The Adventure Game Interpreter (AGI) is a

game engine A game engine is a software framework primarily designed for the development of video games and generally includes relevant libraries and support programs. The "engine" terminology is similar to the term "software engine" used in the software i ...

developed by

Sierra On-Line Sierra Entertainment, Inc. (formerly On-Line Systems and Sierra On-Line, Inc.) was an American video game developer and publisher founded in 1979 by Ken and Roberta Williams. The company is known for pioneering the graphic adventure game genre, ...

. The company originally developed the engine for ''

King's Quest ''King's Quest'' is a graphic adventure game series, released between 1980 and 2016 and created by the American software company Sierra Entertainment. It is widely considered a classic series from the golden era of adventure games. Following th ...

'' (1984), an

adventure game An adventure game is a video game genre in which the player assumes the role of a protagonist in an interactive story driven by exploration and/or Puzzle video game, puzzle-solving. The Video game genres, genre's focus on story allows it to draw ...

which Sierra and IBM wished to market in order to attract consumers to IBM's lower-cost home computer, the

IBM PCjr The IBM PCjr (pronounced "PC junior") was a home computer produced and marketed by IBM from March 1984 to May 1985, intended as a lower-cost variant of the IBM PC with hardware capabilities better suited for video games, in order to compete mor ...

. AGI was capable of running animated, color adventure games with music and sound effects. The player controls the game with a

keyboard Keyboard may refer to: Text input * Keyboard, part of a typewriter * Computer keyboard ** Keyboard layout, the software control of computer keyboards and their mapping ** Keyboard technology, computer keyboard hardware and firmware Music * Musi ...

and, optionally, a

joystick A joystick, sometimes called a flight stick, is an input device consisting of a stick that pivots on a base and reports its angle or direction to the device it is controlling. A joystick, also known as the control column, is the principal cont ...

. After the launch of ''King's Quest'', Sierra continued to develop and improve the Adventure Game Interpreter. They employed it in 14 of their games between 1984 and 1989, before replacing it with a more sophisticated engine,

Sierra's Creative Interpreter Sierra Entertainment, Inc. (formerly On-Line Systems and Sierra On-Line, Inc.) was an American video game developer and publisher founded in 1979 by Ken and Roberta Williams. The company is known for pioneering the graphic adventure game genre ...

History

In late 1982, IBM began work on the PCjr, a lower-priced variant of the

IBM Personal Computer The IBM Personal Computer (model 5150, commonly known as the IBM PC) is the first microcomputer released in the IBM PC model line and the basis for the IBM PC compatible de facto standard. Released on August 12, 1981, it was created by a team ...

with improved

graphics Graphics () are visual images or designs on some surface, such as a wall, canvas, screen, paper, or stone, to inform, illustrate, or entertain. In contemporary usage, it includes a pictorial representation of data, as in design and manufacture ...

and sound. The PCjr's

Video Gate Array Tandy Graphics Adapter (TGA, also Tandy graphics) is a computer display standard for the Tandy 1000 series of IBM PC compatibles, which has compatibility with the video subsystem of the IBM PCjr but became a standard in its own right. PCjr grap ...

video adapter A graphics card (also called a video card, display card, graphics adapter, VGA card/VGA, video adapter, display adapter, or mistakenly GPU) is an expansion card which generates a feed of output images to a display device, such as a computer moni ...

could display up to 16 colors at a time—a major improvement over the

Color Graphics Adapter The Color Graphics Adapter (CGA), originally also called the ''Color/Graphics Adapter'' or ''IBM Color/Graphics Monitor Adapter'', introduced in 1981, was IBM's first color graphics card for the IBM PC and established a de facto computer display ...

's four-color limit. The new sound chip, too, could output a wider range of tones than the

PC speaker A PC speaker is a loudspeaker built into some IBM PC compatible computers. The first IBM Personal Computer, model 5150, employed a standard 2.25 inch magnetic driven (dynamic) speaker. More recent computers use a tiny moving-iron or pie ...

. IBM commissioned Sierra to produce a game that could showcase these new capabilities. They discussed some requirements for the game, and IBM supplied Sierra with a PCjr prototype. They both agreed that the game should be animated—a first for Sierra. A team of six

designers A designer is a person who plans the form or structure of something before it is made, by preparing drawings or plans. In practice, anyone who creates tangible or intangible objects, products, processes, laws, games, graphics, services, or exp ...

and developers, led by designer

Roberta Williams Roberta Lynn Williams (; born February 16, 1953) is an American video game designer and writer, who co-founded Sierra On-Line with her husband, game developer Ken Williams. In 1980, her first game, ''Mystery House'', became a modest commerci ...

