Software for Device-Independent Graphical Input

摘要

A three-level model and a graphics software structure based on the model that was developed with the goal of making graphical applications independent of the input devices are described. The software structure makes graphical applications independent of the input devices in a manner similar to the way the SIGGRAPH CORE proposal makes them independent of the output devices. A second goal was to provide a convenient means for application programmers to specify the user-input language for their applications. The software consists of an input handler and a table-driven parser. The input handler manages a CORE-like event queue, changing input events into terminal symbols and making their terminal symbols available to the parser in a uniform manner. It also removes most device dependencies. The parser is table driven from a Backus-Naur form (BNF) grammer that specifies the user-input language. The lower level grammar rules remove the remaining device dependencies from the input, and the higher level grammar rules specify legal sentences in the user-input language. Implementation of this software is on a table-top minicomputer. Experience with retrofitting existing applications indicates that one can find a grammar that removes essentially all the device dependencies from the application proper.