Night Vision allows a creature or person to see well at night. On nights where the moon is out, beings with night vision can see with the same clarity as during daylight. On clear moonless nights, they can see up to a distance of 100 feet. Dark cloudy nights lower the viewing range of night sighted entities to 30 feet.
Not only does this partition the rules for Night Vision from the description of Elf, it also makes the gift conveniently available for other uses as well. If several races have this same characteristic, this separation can actually save space and, at the same time, make the game design more obvious to the reader. You might even say it simplified the game a smidge, since it took what was originally a rule exception (“Elves can see well in the dark and this is how it works”) and transformed it into a standard gift (“Elves have the gift of Night Vision”). Assuming the game explicitly included the Gift pattern to begin with, adding one more gift to an already existing list does nothing to increase the overall game complexity. It merely adds detail.
Known Uses
Dungeons & Dragons v.3.5 has bulleted “Racial Traits” in its race descriptions (see the Race pattern). These are actually a mixture of anonymous and named gifts rather than what this book calls “traits” (see the Gift and Trait patterns). For example, the Gnome Racial Traits include “+2 racial bonus on saving throws against illusions” and “+4 dodge bonus to Armor Class against monsters of the giant type.” Oddly enough, they actually name some of their Racial Traits, but then go ahead and embed the description for that trait directly in the text anyway: “Low Light Vision: A gnome can see twice as far as a human in starlight, moonlight, torchlight, and similar conditions…”
HARP has “Professional Abilities” (see the Gift and Skill patterns) incorporated into their “Professions” (see the Class pattern). The Professional Abilities section of every Profession is essentially a paragraph listing the effects of any number of anonymous gifts. For example, in the “Warrior Mage” description, it lists the Professional Abilities as: “Warrior Mages may learn spells from the Warrior Mage sphere. Beginning at first level, and then every seventh level thereafter (7th, 14th, etc.). Warrior Mages gain a +10 bonus to the weapon skill of their choice…”
Nobilis uses anonymous rules effectively to present the reader with smooth-flowing prose and a gorgeous layout. The work is undoubtedly one of the most attractive game books in existence. However, for all of its undisputed beauty, the book sometimes leaves the reader wondering what the game’s rules actually are. For example, a Nobilis character’s “Code” incorporates his belief system and is discussed at length. In the initial write-up of RPG Design Patterns, the fact that Nobilis rewards players for faithfully adhering to their Code (via Miracle Point awards) was omitted. This is a crucial role-playing reward that was overlooked until the oversight was corrected in a thread discussing morality and behavior mechanics on The Forge website. Even after learning of the mistake, searching for the detail via the book’s index, and re-reading several chapters, the author still could not find the rule and had to ask for help in discovering it. To quote Tony Lower-Basch (author of Capes), “Page 133, right-most column, middle of the page. It's... oh... one sentence in the middle of a huge page of poetic description of Heaven and Hell. I'm not surprised you missed it.” We quite agree. Most gamers would not take more than one or two gaming sessions to unearth all of the game’s core concepts, especially if there were more than one player doing the reading. Beware, though. A game incorporating many anonymous rules that fell short of the Nobilis aesthetic would find many people losing interest before they fully understood the game.
Structural Patterns (Loose Coupling) 151
Loose Coupling
Intent
Provide a means for one game concept to indirectly reference another game concept without tying one directly to the other.
Also Known As
Not Applicable
Related Patterns
Class, Gift, Rank, Skill
Motivation
This pattern gets its name directly from an important software engineering principle of the same name. Software designers often want various software modules to
communicate with one another without either module depending on the implementation details of the other.
Similarly, game designers sometimes need to create relationships between various pre-defined game entities, such as classes, gifts, skills, and other abilities. In doing so, the game designer may seek a system for which future supplements can be dreamed up, written, and smoothly merged into the pre-existing game. For example, a fantasy game may be originally written with a single core rulebook containing some basic classes, skills, and spells. Depending on customer feedback, the writer may want to create supplements with more classes and spells but no skills. Or, he may find that creating a book of new classes is of far less importance to his customers than the creation of new skills and spells. The point is that, after the game designer gets the initial rule book out on the shelves, he wants the flexibility to expand the game in whatever fashion he deems necessary. And, he wants to be able to accomplish that task without having to go back and publish a second edition of the original book to accommodate the new
materials. In handling these kinds of situations, the Loose Coupling pattern excels.
A game exhibits Loose Coupling if it sets up a relationship between two game entities whereby
1) Neither entity directly refers to the other.
2) Both refer to a third entity that acts as an intermediary.
One of the simplest ways to implement the Loose Coupling pattern is to have rules stating that one game entity has access to a certain number of a second game entity based on some criteria without ever mentioning specifics about the second entity. For example, a game using the Level pattern could state that a player can choose to give his character one skill for every level gained. This sets up an indirect relationship between
a character and his skills through the mechanism of his Level. However, game designers that want niche protection of character abilities may find this solution inadequate (see the Class pattern).
Niche protection can work in harmony with loose coupling by setting up indirect relationships through niche protected mechanisms, such as a rare skill, rather than common mechanisms, such as a character’s Level. For example, various priest classes and a litany of religious spells could be related through an intermediate skill, such as Piety. If Piety is granted only to characters having a priest class, and all religious spells have a requirement that a character possess Piety to use them, then the religious spells have the niche protection the designer seeks. And, the designer can write up any new priest classes or religious spells he needs in the future without modifying what he has already written by virtue of the loose coupling.
