Adventure Game Interpreter is a Game Engine used by Sierra. The engine was originally meant for King's Quest I: Quest For The Crown as a showcase of the PC Jr's capabilities. Resources come in six main categories: "Logic", "View", "Picture", "Sound", "Words", and "Objects".
All logic files in the engine use procedural programming, so both text and scripts related to a room are stored in one "Logic" file. A Debug Room in most games is accessible by pressing Alt+D or typing in a specific phrase. The games are controlled by a keyboard or a joystick, with a Text Parser to input commands into. Words are stored in a "Words" file that allows for synonyms that are in the same group. For instance, to tell someone to stop in Police Quest 1: In Pursuit of the Death Angel, the game accepts "dont move", "freeze", "halt", "hold it", and "stop". Of course, You Can't Get Ye Flask is almost an inevitability. The "object" file stores inventory items and the starting room location for each one.
The engine uses 160x100 16-color vector graphics. First polygons would be drawn on screen and then colored. Each room's design is stored in a "picture" file, with a "visual" bitmap for how it looks and a "priority" bitmap which determines where the ego (the object controlled by the player) can move. Sprites are called "views", consisting of loops (often used for characters turned in different directions) and cels (often used for different frames of a walk cycle), allowing for seamless animation for characters and potentially changing background details. "Sound" files consist of music and sounds, with four voices. At the time, only one voice would generally be used since the only available sound device was the PC Speaker, so the "music" would be differently pitched beeps.
The engine has been succeeded by Sierras Creative Interpreter, which uses object-based programming and officially lasted from 1988 to 1996 (debatably 1997 since Shivers Two: Harvest of Souls has SCI-type resources), receiving much more tremendous updates throughout the years.
Since development in the engine is now possible for anyone thanks to development tools like the AGI Studio, new games by fans are being released to this day. A wiki for potential developers can be found here
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Games:
Produced by Sierra On-Line
- King's Quest I: Quest For The Crown (1984)
- King's Quest II: Romancing the Throne (1985)
- The Black Cauldron (1986)
- King's Quest III: To Heir Is Human (1986)
- Space Quest I: The Sarien Encounter (1986)
- Leisure Suit Larry 1: In the Land of the Lounge Lizards (1987)
- Mixed-Up Mother Goose (1987)
- Police Quest 1: In Pursuit of the Death Angel (1987)
- Space Quest II: Vohaul's Revenge (1987)
- Gold Rush! (1988)
- King's Quest IV: The Perils of Rosella (1988)
- Manhunter: New York (1988)
- Manhunter 2: San Francisco (1989)
