Papay-Shooter/.claude/skills/character-pipeline/SKILL.md

---
name: character-pipeline
description: Import, rig, stylize and animate an anime-styled character into Papaya-Shooter as a selectable skin — keeping the model's own skeleton, artist weights and separate body/cloth/hair meshes, with cloth and hair driven by the spring solver. Use when adding a new playable character, re-importing an existing one, debugging skinning/cloth/hair/animation problems on a character, or changing the cel-shaded look. Triggers on "add a character", "import a skin", "new playable model", "skirt clipping", "hair flailing", "T-posing", "character looks squashed".
---

# Character pipeline

Turns a source model into a playable, cel-shaded, cloth-simulated character skin.

The whole design follows one principle, which is also what the Hoyoverse-class
anime pipelines (Genshin / Star Rail / Zenless Zone Zero) are built on:

> **The character is not one object. It is a body, a set of garments, and hair —
> authored separately, rigged separately, and moved by different systems.**
> The body is skinned and animated. The garments and hair are bone chains that
> the animation never touches; physics moves them. Keeping those separate is
> what makes the result read as an anime character instead of a mannequin in a
> painted-on costume.

Everything below exists to protect that separation.

## The one rule

**If a model arrives with a skeleton, that skeleton ships.** Its bones, its
artist-painted weights, its per-part meshes and its skirt/hair chains all
survive. Only the ANIMATION is moved onto it.

The old route (`strip_rig.py` → `autorig.py` → `merge_animations.py`) solved a
bone-*naming* problem by destroying the asset — 18 meshes became 1, 21 skirt
bones and ~50 hair bones became 0, and 16% of vertices ended up pulled by both
legs. `tools/rig_map.py` solves naming properly now. **Never reach for
`strip_rig.py` or `--rebind`** unless the model genuinely has no skeleton at all.

## Doing it

```bash
# From an already-rigged local model (the normal case)
python tools/pipeline.py --input assets/characters/incoming/<name>.glb --name <name> --rigged

# From a Sketchfab UID (needs SKETCHFAB_API_TOKEN)
python tools/pipeline.py --uid <uid> --name <name>

# From an unrigged mesh — auto-rigs, and accepts the quality loss
python tools/pipeline.py --input <mesh.glb> --name <name>

# Rigged (or auto-rigged) but with NO skirt/hair bones — grow them, or the
# costume is welded solid and the spring solver has nothing to simulate
python tools/pipeline.py --input <model.glb> --name <name> --rigged --grow-cloth
```

Then, once, so Godot sees the new files:

```bash
godot --headless --path . --import
```

The result is `assets/characters/skins/<name>.glb` + `<name>.rig.json`, and a
registry entry in `skins.json` that `SkinManager` picks up with no code change.

Blender is required (`BLENDER_PATH`, or auto-found under
`C:\Program Files\Blender Foundation`). Godot lives at
`C:\Program Files\Godot\Godot_v4.7-stable_win64_console.exe`.

## The stages, and what each one protects

| Stage | Where | Protects |
|---|---|---|
| Fix unlit/emissive materials | `tools/gltf_fix.py` | Textures surviving import at all |
| Resolve bone ROLES, not names | `tools/rig_map.py` | The model's own skeleton |
| Rebuild parenting | `retarget.py::rebuild_hierarchy` | Limbs/cloth following the hips |
| Grow cloth chains (opt-in) | `tools/cloth_bones.py` | A costume that has no bones being able to move at all |
| Subdivide cloth panels | `retarget.py::subdivide_cloth_panels` | A skirt being able to bend at all |
| Retarget clips as rest-relative deltas | `retarget.py::retarget_clip` | Limbs not being twisted by foreign bone roll |
| Leave cosmetic bones unkeyed | `export_optimize_animation_keep_anim_armature=False` | Physics owning the cloth |
| Classify every SURFACE | `tools/surface_map.py` | The runtime never re-guessing what a surface is |
| Write the rig sidecar | `retarget.py::describe_rig` | The runtime never re-guessing anatomy |
| Cel look, per surface class | `LevelMaterials.apply_character_look` | Hair not reading as a solid dark cap |
| Cloth + hair | `characters/spring_bones.gd` | Clothes reading as clothes |
| Per-character judgement calls | `characters/tuning_store.gd` | Art direction not becoming another constant |

## The surface table

The sidecar carries a `surfaces` list saying what each mesh surface IS — `body`,
`cloth`, `hair`, `accessory`, or `linework` (the model's own ink shell, which is
not a surface of the character at all). It is keyed on the MATERIAL name, because
every character in this game arrives with its meshes called `Object_7` through
`Object_32` while material names survive the glTF round trip intact.

