Stencil shadow volume
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Stencil shadow volumes are a method of rendering in 3D computer graphics. Frank Crow introduced shadow volumes in 1977 as the geometry describing the 3D shape of the region occluded from a light source. Tim Heidmann later showed how to use the stencil buffer to render shadows with shadow volumes in real time. Heidmann's approach only worked when the virtual camera was itself not in shadow. Around 2000, several people discovered that Heidmann's method can be made to work for all camera positions by reversing a test based on the z-coordinate. His original method is now known as 'z-pass' and the new method is called 'z-fail'. Sim Dietrich's PowerPoint talk at a Creative Labs talk appears to be the first to mention this, however Cass Everitt and Mark Kilgard's 2002 NVIDIA technical report is the first detailed analysis of the technique. John Carmack of id Software popularized the technique by using it in the Doom 3 video game, so it is often referred to as Carmack's Reverse.
Creative Labs has recently attempted to enforce a patent on z-fail testing.