Shadow volume

Shadows in computer graphics are used for anchoring of objects in a scene. So you can statements about the position of the objects in the scene to make (depth, distance to the surface). Furthermore, the direction of illumination is enhanced by a shadow.

It divides the shadows in the umbra ( umbra) and penumbra ( penumbra ). The umbra is the central, clearly demarcated dark part in the center, the penumbra surrounding the core, the lighter the shade area. The latter is very difficult to calculate, which is why the real-time rendering almost exclusively using point light sources that generate only the umbra.

Another possibility is to calculate the projection of a shadow-casting object, from the light source on a plane. To render soft shadows, a planar light source can be replaced by a plurality of point light sources; the resulting shadow is the sum of the shadow of the light sources. It is likewise possible to erase a hard shadow or draw gradients is. To render hard shadows so-called shadow volumes can be used. Another possibility is shadow maps. The scene is drawn into a Z-buffer from the point of view of the light source ( shadow buffer ) so that it contains the distance to the next illuminated objects. By comparing the depth information in the normal z-buffer with the depth information in the shadow buffer can be determined whether a point is in shadow.

To the shadows realistic, so be calculated using physical models, much time is needed. Examples of algorithms for generating photorealistic shadows are diffuse ray tracing or radiosity.