Design of a Graphic Processor for Computer-Aided Drafting

A drafting system is under development by the CAD-Graphics Laboratory at Carnegie-Mellon University. The purpose of this system is to provide an advanced tool for teaching engineering drawing and as a production tool for designers who regularly produce engineering drawings. The graphic processor is part of the system, which incorporates a set of operations that produce and manipulate graphic entities and that require graphic entities as operands. This paper examines the issues of constructing such a processor. Representations are proposed of 2D graphic objects, including points, line segments and segments generated by conic sections; they are the predefined data types of the system. The geometric primitive operators take these objects as arguments and produce other graphic objects, and allow users to build up various construction operators and drawings with the same flexibility and generality allowed in, say, descriptive geometry. These operators, which are functions, can be combined as macro expressions that are executed by the processor.