3D graphics eBook - Course Materials Repository

Self-shadowing 177
Self-shadowing
Self-Shadowing is a computer graphics lighting effect, used in 3D
rendering applications such as computer animation and video games.
Self-shadowing allows non-static objects in the environment, such as
game characters and interactive objects (buckets, chairs, etc), to cast
shadows 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 not cast a shadow
over the ball.
Shadow mapping
Shadow mapping or projective shadowing 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 been used both
in pre-rendered scenes and realtime scenes in many console and PC
games.
Shadows are created by testing whether a pixel is visible from the light
source, by comparing it to a z-buffer or depth image of the light
source's view, stored in the form of a texture.
Principle of a shadow and a shadow map
If you looked out from a source of light, all of the objects you can see
would appear in light. Anything behind those objects, however, would
be in shadow. This is the basic principle used to create a shadow map.
The light's view is rendered, storing the depth of every surface it sees
(the shadow map). Next, the regular scene is rendered comparing the
depth of every point drawn (as if it were being seen by the light, rather
than the eye) to this depth map.
This technique is less accurate than shadow volumes, but the shadow
map can be a faster alternative depending on how much fill time is
required for either technique in a particular application and therefore
may be more suitable to real time applications. In addition, shadow
Doom 3's unified lighting and shadowing allows
for self-shadowing via shadow volumes
Scene with shadow mapping
Scene with no shadows
maps do not require the use of an additional stencil buffer, and can be modified to produce shadows with a soft edge.
Unlike shadow volumes, however, the accuracy of a shadow map is limited by its resolution.