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Making Countries for Players

Despite the advantages of predefining initial units, this doesn't help when you want variable groups of units to appear in a randomly-generated world. Instead, you should use the make-countries synthesis method. The basic idea is that the method picks a good location for each side's country, scatters an initial set of units around that location, then possibly grows the country outwards. You can do anything from small widely-separated countries to an interlocking nightmare resembling pre-Bismarck Germany. Because of this, and because of the requirement that this method generate random setups that are as fair as possible, you have a great many parameters to work with. These parameters should be tuned carefully - you will probably need to generate and study lots of initial setups, especially if your parameters constrain the countries very tightly; the method cannot backtrack to fix a poor combination of placements.

The first step in country generation is to select a location for each side's country. The location is a point that is the "center" of the country (the exact value will be unimportant to players, and is not used outside this method). The constraints are that the center of each country is farther than country-separation-min from the center of every other country, that the center is within country-separation-max of at least one other country, and that the given initial area of the country (as defined by country-radius-min) includes numbers of cells of each terrain type bounded by country-terrain-min and country-terrain-max.

The reason for the separation constraints is that having countries too close together or too far apart can create serious problems. Consider the poor soul who gets tightly sandwiched between two enemies, thus becoming lunchmeat, ha ha, or the not-quite-so-poor-but-still-unlucky player who ends up on the wrong side of a very large world. (Keep in mind that your players may ask for a much larger world than you were thinking of when you designed the game.)

The terrain constraints help you put the country in a reasonable mix of terrain. For instance, if you want to ensure that your countries include some land, but be on the coast rather than inland, then you should say that the country must have a minimum of 1 sea cell and 1 land cell. (In practice, the values should be higher, so you don't get small islands being used as entire countries and lakes being considered the ocean.) Keep in mind that these constraints may be impossible to satisfy, for instance if a particular world does not have enough of the sort of terrain that is being required in a country. If the basic placement constraints fail, Xconq will just pick a random location, warn about it, and then leave it up to the players to decide on whether to play the game "as it lies".

;;; Keep countries close together, but not too close.

(set country-separation-min 20)
(set country-separation-max 25)

Once Xconq has decided on locations for each country, it then places the initial stock of units. You define this initial stock via the unit properties start-with and independent-near-start. The start-with units start out belonging to the side, while the independent-near-start units are independent. The locations of these units are random within country-radius-min of the center, but are weighted according to the table favored-terrain. This table is very important; it is the percent chance that a unit of a given type will be placed in terrain of the given type. 100 is guaranteed to work, and 0 is an absolute prohibition. Since make-countries tries repeatedly to place each start-with unit until it succeeds, then even terrain with a favored-terrain value of only 10% will get used if there is no other choice, so the table affects the distribution of units rather than the number that get placed. If a starting unit cannot be placed on any available terrain, but can be an occupant, then Xconq will attempt to put it inside some unit already present. This is a good way to begin a game with aircraft at airports rather than in the air.

The upshot is that all this will do a reasonable layout if the parameters are set reasonably. If, however, favored-terrain is never > 0 for the start-with units and the country terrain, but there is some other terrain type for which this would work, Xconq will change the terrain. If even that doesn't work, the method will fail [or just complain?].

This example is from the standard Xconq game:

(set country-radius-min 3)

(add city start-with 1)
(add town independent-near-start 5)

(table favored-terrain 0
  ((town city) plains 100)
  (town (desert forest mountains) (20 30 20))
  )

The net effect is to give each player one city outright and 5 towns nearby. Although created independent, these towns can be easily taken over right at the beginning of a game, so they are a kind of "warmup" (like the pushing of pawns at the beginning of a chess game). The favored-terrain table allows cities to appear only in plains, while giving more options to towns, since they can appear in deserts, forests, and mountains. Even so, towns are 5 times more likely to be in plains, which is reasonable.

The optional last step in country generation is to grow the countries outwards from the initial area. This is basically a simple simulation of the historical forces that give countries their variety of shapes. The algorithm works by deciding whether to add to the country each cell at each distance from the country's center. The chance depends on the terrain type and whether the cell has already been given to another country. Once a cell has been given to the country, then the method decides whether to add a sided or independent unit to the cell, or whether to change the side of an existing unit. Country growth stops when either the absolute maximum radius has been reached, or too few cells have been added to the country, whichever comes first.

This example is from one of the variants of the standard game:

(game-module "standard"
  ...
  (variants
   ...
    ("Large Countries" eval
     (set country-radius-max 100)
     )
  ))

The resulting effect is to make all the countries border on each directly.


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