Visibility silhouettes for semi-analytic spherical integration

1Université de Montréal 2Disney Research Zürich 3Belmont Technology, Inc.

In Computer Graphics Forum, 2014

Teaser
We compute spherical integrals of visibility-masked functions commonly found in rendering, e.g. in ambient occlusion and all-frequency direct illumination. This scene (123.2k triangles) took ~5 minutes to render on a 4-core CPU, independent of the lighting. These results render at 84% to 106% the speed of a noise-free ray-traced image, depending on the lighting.
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Abstract

At each shade point, the spherical visibility function encodes occlusion from surrounding geometry, in all directions. Computing this function is difficult and point-sampling approaches, such as ray-tracing or hardware shadow mapping, are traditionally used to efficiently approximate it. We propose a semi-analytic solution to the problem where the spherical silhouette of the visibility is computed using a search over a 4D dual mesh of the scene. Once computed, we are able to semi-analytically integrate visibility-masked spherical functions along the visibility silhouette, instead of over the entire hemisphere. In this way, we avoid the artifacts that arise from using point-sampling strategies to integrate visibility, a function with unbounded frequency content. We demonstrate our approach on several applications, including direct illumination from realistic lighting and computation of PRT data. Additionally, we present a new frequency-space method for exactly computing all-frequency shadows on diffuse surfaces. Our results match ground truth computed using importance-sampled stratified Monte Carlo ray-tracing, with comparable performance on scenes with low-to-moderate geometric complexity.

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Derek Nowrouzezahrai, Ilya Baran, Kenny Mitchell, Wojciech Jarosz. Visibility silhouettes for semi-analytic spherical integration. Computer Graphics Forum, 33(1):105–117, February 2014. 
@article{nowrouzezahrai14visibility,
    author   = {Nowrouzezahrai, Derek and Baran, Ilya and Mitchell, Kenny and Jarosz, Wojciech},
    title    = {Visibility Silhouettes for Semi-Analytic Spherical Integration},
    journal  = {Computer Graphics Forum},
    volume   = {33},
    number   = {1},
    month    = feb,
    year     = {2014},
    pages    = {105--117},
    doi      = {10/f5t6tf},
    keywords = {all-frequency shadowing, image-based rendering, spherical visibility}
}
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