The Alchemy Screen-Space Ambient Obscurance Algorithm
Date
2011
Journal Title
Journal ISSN
Volume Title
Publisher
ACM
Abstract
Ambient obscurance (AO) produces perceptually important illumination effects such as darkened corners, cracks, and wrinkles; proximity darkening; and contact shadows. We present the AO algorithm from the Alchemy engine used at Vicarious Visions in commercialgames. It is based on a new derivation of screen-space obscurance for robustness, and the insight that a falloff function can cancel terms in a visibility integral to favor efficient operations. Alchemy creates contact shadows that conform to surfaces, capturesobscurance from geometry of varying scale, and provides four intuitive appearance parameters: world-space radius and bias, and aesthetic intensity and contrast. The algorithm estimates obscurance at a pixel from sample points read from depth and normal buffers. It processes dynamic scenes at HD 720p resolution in about 4.5 ms on Xbox 360 and 3 ms onNVIDIA GeForce580.
Description
@inproceedings{10.1145:2018323.2018327,
booktitle = {Eurographics/ ACM SIGGRAPH Symposium on High Performance Graphics},
editor = {Carsten Dachsbacher and William Mark and Jacopo Pantaleoni},
title = {{The Alchemy Screen-Space Ambient Obscurance Algorithm}},
author = {McGuire, Morgan and Osman, Brian and Bukowski, Michael and Hennessy, Padraic},
year = {2011},
publisher = {ACM},
ISSN = {2079-8687},
ISBN = {978-1-4503-0896-0},
DOI = {10.1145/2018323.2018327}
}