If a finer granularity or a more expressive form of niche protection is desired, then the spells could demand more than one requirement from characters, which would be fulfilled in different ways by various classes. For example, if priestly battle spells were distinguished from priestly wrath spells, the spells themselves could specify additional requirements while still avoiding any reference to specific classes (which would destroy the loose coupling). Suppose the Battle spell Fortitude demanded a character possess 5th rank in Piety as well as the gift of “Casting Battle Spells” to use. Suppose further that the class “Berserker” bestowed the skill of Piety and the gift of “Casting Battle Spells” but not the gift of “Casting Wrath Spells”. Then, any character gaining the class of “Berserker” has access to the “Fortitude” spell (as soon as he attains 5th rank in Piety). However, the Berserker character would not have access to wrath spells until he somehow obtains the gift “Casting Wrath Spells” elsewhere.
Example Structure
The following diagram illustrates how an initial Core Rule Book with a Wizard class and a number of spells can be extended by a supplement. The Wizard class of the original Core Rule Book allows access to various spells through the intermediary lore abilities, some of which are Fire Lore based spells. When the supplement is added, the new class of Pyromancer has access to the original Fire Lore based spells and the
Wizard class has access to some new Fire Lore based spells as well. The new Sun Lore, though, gives the Pyromancer access to some new spells that the Wizard cannot learn.
Structural Patterns (Loose Coupling) 153
Applicability
The Loose Coupling pattern makes sense when you want to
1) Design a game that can be easily extended with supplements.
2) Incorporate in the game design lists of pre-defined game components, such as classes, gifts, items, skills, etc.
3) Create flexible relationships between these pre-defined game entities.
If you are designing a self-contained single volume game for which you never intend to write supplements, the Loose Coupling pattern will be of little benefit. If game
simplicity is a high priority, you may want to forego using the Loose Coupling pattern altogether. Loose Coupling introduces a layer of complexity that could be avoided by sacrificing flexibility and extensibility.
Consequences
The Loose Coupling pattern provides a powerful mechanism to create flexible relationships between lists of game entities. It does this at the cost of introducing intermediary components between the lists, and thereby increases game complexity.
Lightning Bolt Spell
(requires Air and Water Lore)
Water Lore
Fire Lore Dragon’s Breath:
Flame Spell
(requires Fire Lore)
Wizard Class
(gives access to Air, Earth, Fire, and
Water Lore)
Air Lore
Earth Lore
Flight Spell
(requires Air Lore)
Dragon Skin Spell
(requires Earth Lore)
Core Rule Book
Supplement
Pyromancer Class
(gives access to Fire and Sun Lore)
Liquid Flame Spell
(requires Fire Lore)
Sun Lore
Searing Sunlight Spell
(requires Sun Lore)
Since the components at both ends of the loosely coupled relationship avoid direct references to the opposing end, players can become confused about what options are available to their characters. In the worst case, players are forced to scan through all available possibilities to determine their choices. This difficulty can be greatly mitigated through the use of other aids, such as tables and/or charts that explicitly list the options. As long as it is made clear that the tables do not represent all conceivable possibilities, merely those contained within a given text or supplement, the benefits of the Loose Coupling pattern remain unchanged.
Implementation Concerns
The Loose Coupling pattern introduces some complexity into a game in order to achieve its beneficial characteristics. However, it is impossible to use Loose Coupling to create relationships between all game entities, because loosely coupled components must, by necessity, directly reference some intermediary entity. So, in the interest of keeping your game complexity from ballooning out of control, it makes sense to decide up front what game elements need to be loosely coupled and which ones should use direct references.
You should pay particular attention to the entities that will serve as “intermediaries” in loosely coupled relationships. If you intend to create a single core rule book to which supplements will add material, you should do your best to include a sufficiently broad spectrum of intermediary objects in your core rule book to support the various
supplements you foresee writing. If you do not have perfect foresight, though, you can still include those intermediaries in the supplements themselves. You risk annoying customers, though, if you create additional supplements based on those new
intermediaries, because using the newest supplements demand both your core rule book and the supplements containing the intermediaries. Even so, it sometimes makes sense to purposefully segment entire game concepts into separate supplements, intermediaries and all. It all depends on how you choose to partition your game.
Samples
Suppose we want to design a game that incorporates psychic powers. We want to provide a wide range of psychic character types, each of which enjoys some niche protection from the others. So, we decide that we want to create a Loose Coupling between various psychic classes that we intend on writing and their powers. We decide to relate the classes and powers through various intermediary skills, which we are calling Psychic Disciplines. Here is an example of how a “Mentalist” class might be loosely coupled to a Psychic Power called “Mental Distraction” through the Psychic Discipline of “Mind over Mind.”
Structural Patterns (Loose Coupling) 155
Mentalist
A mentalist is a spiritualist who focuses on spirit, mind, and body. Although his efforts usually center on the discipline of his own soul and body, his powers extend to influence the minds of others as well.
Prerequisites
The character must attain 9th level in Mind over Body.
Psychic Disciplines: Mind over Mind (+4 rank), Mind over Body (+2 rank)