Glk: An Interface Standard for Interactive Fiction

Introduction

Here's where I talk about what Glk is, why Glk is, and what it's good for. Unfortunately I haven't actually written this bit yet. Until I do, please refer to chapter zero of the specification document, which explains all the basic ideas.

I do, however, have a glowing testimonial.

Glk is a free standard. Here's what I mean by this.

Specification

This is the Glk API Specification, version 0.7.0.

HTML version of Glk specification (broken down into chapters.)
tar.gz file of the HTML version (all at once)
Plain text version of Glk specification
PostScript version of Glk specification

And, just as important,

The "glk.h" header file (for C)

Liberation

If you're going to run a Glk program, you need a Glk library which runs on your machine.

The official and up-to-date archive of Glk libraries is on the IF Archive, under if-archive/programming/glk/implementations. Here is a list of some of them, but it's not a complete list and it is not immune to falling out of date:

CheapGlk library 0.9.1 (C source code for an extremely minimal Glk library; uses only stdio.h, and allows only a single window. Nonetheless, this is a fully Glk-compliant implementation.) [Glk 0.7.0]
GlkTerm library 0.8.1 (C source code for a terminal-window Glk library, implemented using the curses.h screen control library. Should compile on any Unix system or reasonable facsimile, as long as it has the curses.h library. (No relation to the Meldrews.)) [Glk 0.7.0]
GlkTerm library 0.8.1 with wide char support (Same as above, modified to use ncursesw or ncurses to display and accept all Unicode characters which the terminal supports. By Alexander Beels.) [Glk 0.7.0]
MacGlk library 0.8.7 (CodeWarrior library package for a Macintosh Glk library. And source for same.) [Glk 0.6.1]
GlkDOS 0.19.1 (a Glk library for DOS. And source code. By L. Ross Raszewski; see his GlkDOS page for more info.) [Glk 0.6.1]
DosGlk version 1998101701 (an older Glk library for DOS; 16-bit and 32-bit libraries included. And source for same. By Matt Kimball (mkimball@mkimball.org)) [Glk 0.4]
WindowsGlk version 1.2.1 (a Glk library for Windows 95/98/NT/00. And source. By David Kinder.) [Glk 0.6.1]
XGlk library 0.4.11 (C source code for an X Windows Glk library. Should compile on any Unix system which has X installed.) [Glk 0.6.1]
GlkLoader 0.3.0 (C and Perl source for a Unix library that can dynamically load any other Glk library, without recompilation. By Joe Mason.) [Glk 0.6.1]
GlkOte (Javascript library code which implements something analogous to, although not identical to, the Glk API.)

Association

These are source files that come with the Glk API, although they're not actually part of it. If you're writing a Glk library, you'll want to look at them. See the spec for their full ineffable significance.

The Dispatch Layer: This allows virtual machine interpreters (and other run-time systems) to use the Glk API dynamically. To interoperate with the dispatch layer, a Glk library must include gi_dispa.c and gi_dispa.h.
The Blorb Layer: This allows the library to load images and sounds from a portable archive. To interoperate with the Blorb layer, a Glk library must include gi_blorb.c and gi_blorb.h.

Programmification

In addition to a couple of pedagogical sample source files, we have games, interpreters, and other such goodies.

"model.c" (C source code for a simple model IF program; reads a line of text and reacts to it, maintains a status window, etc.)
"multiwin.c" (C source code for another Glk model; this one demonstrates multiple windows, timed input, and Latin-1 characters.)
Model programs package (both model.c and multiwin.c, with a Unix makefile and the startup stubs for both Mac and Unix.)
Dungeon 3.2B for Glk (C source translated from the most recent Fortran source.)
Dungeon 3.2B with GDT for Glk (same as above, but with the in-game debugger -- thanks Paul Goyette.)
Floo (a simple Glk-native scripting language. This gets a whole directory to itself, so look here for interpreters, documentation, etc.)
TADS has been ported to Glk by Stephen Granade. It fits very well -- though that shouldn't be too much of a surprise, since the lessons I learned making MaxTADS went into Glk's design. See the TADS directory on the IF Archive. (The Glk port is included in the main source distribution.)
Hugo has also been ported to Glk. The connection is rather more awkward, because Hugo has a more complex display model that doesn't map well to Glk. Many Hugo features are not supported. Nonetheless, see the Hugo directory on the IF Archive. And here is the Mac executable (v25), which I support.
Nitfol is a Glk-based Z-machine interpreter, written by Evin Robertson. See also the Nitfol directory on the IF Archive.
Zeal is another Glk-based Z-machine interpreter, written by Jeremy Condit.
Grpad is a demo / test for Glk graphics windows, written by L. Ross Raszewski.

Execution

And if you're not into compiling, you can download the Glk programs as ready-to-run executables, for a couple of platforms at least.

Glulx is a virtual machine designed for IF; the interpreter uses Glk.
Mac executables of model.c and multiwin.c (built with MacGlk.)
Mac executable of Dungeon 3.2B (built with MacGlk.)
DOS executable of Dungeon 3.2B (built with DosGlk '101701. Matt says it's 32-bit only.)
Floo (executables here too.)