CANVAS: C++ objects for easy graphics on an Evans and Sutherland PS390 terminal. User's guide

摘要

The C++ classes described in this note comprise an attempt to provide an object-oriented approach, and if there was ever a graphics terminal naturally suited to object-oriented programming, the PS390 is it. Since a canvas is not a program but a variable to be used in programs, users can write software to suit their particular needs. By simply declaring canvas variables the application program is provided with an object which accepts data and displays it automatically. Any number of canvases can be placed anywhere on the screen, so data can be viewed in a variety of ways simultaneously. Further, the ''real-time'' transformation capabilities of the PS390 are activated in one step by ''connecting'' its external devices, the dials and the puck, to the desired canvas. There is no need for the applications programmer to construct his own function networks, choose names for nodes, and do any of the other administrative tasks laid out in the manuals, including connecting the terminal to a host computer and initializing it. These are handled automatically by the canvases themselves, thus removing this clutter from the application program.