2011

3 Browse to and select your image file, and click Open.
4 You may then need to adjust some of the texture parameters of the new material, for example its scale,
rotation, offset or reflection (if it’s back to front). These may all be edited in the Texture tab. See “Edit
Presenter Materials
” on page 357 for more information.
Advanced Materials
Internally, a material is defined by four shaders from different classes: Color, Transparency, Reflectance and
Displacement. Each class of shader controls a different aspect of a material's behavior. There are many types of
shader in each class, each type being defined by its own set of parameters.
■ A Color shader is used to define the color of a surface at any point in space. It may be as simple as a plain
color which specifies all parts of the surface to have a uniform color, or it may define complex surface patterns
such as marble or wood. Every material must have a color shader.
■ The behavior of a surface in the presence light is represented by a reflectance shader which defines how
much light is reflected by the surface towards the viewer. Shaders of this class may be thought of as defining
a surface’s “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
” on page 472), 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
Advanced Materials | 359