`SkinSurfaces` reads it and `apply_character_look` acts on it: hair takes a much
thinner outline than the body, cloth a heavier one and a crisper terminator,
accessories the heaviest. `SkinnedPlayerModel.surfaces_of(cls)` answers the
question for anything else that needs it.

Backfill a character that predates it, without re-importing:

```bash
blender --background --python tools/surface_map.py -- \
    assets/characters/skins/<name>.glb
```

New imports get it from `describe_rig`, built from the same chains the solver
uses, so the surface table and the cloth solver can never disagree about which
bones are a skirt.

## Per-character judgement

Anything derivable from the skeleton is derived. What is left is genuinely an
artist's call, and it lives in layered JSON rather than in a constant:

| File | Scope | Class |
|---|---|---|
| `assets/characters/weapon_holds.json` | character + weapon | `WeaponHoldTuning` |
| `assets/characters/rig_anchors.json` | character | `RigAnchors` |

Both layer `defaults` → `skins.<skin>._all` → `skins.<skin>.<subject>` through
`TuningStore`. An absent file means "use what the code derives", so nothing here
is required for the game to run. Adding a knob is adding a row to a `KNOBS` spec
table — the lab builds its whole UI from those.

`RigAnchors` is where "the grip sits here in the palm" lives. A hand bone's
origin is the WRIST; how far down the palm a grip belongs depends on the
character's hand and cannot be derived. It defaults to identity, and identity is
exactly the derived mount. Do **not** put a fixed rotation on the weapon mount
instead — a bone attachment is expressed in the BONE's axes, no two rigs agree on
those, and that constant is why the hand mount points were once wrong on every
character.

## The rig lab

```bash
godot --path . res://debug/rig_lab.tscn
```

Pick a character, a weapon, a pose or a single clip. Drag sliders for the HOLD
(character + weapon) and the ANCHORS (character), and save. Click a surface class
to isolate it — that is how the classifier gets checked: click `hair` and
anything else still standing was misclassified.

## Read before you touch anything

Load the reference that matches what you are doing. They are short and each one
is a list of things that cost a debugging cycle to learn.

- **`references/failure-modes.md`** — **read this first.** Seven characters
  shipped "All checks passed" and four were visibly broken. What each failure
  was, why the suite missed it, and the rule that generalises it to any model.
- **`references/separation.md`** — body vs. garments vs. hair: what must stay
  separate, how cloth chains are detected and classed, why cloth is never
  skinned to a leg, and the ZZZ-convention mapping.
- **`references/growing-cloth-bones.md`** — what to do when the source has no
  skirt or hair bones: how the chains are fitted to the geometry and re-weighted.
- **`references/rigging.md`** — role resolution, hierarchy rebuild, cloth panel
  subdivision, twist bones, joint helpers, the retarget maths.
- **`references/cloth-and-hair.md`** — the position-based spring solver, its
  colliders, per-class tuning, collision hulls, LOD and cost.
- **`references/stylization.md`** — cel shading, outlines, the imported
  line-work trap, eyes, materials.
- **`references/verification.md`** — every measuring tool, what each one
  actually measures, and the pose-reading trap that invalidated all of them
  once. **Read this before trusting any measurement.**

## Non-negotiables

1. **Never join meshes.** Per-part meshes are how body, cloth and hair stay
   separable — for materials, for the outline pass, and for the cloth solver's
   hull extraction.
2. **Never key cosmetic bones.** If a clip has tracks on skirt/hair bones, the
   AnimationPlayer overwrites the solver every frame and the cloth goes rigid.
3. **Never skin cloth to a leg.** A vertex weighted 0.9 to a thigh cannot be
   moved by its own cloth bone, so the solver loses the authority to push it out
   of that thigh — and the leg still overtakes it. There was a
   `bind_cloth_to_legs()`; it is deleted, and the note above its grave in
   `retarget.py` says why.
4. **Never run `SkinLegRepair` on authored weights.** It snaps weights and
   deletes triangles. It exists only to undo auto-rigging. It is gated on
   `weights_authored`, which is MEASURED, not assumed.
5. **Measure from inside the modifier pass.** See `references/verification.md`.
6. **Never assume an axis.** Up, forward and scale are all measurable from the
   skeleton. Assuming +Z is up scaled three characters 7x and left them on their
   backs — and the height check passed on every one of them, because the number
   being normalised always comes out right whether or not it was the right
   number. See `references/failure-modes.md`.
7. **Never look a bone up by name.** `tools/rig_map.py` resolves roles and writes
   them to the sidecar so nothing downstream has to guess. Any hardcoded spelling
   — `_find_bone(["RightHand", ...])`, a `thigh`/`shin` substring test — is a rig
   this project has not met yet. Four characters could not hold a gun because of
   exactly one such lookup.

