Shaders and Texturing - An Introduction to Computer Graphics for Artists - page 183

Fig. 11.3 A cloth shader applied to a cloth object

Hair shaders control the creation of individual hairs and the appearance of each
hair. Some use particle systems to represent the individual hairs, others use curves.
Texture maps for a hair shader defi ne the color of individual hairs, their length, and
the degree of curl. There may be more options than this, but these three are the mini-
mum values needed to generate hair.

11.3.2 Cloth

The diffi culty of rendering cloth convincingly is that it is made of many small fi bers
that create an easily seen micro-texture that affects the way light interacts with the
cloth and how the cloth behaves when animated (Ishida et al. 2012 ). Procedural
cloth shaders (Fig. 11.3 ) defi ne the underlying yarn pattern of various types of cloth
and use this to determine how the cloth should refl ect light at close range (Irawan
and Marschner 2012 ). This type of shader might be manipulated by an artist to make
specifi c weaves, wear patterns, or color changes within the cloth. For each of these,
texture maps may be used.

11.3.3 Water

Water is characterized by large geometric forms that are fi lled by smaller ones. In
addition to these characteristics, the water may have even smaller forms such as
foam or spray. To represent these things realistically in geometry alone would be
impossible because of the number of elements engaged in a constant state of defor-
mation. There are particle-based solutions and shader-based solutions (Fig. 11.4 ).
For large-scale subjects, such as oceans or rivers, shaders are the preferred solution.
Depending on the implementation used, textures may or may not be necessary
(Denny and Rogers 2010 ).