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MultiLocs

The standard adv3Lite containment model normally assumes that each game object resides in its own container, meaning that normally an object can only be in one place at a time. Occasionally, however, we may want to define an object that’s present in multiple locations, such as the sky (present in every outdoor room), or a distant mountain visible from many different locations, or, perhaps, a floor running through several rooms in a house. For situations such as these we can use a MultiLoc

Defining a MultiLoc

To define a simple MultiLoc, add MultiLoc to the class list of the item you want to define before Thing (or a class derived from Thing) and set its locationList property to the list of locations in which you wish the MultiLoc object to be present. The locationList property can contain a list of Rooms, but it can also contain one or more regions, which makes it particular easy to place a MultiLoc in every room in a given region. For example, to define a night sky object that appears in every Room in the outdoors Region you could do something like this:

    sky: MultiLoc, Thing 'sky; dark tiny crescent; moon stars'
       "The sky is dark tonight, with only a crescent moon showing among the myriad of stars. "
       isDecoration = true
       notImportantMsg = 'The sky is way too far above your head. '
       locationList = [outdoors]
    ;

It is very convenient to be able just to specify the region in the locationList of a MultiLoc, instead of having to list each room its in individually (though you can do it that way), but sometimes you may run into a situation where you want a MultiLoc to be present in every room in a region apart from one or two exceptions. Suppose, for example, we want a MultiLoc to represent the ceiling in every room in the house, but for some reason we have a custom ceiling in the kitchen, so we don’t want our MultiLoc ceiling there as well. Instead of having to list all the other rooms we want the ceiling in by hand, we can specify the region and then use the exceptions property to list the rooms we don’t want our plain vanilla MultiLoc ceiling to appear in:

    ceiling: MultiLoc, Thing 'ceiling'
       
       isDecoration = true
       notImportantMsg = 'You can\'t reach the ceiling. '
       locationList = [indoors]
       exceptions = [kitchen]
    ;

It is no coincidence that these two examples both use decoration-type objects. That is generally the only safe way to use a MultiLoc, since as soon as we allow the player to interact with it any way beyond examining (and perhaps smelling, touching and listening to it) we run the risk that the game will produce illogical results because what the player does to the MultiLoc in one location will apply to the MultiLoc in every location. For example, suppose we wanted to add a floor to every room in the indoors region. Since in real life a floor is something we can stand on and put things on we might be tempted to do this:

    floor: MultiLoc, Thing 'floor;;ground'  // DON'T DO THIS!!!
       
       contType = On  
       isEnterable = true
       locationList = [indoors]   
    ;

But this would be catastrophic, for as soon as the player placed an object on the floor, that object would appear on the floor of every room in the house (since it’s actually the same floor), which is almost certainly not what we want. If you want to define MultiLoc object safely, make it a decoration, like this:

    floor: MultiLoc, Thing 'floor;;ground' 
       
       isDecoration = true
       locationList = [indoors]   
    ;

Or at the most, perhaps:

    floor: MultiLoc, Thing 'floor;;ground' 
       isDecoration = true   
       decorationActions = [Examine, Feel, SmellSomething]  
       feelDesc = "The floor feels reassuringly solid. "
       smellDesc = "There's a faint smell of floor polish. "
       locationList = [indoors] 
    ;

The first of these is probably better, however, since if the floor responds to everything except EXAMINE with “The floor is not important” players will pretty quickly realize it’s simply a decoration object they don’t need to interact with. In fact, though, you’ll hardly ever need to define a MultiLoc to represent the floor or ground in your own code, since adv3Lite already provides a Floor class which takes care of it for you. You’d only need to define your own if you wanted to replace the library’s default implementation with something different.

Under certain circumstances, however, it may be both legitimate and safe to define a MultiLoc that does provide a bit more action. These circumstances are:

  1. The MultiLoc genuinely does represent a single object at a single spot, and not an extended object (like the ground or the sky) or similar objects in multiple location (like floors and ceilings in a house).
  2. The reason for defining it as a MultiLoc is that it is right on the boundary of two or more rooms and is equally accessible from each of them.

