# Quaternius modular parts

Build inputs for outfit, hair and accessory variety. Committed like the three whole-body
sources, so `build` works from a fresh checkout without the upstream pack.

## Where they come from

The upstream *Ultimate Modular Characters* pack is distributed as a Google Drive folder
(<https://drive.google.com/drive/folders/1USAAquX2JJWuA2m6zol0KUkFe3UkZ8zX>, CC0 1.0). It cannot be
fetched reproducibly by a script, so the owner downloads it **once** into the gitignored
`tmp/quaternius-intake/`. Everything after that is scripted:

```sh
python3 tools/quaternius_parts.py inventory --dir tmp/quaternius-intake
python3 tools/quaternius_parts.py extract \
  --file tmp/quaternius-intake/<file>.glb --mesh <mesh> --part <part>
python3 tools/quaternius_parts.py verify --dir assets/models/blender_src/quaternius/parts
```

`inventory` and `verify` run outside Blender; `extract` needs Blender, because it rewrites the skin.
The pack itself is never committed — only the parts that are actually used, each with its SHA-256
recorded here and in `CREDITS.md`.

## Part contract

A part is **one skinned mesh on the 62-joint rig**:

- one mesh object, parented to the rig's armature, carrying `JOINTS_0`/`WEIGHTS_0`;
- the standard joint names (`Hips`, `Chest`, `Head`, `UpperArm.L`, …). The rig check in
  `quaternius_parts.py verify` fails a part that is missing any of them, because
  `NpcAvatar` maps those bones;
- materials named after a contract slot (`skin`, `cloth`, `pants`, `hair`, `accessory`) so the
  runtime tint reaches them, or a fixed-colour detail name that is deliberately not tinted;
- triangles counted against the character budget: base body plus every joined part must stay
  inside 24,000 triangles and 24,000 glTF vertices.

The builder drops the part's own armature when it joins the mesh onto a base body, because the base
already owns the skeleton and two armatures would duplicate every bone. Weights survive the join
because Blender merges vertex groups by name.

## Assigning parts to a role

```python
"npc_vest": {"layer": "vest", "base": "worker", "parts": ["hivis_vest"], ...}
```

`build` joins those parts after the body join and before the material slot map, so the part's
materials go through the same slot mapping as the base. The T-pose cache is keyed on the part list.

## Kept parts

| Part | Source file | SHA-256 | Tris |
| --- | --- | --- | --- |
| _(none yet — the pack has not been intaken)_ | | | |