SuperPaint: An Early Frame Buffer Graphics System

the early 1970s, integrated-circuit memories of significant size (1 Kbit and greater) became available. These chips made it practical for the first time to build a digital memory system— specifically, what came to be known as a frame buffer—containing enough bits to hold a standard video image. Minimally, a video image contained 640 pixels horizontally, 480 pixels vertically, and 8 bits in depth, for a total of 307,200 bytes. 1 This development in turn opened the door to the now-familiar world of pixel graphics and the use of digital technology in a wide range of imaging applications. SuperPaint, one of the first pixel-based frame buffer systems, originated in the Computer Science Lab at the Xerox Palo Alto Research Center (PARC). 2 I initiated this project at PARC in 1972, designed most of the hardware for the system, fabricated it with help from a number of other lab members in early 1973, and coaxed it into displaying its first picture in early April 1973. I also wrote most of the software for the system over a period of several years. Alvy Ray Smith, Bob Flegal, and Patrick Baudelaire also wrote significant routines and made other contributions to the project. Of course, the advantages of raster scan displays over line-drawing calligraphic displays were well known at the time. But from a larger perspective, we realized that the development of SuperPaint signaled the beginning of the synergy of two of the most powerful and pervasive technologies ever invented: digital computing and video or television. At least two major problems had to be solved: • making a digital frame buffer that operated at video rates and was fully compatible with video displays, cameras, recorders and other television technology, and • finding ways for a human user to create and interact with full-color 2D images and, later, animations. The former required some clever engineering. For the latter, we borrowed heavily from well-developed painting, graphic arts, and animation techniques in traditional media. Hardware description The SuperPaint frame-buffer memory system consisted of 16 printed circuit cards filled with 2-Kbit shift register chips (Intel 2401)— altogether, 640 × 486 × 8 bits. We used shift register memories rather than the just-introduced 1-Kbit dynamic RAM parts (Intel 1103) because of their significantly higher bit density (more than a factor of 2), lower cost, and established reliability. The entire memory recirculated as one long 307,200-pixel shift register, which was shifted …