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\ \ \ \ \ OMNIGRAPH: SIMPLE TERMINAL- INDEPENDENT GRAPHICS SOFTWARE BY ROBERT F. SPROULL CSL 73-4 DECEMBER 10,1973 This paper describes a graphics subroutine package for driving a number of different display devices with any of three different programming languages. The Omnigraah system is designed for routine graphics appl ications, not for high-performance terminals. The success of the design is largely due to the modest aims of the routines and to the particularly simple framework chosen for the graphics facilities. The paper cites a number of design errors in the initial Omnigraph routines, and suggests improvements. The Omnigraph Reference Manual is reprinted as an appendix. XEROX PALO ALTO RESEARCH CENTER 3180 PORTER DRIVE/PALO ALTO/CALIFORNIA 94304 1 I. INTRODUCTION The rapid development of low cost graphics terminals has created a new customer for computer services who wants to view simple drawings or graphs resulting from computer calculations. He is not an accomplished graphics programmer and has probably never heard of Sketchpad; he attaches his terminal to whatever computer resources can be found, preferably timesharing services; his favorite programming language, if he is a programmer, is doubtless FORTRAN. In short, this new user is nei ther prepared to undertake construction of a graphics programming system nor willing to devote time to issues tangential to his application. Such a user often relies on "graphics subroutine packages" provided by terminal manufacturers. This software presents speCial disadvantages both to the user and to the computer facility which must support it. The user suffers because the software is often poorly designed and documented. None of the software aids in minimizing the number of annoying and time-consuming screen erasures on storage-tube terminals; it often fails to provide even rudimentary graphical operators such as coordinate transformation and windowing; and furthermore, it is frequently riddled with idiosyncratic features, such as curve-drawing capabilities, that are unique to the terminal. Thus, in many ways the deSign of the software needlessly obscures the basic simplicity of creating drawings. Even when subroutine packages are thoughtfully designed, they are still troublesome to the computer facility. The staff must support many different subroutine sets, one for each different terminal or different progranuning language desired by users. Users of different kinds of terminals cannot share programs; programs written for one terminal require alterations to use another. Similarly. the computer facility is hampered in providing graphics services, such as graph-plotting, on many different terminals because a separate program is required for each terminal. For the same reason