Chris Crawford on Game Design

AI

Although Eastern Front (1941) is remembered primarily for its scrolling map, I can take no credit for that; it was built into the hardware. The design element of which I am most proud is the AI for the game. At a time when many wargames were still being written in BASIC, my design boasted two major innovations.

The first of these was the threaded execution. All of the I/O was executed during the Vertical Blank Interrupt (VBI), a routine that executed once each 60th of a second, synchronized with the vertical blank period of the television set. This was the only good time to mess with the display, as changes to the display while the beam was drawing it were likely to yield irritating rips or tears in the image. So I set up all I/O through the ...