# HitReactionTrigger

## HitReactionTrigger Inspector

`HitReactionTrigger` is a **drop‑in component** for any projectile, melee weapon, or explosion fragment that should cause procedural reactions on impact. It handles collision detection, figures out the best hit direction, and calls `HitReactionController.React()`—so you don’t have to write a single line of glue code.

> **Add via:** *Component ▸ Hit Reactions ▸ Hit Reaction Trigger* or include it in your projectile / weapon prefab.

***

### Inspector Reference

#### 1. Which target layers should react?

| Field            | Default                | Description                                                                                                                               |
| ---------------- | ---------------------- | ----------------------------------------------------------------------------------------------------------------------------------------- |
| **React Layers** | `Everything` (bitmask) | Only collisions with these layers will forward a `React()` call. Exclude *Environment*, *Terrain*, etc., to avoid unnecessary processing. |

#### 2. Lifecycle

| Field              | Default | Description                                                                                      |
| ------------------ | ------- | ------------------------------------------------------------------------------------------------ |
| **Destroy On Hit** | ✔️      | If true, destroys the projectile GameObject after a successful hit—ideal for bullets and arrows. |
| **Destroy Delay**  | `0`     | Time (seconds) to wait before destroying. Useful when you need to play impact VFX first.         |

*(All other properties are hidden—it’s intentionally lightweight.)*

***

### How It Works

1. **OnCollisionEnter** fires.
2. Checks if the other collider’s layer is inside **React Layers**. If not → exit.
3. Tries to get a `BodyPartReactor` on `collision.transform`. If none → exit.
4. Searches parent hierarchy for a `HitReactionController`.
5. Calculates **hit direction** using fallback order:
   1. **Rigidbody velocity** (`Rigidbody.linearVelocity`).
   2. **Transform delta** from previous frame (`transform.position - _lastPos`).
   3. **Collision normal** (negated) if object didn’t move.
6. Calls `controller.React(part.name, hitDir, contactPoint)`.
7. Optionally destroys itself after **Destroy Delay**.

***

### Best Practices

* **Separate layers per team:** In PvP games, configure *PlayerProjectiles* vs. *EnemyCharacters* to avoid friendly fire reactions.
* **Melee weapons:** Place a thin *Trigger Collider* along the blade and enable `Is Trigger` on the collider. The component still works; just swap `OnCollisionEnter` for `OnTriggerEnter` if you need continuous overlap.
* **Grenade shrapnel:** Spawn multiple sphere colliders with triggers enabled; each can carry a `HitReactionTrigger` that destroys itself on the first contact.
* **Pooling systems:** Remember to reset (or disable) `Destroy On Hit` if the pooled projectile should live through multiple bounces.

***

### Extending the Trigger (Hooks)

Need custom logic (e.g., apply damage, play VFX)? Derive a subclass:

```csharp
public class DamageTrigger : HitReactionTrigger {
    public int damage = 25;

    protected override void OnReactionForwarded(GameObject target) {
        target.GetComponent<Health>()?.Take(damage);
    }
}
```

*(Override method not in base yet? Fork the script—only 60 lines!)*

***

#### Next Up

With all four components covered, jump into **Recipes & Workflows** to apply them in common gameplay scenarios.


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