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grotz — a Z-code interactive fiction interpreter for GTK

Version 0.2c, April 2012

grotz grotz is a GTK port of Frotz — the classic Z-code game engine. grotz, like Frotz, is intended for playing 'interactive fiction' games compiled for the Inform Z-machine platform. Although the Z-machine is, in a sense, an archaic and defunct platform, many games and stories were developed for it, and more continue to be written. grotz makes a reasonable job of playing most of the original Infocom games — Zork, Arthur, Lurking Horror, etc — including (to some extent) graphics and sound. The world of interactive fiction has moved on since the Infocom days, but these old games still exercise a Z-code interpreter thoroughly — more so than modern developments which rely less on the Z-machine to provide the complete user interface.

grotz is intended to support Linux and Windows using exactly the same code and build files. It is written entirely in C, and uses a single-Makefile build system which is very simple, and could probably be adapted to compile for other platforms on which GTK runs. The primary platform is Linux — there are already good Z-code interpreters for Windows. It's always struck me as anomalous that there are few stable, feature-rich Z-code platforms designed for modern Linux desktops. Of course, there is Gargoyle — but Gargoyle's focus seems to be on typography rather than comprehensive, specific Z-machine support.

grotz is far from being a finished product, but at present it seems to be basically functional. Bug reports, etc., are welcome; bug fixes even more so ;)


  • Supports all the Z-code versions that Frotz supports, and adds support for zblorb archives
  • Some support for Z-code version 6 graphics (see below)
  • Uses variable-pitch fonts where possible, which most people find easier to read than console fonts
  • Unicode support, both for keyboard and screen
  • Mouse support, with games the implement it. You can move around by clicking the compass rose in Zork Zero, for example
  • Transparent and true-colour text support, as defined in version 1.1 of the ZMachine specification
  • Supports Amiga-style box graphics, for those games that require this feature (e.g., Beyond Zork)
  • Transcript/scrollback viewer
  • Rudimentary sound support


grotz with a text-only game

'Box art' support in Beyond Zork

There are some outstanding issues with colour rendering in some V6 games

Building and installing

One of the goals of grotz is to build on Linux and Windows (using MinGW and Msys) using unsophisticated build tools. In principle, all that is required are GTK development libraries and headers, and a C compiler.

Building the program ought to be as simple as unpacking the source code and typing make bundle. This should compile everything, and copy the compiled binary and supporting libraries to the platfom-specific subdirectory of the deploy directory. In the Linux case, there will be no additional libraries, because we expect to find them at the system level. On Windows, binaries of the GTK libraries are copied alonside the program executable, making a big bundle ready for the Windows installer.

On Windows, the source code comes with the development version of GTK bundled, as most Windows developers do not have this. All this stuff is in the winstuff directory.

The assumed use of Msys allows us to treat Windows and Linux builds as essentially the same. Msys provides Windows versions of the usual Unix cp, etc., commands, and the Makefile asumes that these are locatable on the %PATH%.

Running grotz

You can specify a Z-code story file on the command line, or by selecting File|Open... Infocom version 6 files with graphics have an additional complexity — more on this below. When a story is running, most menu options will be disabled — the Z-machine specification provides no facility by which the state of play or the environment can be changed other than by the text typed by the user. To use the menu again, you'll have to exit the current story (usually by typing 'quit'). You can quit the program at any time, but the game state will not be saved unless you save it through the game itself.

It's important to bear in mind that Z-code is an archaic format, from the early days of personal computing. There's a limit to how much can be done to modernize the look and feel of Z-code games. Some Z-code games, for example, do their own character input and editing — and they often don't do it very well. If a Z-code program asks for input a line at a time, then at least the Z-code interpreter can provide line-editing facilities. But even then the program will probably be drawing a prompt, and expecting input to be echoed to the screen just like on a terminal. grotz does what it can to wrap a modern user interface around an ancient virtual machine architecture — but that often turns out to be not very much.

