The Alchemy Screen-Space Ambient Obscurance Algorithm

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Date
2011
Authors
McGuire, Morgan
Osman, Brian
Bukowski, Michael
Hennessy, Padraic
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
}
}
Citation
URI
https://doi.org/10.1145/2018323.2018327
Collections
High-Performance Graphics 2011