AGI FOR NEWBIES
Nat Budin and Dark Fiber
Table of Contents
- Introducing AGI
- Nuts and Bolts
- An Introduction to LOGIC
(Revised September 5, 1998)
A scene from Sierra's King's Quest 3
What is an adventure game?
OK, let’s start off with the basics. An adventure game is a type
of computer game. There has been much dispute over the specifics,
but a general rule of thumb is that if the game doesn’t have levels or
“health points,” and throughout the game the player controls the
protagonist, who walks around picking up objects and using them, it’s
an adventure game.
In its simplest form, an adventure game consists of a series of “rooms”
(although some may not be indoors) which the player can cause the main
character to travel through. The player can pick up objects, use
them, travel to a new room where they pick up new objects, use them,
But it’s more than that. An adventure game also consists of
puzzles. For example, say the game starts with the main character
trapped in a room with a bomb in it. The player has approximately
10 minutes before the bomb explodes, killing the player and demolishing
the room. The player may not necessarily know that when the game
starts. There could, for example, be a note on a table in the
center of the room.
What is the player to do? Well, there’s an intriguing window on
the side of the room. But it’s too high to reach. So the
player pushes a chair over to the window and stands on it. Prying
the window open with a chisel, the player glances out the window and
notices a key in a bird’s nest. Maybe this is the key to the
room’s exit! But unfortunately, there’s a ferocious bird in the
nest. So the player feeds the bird some bird seed. It
greedily gobbles it up, but that did no good at all. Supposing I
threw it onto the ground, the player thinks. So he does.
Distracted, the bird allows the player to acquire the key.
Yay! Now we’re out of the room. Now how can we deal with
the guards at the door?
That’s an example of one puzzle in an adventure game. A “short”
adventure game might have 5 to 10 puzzles in it. A longer,
commercial adventure game could easily have 30 to 40, or even more,
What is AGI?
In the early 1980’s, a new start-up company operating out of
California, Sierra On-Line, released Mystery House. The game
became popular, because of its (for then) good graphics, well-developed
plot, and tough puzzles. Sierra quickly released another
adventure game, called Wizard and the Princess. This also sold
AGI stands for, logically enough, “Adventure Game Interpreter.”
Sierra created AGI in order to create what they billed as “3-D Animated
Adventure Games.” The first one was “King’s Quest” by
Roberta Williams (later to be known as “King’s Quest I: Quest for the
Crown”). That sold well, so Williams released “King’s Quest II:
Romancing the Throne” soon afterward. More games followed,
including “Space Quest I,” “Space Quest II,” “Manhunter: New York,”
“Police Quest I,” and “Mixed-up Mother Goose,” to name just a few.
(In this case, “3-D” does not refer to 3-dimensional rendering or
environments. Instead, it refers to the fact that Sierra’s
adventure games allowed a more realistic type of interaction with the
game. Essentially, it was a marketing gimmick. The new
G-Engine (used in the upcoming “King’s Quest: Mask of Eternity”) will
support true 3-D environments.)
By the time Roberta Williams was writing “King’s Quest IV: The Perils
of Rosella,” Sierra decided that they needed a new, more powerful
adventure game system. This was eventually called “SCI,” (Sierra
Creative Interpreter), and featured full-resolution EGA graphics
(320x200, 16 colors), support for advanced sound cards such as the
AdLib and the Roland MT-32, and a new interface.
More systems followed, notably SCIV (SCI for VGA), SCIW (SCI for
Windows), and the new G-Engine. Meanwhile, in 1996, an
Internet-based group of Sierra fans got together on a special task: to
crack the AGI.
This was not quite as simple as it sounded. Sierra games have
their own special interpreted languages, as well as encryption, and in
some cases, compression. Combine that with proprietary file
formats and physically-based copy protection and you’ve got one big
task. At the time of this writing (mid-April 1998), the ability
to create one’s own AGI games from scratch or template is still fairly
new, and there are still no SOUND editors for AGI games. Still,
one can create a full-featured adventure game with AGI at this point in
time, as you will see in the chapters to come!
