Stacking¶

Stacking controls what happens when the same Gameplay Effect class is applied more than once. Does it create a separate instance each time? Does it increment a counter? Does it refresh the duration? The stacking configuration determines all of this.

Stacking Types¶

The EGameplayEffectStackingType enum defines three modes:

None (No Stacking)¶

EGameplayEffectStackingType::None

Each application creates a separate independent instance in the Active GE Container. If you apply the same buff three times, you get three distinct active effects, each with its own duration timer and modifier contribution.

This is the default and the simplest. It's appropriate when you want effects to be fully independent — for example, separate DoT effects from different sources that all tick independently.

AggregateBySource (Stack Per Source)¶

EGameplayEffectStackingType::AggregateBySource

Multiple applications of the same GE from the same source are combined into a single instance with a stack count. Applications from different sources create separate instances.

Example: Player A applies Poison to a boss. Applying Poison again from Player A increments the stack. Player B also applying Poison creates a separate stack. The boss has two Poison instances — one from each source — each with their own stack count.

AggregateByTarget (Stack Per Target)¶

EGameplayEffectStackingType::AggregateByTarget

Multiple applications of the same GE on the same target are combined into a single instance, regardless of who applied it. Only one instance ever exists per target.

Example: Anyone applying Sunder Armor to a boss increments the same stack count. There's only ever one Sunder Armor instance on the boss, no matter how many different players are applying it.

Stack Limit¶

StackLimitCount sets the maximum number of stacks. A value of 0 or -1 means no limit — stacks can grow indefinitely.

When an application would push the stack count above the limit, overflow handling kicks in (see below).

Stacking Policies¶

When a stack is successfully added (not overflowing), several policies control what happens:

Duration Refresh Policy¶

EGameplayEffectStackingDurationPolicy controls what happens to the duration timer when a new stack is added:

Period Reset Policy¶

EGameplayEffectStackingPeriodPolicy controls what happens to the periodic timer:

Stack Expiration Policy¶

EGameplayEffectStackingExpirationPolicy controls what happens when the duration timer expires:

bFactorInStackCount¶

When true, modifier magnitudes are automatically multiplied by the current stack count. When false, the stack count has no effect on magnitudes (you would handle scaling manually, perhaps in an Execution Calculation).

Overflow¶

When an application attempts to add a stack beyond StackLimitCount:

1. OverflowEffects — These GEs are applied to the target when overflow occurs. This fires whether or not the overflow application itself succeeds.

2. bDenyOverflowApplication — If true, the overflowing application is rejected. The duration and context are not refreshed. If false, the application "succeeds" (duration/context may refresh depending on policies) but the stack count stays at the limit.

3. bClearStackOnOverflow — If true (and bDenyOverflowApplication is also true), the entire stack is cleared on overflow. This creates a "burst" pattern: stacks build up to the limit, the next application clears them all and triggers an OverflowEffect.

Practical Examples¶

Stacking DoT (Poison Stacks)¶

A poison that stacks up to 5 times, with damage scaling per stack:

The modifier does -5 HP per tick. At 3 stacks, it does -15 per tick. Reapplying refreshes the 10s timer. Maxes at 5 stacks.

Non-Stacking Buff That Refreshes¶

A speed boost that doesn't stack but refreshes its duration when reapplied:

This is a common pattern. Effectively, you get one instance of the buff that refreshes its timer every time it's reapplied. Using stacking with a limit of 1 is the standard way to implement "refresh on reapply" in GAS.

Stacking Armor Debuff (Sunder)¶

An armor debuff that stacks per source, decays one stack at a time:

Each source can apply up to 3 stacks. When the timer expires, one stack drops and the timer resets. The debuff gradually fades rather than disappearing all at once.

Burst Pattern (Combo Finisher)¶

A charge mechanic where stacks build up, and on overflow the accumulated energy releases:

Each hit adds a stack. On the 5^th hit (overflow), all stacks are cleared and GE_ComboFinisher is applied. The finisher GE can read how many stacks were cleared if needed.

Tips¶