McGuire, MorganOsman, BrianBukowski, MichaelHennessy, PadraicCarsten Dachsbacher and William Mark and Jacopo Pantaleoni2016-02-182016-02-182011978-1-4503-0896-02079-8687https://doi.org/10.1145/2018323.2018327Ambient 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.I.3.3 [Picture/Image Generation]Display AlgorithmsI.3.7 [Three Dimensional Graphics and Realism]Colorshadingshadowingand textureambient occlusionambient obscurancescreen space10.1145/2018323.201832725-32