Implementing Attribute-Based Stat Dependencies

In this lesson, you will learn how to automate character stat updates by using the PostGameplayEffectExecute function to handle attribute dependencies.

The Logic of Dependency

In a robust Gameplay Ability System (GAS), changing one attribute often requires a ripple effect on others. For example, if your character takes "Damage," you don't just want a raw number floating in a buffer; you want that value to instantly subtract from "Health."

While PreAttributeChange is perfect for clamping values (like keeping Health between 0 and MaxHealth), PostGameplayEffectExecute is the appropriate place to handle the side effects of an attribute change. This function triggers only after a GameplayEffect has successfully modified an attribute, making it the ideal spot to perform math-heavy dependencies.

Implementation Pattern

When PostGameplayEffectExecute is called, you receive a FGameplayEffectModCallbackData struct. You should inspect the EvaluatedData.Attribute to see which stat changed, then apply your logic accordingly.

void UMyAttributeSet::PostGameplayEffectExecute(const FGameplayEffectModCallbackData& Data)
{
    Super::PostGameplayEffectExecute(Data);

    if (Data.EvaluatedData.Attribute == GetDamageAttribute())
    {
        // 1. Capture the incoming damage value
        float LocalDamage = GetDamage();
        SetDamage(0.0f); // Reset damage so it doesn't persist

        if (LocalDamage > 0.0f)
        {
            // 2. Apply dependency: Subtract from Health
            float NewHealth = GetHealth() - LocalDamage;
            SetHealth(FMath::Clamp(NewHealth, 0.0f, GetMaxHealth()));
        }
    }
}

Why Use This Instead of Abilities?

You might wonder why we don't just use a Gameplay Ability to subtract health. Using PostGameplayEffectExecute ensures that your stat dependency is data-driven and guaranteed. Regardless of how the damage was dealt (a sword swing, a poison trap, or a falling rock), the Attribute Set itself manages the math. This centralizes your balancing logic, ensuring your game rules remain consistent across all gameplay systems without requiring manual hookups in every individual ability.

Key Takeaway: Use PostGameplayEffectExecute within your AttributeSet to trigger secondary attribute updates, ensuring that stat dependencies are handled automatically and consistently whenever a Gameplay Effect modifies a core value.