An example might be a fountain that stands right at the centre of a square you’re implementing as four different locations. The fountain is accessible from each corner of the square, so if you throw a coin into it from one corner you could indeed retrieve the coin from another:

    fountain: MultiLoc, Thing 'fountain;large ;water fish mouth'
       "It's a large fountain in the form of an improbable looking fish with water gushing from its mouth. " 
       isFixed = true
       contType = In
       locationList = [squareNE, squareNW, squareSE, squareSW] 
    ;

If we had defined a square region we could simply have used that in the locationList, but this seemed a good idea to show what a MultiLoc with an explicit list of rooms looks like.

Moving MultiLocs

It may sometimes be necessary to move MultiLocs around. For example, if the game with the night sky defined long enough was meant to go on into the next day, at some point it might be necessary to remove the night sky with its moon and stars and replace it with a daytime one with the sun and some clouds. The following methods are available for moving MultiLocs around:

The location of a MultiLoc

You can test whether a MultiLoc is present in a location by using the isIn(loc) or isDirectlyIn(loc) methods, just as you do on a Thing. MultiLoc also defines its own version of the location property, which you should never override. In one sense the location property of a MultiLoc ought to be meaningless, since a MultiLoc generally does not reside in only one location, but for certain purposes the library needs to use a MultiLoc’s location property, since certain calculations it makes assume that every physical object defines one, and it may occasionally be useful in game code to be able to make the same assumption when writing code that may apply to any object. The location property of a MultiLoc is taken to be the location of the current actor (or of the player character if no actor is defined), provided the MultiLoc is present there. Otherwise the location property is taken to be the last place the MultiLoc was seen.

Initializing a MultiLoc’s Location

All the examples above have used the locationList property to define where we want a MultLoc to start out. As we’ve seen, this property can contain a list of Rooms, other Things and/or Regions. We could also use the initialLocationList property and it would appear to work in just the same way. If you define a MultiLoc with an empty initialLocationList, adv3Lite copies the locationList to the initialLocationList, and then proceeds to initialize the locationList just as it would have done had you defined a lis of Rooms and/or Regions directly on the initialLocationList property.

What happens during this initialization is that any Regions in the initialLocationList are expanded into their constituent rooms and then added to the locationList property (with any duplicates being removed, to ensure that the same Room isn’t listed twice). For example, suppose your outdoors region contains the Rooms courtyard, gravelPath and garden, and suppose you define a MultiLoc sky object with a locationList of \[outdoors, riverBank, meadow\]. After your sky object is initialized its initialLocationList will be \[outdoors, riverBank, meadow\] and its locationList will be \[courtyard, gravelPath, garden, riverBank, meadow\]. Thereafter, initialLocationList will remain unchanged (unless, of course, you deliberately change it in your own code) while locationList will be updated to reflect any changes caused by using moveIntoAdd(), moveOutOf() and moveInto() (so don’t try to change locationList directly in your own code, or you’ll probably upset things).

MultiLoc also defines an initialLocationClass property and an isInitiallyIn(obj) method, which are intended to work together. If initialLocationClass is not nil then every instance of that class will be added to the MultiLoc’s locationList provided isInitiallyIn(obj) returns true for that instance (where obj is the instance in question). One reason for this feature is to facilitate the implementation of the Floor class, but you may find other uses for it in your own code.

Note that any locations added to the location list via initialLocationClass will be in addition to those defined on initialLocationList, and that any locations defined in the exceptions list will be removed from the location list after those defined in both initialLocationList and initialLocationClass have been added.

You may be wondering why you’re allowed to use either the locationList or the initialLocationList property to accomplish essentially the same task: defining the initial set of locations in which a MultiLoc resides. One reason is that locationList is a bit less of a mouthful to type; another is to ensure backward compatibility with game code written for earlier versions of adv3Lite that didn’t provide the initialLocationList property. Which of the two you use is entirely up to you (for instance, you may prefer to define initial locations on initialLocationList because it seems clearer that way), just so long as you use one or the other and don’t try to use both. If you define both locationList and initialLocationList on the same MultiLoc, whatever you put in locationList will simply be ignored.

adv3Lite Library Manual
Table of Contents | The Core Library > MultiLocs
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