2012

Table Of Contents
surface towards the viewer. Shaders of this class may be thought of as
defining a surfaces finish, and are used to model properties such as
matte, metal, and plastic.
A transparency shader is used to define how transparent or opaque a
surface is, and thus how much light is able to pass through it. Transparency
shaders range from a simple uniform transparency to more complex regular
or irregular eroded patterns that would be more difficult to represent using
modelling techniques. A material without a transparency shader is
completely opaque.
Small surface perturbations can be supported by means of displacement
shaders. Typically, a displacement shader will give an otherwise smooth
surface an irregular or indented appearance. Displacement shaders are used
to represent features that would be difficult, impossible, or inefficient if
conventional modelling techniques were used. For example, rough metal
castings and the regular indentations produced by pressed sheet metal can
be simulated.
Normally, the Material Editor displays a selection of the most important
parameters from all shaders within the Materials tab. If the user profile is
set to Developer on the Interface node in the Options Editor (see
Presenter Page), then all four shaders can be edited and changed individually.
Some shaders are described as wrapped. These define a flat, two dimensional
material, like wallpaper. Wrapped materials need a texture space shader to
define how they should be applied to (wrapped around) a three dimensional
object. Materials that include a wrapped shader can also include a texture
space shader. A special type of texture space shader, called a layout shader,
can be used to transform (rotate, stretch, offset) the two dimensional material
before it is applied to the three dimensional object. Transforms are based
around an origin point, which by default, is the top left corner of the image
(refer to the diagram below, where the image is inscribed in the red square,
which is then repeated. The default origin is Point 1). Selecting the Offset
Center check box will reposition the origin to the center of the image (Point
2). Finally, in Developer profile, you can edit the Decal Mode, choosing
from either Default or Normalized. Selecting Normalized will move the
origin to the lower-left corner of the image (Point 3, with the Offset Center
option cleared). With both Normalized and Offset Center selected, the
origin will be repositioned in the center of the repeated image, directly below
(Point 4).
562 | Chapter 13 Create Photorealistic Visualizations