2. Output Primitives
Output Primitives are some basic geometric structures which are used as terms to describe a scene.
These output primitives can be grouped into sets to form a complex geometric structure.
Each output primitive is specified with input coordinate data and other information about the way that object is to be displayed.
Points and straight line segments are the simplest geometric components of pictures.
Additional output primitives that can be used to construct a picture include circles and other conic sections, quadric surfaces, spline curves and surfaces, polygon color areas, and character strings.