Gameplay Effects

Gameplay Effects are reponsible for applying attribute modifications. The built-in Gameplay Effect caters for numerous scenarios, such as damage-over-time effects, temporary buffs, permanent buffs, etc. These should generally be sufficient for nearly all use cases.

We'll create a simple Gameplay Effect that applies a temporary buff that increases a character's current health by 1 for 5 seconds, and then reverts it. For this exercise, you should have an Attribute representing health ready to go.

Creating a Gameplay Effect

Begin by creating a new Gameplay Effect asset by going to Asset | Create | Gameplay Ability System | Gameplay Effect Definition, and give it a useful name.

Define the properties of the Gameplay Effect:

Gameplay Effect

The Duration Policy determines how long the Gameplay Effect is applied for. Available options are: Instant, Infinite, Has Duration.

An Instant Gameplay Effect is applied and then removed the same frame. This is used to capture one-off instances of attribute changes, such as taking damage. Infinite Gameplay Effects remain on the character indefinitely, until removed through interaction with other Gameplay Effects or Abilities. These are useful for temporary buffs that don't expire, or expire due to some condition other than time, such as bonus armour due to equipping armour, where the bonus is lost once the armour is unequipped. Has Duration Gameplay Effects remain on the character until their timer expires, or due to interaction with other Gameplay Effects or Abilities. The duration of the timer is controlled through the Duration Modifier and Duration Multiplier properties. Examples of Has Duration Gameplay Effects could include a temporary strength buff that lasts for 5 seconds.

The Duration Modifier and Duration Multiplier is used if the Duration Policy of the Gameplay Effect is Has Duration. It is ignored for Instant and Infinite Duration Policy.

Duration Modifier

The Duration Modifier calculates the base duration of the Gameplay Effect, using an asset derived from ModifierMagnitudeScriptableObject to do the calculation by calling its CalculateMagnitude method. For this example, we'll use the Simple Float Modifier Magnitude (included in the package), which we can configure to always provide a value of 1, allowing us to use the Duration Multiplier property to determine how long the effect should last.

Create the Simple Float Modifier Magnitude asset by going to Asset | Create | Gameplay Ability System | Gameplay Effect | Modifier Magnitude | Simple Float, and set the Scaling Function curve to a straight horizontal line: y = 1:

.

Assign this new asset to the Duration Modifier of the Gameplay Effect, and set the Duration Multiplier to 5 so the effect lasts for 5 seconds.

Attribute Modifiers

The attribute modifications in Attribute Modifiers take place when the Gameplay Effect is applied. Each Attribute Modifier needs to define:

1. The Attribute to modify
2. The mathematic Operation that takes place - Add, Multiple, or Override
3. The Modifier Magnitude, same as that defined for the Duration, but here it is used to calculate the magnitude of the Attribute modification.
4. The Multplier, which multiplies the result from the Modifier Magnitude.

For this sample, select any suitable Attribute already created, such as health, and select the Simple Float Modifier Magnitude created earlier, so we can use the Multiplier property to control the magnitude. Set the Multiplier to 1, and the Operation to Add. This will increase the target Attribute by 1 while the Gameplay Effect is active.

Gameplay Effect Tags

For this example, we'll define an Asset Tag only. Create a new Gameplay Tag via the Assets | Create | Gameplay Ability System | Tag menu, and call it Stats.Health.Buff. We won't worry about setting up it's ancestors.

Assign this new tag to the Asset Tag of our new Gameplay Effect.

Activating the Gameplay Effect

Usually, a Gameplay Effect is activated using an Ability, but for this example, you'll manually apply it using a method of your choice (e.g. a GUI button, or an input event).

Applying a Gameplay Effect is a two-step process:

1. Create a Gameplay Effect Spec, which is a unique instance of a Gameplay Effect.
2. Apply the Gameplay Effect Spec to a character

Assuming the AbilitySystemCharacter is called abilitySystemCharacter, and the Gameplay Effect is gameplayEffect:

// Variables required:
// abilitySystemCharacter - reference to the Ability System Character component that is performing the action
// gameplayEffect - reference to the created Gameplay Effect Scriptable Object asset
GameplayEffectSpec spec = abilitySystemCharacter.MakeOutgoingSpec(gameplayEffect);
abilitySystemCharacter.ApplyGameplayEffectSpecToSelf(spec);

When this code is executed, the Ability System Character will have their health reduced by 1 for 5 seconds, and then it will revert back, and will also have the Stats.Health.Buff Gameplay Tag applied while the Gameplay Effect is active. Since we have not added any other Gameplay Effect conditions (using Gameplay Tags), this Gameplay Effect can be applied endlessly (with an instance of Stats.Health.Buff for each active application). If we wished for only 1 instance of this Gameplay Effect to be applied at any given time, we could add the Stats.Health.Buff Gameplay Tag to the Granted Tags list and the Application Required Tags / Ignore Tags list.