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<title>DM4 §9: Directions and the map</title>
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<h2>§9 Directions and the map</h2>
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<blockquote>I wisely started with a map, and made the story fit
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(generally with meticulous care for distances). The other way about
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lands one in confusions and impossibilities, and in any case it is
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weary work to compose a map from a story – as I fear you have found.<br>
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— J. R. R. Tolkien (1892–1973), to Naomi Mitchison,
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25 April 1954</blockquote>
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<p class="normal"><span class="atleft"><img src="dm4-122_1.jpg" alt=""></span>
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‘Ruins’ so far contains two disconnected rooms. It is
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time to extend it into a modest map in which, as promised, the Square
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Chamber lies underneath the original Forest location. For the map
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of the finished game, see <a href="s23.html">§23</a> below,
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but here is the beginning of the first level beneath ground, showing
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the Square Chamber and its two main side-chambers:</p>
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<p class="lynxonly"></p>
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<table align="center" class="objtree">
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<tr><td><tt>Square Chamber</tt></td>
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<td><tt>Wormcast</tt></td></tr>
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<tr><td>|</td><td colspan="2" rowspan="4"></tr>
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<tr><td><tt>Corridor</tt></td></tr>
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<tr><td><tt>Shrine</tt></td></tr>
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<p class="normal">To make these map connections, we need to add:</p>
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<p class="lynxonly"></p>
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<pre class="code">u_to Forest, e_to Wormcast, s_to Corridor,</pre>
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<p class="normal">to the Square Chamber. This seems a good point to
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add two more map connections, or rather non-connections, to the Forest
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<p class="lynxonly"></p>
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u_to "The trees are spiny and you'd cut your hands to ribbons
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trying to climb them.",
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cant_go "The rainforest is dense, and you haven't hacked
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through it for days to abandon your discovery now. Really,
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you need a good few artifacts to take back to civilization
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before you can justify giving up the expedition.",
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<p class="normal">The property <code>cant_go</code> contains what
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is printed when the player tries to go in a nonexistent direction,
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and replaces “You can't go that way”. Instead of
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giving an actual message you can give a routine to print one out,
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to vary what's printed with the circumstances. The Forest needs a
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<code>cant_go</code> because in real life one could go in every
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direction from there: what we're doing is explaining the game
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rules to the player: go underground, find some ancient treasure,
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then get out to win. The Forest's <code>u_to</code> property is
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a string of text, not a room, and this means that attempts to go
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up result only in that string being printed.</p>
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<a id="p123" name="p123"></a>
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<p class="aside"><span class="warning">▲</span>
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Here's how this is done. When the library wants to go in a certain
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direction, let's say “north”, it sends the message
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<code>location.n_to()</code> and looks at the reply: it takes
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<code>false</code> to mean “Player can't go that way” and
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says so; <code>true</code> means “Player can't go that way,
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and I've already said why”; and any other value is taken as
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<a id="ex8" name="ex8"></a>
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<p class="aside"><span class="warning"><b>•</b>
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<b><a href="sa6.html#ans8">EXERCISE 8</a></b></span><br>
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Many early games have rooms with confused exits: ‘Advent’
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has Bedquilt, ‘Acheton’ has a magnetic lodestone which
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throws the compass into confusion, ‘Zork II’ has a
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spinning carousel room and so on. Make the Wormcast room in
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‘Ruins’ similarly bewildering.</p>
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<p class="dotbreak">� � � � �</p>
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<p class="normal">For each of the twelve standard Inform directions
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there is a “direction property”:</p>
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<p class="lynxonly"></p>
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n_to s_to e_to w_to d_to u_to
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ne_to nw_to se_to sw_to in_to out_to
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<p class="normal">Each direction also has a “direction object”
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to represent it in the game. For instance, <code>n_obj</code> is
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the object whose name is “north” and which the player
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invokes by typing “go north” or just “n”.
