Multiresolution image-space rendering for interactive global illumination

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Nichols, Gregory Boyd
The University of Iowa; University of Iowa
global illumination; gpu; rendering; Computer Sciences
thesis / dissertation description
Global illumination adds tremendous visual richness to rendered images. Unfortunately, such illumination proves quite costly to compute, and is therefore often coarsely approximated by interactive applications, or simply omitted altogether. Global illumination is often quite low-frequency, aside from sharp changes at discontinuities. This thesis describes three novel multiresolution image-space methods that exploit this characteristic to accelerate rendering speeds. These techniques run completely on the GPU at interactive rates and require no precomputation, allowing fully dynamic lighting, geometry, and camera.The first approach, multiresolution splatting, is a novel multiresolution method for rendering indirect illumination. This work extends reflective shadow maps, an image space method that splats contributions from secondary light sources into eye-space. Splats are refined into multiresolution patches, rendering indirect contributions at low resolution where lighting changes slowly and at high resolution near discontinuities; this greatly reduces GPU fill rate and enhances performance.The second method, image space radiosity, significantly improves the performance of multiresolution splatting, introducing an efficient stencil-based parallel refinement technique. This method also adapts ideas from object-space hierarchical radiosity methods to image space, introducing two adaptive sampling methods that allow much finer sampling of the reflective shadow map where needed. These modifications significantly improve temporal coherence while maintaining performance.The third approach adapts these techniques to accelerate the rendering of direct illumination from large area light sources. Visibility is computed using a coarse screen-space voxelization technique, allowing binary visibility queries using ray marching. This work also proposes a new incremental refinement method that considers both illumination and visibility variations. Both diffuse and non-diffuse surfaces are supported, and illumination can vary over the surface of the light, enabling dynamic content such as video screens.