| Description |
An experimental language for display programming, called DIAL, has been developed for the PDP-10 and the UNIVAC 1559 display. It is experimental in the sense that it was originally conceived as a means of testing out some ideas, and the best way to test them seemed to be to produce a language that others could use. The language is a subset of ALGOL (hence the name: Display Algol), with additional facilities for graphical input and output. It cannot deal with floating - point numbers and can only handle strings in a limited fashion. Also, it lacks any facilities for rotating pictures or for displaying three-dimensional objects. On the other hand, it does include features which may make it easier to develop display programs. The principal distinguishing feature of Dial is the ability to defined is play procedures. These are identical in almost every respect to ordinary procedures, but serve the additional purpose of defining the structure of the picture on the screen. In this respect they take the place of the traditional structured display file, which in Dial does not exist. The only display file created by Dial programs is a linear list of vectors which is sent to the display. The chief difference between display procedures and other Dial procedures lies in the way they are called. A typical display procedure call might be: CAPAC AT 100, 200 SIZE 20; Display procedures may be defined in terms of basic graphical primitive (lines, points, etc.) or by means of calls to other display procedures. Also included in Dial are statements for defining the interactive processes with in the program. Dial does not permit a very, high degree of graphical interaction: it is not possible to program operations like drawing rubber-band lines or dragging objects around the screen. It i s not clear whether this necessarily means that Dial programs are less efficient interactively; in any case, Dial is designed to function under a time-sharing environment where it is difficult to create continuously changing pictures. |