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So there are normally twelve of these, too:</p>
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<p class="lynxonly"></p>
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n_obj s_obj e_obj w_obj d_obj u_obj
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ne_obj nw_obj se_obj sw_obj in_obj out_obj
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<p class="normal">Confusing the direction objects with the direction
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properties is easily done, but they are quite different. When the
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player types “go north”, the action is <code>Go n_obj</code>,
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with <code>noun</code> being <code>n_obj</code>: only when this action
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has survived all possible before rules is the <code>n_to</code> value
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of the current location looked at.</p>
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<p class="aside"><span class="warning">▲</span>
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The set of direction objects is not fixed: the current direction
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objects are the children of a special object called <code>compass</code>,
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and the game designer is free to add to or take from the current
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stock. Here for instance is the definition of “north”
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made by the library:</p>
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<p class="lynxonly"></p>
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CompassDirection n_obj "north wall" compass
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with name 'n' 'north' 'wall', door_dir n_to;
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<p class="aside"><code>CompassDirection</code> is a class defined
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by the library for direction objects. <code>door_dir</code> is
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a property more usually seen in the context of doors (see
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<a href="s13.html">§13</a>) and here tells Inform which
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direction property corresponds to which direction object.</p>
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<a id="p124" name="p124"></a>
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<a id="ex9" name="ex9"></a>
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<p class="aside"><span class="warning"><b>•</b>▲
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<b><a href="sa6.html#ans9">EXERCISE 9</a></b></span><br>
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In the first millennium A.D., the Maya peoples of the Yucatán
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Peninsula had ‘world colours’ white (<i>sac</i>),
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red (<i>chac</i>), yellow (<i>kan</i>) and black (<i>chikin</i>)
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for what we call the compass bearings north, east, south, west
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(for instance west is associated with ‘sunset’, hence
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black, the colour of night). Implement this.</p>
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<a id="ex10" name="ex10"></a>
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<p class="aside"><span class="warning"><b>•</b>▲
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<b><a href="sa6.html#ans10">EXERCISE 10</a></b></span><br>
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In Level 9's version of ‘Advent’, the magic word “xyzzy”
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was implemented as a thirteenth direction. How can this be done?</p>
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<a id="ex11" name="ex11"></a>
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<p class="aside"><span class="warning"><b>•</b>▲
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<b><a href="sa6.html#ans11">EXERCISE 11</a></b></span><br>
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(Cf. ‘Trinity’.) How can the entire game map be
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suddenly east�west reflected?</p>
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<a id="ex12" name="ex12"></a>
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<p class="aside"><span class="warning"><b>•</b>▲▲
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<b><a href="sa6.html#ans12">EXERCISE 12</a></b></span><br>
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Even when the map is reflected, there may be many room descriptions
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referring to “east” and “west” by name.
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Reflect these too.</p>
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<a id="ex13" name="ex13"></a>
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<p class="aside"><span class="warning"><b>•</b>▲▲
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<b><a href="sa6.html#ans13">EXERCISE 13</a></b></span><br>
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Some designers find it a nuisance to have to keep specifying all
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map connections twice: once east from <i>A</i> to <i>B</i>, then a second time
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west from <i>B</i> to <i>A</i>, for instance. Write some code to go in the
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<code>Initialise</code> routine making all connections automatically
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<p class="aside"><span class="warning"><b>•</b>
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<b>REFERENCES</b></span><br>
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‘Advent’ has a very tangled-up map in places (see the
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mazes) and a well-constructed exterior of forest and valley giving
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an impression of space with remarkably few rooms. The mist object uses
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<code>found_in</code> to the full, and see also the stream (a single
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object representing every watercourse in the game). Bedquilt and
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the Swiss Cheese room offer classic confused-exit puzzles.
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<span class="warning"><b>•</b></span>For a simple movement rule
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using <code>e_to</code>, see the Office in ‘Toyshop’.
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<span class="warning"><b>•</b></span>The opening location of Infocom's
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‘Moonmist’ provides a good example of <code>cant_go</code> used
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to guide the player in a tactful way: “(The castle is south of
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<span class="warning"><b>•</b></span>The library extension <tt>"smartcantgo.h"</tt>
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by David Wagner provides a system for automatically printing out
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“You can only go east and north.”-style messages.
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<span class="warning"><b>•</b></span>Ricardo Dague's <tt>"cmap.h"</tt>
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constructs maps of American-style cities. The same author's <tt>"makemaze.inf"</tt>
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prints out Inform source code for random rectangular mazes.
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<span class="warning"><b>•</b></span>Nicholas Daley and Gunther Schmidl
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have each independently written a <tt>"dirs.h"</tt>
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providing a “dirs” or “exits” verb which
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lists available exits. Marnie Parker's <tt>"dirsmap.h"</tt>
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goes further by plotting up exits in map style or writing them out
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in English, at the player's discretion.
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<span class="warning"><b>•</b></span>Brian D. Smith's example program
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<tt>"spin.inf"</tt> abolishes the convention that a player
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has an in-built ability to know which way is north: it replaces conventional
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compass directions with “left”, “right”,
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“ahead” and “back”.</p>
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