The Adventure Game Interpreter (AGI) is a

game engine A game engine is a software framework primarily designed for the development of video games which generally includes relevant libraries and support programs such as a level editor. The "engine" terminology is akin to the term " software engine" u ...

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 ge ...

. 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 ...

'' (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-solving. The genre's focus on story allows it to draw heavily from other narrative-based m ...

that Sierra and

IBM International Business Machines Corporation (using the trademark IBM), nicknamed Big Blue, is an American Multinational corporation, multinational technology company headquartered in Armonk, New York, and present in over 175 countries. It is ...

wished to market in order to attract consumers to IBM's lower-cost

home computer Home computers were a class of microcomputers that entered the market in 1977 and became common during the 1980s. They were marketed to consumers as affordable and accessible computers that, for the first time, were intended for the use of a s ...

, 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 * Mus ...

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. Also known as the control column, it is the principal control devic ...

. 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, the Sierra Creative Interpreter.

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 ...

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 the data, as in design and manufa ...

and sound. The PCjr's Video Gate Array video adapter 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 standard, de fac ...

'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 exper ...

and developers, led by designer Roberta Williams, 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 Retail, retailer based in Fort Worth, Texas that made leather goods, operated the RadioShack chain, and later built personal computers. Tandy Leather was founded in 1919 as a leather supply store ...

released the

Tandy 1000 The Tandy 1000 was the first in a series of IBM PC compatible home computers produced by the Tandy Corporation, sold through its Radio Shack and Radio Shack Computer Center stores. Introduced in 1984, the Tandy 1000 line was designed to offer af ...

, an

IBM PC compatible An IBM PC compatible is any personal computer that is hardware- and software-compatible with the IBM Personal Computer (IBM PC) and its subsequent models. Like the original IBM PC, an IBM PC–compatible computer uses an x86-based central p ...

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 computers, including the

Apple II Apple II ("apple Roman numerals, two", stylized as Apple ][) is a series of microcomputers manufactured by Apple Computer, Inc. from 1977 to 1993. The Apple II (original), original Apple II model, which gave the series its name, was designed ...

, Apple IIGS, Mac (computer), Mac, Amiga, and

Atari ST Atari ST is a line of personal computers from Atari Corporation and the successor to the company's Atari 8-bit computers, 8-bit computers. The initial model, the Atari 520ST, had limited release in April–June 1985, and was widely available i ...

, but IBM PC compatibles 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: the Sierra Creative Interpreter, 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''. Objects can contain data (called fields, attributes or properties) and have actions they can perform (called procedures or methods and impl ...

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

point-and-click Point and click are one of 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 or other pointing device (''click''). An example of point and click is in hypermedi ...

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 ...

hardware.

Technical design

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

assembly language In computing, assembly language (alternatively 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 bet ...

, so the programmers created a

to simplify development. The engine comprised a

bespoke ''Bespoke'' () describes anything commissioned to a particular specification, altered or tailored to the customs, tastes, or usage of an individual purchaser. In contemporary usage, ''bespoke'' has become a general marketing and branding concep ...

programming language A programming language is a system of notation for writing computer programs. Programming languages are described in terms of their Syntax (programming languages), syntax (form) and semantics (computer science), semantics (meaning), usually def ...

called the Game Adaptation Language, a

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

, 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 (normal ...

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

high-level programming language 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 ''elements'', be ea ...

that resembled C. This was compiled into

, which was executed by the

interpreter Interpreting is translation from a spoken or signed language into another language, usually in real time to facilitate live communication. It is distinguished from the translation of a written text, which can be more deliberative and make use o ...

. Like Sierra's earlier adventure titles, such as '' Wizard and the Princess'' (1980), AGI games used

vector graphics Vector graphics are 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 displ ...

. The PCjr accepted

floppy disk A floppy disk or floppy diskette (casually referred to as a floppy, a diskette, or a disk) is a 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 with a ...

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 made up of line segments connected to form a closed polygonal chain. The segments of a closed polygonal chain are called its '' edges'' or ''sides''. The points where two edges meet are the polygon ...

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 memory used to store data temporarily 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 as ...

, 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 ...

computer architectures, which were the

state of the art The state of the art (SOTA or SotA, sometimes cutting edge, leading edge, or bleeding 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 contex ...

s 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 (India), in India ** Commodore (United States) ** Commodore (Canada) ** Commodore (Finland) ** Commodore (Germany) or ' ...

's Amiga series, and

Apple An apple is a round, edible fruit produced by an apple tree (''Malus'' spp.). Fruit trees of the orchard or domestic apple (''Malus domestica''), the most widely grown in the genus, are agriculture, cultivated worldwide. The tree originated ...

'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 desig ...

AGI to three

8-bit In computer architecture, 8-bit integers or other data units are those that are 8 bits wide (1 octet). Also, 8-bit central processing unit (CPU) and arithmetic logic unit (ALU) architectures are those that are based on registers or data bu ...

computer models: the

TRS-80 Color Computer The RadioShack TRS-80 Color Computer, later marketed as the Tandy Color Computer, is a series of home computers developed and sold by Tandy Corporation. Despite sharing a name with the earlier TRS-80, the Color Computer is a completely different ...

, 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 Inc., Apple Computer. It was released in January 1983 as the successor to the Apple II Plus. The ''e'' in the name stands for ...

, and the

Apple IIc The Apple IIc is a personal computer introduced by Apple Inc. shortly after the launch of the Macintosh 128K, original Macintosh in 1984. It is essentially a compact and portable version of the Apple IIe. The IIc has a built-in floppy disk driv ...

History

Technical design

AGI-based games published by Sierra On-Line

Table Notes

See also

Notes

External links

Further reading