The Invention of Battlezone - IEEE Spectrum
Three-dimensional displays first appeared on computer screens in the 1960s, and very large machines could manipulate those images in real time. However, it wasn't until 1980 that a video game player could maneuver at will through an imaginary landscape, wreaking havoc until brought to an untimely end by enemy tanks. Battlezone, a first-person tank game, was made possible by a vector display unit used by Atari Inc. in Sunnyvale, California. This technology was first employed in Asteroids, which came out the previous year.
According to Videa's Ed Rotberg, who wrote computer code for the game, Battlezone required three microprocessors: a 6502 to control the gameplay, a custom processor for the display, and another processor built from 2901 bit-slice processors to handle the mathematics. The display generator and the game microprocessor operated either in parallel or in sequence with the others.
The Technology Behind Battlezone
"It was pretty fast," said Mr. Rotberg. "Quite often it wasn't worth going off and doing something else—you just waited for the math box to finish." The math box in Battlezone solved the matrix equations for vanishing-point perspective for all objects on the screen, allowing movement on a horizontal plane by reducing the matrix from 4 by 4 to 2 by 2.
While Battlezone is a vector game where objects consist of points connected by lines, controlling the number of objects on the screen stretched the abilities of the three microprocessors. To address this issue, Mr. Rotberg had to work closely with his graphic designer, Roger Hector, to optimize the game for performance.
Overcoming Technical Challenges
Although Battlezone does not directly deal with the hidden-line problem, it uses diminished brightness to indicate distance and must cope with the challenges of clipping objects on the screen. The hardware allows drawing about half a screen off each side, which helps considerably in managing object visibility.
"We did an end run around the problem," explained Mr. Rotberg. "The hardware lets you draw about half a screen off each side, which helps considerably. You calculate where the center points are and determine whether or not you're going to display an object, and if you are, you draw all its lines regardless of whether or not they'll be on the screen."
Development and Realism
Battlezone took 15 months to develop, with some additional features like an erupting volcano added for entertainment value. Mr. Rotberg mentioned that if given the opportunity to develop the game with today's technology, he would incorporate a color vector display and leverage newer microprocessors and memory for enhanced realism and complexity.
Mr. Rotberg also worked on a version called Army Battlezone, featuring a rolling landscape and U.S. and Soviet tanks, under duress as requested by a company contracted by the Army for training purposes. Despite his initial reluctance, the project was completed to meet the Army's specifications, demonstrating the adaptability and versatility of the original Battlezone concept.
This article was originally published in the December 1982 issue of IEEE Spectrum as part of a special report on "Video games: The electronic big bang." A PDF version is available on IEEE Xplore.