Why use AGI?
“Okay,” you may say, “so I can create a full-featured graphical
adventure game. Still, why would I want to use half-resolution
EGA graphics and no mouse?” There are several compelling reasons
to use AGI.
- Price – Free!
Yeah, you read right. Nada! Zero! As of this writing,
all AGI tools are freeware, and it seems likely to remain that way
- Ease of use – AGI Studio
1.31 (the only full-featured AGI editing suite as of this writing)
comes with an easy-to-use template game. This template includes
all of the basic adventure game features, such as menus, character
control, and a rudimentary, expandable vocabulary. In addition,
AGI LOGIC is a very easy language to learn and to program in.
- System requirements – The
AGI interpreter itself runs on an IBM PCjr. It will probably run
on that old IBM you’ve got locked up in the attic. To run AGI
Studio, you need Windows 95. But judging from the fact that
you’re viewing this document, it’s likely that you’ve already got Win95.
- Professional look – The
AGI interpreter has that wonderful Sierra interface built right into
it! You have to do no interface programming whatsoever to write
an adventure game in AGI. Anyone who’s ever played an AGI game
will instantly understand your game’s interface.
- Nostalgia – Maybe you’re
one of the many AGIers who love AGI strictly because of
nostalgia. Don’t you have fond memories of playing <your
favorite Sierra game here>? And haven’t you ever asked
yourself, “how did they do that?” Now you can find out.
AGI also compares favorably with other popular adventure-game
systems. Let’s compare AGI with a few of them.
- TADS – TADS does not
support graphics or sound, nor is it likely (judging from the fact that
TADS stands for “Text Adventure Design System”) that TADS will ever
support either. While many adventure gamers (IFers) do not mind
plain text, most IF players do not mind graphics either.
- HTML TADS – This new
version of TADS supports HTML markup, sound and graphics. While
it is a huge leap forward (technologically speaking) from the original
TADS, it still does not support animated graphics like AGI does.
In addition, it is currently only available to those with Windows
95. (The original TADS supports Mac, Windows, DOS, Unix, Linux,
and lots of other systems as well.)
- Inform 6 – While Inform
supports graphics and (to some extent) sound, these features are very,
very simple. AGI offers much wider support of them.
Z-Machine code (Inform’s output format) is very portable.
However, AGI interpreters are being written in languages such as Java,
so support for AGI games will soon become much more widespread than it
- QuestMaker – QuestMaker
mimics the look and feel of AGI games. However, its sound support
only supports one voice, while AGI’s supports 4 with volume
control. In addition, QuestMaker is shareware. AGI is free.
- SCRAMM – This very
promising young project looks like it will support far more high-tech
features than AGI ever will, such as digital sound, SVGA high-res
graphics, and point-and-click. However, this project has just
been started and it will probably take at least a year before any beta
executables are released.
Enough! If I haven’t convinced you already, I probably never will!
Hold on to your hats…
Stay tuned to this station for Chapter 2, “Nuts and Bolts,” coming soon
to a theater near you! The upcoming chapter will include
information about the AGI file formats and how the interpreter works.
Nelson, Graham: The Craft of the Adventure (available from his Inform
page at http://www.gnelson.demon.co.uk/inform.html) An excellent read
for new adventure gamers and adventure game developers.
Comprehensive and easy to understand.
Various Authors: AGI Specifications (available from
http://www.ozemail.com.au/~ptrkelly/agi/specs) A whole lot of
documentation (mostly technical) pertaining to the AGI. This
document is also recommended in following chapters.
Inform Home Page – http://www.gnelson.demon.co.uk/inform.html
TADS Home Page – http://www.direct.ca/tela/tads/
HTML TADS Home Page – http://www.direct.ca/tela/html-tads/
SCRAMM Home Page – http://come.to/scramm
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