DM4 §9: Directions and the map

## §9 Directions and the map

> I wisely started with a map, and made the story fit (generally with meticulous care for distances). The other way about lands one in confusions and impossibilities, and in any case it is weary work to compose a map from a story – as I fear you have found.
> — J. R. R. Tolkien (1892–1973), to Naomi Mitchison, 25 April 1954

‘Ruins’ so far contains two disconnected rooms. It is time to extend it into a modest map in which, as promised, the Square Chamber lies underneath the original Forest location. For the map of the finished game, see §23 below, but here is the beginning of the first level beneath ground, showing the Square Chamber and its two main side-chambers:

`Square Chamber` | — | `Wormcast`
`Corridor`
`Shrine`

To make these map connections, we need to add:

    u_to Forest, e_to Wormcast, s_to Corridor,

to the Square Chamber. This seems a good point to add two more map connections, or rather non-connections, to the Forest as well:

    u_to "The trees are spiny and you'd cut your hands to ribbons
        trying to climb them.",
    cant_go "The rainforest is dense, and you haven't hacked
        through it for days to abandon your discovery now. Really,
        you need a good few artifacts to take back to civilization
        before you can justify giving up the expedition.",

The property `cant_go` contains what is printed when the player tries to go in a nonexistent direction, and replaces “You can't go that way”. Instead of giving an actual message you can give a routine to print one out, to vary what's printed with the circumstances. The Forest needs a `cant_go` because in real life one could go in every direction from there: what we're doing is explaining the game rules to the player: go underground, find some ancient treasure, then get out to win. The Forest's `u_to` property is a string of text, not a room, and this means that attempts to go up result only in that string being printed.

▲ Here's how this is done. When the library wants to go in a certain direction, let's say “north”, it sends the message `location.n_to()` and looks at the reply: it takes `false` to mean “Player can't go that way” and says so; `true` means “Player can't go that way, and I've already said why”; and any other value is taken as the destination.

• EXERCISE 8
Many early games have rooms with confused exits: ‘Advent’ has Bedquilt, ‘Acheton’ has a magnetic lodestone which throws the compass into confusion, ‘Zork II’ has a spinning carousel room and so on. Make the Wormcast room in ‘Ruins’ similarly bewildering.

· · · · ·

For each of the twelve standard Inform directions there is a “direction property”:

    n_to     s_to     e_to     w_to     d_to     u_to
    ne_to    nw_to    se_to    sw_to    in_to    out_to

Each direction also has a “direction object” to represent it in the game. For instance, `n_obj` is the object whose name is “north” and which the player invokes by typing “go north” or just “n”. So there are normally twelve of these, too:

    n_obj    s_obj    e_obj    w_obj    d_obj    u_obj
    ne_obj   nw_obj   se_obj   sw_obj   in_obj   out_obj

Confusing the direction objects with the direction properties is easily done, but they are quite different. When the player types “go north”, the action is `Go n_obj`, with `noun` being `n_obj`: only when this action has survived all possible before rules is the `n_to` value of the current location looked at.

▲ The set of direction objects is not fixed: the current direction objects are the children of a special object called `compass`, and the game designer is free to add to or take from the current stock. Here for instance is the definition of “north” made by the library:

    CompassDirection n_obj "north wall" compass
      with name 'n' 'north' 'wall', door_dir n_to;

`CompassDirection` is a class defined by the library for direction objects. `door_dir` is a property more usually seen in the context of doors (see §13) and here tells Inform which direction property corresponds to which direction object.

•▲ EXERCISE 9
In the first millennium A.D., the Maya peoples of the Yucatán Peninsula had ‘world colours’ white (sac), red (chac), yellow (kan) and black (chikin) for what we call the compass bearings north, east, south, west (for instance west is associated with ‘sunset’, hence black, the colour of night). Implement this.

•▲ EXERCISE 10
In Level 9's version of ‘Advent’, the magic word “xyzzy” was implemented as a thirteenth direction. How can this be done?

•▲ EXERCISE 11
(Cf. ‘Trinity’.) How can the entire game map be suddenly eastwest reflected?

•▲▲ EXERCISE 12
Even when the map is reflected, there may be many room descriptions referring to “east” and “west” by name. Reflect these too.

•▲▲ EXERCISE 13
Some designers find it a nuisance to have to keep specifying all map connections twice: once east from A to B, then a second time west from B to A, for instance. Write some code to go in the `Initialise` routine making all connections automatically two-way.

• REFERENCES
‘Advent’ has a very tangled-up map in places (see the mazes) and a well-constructed exterior of forest and valley giving an impression of space with remarkably few rooms. The mist object uses `found_in` to the full, and see also the stream (a single object representing every watercourse in the game). Bedquilt and the Swiss Cheese room offer classic confused-exit puzzles. •For a simple movement rule using `e_to`, see the Office in ‘Toyshop’. •The opening location of Infocom's ‘Moonmist’ provides a good example of `cant_go` used to guide the player in a tactful way: “(The castle is south of here.)” •The library extension `"smartcantgo.h"` by David Wagner provides a system for automatically printing out “You can only go east and north.”-style messages. •Ricardo Dague's `"cmap.h"` constructs maps of American-style cities. The same author's `"makemaze.inf"` prints out Inform source code for random rectangular mazes. •Nicholas Daley and Gunther Schmidl have each independently written a `"dirs.h"` providing a “dirs” or “exits” verb which lists available exits. Marnie Parker's `"dirsmap.h"` goes further by plotting up exits in map style or writing them out in English, at the player's discretion. •Brian D. Smith's example program `"spin.inf"` abolishes the convention that a player has an in-built ability to know which way is north: it replaces conventional compass directions with “left”, “right”, “ahead” and “back”.