Configuration file

grotz creates a directory $HOME/.grotz on Linux or c:\Users\[user]\AppData\Roaming\grotz on Windows. The configuration file grotz.ini is saved in this directory, as are certain temporary files. There are certain settings in the configuration file that are not accessible through the GUI — these are described below.

Font issues

grotz will allow any font present on the system to be used for the display. However, although Inform's specification does hint at the possibility of using variable-pitch fonts, the screen model is implicitly based on a fixed size rectangular grid of cells. That remains true even for version 6. Z-code games and stories can, and nearly always do, position text at absolute row and column positions. The screen model does allow for wrapping and scrolling of text, so in principle a Z-code program could output text in large blocks and allow the interpreter to flow it nicely onto the screen. In practice, the code generated by Z-code compilers, even modern ones, outputs text word-by word at specified screen positions. All this makes it very difficult to organize text in a book-like way.

In short, selecting a variable-pitch font may work reasonably well with some games and stories. It will often be necessary to adust the screen size and font to find a workable combination. Bear in mind that the screen size is worked out to accomodate the longest possible row of characters of a particular font. With variable pitch, many of the rows will be unfilled, because most characters are less wide than the largest in the font. There will therefore be a substantial ragged right margin regardless of the font and size settings, because grotz has no way of knowing that the story won't output a whole row of X's or something (and, in fact, this kind of behaviour is not uncommon). Having said all that, in practice the use of variable-pitch fonts works pretty well, considering all the problems, and is recommended.

Unicode support

grotz supports unicode output and, to some extent, input — to the extent that Z-machine, the operating system, GTK, and installed fonts do. Running David Kinder's Unicode.z5 test program should produce either reasonable output, or complaints about missing fonts (I forgot to install Coptic support on my Linux desktop machine, for some reason). If it produces nothing but question marks or hex boxes, something is wrong.

Unicode characters can be entered so long as they are available as a single keystroke, and so long as GTK understands what unicode symbols the keystrokes map on to. The 'dead key' method of entering extended key codes is not, as yet, supported.

Please note that unicode support depends on a co-operative operating system configuration. grotz cannot itself make up for missing fonts or libraries, or a dubious locale configuration.

zblorb support

Many IF authors now provide Z-code programs bundled into 'blorb' archives. Such files typically have names ending in '.zblorb'. Files with similar names, like '.gblorb' may well be in the same format, but probably don't contain Z-code but some other IF format.

grotz will unpack a .zblorb file and will run the Z-code therein, if it finds any. The Z-code is unpacked into the program's home directory ($HOME/.grotz on Linux) and are not deleted on exit — you never know, they might be useful. If the zblorb file contains authorship information and/or a cover image, these will displayed if you select Help|About this story... from the menu.

grotz will treat a file as a zblorb if its name end .zblorb or .zlb.

Another use of blorb files is to provide more modern representations of the graphics and sound used in the Infocom games — see the sections on graphics and sound support for more information.

V6 graphics issues

A very small number of games were produced by Infocom using the graphical version of the Z-machine, version 6. The best-known of these is probably Zork Zero. This game, like all the other Inform games, remains under copyright, so more modern re-implementations are not widely available. Z-machine version 6 required the graphics to be supplied in a separate file to the Z-code program, and in a very peculiar, proprietary format. I have not attempted to support this format in grotz — the amount of work involved for a handful of defunct games is just prohibitive. However, versions of the Zork (and other) graphics are widely available redrawn in the more modern PNG format, bundled up inside blorb archives. grotz will attempt to display graphics in this format. To use this feature, the graphics file should have the same name as the main story file, but with a .blb extension, and be in the same directory. The same method is used to provide sound effects (see below), and in principle there might be a complication about what file to use if a game uses both graphics and sound. However, so far as I can tell, none of the original Infocom games did, and more modern games would probably package the graphics and/or sound up with the executable code in a single blorb file.

The original Inform graphics were drawn for a 320x200 pixel screen. In practice, such a resolution is unusable on modern display hardware, even if the fonts can be set to provide such a size. There is no straightforward way for for grotz to work out what resolution screen graphics were originally intended for — the blorb specification does define a possible method but, like everything to do with the blorb specification it thoroughly Byzantine in its complexity. grotz therefore assumes that all graphics are drawn for a 320x200 pixel screen, and scales to fit the current true screen size.

