# Ep.12 — Bone Mirror

https://youtu.be/dygdHA5scrQ?si=2bL6WV1jkEIouzTq

## Overview

Used to **copy additional bones** made on one side to the **opposite side**.  
Explains how to use BipedPlus **Edit Utils → Bone Mirror** instead of the 3ds Max **default Bone Mirror**, which tends to produce misaligned results.

> **Bone Mirror** = **bone placement/creation** stage. Left↔Right **pose** copying is done in **Ani Utils** (Ep.9·14).

## Max Default Bone Mirror — What's Inconvenient

- Mirrors based on the selected bone's **pivot (origin)**, which often results in **misalignment** rather than a true reflection across the **character's center (X=0)**.
- Fixing it requires **manually calculating world X coordinates** — which is tedious.

## BipedPlus Bone Mirror — How to Use

Open **Bone Mirror** in the **Edit Utils** area.

### Options (simplified)

| Option | Meaning |
|------|------|
| **Mirror Plane** | **Mirror plane** — usually the **YZ plane** (= left↔right flip from the **character's front**) |
| **X Flip** | **Flip** along the **X axis** |
| **Headless Axis** | Which axis to rotate around during mirror — usually **Z** for Biped. **Keep default** recommended |

```
        │ Mirror Plane (YZ)
   Left │ Right
   ────┼────
        │
```

### Steps

1. **Select all bones** that will be the mirror source (usually the **Left** side chain).
2. **Hierarchy** → **Parent** — to preserve the **child bone structure** (may need to lock Parent manually at first).
3. Execute **Mirror**.
4. Verify that **Left / Right** names changed **per convention**.
5. Move them and test that the **Z-axis rotation** etc. is **symmetrical**.

## When to Use

- When creating **custom Hair/prop bones** on one side (like Ep.11) and **cloning to the opposite side**.
- For **front-based symmetry** instead of the Max default Mirror.

## Notes

- If **Hierarchy Parent** is not set correctly, the **parent may detach** or the tree can break.
- **Do not casually change Headless Axis**.
- **Rigging Info Update** after mirroring (Ep.10).