3.1.1 What is a Cogsys Extension Routine (CXR) ?

A Cogsys extension is a file that Cogsys loads and executes at run time which provides additional capabilities. You can think of an extension as part of the main Cogsys program that only gets used when it needs to be. Its mechanism is similar to plug-ins for Netscape Navigator.

Technically, an extension is a kind of dynamically linked library. Dynamically linked libraries are present in most operating systems: on Windows these files usually named with the `.DLL' extension; on Unix, they are called `libname.so'. Cogsys runs in DOS, however, which does not provide a standard means of using dynamically linked libraries. Cogsys extensions therefore have their own implementation and extension (`*.CXR'). Also, CXRs provide certain capabilities that traditional DLL's can not Cogsys Extensions.

What can an extension do? In theory, anything the real Cogsys does. In practice, the only extensions that have been created which the main program knows how to call are used for dynamically creating pictures. An extension routine that creates such images is called a picture generator.