A graphics subroutine package for the Neuroscience Display Processor

Abstract

The Neuroscience Display Processor (NDP) has been developed at the University of North Carolina for displaying two- and three-dimensional structures, and two-dimensional graphs. To make easy the displaying of graphs and other drawings on a refresh CRT or on a digital plotter, a subroutine package has been produced for the scientist programming in FORTRAN. Various levels of access (implemented as levels in a hierarchy of subroutines) provide increasing flexibility at the cost of increasing programming complexity. At the highest level, and with the least effort (i.e., with a single subroutine call), a programmer may display a graph accompanied by coordinate axes with scales, a title, and axis labels. The programmer may optionally display two such graphs on the CRT simulataneously. He may also display several graphs on the same set of coordinate axes. Graphs may be displayed without coordinate axes, etc., to facilitate the drawing of many superimposed graphs on hard copy.An NDP daslgn assumption that the general-purpose computer refreshes the CRT has far-reaching effects on the software design. That assumption, space and time constraints, the use of FORTRAN, and the provision of various options appropriate for the area of application all result in the programmer's being provided with a single subroutine to be called inside a refresh loop, with many switches as parameters.Where the needs of the application are not net by the capabilities aentloned above, the programmer may replace the single subroutine call by the use of several subroutines at lower levels as building blocks, with which to construct his own graphs or other drawings, thereby sacrificing some ease of programming for increased flexibility. The programmer nay call a subroutine to display a real number or an integer at a specified spot on the screen. He may display a character string. At a still lower level, the programmer say call for the display of a single character. At the lowest level of FORTRAN call, the programmer may specify that either polygons or series of disconnected lines or dots be drawn, nay indicate whether they are to be drawn on the CRT or on the plotter, and may load the rotation-and-translation matrix of the NDP.