, worked on the game that was eventually titled ''

''. Among the developers were Chuck Tingley and Ken MacNeill (later releases also credit Chris Iden. An Apple II version credits Arthur Abraham). IBM premiered the PCjr in 1984; it did not sell well and, therefore, neither did ''King's Quest''. However, later that year

Tandy Corporation Tandy Corporation was an American family-owned leather goods company based in Fort Worth, Texas, United States. Tandy Leather was founded in 1919 as a leather supply store. By the end of the 1950s, under the tutelage of then-CEO Charles Tandy, ...

released the

Tandy 1000 The Tandy 1000 is the first in a line of IBM PC workalike home computer systems produced by the Tandy Corporation for sale in its Radio Shack and Radio Shack Computer Center chains of stores. Overview In December 1983, an executive with Tandy C ...

, an

IBM PC compatible IBM PC compatible computers are similar to the original IBM PC, XT, and AT, all from computer giant IBM, that are able to use the same software and expansion cards. Such computers were referred to as PC clones, IBM clones or IBM PC clones. ...

that succeeded where the PCjr failed. ''King's Quest'' caused a sensation in the burgeoning market of PC-compatible computers, and Sierra sold more than half a million copies. They ported it to other

computing platform A computing platform or digital platform is an environment in which a piece of software is executed. It may be the hardware or the operating system (OS), even a web browser and associated application programming interfaces, or other underlying s ...

s, including the

Apple II The Apple II (stylized as ) is an 8-bit home computer and one of the world's first highly successful mass-produced microcomputer products. It was designed primarily by Steve Wozniak; Jerry Manock developed the design of Apple II's foam-m ...

, Apple IIGS,

Macintosh The Mac (known as Macintosh until 1999) is a family of personal computers designed and marketed by Apple Inc., Apple Inc. Macs are known for their ease of use and minimalist designs, and are popular among students, creative professionals, and ...

Amiga Amiga is a family of personal computers introduced by Commodore in 1985. The original model is one of a number of mid-1980s computers with 16- or 32-bit processors, 256 KB or more of RAM, mouse-based GUIs, and significantly improved graphi ...

, and

Atari ST The Atari ST is a line of personal computers from Atari Corporation and the successor to the Atari 8-bit family. The initial model, the Atari 520ST, had limited release in April–June 1985 and was widely available in July. It was the first pers ...

, but the PC remained the primary platform for their games. In 1988, with the release of '' King's Quest IV: The Perils of Rosella'', Sierra debuted a more sophisticated game engine:

, or SCI. Since the SCI engine required a more powerful home computer, Sierra released an AGI version of the game at the same time. However, Sierra overestimated consumer demand for the lesser version, and ceased production. The following year, Sierra published its final AGI-based title, '' Manhunter 2: San Francisco'', then focused exclusively on SCI for new adventure game development. Among SCI's enhancements were a more versatile scripting system, an

object-oriented programming Object-oriented programming (OOP) is a programming paradigm based on the concept of "objects", which can contain data and code. The data is in the form of fields (often known as attributes or ''properties''), and the code is in the form of pr ...

model, higher-resolution graphics (320×200 rather than 160×200), a

point-and-click Point and click are the actions of a computer user moving a pointer to a certain location on a screen (''pointing'') and then pressing a button on a mouse, usually the left button (''click''), or other pointing device. An example of point and cli ...

interface, and support for additional

sound card A sound card (also known as an audio card) is an internal expansion card that provides input and output of audio signals to and from a computer under the control of computer programs. The term ''sound card'' is also applied to external audio i ...

hardware.

Technical design

The technical complexity of ''King's Quest'' made it a burden to write in

assembly language In computer programming, assembly language (or assembler language, or symbolic machine code), often referred to simply as Assembly and commonly abbreviated as ASM or asm, is any low-level programming language with a very strong correspondence be ...

, so the programmers created a

to simplify development. The engine comprised a

bespoke The word ''bespoke'' () has evolved from a verb meaning 'to speak for something', to its contemporary usage as an adjective. Originally, the adjective ''bespoke'' described tailor-made suits and shoes. Later, it described anything commissioned t ...

programming language A programming language is a system of notation for writing computer programs. Most programming languages are text-based formal languages, but they may also be graphical. They are a kind of computer language. The description of a programming ...

called the Game Adaptation Language, a

compiler In computing, a compiler is a computer program that translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily used for programs that ...

