Autodesk 507B1-90A211-1301 User Guide - Page 321

3 Browse to the location of and select your image file, then 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 306 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. ■ 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. ■ 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. ■ 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 material tab. If the user profile is set to Developer in the Options Editor (see "Presenter Page" on page 436), then all four shaders can be edited and changed individually. Some shaders are described as "wrapped". These define a flat, two dimensional material, like wall paper. 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 hand 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 | 309