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| − | The bonus system of VCMI is a set of mechanisms that make handling of different bonuses for heroes, towns, players and units easier. The system consists of a set of nodes representing objects that can be a source or a subject of a bonus and two directed acyclic graphs (DAGs) representing inheritance and propagation of bonuses. Core of bonus system is defined in HeroBonus.h file.
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| − | Here is a brief sketch of the system (black arrows indicate the direction of inheritance and red arrows the direction of propagation):
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| − | [[File:Bonus system.png|center]]
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| − | == Propagation and inheritance ==
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| − | Each bonus originates from some node in the bonus system, and may have propagator and limiter objects attached to it. Bonuses are shared around as follows:
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| − | # Bonuses with propagator are propagated to "matching" descendants in the red DAG - which descendants match is determined by the propagator. Bonuses without a propagator will not be propagated.
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| − | # Bonuses without limiters are inherited by all descendants in the black DAG. If limiters are present, they can restrict inheritance to certain nodes.
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| − | Inheritance is the default means of sharing bonuses. A typical example is an artefact granting a bonus to attack/defense stat, which is inherited by the hero wearing it, and then by creatures in the hero's army.
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| − | A common limiter is by creature - e.g. the hero Eric has a specialty that grants bonuses to attack, defense and speed, but only to griffins.
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| − | Propagation is used when bonuses need to be shared in a different direction than the black DAG for inheritance. E.g. Magi and Archmagi on the battlefield reduce the cost of spells for the controlling hero.
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| − | === Technical Details ===
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| − | * Propagation is done by copying bonuses to the target nodes. This happens when bonuses are added.
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| − | * Inheritance is done on-the-fly when needed, by traversing the black DAG. Results are cached to improve performance.
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| − | * Whenever a node changes (e.g. bonus added), a global counter gets increased which is used to check whether cached results are still current.
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| − | == Operations on the graph ==
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| − | There are two basic types of operations that can be performed on the graph:
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| − | === Adding a new node ===
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| − | When node is attached to a new black parent <ref>the only possibility -> adding parent is the same as adding a child to it</ref>, the propagation system is triggered and works as follows:
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| − | : For the attached node and its all red ancestors
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| − | :: For every bonus
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| − | ::: Call propagator giving the new descendant -> then attach appropriately bonuses to the red descendant of attached node (or the node itself).
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| − | E.g. when a hero equips an artifact, the hero gets attached to the artifact to inherit its bonuses.
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| − | === Deleting an existing node ===
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| − | Analogically to the adding a new node, just remove propagated bonuses instead of adding them. Then update the hierarchy.
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| − | E.g. when a hero removes an artifact, the hero (which became a child of the artifact when equipping it) is removed from it.
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| − | Note that only ''propagated'' bonuses need to be handled when nodes are added or removed. ''Inheritance'' is done on-the-fly and thus automatic.
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| − | == Limiters ==
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| − | If multiple limiters are specified for a bonus, a child inherits the bonus only if all limiters say that it should.
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| − | So e.g. a list of multiple creature type limiters (with different creatures) would ensure that no creature inherits the bonus. In such a case, the solution is to use one bonus per creature.
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| − | == Propagators ==
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| − | == Calculating the total value of a bonus ==
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| − | *[[List of bonus value types]]
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| − | {{Bonuses}}
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| − | == Automatic generation of bonus description ==
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| − | TBD
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| − | =Notes=
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| − | <references/>
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