## After importing

```bash
godot --headless --path . -s res://debug/spawn_smoke_test.gd      # 29 checks
godot --headless --path . -s res://debug/surface_class_check.gd   # every surface classified
godot --headless --path . -s res://debug/character_picker_check.gd # the escape-menu roster
godot --headless --path . -s res://debug/rig_anchor_check.gd      # anchors move the weapon
godot --headless --path . -s res://debug/cloth_clip_check.gd      # leg-through-cloth
godot --headless --path . -s res://debug/cloth_settle_check.gd    # idle stability
godot --headless --path . -s res://debug/cloth_perf_check.gd      # ms per character
godot --headless --path . -s res://debug/travel_dir_check.gd      # legs face travel
```

And LOOK at it, which is where four of the last five real defects were found:

```bash
godot --path . -s res://debug/roster_capture.gd -- <dir>   # every character, one shot each
godot --path . -s res://debug/ui_capture.gd -- <dir>       # every menu screen
godot --path . res://debug/rig_lab.tscn -- shot <png> <skin>
```

`surface_class_check` fails on any surface that falls through to the heuristic
rather than resolving from the table. That is deliberate: a model whose names
stopped matching still RENDERS, because the fallback catches it — it just
quietly loses its per-class art direction, which is exactly the kind of
regression nothing else would report.

What "good" looks like on Taila, for calibration:

| Measure | Good | Bad |
|---|---|---|
| Idle skirt movement | < 0.1 deg/frame | 0.5+, or never decaying |
| Leg inside cloth, idle/walk | < 25 mm | 100 mm |
| Leg inside cloth, run/slide/dash | ~95 mm *(current, unsolved)* | — |
| Solver cost | ~2.6 ms/character | 10 ms |
| Stride vs. travel direction | < 10° (except a capped sidestep) | 90° |
| Bind-pose AABB | tall on the hips→head axis, others < 2.5 m | tallest axis is depth |

## Characters currently shipping

The six in `skins.json`, with what `surface_class_check` reports:

| Skin | Source | Cloth chains | Surfaces |
|---|---|---|---|
| taila | rigged, Sketchfab CC-BY | 35 | 18 — body 6, cloth 7, hair 1, linework 4 |
| kiyoko | VRoid, CC-BY | 20 | 13 — body 8, cloth 3, hair 2 |
| aria | VRoid, CC-BY | 15 | 15 — body 9, cloth 4, hair 2 |
| momo | VRoid, CC-BY | 9 | 5 — body 2, cloth 1, hair 2 |
| miku | unrigged source, auto-rigged | 0 | 4 — body 3, hair 1 *(one mesh, four surfaces)* |
| mannequin | Quaternius CC0, from the animation library | 0 | 2 — body 2 |

## Known-unsolved

- **Peak cloth clipping** in a run, slide and dash sits at ~95 mm of thigh
  inside the skirt. Idle, walk and fall are clean. The solver sees the contact
  and pushes on it every iteration; the remaining gap is a standing fight
  between the collision and the garment's own shape constraints.
- **No foot IK.** Feet do not plant on ground height, so stairs and uneven
  ground read as sliding.
- **No strafe or backpedal clips.** Direction is conveyed by yawing the hips
  (`SkinnedPlayerModel._update_travel`), which is capped, so a pure sidestep
  still runs its legs ~40° off the direction of travel.
- **momo's idle pose is wrong** — arms overhead and a pinched waist. Every
  assertion passes on her: she loads, animates, classifies and mounts a weapon.
  It shows up only in `roster_capture`. Her source rig is the reason to suspect —
  its bones are auto-named (`Item_O_Sphere_005`, `Unused_Noname_004`,
  `Root_001_001`), so the role resolver has almost nothing to go on, and a limb
  role claimed by the wrong bone would look exactly like this. Start by dumping
  her resolved roles against her skeleton.
- **A stray `Icosphere` ships inside every skin GLB** — 42 vertices, no parent,
  no vertex groups. It rides in from the animation library. Harmless, and now
  skipped by construction rather than by name in `surface_map`, but the export
  should not be producing it.