Note that the original Inform games were designed to flow text around the graphics, so getting the graphics sizes right is a matter of some importance. If the graphics you have are not for a 320x200 screen, then it might be necessary to tell grotz the original screen size. At present, there is no way to do this through the GUI (sorry), but you can put the relevant settings into the configuration file:

So far, I've not come across any redrawn graphics files for any of the original Infocom games that use anything by 320x200, so the need to provide an easy way to change the resolution does not seem to be a pressing one.

Colour issues

grotz tries to respect the original Z-machine colour assignments, ugly as they are. Because the original Z-machine spec did not recognize the need for transparent text, problems arise when overlaying text onto images. grotz tries to work around these the same way the Windows Frotz does — it samples the screen colour under the cursor, then maps the colour value onto an index in a table. This index is then passed around the Z-machine VM as if it were a standard colour code. The efficacy of this technique is somewhat variable. The 'true colour' mode of the Z-machine 1.1 spec. is also supported, using the same mechanism.

If the game does not set any colours, then default foreground and background colours are used. These can be configured in the preferences dialog. It is also possible to set grotz to ignore the game's own colour settings, in which case defaults are always used. Ignore game colours is not advisable with games like Beyond Zork, which use colour assignments to highlight menu selections. Results are likely to be unpredictable if the game uses transparency, or if you change colour settings in mid-game.

Sound support

...is rudimentary. Sounds need to be packaged into blorb files in the same manner as described for V6 graphics. Sounds suitable for the original Infocom games (Sherlock, Lurking horror, etc) are widely available in this format. grotz does not attempt to play any sound itself — why should it, when there are any number of perfectly satisfactory audio players for Linux? Instead, when called on to play a sound it will unpack the sound into the temporary directory, and then invoke the script grotz_playmedia.sh (or grotz_playmedia.bat on Windows). As shipped, this script will invoke mplayer, passing arguments representing the number of repetitions of the effect, volume, etc. The Windows .bat file will also try to invoke mplayer, in the directory c:/program files/SMplayer/mplayer. The batch or script files can readily be edited to invoke an alternative media player, or mplayer in a different location, if necessary.

This method of producing sounds works pretty well on Linux, because mplayer is fast to start up, and can be run invisibly in the background. One complication of this approach is that grotz only finds out that sound playback has finished if it gets notified by the OS that the media playing process has terminated. This method seems to work reasonably reliably on Linux, but less predictably on Windows.

The use of an external player is less satisfactory on Windows. mplayer is a console application, and it is difficult to prevent a 'DOS box' popping up when sound is played, at least momentarily. It might be possible to change the Windows batch file to launch a different player — but Windows Media Player is even less satisfactory because, even though you can launch it to play a specific file, it won't close that file when playback is finished, unless you take manual action.

The entire set of Infocom games use about 30 sound effects between them, and I'm not aware that anybody else is producing IF stories that use sound. If there is a substantial demand, it would certainly be possible to implement sound playback directly in grotz, in a way that would work on Linux and Windows. But at present it hardly seems worth the considerable development effort that would be involved.

Keyboard input

grotz should recognize all keystrokes that generate a unicode or ASCII character (although the Z-machine program might not). The following keystrokes have a particular meaning during line input.
ctrl-vpaste at cursor position
ctrl-d'end of input'. Actually enters the text quit+Enter, as if from the keyboard, as this is the usual way of quitting most IF games
ctrl+kerase text from the cursor to end of line
ctrl+cerase whole line
backspacedeletes the character behind the cursor
deletedeletes the character under the cursor
ctrl+rightmoves forward to the next word
ctrl+leftmoves back to the previous word
up/downmoves through the history list of previous lines
These keystrokes are only effective if a game or story asks for input a line at a time. Most do, but a few do input character by character. How that works out depends on how well the programmer implemented it — the behaviour cannot be changed by grotz.

