Self-Shadowing is a

computer graphics Computer graphics deals with generating images with the aid of computers. Today, computer graphics is a core technology in digital photography, film, video games, cell phone and computer displays, and many specialized applications. A great de ...

lighting Lighting or illumination is the deliberate use of light to achieve practical or aesthetic effects. Lighting includes the use of both artificial light sources like lamps and light fixtures, as well as natural illumination by capturing daylig ...

effect, used in 3D rendering applications such as computer animation and

video game Video games, also known as computer games, are electronic games that involves interaction with a user interface or input device such as a joystick, controller, keyboard, or motion sensing device to generate visual feedback. This fee ...

s. Self-shadowing allows non-static objects in the environment, such as game characters and interactive objects (buckets, chairs, etc.), to cast

shadow A shadow is a dark area where light from a light source is blocked by an opaque object. It occupies all of the three-dimensional volume behind an object with light in front of it. The cross section of a shadow is a two-dimensional silhouette, ...

s on themselves and each other. For example, without self-shadowing, if a character puts his or her right arm over the left, the right arm will not cast a shadow over the left arm. If that same character places a hand over a ball, that hand will cast a shadow over the ball. One thing that needs to be specified is whether the shadow being cast is dynamic or static. A wall with a shadow on it is a static shadow. The wall is not moving and so its geometric shape is not going to move or change in the scene. A dynamic shadow is something that has its geometry changes within a scene. Self-Shadowing methods have trade-offs between quality and speed depending on the desired result. To keep speed up, some techniques rely on fast and low resolution solutions which could result in wrong looking shadows which may be out of place in a scene. Others require the CPU and GPU to calculate with algorithms the exact location and shape of a shadow with a high level of accuracy. This requires a lot of computational overhead, which older machines could not handle.

Techniques

Height Field Self-Shadowing

A technique was created where a shadow on a rough surface can be calculated quickly by finding the high points along from the light source's origin and ignoring any other geometric points underneath the peaks. Imagine a sunrise in the mountains where the light hits a peak behind you but you are still in the dark. The computer wouldn’t need to worry about you needing a shadow or light since you are below the peak behind you. “Height Field Self-Shadowing” renders self-shadows on dynamic height fields under dynamic light environments in real time.

3D Hair

Self-Shadowing can be used for interactive hair animation, which is normally very difficult for computers to render due to the major increase in individual geometric shapes that hair can take. Self shadowing is a major part of a 3d application that contributes to the impression of volume.

Shadow volume

Shadow volume Shadow volume is a technique used in 3D computer graphics to add shadows to a rendered scene. They were first proposed by Frank Crow in 1977 as the geometry describing the 3D shape of the region occluded from a light source. A shadow volume divi ...

is one way that self-shadowing can be used in a 3D image or scene. The method basically makes a 3D object occupy an enclosed volume in a scene where a shadow is being cast. This allows the renderer, or

shader In computer graphics, a shader is a computer program that calculates the appropriate levels of light, darkness, and color during the rendering of a 3D scene - a process known as ''shading''. Shaders have evolved to perform a variety of speci ...

, to perform an analysis on whether or not the point or

pixel In digital imaging, a pixel (abbreviated px), pel, or picture element is the smallest addressable element in a raster image, or the smallest point in an all points addressable display device. In most digital display devices, pixels are the ...

is inside a shadowed area. This eventually allows the program to determine how the object will be lit.

Shadow Maps

shadow mapping Shadow mapping or shadowing projection is a process by which shadows are added to 3D computer graphics. This concept was introduced by Lance Williams in 1978, in a paper entitled "Casting curved shadows on curved surfaces." Since then, it has b ...

is another method which creates approximate shadows from a set position to create very diffuse shadows that may not be entirely accurate.

Radiosity Normal Mapping

Chris Green of

Valve A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fitting ...

, a

maker, says that bump map data is derived from geometric descriptions of the objects surface significant lighting cues due to lighting occlusion by surface details are not calculated. A common fix is to use an additional texture channel to create an

ambient occlusion In 3D computer graphics, modeling, and animation, ambient occlusion is a shading and rendering technique used to calculate how exposed each point in a scene is to ambient lighting. For example, the interior of a tube is typically more occluded ...

field. This only provides a darkening effect that is not connected to the direction of the light source on acting on the surface.

History

was proposed by Frank Crow in 1977.Crow, Franklin C
"Shadow Algorithms for Computer Graphics"
''Computer Graphics (SIGGRAPH '77 Proceedings)'', vol. 11, no. 2, 242-248. The advantage of a shadow volume was that is could be used to shadow everything, including itself.

References

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