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[stranno]

US6384822B1 - Method for rendering shadows using a shadow volume and a stencil buffer - Google Patents

A method for real-time shadow rendering in a 3-D graphics scene uses an inverted z-test to mark a shadow area in a stencil buffer. Front and back facing shadow volume polygons are rendered subsequent to rendering the scene and corresponding stencil buffer entries are incremented for pixels...

patents.google.com

Popularised by Doom 3 but previously seen in other games, like the infamous Activision Value's Secret Service: Security Breach.

 

[SidViscous]

Creative blackmailed him into advertising their sound cards in Id games in order to let him use his own technique he invented (but neglected to patent) in his own games.