A model for graphical interaction

Much attention has been paid recently to graphics packages which provide standard mechanisms for graphical output in a device-independent way. These packages usually attempt to model a repertoire of input tools in a similarly abstract way. While implementing the Graphical Kernel System (GKS) it was observed that the model for handling interactive input was unnecessarily complicated; an alternative scheme was, therefore, designed and implemented offering considerable generality and device independence. This approach is based on the use of a command interpreter driven by a character stream multiplexing the data from the various input tools attached to a terminal. This implementation has proved portable between several different terminals using disparate input devices. A further result was the development of a terminal emulation program for a simple microcomputer, which works with the software described to provide many of the facilities normally associated with high-performance workstations