The Alchemy screen-space
ambient obscurance algorithm
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in Proceedings of ACM SIGGRAPH / Eurographics High-Performance Graphics 2011 (HPG '11)
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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 commercial games. 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, captures obscurance 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 on NVIDIA GeForce580.
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Acknowledgements
BibTex
@inproceedings{VV11AlchemyAO,
author = {Morgan McGuire and Brian Osman and Michael Bukowski and Padraic Hennessy},
title = {The Alchemy Screen-Space Ambient Obscurance Algorithm},
month = {August},
year = {2011},
booktitle = {High-Performance Graphics 2011},
location = {Vancouver, BC, Canada},
url = {http://graphics.cs.williams.edu/papers/AlchemyHPG11/}
}