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.

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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Text Reference

Derek Nowrouzezahrai, Ilya Baran, Kenny Mitchell, Wojciech Jarosz. Visibility Silhouettes for Semi-Analytic Spherical Integration. Computer Graphics Forum, 33(1):105–117, February 2014.

BibTex Reference

@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 = "10.1111/cgf.12257",
    keywords = "all-frequency shadowing, image-based rendering, spherical visibility"
}

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© The Author(s). This is the author's version of the work. It is posted here by permission of The Eurographics Association for your personal use. Not for redistribution. The definitive version is available at diglib.eg.org.