Adventure Game Interpreter
| Industry | Video game development |
|---|---|
| Founded | 1980 |
| Founder | Ken and Roberta Williams |
| Headquarters | United States |
| Products | Adventure Game Interpreter (AGI), Sierra Creative Interpreter (SCI) |
The Adventure Game Interpreter (AGI) is a game engine created by Sierra On-Line specifically for the 1984 title King's Quest. This project was part of a collaboration between Sierra and IBM to highlight the capabilities of IBM's more affordable home computer, the IBM PCjr.
AGI facilitated the creation of animated, colorful adventure games featuring music and sound effects, with control options including keyboard input and an optional joystick.
Following the release of King's Quest, Sierra continued to utilize and enhance AGI across 14 additional games between 1984 and 1989, before transitioning to the more sophisticated Sierra Creative Interpreter.
History
In late 1982, IBM introduced the PCjr, a budget-friendly version of the IBM Personal Computer that boasted improved graphics and audio features. Its Video Gate Array adapter supported up to 16 colors, surpassing the earlier four-color limitation, while its new sound chip delivered richer audio compared to the original PC speaker.
IBM engaged Sierra to develop a game that would demonstrate these enhanced capabilities. After obtaining a PCjr prototype, Sierra decided to produce an animated game—a first for the company. Under the leadership of designer Roberta Williams, a team of six crafted what became King's Quest. Key developers included Chuck Tingley and Ken MacNeill; subsequent Apple II versions also credited Chris Iden and Arthur Abraham.
Although the PCjr was launched in 1984, its commercial performance was disappointing, restricting early sales of King's Quest. The introduction of the Tandy 1000, an IBM PC-compatible system, later boosted demand. King's Quest achieved significant success in the PC-compatible market, selling over 500,000 copies. Sierra expanded its availability by porting it to platforms such as Apple II, Apple IIGS, Macintosh, Amiga, and Atari ST; however, IBM PC compatibles remained their main focus.
In 1988, Sierra released the advanced Sierra Creative Interpreter (SCI) engine alongside King's Quest IV: The Perils of Rosella. Because SCI required more powerful hardware, Sierra also issued an AGI version concurrently but overestimated market interest and soon discontinued it.
The last game developed using AGI was Manhunter 2: San Francisco (1989). Afterward, Sierra dedicated itself exclusively to SCI for adventure titles. SCI introduced improved scripting capabilities, an object-oriented design, higher-resolution graphics (320×200 compared to AGI’s 160×200), a point-and-click interface, and broader sound card compatibility.
Technical design
The complexity involved in creating King's Quest made assembly language programming impractical, leading to the development of a dedicated game engine to simplify production. This system comprised a custom programming language known as Game Adaptation Language, alongside a compiler and a bytecode interpreter called the Adventure Game Interpreter. The Game Adaptation Language was a high-level language similar to C, which compiled into bytecode executed by the interpreter.
Building on Sierra’s earlier works like Wizard and the Princess (1980), AGI titles employed vector graphics instead of raster graphics to save disk space on the PCjr’s 360 KB floppy disks. In King's Quest, polygons were rendered first before being filled with color. From AGI version 2 onward, graphical elements were drawn into an off-screen buffer before being transferred (blitted) into video memory. This method optimized resource usage and eliminated rendering glitches on screen.
AGI was mainly designed for 16-bit computer architecture systems common in home computers such as IBM PC compatibles, Atari ST, Commodore’s Amiga, and Apple Macintosh. Additionally, Sierra adapted AGI for three 8-bit machines: the TRS-80 Color Computer, Apple IIe, and Apple IIc.
AGI-driven titles released by Sierra On-Line
See also
External links
Retrieved August 15, 2014