AutoCAD ActiveX Automation Extensions in Visual LISP

Abstract

In this second instalment of the “graphic codes” column, we set out the basics of the ActiveX extensions and apply them in AutoCAD together with Visual LISP, the evolution of AutoLISP; the AutoCAD ActiveX Automation extensions form a communication protocol that makes it possible to manipulate AutoCAD programmatically, both from within and from outside AutoCAD. This is achieved by exposing AutoCAD objects to the “outside world”, making them accessible from many programming languages and environments and other applications.
ActiveX controls apply to various components arranged in a hierarchy, all of which can be identified as either objects or collections (sets of objects). Both are containers which, in what is termed the object model, make available: properties, which allow you to set or retrieve information about an object’s state; methods, which allow an action to be performed on an object; events, which are actions initiated by the user or occurrences to which a program responds. The topic provides an opportunity to produce a code listing containing forty-two auxiliary functions and two main functions which, given two circles, determine, and optionally draw, their radical axis and the Apollonius circle² uniquely associated with them.