Gamedev Hub

Hysteresis (State Stability)

Hysteresis is the dependence of the state of a system on its history. In game development, it is the primary tool used to prevent “fluttering”—the annoying bug where a system rapidly toggles between two states due to minor fluctuations.

1. The “Fluttering” Problem

Imagine an AI that chases the player if they are closer than 10 units.

• Distance = 10.01: AI Idles.
• Distance = 9.99: AI Chases.

If the player stands right on that 10-unit boundary, the AI will jitter between Idle and Chase every frame, causing broken animations and logic loops.

2. The Solution: Dual Thresholds

Hysteresis solves this by using different values for entering and exiting a state. This creates a “buffer zone” (or deadband).

• Condition to Enter Chase: Distance < 10m.
• Condition to Exit Chase: Distance > 13m.

Now, once the AI starts chasing, the player has to move significantly further away (the extra 3m) for the AI to give up. This ensures the behavior is stable and intentional.

3. Implementation (C# Example)

bool isChasing = false;

void Update() {
    float dist = Vector3.Distance(player.position, transform.position);

    if (!isChasing && dist < 10f) {
        isChasing = true;
        StartChasing();
    } 
    else if (isChasing && dist > 13f) {
        isChasing = false;
        ReturnToPatrol();
    }
}

4. Common Use Cases

• AI Behavior: Switching between aggressive and defensive modes.
• Physics Triggers: Prevents a player from “rapidly entering/exiting” a zone if they stand on the edge.
• Audio: Ducking music volume based on gameplay intensity.
• LOD (Level of Detail): Preventing a mesh from rapidly swapping between High and Low detail versions.

5. Summary

Hysteresis makes your game feel “confident.” It ensures that once a decision is made, it sticks until a clear threshold is crossed in the opposite direction.