Ideas for Stendhal/Effects

Players, creatures and other entities can be temporarily under the influence of certain effects. For example a player will constantly heal at a certain rate, because he is already eating. Or a creature could be slowed down, because a player has casted a kind of freeze spell to it.

To fully support effects client and server side, we first need to consider, which properties are needed at which side and for which purpose. We also need to think about how an effect is applied when an effect of the same kind is already there, i.e. a player eats more than one meat.

Effect	Client Side	Server Side
heal over time	name, type, world effect	amount, frequency, how often?, inactive
damage over time	name, type, world effect	amount, frequency, how often?, source, inactive
buff / debuff	name, type, value affected, world effect	inactive
cooldown	name, type, affected, world effect	...
outfit	name, type, world effect	...

TODO: class diagram

TODO: sequence diagram

Description

The following information on status ailments and enhancements commonly found in traditional RPGs. Here can be found descriptions and some ways to possibly implement a versatile status effect system into Stendhal.

Status can temporarily affect a character's ability to do certain functions or alter stats such as HP, mana, defense, attack, etc. Status is usually inflicted through item usage, spells or physical attacks. Occasionally characters receive a status through game progression, such as speaking with an NPC or an event is triggered. Effects are generally nullified by the use of items or magic spells. Some effects, such as "sleep", are often alternatively cured by the character receiving a physical attack. Resistances to negative statuses can be acquired through special actions, such as spells or using items, or by equipping imbued items.

Distinction from Elemental

Status is distinct from elemental enhancements, though elemental resistance itself could be considered a status. For example, an entity could have a status effect called "warm" that protects against ice attacks. The major distinction is that status infliction is not intended to have a direct effect on the strength of the attack itself, but rather to cause a condition to enhance or impede the target's abilities.

Elemental attacks and resistances

Elemental attacks are used to compound the strength of a physical or magic attacks against enemies with a weak resistance to said element. If the target has a strong resistance to the element then the strength of the attack is reduced to below the normal range. If the target has a weakness to a particular elemental attack, then it does greater damage than a normal attack.

Status Ailments

A status ailment is a negative effect on the character. Effects can reduce/impede the characters ability to do an action or cause a temporary reduction in stats.

List of common ailments used in RPG games

Common Names	Common Functions	Suggested for Stendhal
blind, dark, darkness	player's attack accuracy is reduced	same
burn, burning	• character gradually, or each turn, loses HP • lowered physical attack	same
confuse, confusion, confused, muddle	character is uncontrollable and acts randomly	Implemented: walking is limited to using directional arrows inverted (as poison is currently)
death, instant death, KO	character is instantly KO'd	not recommended
dizzy	physical attack evasion is reduced	same
doom, condemned	character is KO'd after a predetermined period of time if ailment isn't removed	not recommended
fear	attack and defense are weakened	same
freeze, freezing, frozen	character can not move to a new position	same
oil	character is more susceptible to fire-based attacks	same
paralysis, paralized	usually disables a certain ability temporarily	cannot physically attack for a time or until cured
poison	character loses HP over time	Implemented
shock	character cannot act	Implemented: while walking character stops after specified number of steps (player must resume walking)
silence, mute	character is unable to cast magic spells	same
sleep	character is unable to act for a predetermined amount of time or until awoken	same
slow, heavy	character's attack is delayed	same or slowed walking
stone, petrified	character is unable to act until status removed	not recommended
tiny, shrink, toad, frog, imp	• significantly decreases attack and defense • character's sprite transformed to correspond with affliction • commands become limited sometimes reduced to only physical attacks	not recommended
weaken	temporarily reduces character's max HP	same
zombie	• healing items have the opposite effect • causes immunity to poison in some games • character is uncontrollable	implemented: slowed walking

Some of the status ailments mentioned above are "not recommended" because they are too risky for single character games. However, the risk could be reduced if there was a system to revive KO'd characters. Included in the system the player should have the option to wait to be revived/cured or teleport to the respawn point, thus sacrificing a greater amount of XP.

Status Enhancements

Status enhancements give the character a certain "buffer" and can increase specific abilities or stats.

List of common enhancement statuses in RPG games

Effect Name	Common Function	Suggested for Stendhal
autoraise	character is instantly revived, one time, on KO	same
eat, eating	restore HP over time	Implemented
focus, concentrate	increases power or accuracy of next physical or magical attack	same
haste	decreases wait time between attacks	same or quickened walking
protect	increases defense	same
reflect	reflects magic back onto the caster	same
regen, regenerate	restore HP over time	same
shell	increases magic defense	same
special	usually a state that allows the player to take special actions not normally available	none

Mixed Effects

Mixed status effects generally give the character some kind of enhancement but at the loss of another function.

List of effects

Effect Name	Common Function	Suggested for Stendhal
berserk	physical attack strength is greatly increased but control over character is lost	not recommended
focus, concentrate	Same as above but player loses a turn or turn is slowed	none

Possible Implementation

Needed Changes To Entities

Some spell like Freeze or Weaken Creature temporarily affect specific attributes of an entity. As it is reasonable not to change the attributes themselves, it is necessary to add attribute modifiers to an entity.

A first approach would store the modifier factors in a class and the entity classes compute an attribute's value by summing up all modifiers and applying it to the actual attribute's value. To reflect the temporal nature of a modifier it is capable of determining its validity based on a timestamp within the method isValid. This approach has the obvious disadvantage, that within GuidedEntity the modifiers for not existing attributes are available.

The second approach uses an additional layer of indirection to hide the modifiers for not existing attributes. On each level of the entity inheritance hierarchy is a specific modifier defined that is called to calculate the modified value.

The TurnNotifier is used to clean up expired modifiers. As a modifier is able to distinguish between being valid and not, it is not necessary, that this clean up helper runs every second or even more frequently.

• Attribute modifiers variants
• 

  Simple modifier

• 

  Modifier concept hiding the "full" modifiers

The second option has been implemented. It has been removed later due to compatibility reasons.

Player Resistance & Status

• Player has a keyed slot (status_resistance(s)) where status can be added/removed.
  • "key" is status name and "value" is the resistance value (0-100 or 0.0-1.0).

• Creature has keyed status slot (status_attack) for attacks.
  • "key" is status name and "value" is probability of status being applied to player.

• Player's resistance value is applied to creature's status probability during attack.

• Player has a second keyed slot (status) that carries the current statuses of the player.
  • "key" is status name and "value" is duration of status.
  • Each turn the key is checked and resulting action applied.

• Statuses induced by actions, such as spells, items, etc., should be saved to the database so they are not lost at logout.

Creature Resistance & Status

• The same can be applied reversed. Players can have "attack" slots and creatures "resistance".
  • Allows players to inflict status effects on creatures.

Display Indicators

These are some ideas for status indicators:

Name	Overlay Symbol	Example
poison	green bubbles floating up from the head
blind	black smoke floating in front of character's eyes
zombie	sprite colors become pale greenish
shock	electric-like images at the side of character
confused	question mark (or stars) near or circling character's head