Appearances provide rendering information about a 3D surface. Appearances may detail the color of the surface, the reaction of the surface to lighting, or provide an image as a texture, which is applied in conjunction with the texture coordinates.
Appearances may be shared between surfaces, including across features. Appearance information is not stored directly on geometries, but in a central location called the FMELibrary. Geometries only store a unique identifier to appearances, called appearance references. References to appearances shared in the FMELibrary are integers greater than 0. Each surface has, at most, one appearance reference per side.
An appearance reference of -1 on either the front or back side of a surface indicates that this side of the surface does not exist. Systems that render these geometries are expected to "cull" sides that do not exist. For more information, see Sidedness.
Each appearance can optionally contain a reference to a single texture.
Hierarchical Appearance Inheritance
An appearance reference of 0 is a special case and does not refer to any specific appearance information. If this geometry is part of a hierarchical geometry, a value of 0 means it inherits the appearance information from its parent or container geometry.
For example, a collection of surfaces, such as a multi surface, composite surface, or mesh, may store a specific appearance at the parent level for each side. Here, this value is inherited by all children with an appearance reference of 0. In the case of several levels of nested collections, the child surface inherits the appearance of the nearest parent that contains a non-zero appearance reference.
Appearance references may also exist on some solid geometries, and are meant to provide inheritable properties for any surfaces they may contain. In this way, solids may be considered similar to collections of surfaces.
If there is no appearance information to inherit, then an appearance reference value of 0 implies that all rendering decisions are "default" according to whatever application renders this geometry.
A name that helps you remember what the appearance is for, such as "castle wall" or "house roof". It does not have to be unique.
The typical, colloquial meaning of the color of an object. This is the essential color that is revealed under pure white light. It is perceived as the color of the object rather than a reflection of the light.
The color that the object reflects when illuminated by color from the surrounding medium rather than direct light.
The color of the light reflected from the object through specular reflection (the type of reflection that is characteristic of light reflected from a shiny surface).
Color of the light that the object is emitting itself.
A value from 0.0 to 1.0 that specifies the shine of specular reflection, with 0.0 being completely dull and 1.0 extremely shiny.
The transparency level of the appearance, with 0.0 being completely transparent and 1.0 completely opaque.
An integer value representing a texture stored in the FMELibrary.