Objects in are composed of relatively simple primitive objects. These primitives may be used by themselves, or they may be combined to form more complex objects known as aggregates. A special family of aggregate objects, Constructive Solid Geometry or CSG objects, are the result of a boolean operations applied to primitive, aggregate, or CSG objects.
This chapter describes objects from a strictly geometric point of view. Later chapters on surfaces, textures, and shading describe how object appearances are defined.
An instance is an object that has optionally been transformed and textured. They are the entities that are actually rendered by ; when you specify that, for example, a textured sphere is to be rendered, you are said to be instantiating the textured sphere. An instance is specified as a primitive, aggregate, or CSG object that is followed by optional transformation and texturing information. Transformations and textures are described in Chapters 7 and 8 respectively.