Academic journal article Visible Language

The Xerox Alto Font Design System

Academic journal article Visible Language

The Xerox Alto Font Design System

Article excerpt

Introduction

The Xerox Alto font design system was designed and built around 1974, at Xerox PARC's Computer Science Laboratory, initially as an experimental tool for helping in the production of digital typefonts for a growing number of prototype xerographic laser printers and display devices with very diverse resolution characteristics. At that time, it would have been presumptuous to imagine that the same system, only slightly adapted, would be in regular use, some ten years later, as a font digitization system for the Xerox printer product line.

Despite its daily usefulness, the system today [1985] shows sure signs of obsolescence in its performance and many of its implementation details, in both software and hardware. By current standards, however, it still performs quite well, and this endurance is a tribute to the quality of the overall design by Robert Sproull and to the remarkably advanced concepts incorporated in the Alto computer.

I will not attempt in this paper to present a comprehensive and detailed description of the operation of the system, which is fully described in a user 's manual [1]. I prefer to give simply an overview of the system, trying to bring a critical eye on the design and the implementation of the software, a point of view now facilitated by time and distance. Before going further, it is important to stress that the system discussed here is an internal system, not a Xerox product, and that all the opinions expressed here are strictly those of the author and only engage himself.

General principles and overall organization

In the Alto system, as in several other systems [2], font production is basically a two-step process, resting on the geometrical representation of a character in outline form.

The process is illustrated in Figure 1. It is implemented by two main computer programs. FRED is an interactive graphics program used for defining the geometric outline of characters as mathematical spline curves. PREPRESS is used for creating automatically the appropriate digitized character in the form of a matrix of dots, for a given point size and a given printer (a process called scan-conversion). It is also used for touching up by hand the resulting dot matrix, also called a bitmap. (The DRAW program showed in Figure 1 is marginal to the process.)

The whole software was programmed for the Alto experimental workstation, a strikingly original personal computer, designed and built at Xerox PARC [3]. Its general size, performance and configuration (including a high resolution graphics display) made it well suited for interactive graphical interactions and friendly user interfaces relying on visual feedback. It has been the forerunner in a well-followed design trend of high-powered computers which has led to such recent products as the Apollo and Sun computers, the Xerox Star, Apple Lisa office workstations, and the Apple Macintosh personal computer.

With the exception of a television camera for scanning type artwork and its associated computer interface. the equipment configuration (portrayed in Figure2) is the standard desk size Alto station in its more recent extended memory version (Alto II), featuring:

standard keyboard;

the now popular table top pointing device called the mouse ;

one or two disk drives with removable cartridges:

a connection to the Ethernet local network. allowing direct communication with printers and file storage servers:

a black and white graphics display. with a resolution of 600 by 800 dot.

Overview of FRED

FRED is primarily an interactive graphics editor for creating and modifying 'images ' composed of straight lines and spline curves. In fact, its graphics editing functions are quite general and are not specialized for handling letterform outlines. They include commands for defining, deleting, moving, copying, transforming by symmetry, and redefining lines, curves and pieces of curves. These operations are activated by selection from the main menu and are executed interactively by pointing with the mouse in the drawing area (Figure 3). …

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