Carmack's Reverse
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Carmack's Reverse is a computer graphics technique for stencil shadow volumes that solves the problem of when the viewer's "eye" enters the shadow volume by tracing backwards from some point at infinity to the eye of the camera. Although it was originally discovered by William Bilodeau and Michael Songy, who filed a patent for it in 1999, John Carmack discovered it independently in 2002 during the development of Doom 3 and is generally given credit for it since he, unlike Bilodeau and Songy, advertised his discovery to the larger public.
Software patent controversy
A week before the game's release, it became known that an agreement to include EAX technology in Doom 3 reached by id Software and Creative Labs was heavily influenced by a software patent owned by the latter company. The patent dealt with a technique for rendering shadows called Carmack's Reverse, which was developed independently by both John Carmack and programmers at Creative Labs. id Software would have been putting themselves under legal liability if they used the technique in the finished game, so to defuse the issue, id Software agreed to license Creative Labs sound technologies in exchange for indemnification against lawsuits. [1] (http://www.shacknews.com/onearticle.x/32824)
External links
- Explanation on GameDev.net (http://www.gamedev.net/columns/hardcore/shadowvolume/page2.asp)
- USPTO patent entry 6,384,822 (http://patft.uspto.gov/netacgi/nph-Parser?u=/netahtml/srchnum.htm&Sect1=PTO1&Sect2=HITOFF&p=1&r=1&l=50&f=G&d=PALL&s1=6384822.WKU.&OS=PN/6384822&RS=PN/6384822)