledged global illumination. It is a big challenge to answer hundreds or thousands of visibility queries within a fraction of a second in order to reach real-time frame rates, which is one goal that we want to achieve in this thesis. The contribution of this thesis are four novel algorithms that provide solutions for efficient visibility interactions in order to achieve high-quality output-sensitive real-time rendering, and are general in the sense that they work with any kind of 3D scene configuration. First we present two methods dealing with the issue of automatically partitioning view space and object space into useful entities that are optimal for the subsequent visibility computations. Amazingly, this problem area was mostly ignored despite its importance, and view cells are mostly tweaked by hand in practice in order to reach optimal performance a very time consuming task. The first algorithm specifically deals with the creation of an optimal view space partition into view cells using a cost heuristics and sparse visibility sampling. The second algorithm extends this approach to optimize both view space subdivision and object space subdivision simultaneously. Next we present a hierarchical online culling algorithm that eliminates most limitations of previous approaches, and is rendering engine friendly in the sense that it allows easy integration and efficient material sorting. It reduces the main problem of previous algorithms the overhead due to many costly state changes and redundant hardware occlusion queries to a minimum, obtaining up to three times speedup over previous work. At last we present an ambient occlusion algorithm which works in screen space, and show that high-quality shading with effectively hundreds of samples per pixel is possible in real time for both static and dynamic scenes by utilizing temporal coherence to reuse samples from previous frames.