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Unix Programming - Unix Interface Design Patterns - The Roguelike Pattern

The Roguelike Pattern

The roguelike pattern is so named because its first example was the dungeon-crawling game rogue(1) (see Figure11.2) under BSD; the adjective “roguelike” for this pattern is widely recognized in Unix tradition. Roguelike programs are designed to be run on a system console, an X terminal emulator, or a video display terminal. They use the full screen and support a visual interface style, but with character-cell display rather than graphics and a mouse.

Figure11.2.Screen shot of the original Rogue game.

                                                a) some food
                                                b) +1 ring mail [4] being worn
-----------------------              ########## c) a +1,+2 mace in hand 
|                     +###############          d) a +1,+0 short bow
|                     |                         e) 28 +0,+0 arrows
---------------+-------                         f) a short bow
               #                                i) a magnesium wand
               #                                g) a magnesium wand
             ###               ---------------- j) a potion of detect things
     --------+----------       |                l) a scroll of teleportation
     |                 |      #+                --press space to continue--
     |                 |      #|                 |             #
     |                 +#######|                 |            ##
     |                 |       |                 +##############
     --------+----------       -------------------             #
        ######                                                 #
  ------+----------                                            ######
  |...........@..!|                                                 #
  |...........%...|                 ----------------                #
  |...............|                #+              |          #######
  |...............+#################|              |          #
  |...............|                 |              +###########
  -----------------                 ----------------
Level: 3  Gold: 73     Hp: 36(36)   Str: 14(16) Arm: 4  Exp: 4/78

Commands are typically single keystrokes not echoed to the user (as opposed to the command lines of the ed pattern), though some will open a command window (often, though not always, the last line of the screen) on which more elaborate invocations can be typed. The command architecture often makes heavy use of the arrow keys to select screen locations or lines on which to operate.

Programs written in this pattern tend to model themselves on either vi(1) or emacs(1) and (obeying the Rule of Least Surprise) use their command sequences for common operations such as getting help or terminating the program. Thus, for example, one can expect one of the commands ‘x’, ‘q’, or ‘C-x C-c’ to terminate a program written to this pattern.

Some other interface tropes associated with this pattern include: (a) the use of one-item-per-line menus, with the currently-selected item indicated by bold or reverse-video highlighting, and (b) ‘mode lines’ — program status summaries carried on a highlighted screen line, often near the bottom or at the top of the screen.

The roguelike pattern evolved in a world of video display terminals; many of these didn't have arrow or function keys. In a world of graphics-capable personal computers, with character-cell terminals a fading memory, it's easy to forget what an influence this pattern exerted on design; but the early exemplars of the roguelike pattern were designed a few years before IBM standardized the PC keyboard in 1981. As a result, a traditional but now archaic part of the roguelike pattern is the use of the h, j, k, and l as cursor keys whenever they are not being interpreted as self-inserting characters in an edit window; invariably k is up, j is down, h is left, and l is right. This history also explains why older Unix programs tend not to use the ALT keys and to use function keys in a limited way if at all.

Programs obeying this pattern are legion: The vi(1) text editor in all its variants, and the emacs(1) editor; elm(1), pine(1), mutt(1), and most other Unix mail readers; tin(1), slrn(1), and other Usenet newsreaders; the lynx(1) Web browser; and many others. Most Unix programmers spend most of their time driving programs with interfaces like these.

The roguelike pattern is hard to script; indeed scripting it is seldom even attempted. Among other things, this pattern uses raw-mode character-by-character input, which is inconvenient for scripting. It's also quite hard to interpret the output programmatically, because it usually consists of sequences of incremental screen-painting actions.

Nor does this pattern have the visual slickness of a mouse-driven full GUI. While the point of using the full screen interface is to support simple kinds of direct-manipulation and menu interfaces, roguelike programs still require users to learn a command repertoire. Indeed, interfaces built on the roguelike pattern show a tendency to degenerate into a sort of cluttered wilderness of modes and meta-shift-cokebottle commands that only hard-core hackers can love. It would seem that this pattern has the worst of both worlds, being neither scriptable nor conforming to recent fashions in design for end-users.

But there must be some value in this pattern. Roguelike mailers, newsreaders, editors, and other programs remain extremely popular even among people who invariably run them through terminal emulators on an X display that supports GUI competitors. Moreover, the roguelike pattern is so pervasive that under Unix even GUI programs often emulate it, adding mouse and graphics support to a command and display interface that still looks rather roguelike. The X mode of emacs(1), and the xchat(1) client are good examples of such adaptation. What accounts for the pattern's continuing popularity?

Efficiency, and perceived efficiency, seem to be important factors. Roguelike programs tend to be fast and lightweight relative to their nearest GUI competitors. For startup and runtime speed, running a roguelike program in an Xterm may be preferable to invoking a GUI that will chew up substantial resources setting up its displays and respond more slowly afterwards. Also, programs with a roguelike design pattern can be used over telnet links or low-speed dialup lines for which X is not an option.

Touch-typists often prefer roguelike programs because they can avoid taking their hands off the keyboard to move a mouse. Given a choice, touch-typists will prefer interfaces that minimize keystrokes far off the home row; this may account for a significant percentage of vi(1)'s popularity.

Perhaps more importantly, roguelike interfaces are predictable and sparing in their use of screen real estate on an X display; they do not clutter the display with multiple windows, frame widgets, dialog boxes, or other GUI impedimenta. This makes the pattern well suited for use in programs that must frequently share the user's attention with other programs (as is especially the case with editors, mailers, newsreaders, chat clients, and other communication programs).

Finally (and probably most importantly) the roguelike pattern tends to appeal more than GUIs to people who value the concision and expressiveness of a command set enough to tolerate the added mnemonic load. We saw above that there are good reasons for this preference to become more common as task complexity, use frequency, and user experience rise. The roguelike pattern meets this preference while also supporting GUI-like elements of direct manipulation as an ed-pattern program cannot. Thus, far from having only the worst of both worlds, the roguelike interface design pattern can capture some of the best.

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