Emulation issues

grotz identifies itself to Z-code programs as an Atari Amiga, unless you specify otherwise. The idenfication can be changed from the Settings dialog. For the most part, the changes are quite subtle, and concern the colours that will be used and (occasionally) what keystrokes are used for menu navigation.

Limitations and quirks

  • Line editing is not as comprehensive as it might be. There is no tab completion, and you can't edit within the line itself. You can't select cursor position with the mouse, because a mouse click is a valid input in its own right to the Z-machine. However, since Z-code line input is typically limited to 60 characters, this might not be a deal-breaking issue.
  • There are no 'hot keys' for features like enabling tracing (as Frotz provides).
  • Games or stories that set the absolute text position in screen units will potentially look quirky with a variable-font display. This is a fundamental limitation of the Z-machine design.
  • Most modern games and stories will output text in such a way that the interpreter can break lines sensibly at work boundaries. But many stull use a fixed-path area for status lines, etc., which cannot be reflowed. grotz will not prevent you making the screen too small to show these areas properly (but it's pretty obvious when this has happened).
  • You can't cut and paste text from the text display to the input line. The display is essentially a graphics terminal and, once text is rendered onto it, it has no recollection of the actual characters. As a sort of workaround, you can cut and paste text from the transcript window into the input line.

Known issues

  • Some PNG graphics files display with rather odd colours. This, I believe, is because they were originally created without a colour palette, and conversion to PNG has forced a palette on them. There is a complicated work-around for this involving 'adaptive palette' chunks in blorb files, but implementing the workaround seems like an awful lot of work for very little benefit.
  • If running the debug build on Linux, stdout and stderr should be redirected. For some reason, the logging seems to be capable of breaking the console.
  • The user interface allows font and screen size to be changed during execution of a game, but the results can be unpredictable — Z-machine makes little provision for run-time environment changes.
  • grotz attempts to work around a number of bugs (or at least oddities) in Infocom's games. For example, in Beyond Zork the game puts data into the input buffer which differs in case from what it actually displays on screen. These workarounds have a variable success rate
  • Most Z-code games and stories that use menus draw their own, using the Z-machine's graphics and mouse capbilities. There is a 'proper' menu facility in the Z-code specification, but grotz does not support it. The reason is that I have been unable to find a single game or story that requires it. I would be happy to implement support if anybody can provide an example of its use.
  • No support for languages that use right-to-left text
  • Some errors in the Z-machine are so intractable that the only solution is to shut down the program completely. This is not very elegant
  • On Windows, some fonts do not seem to be rendered with fonts that match their names. I suspect that this is a GTK issue, not a problem in grotz. Moreover, some fonts appear to have baselines in odd places, again only on Windows. With these fonts some characters may be clipped
  • In order to reduce the amount of computation, I have in places made assumptions about how the sizes of different members of a font family relate to one another, rather than having the exact sizes calculated by the layout engine. It's possible that these assumptions will fail with some fonts, and text might be clipped with certain typefaces

Authors and credits

The original implementation of Frotz was by Stefan Jokish, around 1997. It was subsequently developed and extended by a number of people, notably Galen Hazelwood, Jim Dunleavy, David Griffith, Alembic Petrofsky, and Daniel Schepler.

Frotz was extended with full Unicode support by David Kinder, who wrote WindowsFrotz — the source for which I referred to extensively in developing grotz.

grotz is released under the GNU Public Licence, version 2.0.




  • Minor bug fixes
  • Added option to ignore game colours


  • Fixed the 'more...' prompt so that it does not push text to the right
  • Made the caret visible in single-key keyboard read operations
  • Added error reporting level selection the Settings dialog
  • If a game clears the whole screen to a particlar colour, that colour is now also used for the unpainted areas of the main window (e.g., margins). This makes games like Beyond Zork that draw their own dark backgrounds look nicer, at the expense of a bit more screen flicker at times.


First public release
Copyright © 1994-2015 Kevin Boone. Updated Feb 08 2013