shadow volume

Render the shadow volumes (only their back faces are rendered).

Frank Crow published a paper describing the theory of shadow volumes in 1977.

Shadow volume is a technique used in 3D computer graphics to add shadows to a rendered scene.

This approach has problems when the eye itself is inside a shadow volume (for example, when the light source moves behind an object).

Interactive shadow volume rendering was popularized by the video game Doom 3.

The basic steps for forming a shadow volume are:

Shadow mapping and shadow volumes are two common modern techniques for creating shadows.

Unlike shadow volumes, however, the accuracy of a shadow map is limited by its resolution.

Neither of these techniques clip the shadow volumes, causing the shadows to extend down walls and through geometry.

Crow also proposed the shadow volume technique for generating geometrically accurate shadows.

This refers to an implementation of stencil buffered shadow volume algorithms.

The edges forming the silhouette are extruded away from the light to construct the faces of the shadow volume.

The Tome of Shadows Volume I can be read here.

A discussion of this capability and its use with shadow volumes was presented at the Game Developers Conference in 2005.

Shadow volume (a stencil buffer technique creating shadows)

Alternatively one can give the stencil buffer a +1 bias for every shadow volume the camera is inside, though doing the detection can be slow.

Render the shadow volumes.

Shadow volumes have become a popular tool for real-time shadowing, alongside the more venerable shadow mapping.

Per-pixel lighting is commonly used with techniques like normal mapping, bump mapping, specularity, and shadow volumes.

On more recent GPU pipelines, geometry shaders can be used to generate the shadow volumes.

Shadow volumes tend to cover large portions of the visible scene, and as a result consume valuable rasterization time (fill time) on 3D graphics hardware.

This can be remedied by adding a "cap" surface to the front of the shadow volume facing the eye, such as at the front clipping plane.

Rasterization time of the shadow volumes can be reduced by using an in-hardware scissor test to limit the shadows to a specific onscreen rectangle.

This enables a game developers to achieve realistic lighting without having to complicate the scene geometry or resort to expensive real-time shadow volume computations.

A shadow volume divides the virtual world in two: areas that are in shadow and areas that are not.