, and a

bytecode Bytecode (also called portable code or p-code) is a form of instruction set designed for efficient execution by a software interpreter. Unlike human-readable source code, bytecodes are compact numeric codes, constants, and references (norma ...

interpreter (the Adventure Game Interpreter). The Game Adaptation Language was a

high-level programming language In computer science, a high-level programming language is a programming language with strong Abstraction (computer science), abstraction from the details of the computer. In contrast to low-level programming languages, it may use natural language ...

that resembled C. This was compiled into

, which was executed by the interpreter. Like Sierra's earlier adventure titles, such as ''

Wizard and the Princess ''Wizard and the Princess'' (also ''The Wizard and the Princess'', with a leading article) is a graphic adventure game written for the Apple II and published in 1980 by On-Line Systems. It was the second title released in the '' Hi-Res Adventure ...

'' (1980), AGI games used

vector graphics Vector graphics is a form of computer graphics in which visual images are created directly from geometric shapes defined on a Cartesian plane, such as points, lines, curves and polygons. The associated mechanisms may include vector display a ...

. The PCjr accepted

floppy disk A floppy disk or floppy diskette (casually referred to as a floppy, or a diskette) is an obsolescent type of disk storage composed of a thin and flexible disk of a magnetic storage medium in a square or nearly square plastic enclosure lined w ...

s with a capacity of 360 kilobytes, and

raster graphics upright=1, The Smiley, smiley face in the top left corner is a raster image. When enlarged, individual pixels appear as squares. Enlarging further, each pixel can be analyzed, with their colors constructed through combination of the values for ...

would have consumed an excessive amount of disk space. Instead, ''King's Quest'' drew

polygon In geometry, a polygon () is a plane figure that is described by a finite number of straight line segments connected to form a closed ''polygonal chain'' (or ''polygonal circuit''). The bounded plane region, the bounding circuit, or the two toge ...

s on the screen, and then colored them. Beginning with AGI version 2, the game engine drew graphics in an off-screen

data buffer In computer science, a data buffer (or just buffer) is a region of a memory used to temporarily store data while it is being moved from one place to another. Typically, the data is stored in a buffer as it is retrieved from an input device (such a ...

, then blitted them into video memory. This approach was not just to economize use of system resources; it also prevented the game from revealing hidden objects while it drew the screen. AGI was principally developed for

16-bit 16-bit microcomputers are microcomputers that use 16-bit microprocessors. A 16-bit register can store 216 different values. The range of integer values that can be stored in 16 bits depends on the integer representation used. With the two mos ...

computer architecture In computer engineering, computer architecture is a description of the structure of a computer system made from component parts. It can sometimes be a high-level description that ignores details of the implementation. At a more detailed level, t ...

s, which were the

state of the art The state of the art (sometimes cutting edge or leading edge) refers to the highest level of general development, as of a device, technique, or scientific field achieved at a particular time. However, in some contexts it can also refer to a level ...

in home computers at the time. These included the

, the

Commodore Commodore may refer to: Ranks * Commodore (rank), a naval rank ** Commodore (Royal Navy), in the United Kingdom ** Commodore (United States) ** Commodore (Canada) ** Commodore (Finland) ** Commodore (Germany) or ''Kommodore'' * Air commodore, a ...

's Amiga series, and

Apple An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple fruit tree, trees are agriculture, cultivated worldwide and are the most widely grown species in the genus ''Malus''. The tree originated in Central Asia, wh ...

's Macintosh computers. In addition, Sierra

ported In software engineering, porting is the process of adapting software for the purpose of achieving some form of execution in a computing environment that is different from the one that a given program (meant for such execution) was originally desi ...

AGI to three

8-bit In computer architecture, 8-bit Integer (computer science), integers or other Data (computing), data units are those that are 8 bits wide (1 octet (computing), octet). Also, 8-bit central processing unit (CPU) and arithmetic logic unit (ALU) arc ...

computer models: the

TRS-80 Color Computer The RadioShack TRS-80 Color Computer, later marketed as the Tandy Color Computer and sometimes nicknamed the CoCo, is a line of home computers developed and sold by Tandy Corporation. Despite sharing a name with the earlier TRS-80, the Color Co ...

, the

Apple IIe The Apple IIe (styled as Apple //e) is the third model in the Apple II series of personal computers produced by Apple Computer. The ''e'' in the name stands for ''enhanced'', referring to the fact that several popular features were now built-in ...

, and the

Apple IIc The Apple IIc, the fourth model in the Apple II series of personal computers, is Apple Computer's first endeavor to produce a portable computer. The result was a notebook-sized version of the Apple II that could be transported from place to pl ...

AGI-based games published by Sierra On-Line

Table Notes

Notes

External links

* {{Curlie, Games/Video_Games/Adventure/Graphical_Adventures/Design_and_Development/Authoring_Systems/Sierra/AGI/ Retrieved August 15, 2014