# Advanced

## Advanced

Deep‑dive mechanics, edge‑case tweaks, and performance guidelines for shipping projects.

***

### 6.1 Axis Locks & Directional Hits

#### Concept

*Axis locks* zero‑out specific axes **after** the random / directional offset has been chosen. Use them to guarantee that a character never rolls upside‑down or that a turret stays level.

#### Workflow

1. In your `ReactionProfile`, set **Rotation Axis Mask** or **Translation Axis Mask** (values 0–1).
2. Toggle **Use Local Hit Direction** in `ReactionProfile`to decide whether the mask is applied in bone‑local space (common) or world space (rare).
3. Combine with **Use Contact‑Point Direction** to switch between *origin → bone* vectors and projectile velocity.

> **Tip:** For top‑down games, lock the Y rotation (pitch) so hits only spin characters on the Z‑axis.

***

### 6.2 Follow‑Through Chains

#### Goal

Create natural secondary motion—gear, hair, or child bones lag behind the main impact.

#### Setup

1. On the **primary** `BodyPartReactor` (e.g., Chest) add followers:
   * Drag the **Head** bone into **Follow Objects** list.
   * **Follow Rot Weight** ≈ 0.25, **Follow Pos Weight** ≈ 0.1.
2. On Head you can still keep its own reactor for direct hits.

#### Best Practices

* Chain order: *torso → shoulders → head → props*.
* Keep weights < 0.5 to avoid double‑moving (follower + self‑reactor).

***

### 6.3 Slow‑Blend for Heavy Impacts

Enable **Slow Blend Mode** to multiply the profile’s *Blend‑In Speed* by **Slow Blend Multiplier** (0–1). This makes the reaction appear *heavier* without changing strength.

```csharp
if (impactForce > 120f)
    chestReactor.slowBlendMode = true;
else
    chestReactor.slowBlendMode = false;
```

***

### 6.4 Performance & GC

| Concern            | Recommendation                                                                                                            |
| ------------------ | ------------------------------------------------------------------------------------------------------------------------- |
| **Per‑frame math** | All trig done on 3–10 bones → sub‑0.1 ms on modern CPUs.                                                                  |
| **Garbage**        | Allocation‑free. Randoms use `UnityEngine.Random.Range` (no boxing).                                                      |
| **Physics cost**   | System itself adds none; use primitive colliders and pooled projectiles to keep PhysX cheap.                              |
| **Burst / DOTS**   | Not required—system is already CPU‑light, but you can port `BodyPartReactor.Update()` to Burst if profiling shows spikes. |

***

### 6.5 Networking / Determinism

Because the system is pure math on floats and doesn’t sample animation curves at runtime, reactions can be reproduced **deterministically** across clients.

1. Sync only these parameters on hit:
   * `partName` (string or enum)
   * `hitDirection` (normalized Vector3, 16 bits per component works)
   * `hitPoint` (optional—needed only if profile uses contact‑point direction)
2. On each client call `React()` with the same values.
3. Ensure all clients load identical **ReactionProfile** assets (GUID match). Prefer AssetBundles or Addressables to avoid mismatches.

> **Rollback netcode:** Because reactions are purely cosmetic, you can skip rewinding bones—simply apply the hit on the presentation frame.

***

### 6.6 Editor Automation & Gizmos

* Coming in a future update: **Bone Auto‑Setup Wizard** that scans your rig and adds reactors to common bones with a single click.
* Enable **Gizmos** to visualize hit directions and axis masks while tuning profiles in Play Mode.


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