# ADR-0015: NPC model variety sourcing

- **Status:** Superseded by [ADR-0017](0017-quaternius-npc-base.md) (2026-11-05)
- **Date:** 2026-11-03

## Superseded

ADR-0017 replaces the generator-first decision below: Quaternius is now the
primary NPC base. The evaluation, licence rules and consequences remain as the
record of the 2026-11-03 decision.

## Context

The library has eight skinned characters, and role/seed selection reuses them
across the three venues. Crowds therefore repeat the same faces, builds and
outfits. The existing contract is strict: `npc_base` mesh node, 13 named bones at
fixed rest positions, five tint slots, front on Blender −Y and an 8,000
triangle/vertex budget.

A review compared free/open-source sources against that contract. Quaternius
Ultimate Modular (CC0), Kenney Blocky Characters (CC0), Khronos CesiumMan and
RiggedFigure (CC BY 4.0) and the MakeHuman base mesh (CC0) were imported and
measured. None was a drop-in; the full results are in
[`docs/assets/npc-model-sourcing.md`](../assets/npc-model-sourcing.md).

## Decision

1. **Ship only CC0, or CC BY with recorded attribution.** No service asset whose
   terms restrict redistribution may be used.
2. **Extend the project-owned procedural generator as the primary path** for
   shipped NPC variety. The first target is four crowd-variety looks, bringing
   the library to twelve characters.
3. **Keep Quaternius as a reviewed reference/prototype, not a shipped base.** A
   contract retarget is a no-go because the source is a T-pose 62-bone realistic
   rig with substantially different proportions from the arm-down 13-bone
   contract. A future external-rig path would need its own ADR covering its
   skeleton, animation source and per-model gear offsets.
4. **MakeHuman is deferred to a separate local development pipeline.** Its CC0
   base mesh can be decimated into budget, but it needs retopology, a custom rig
   and project-owned clothing before it is usable. It must not become a CI or
   build dependency.
5. **Commit research previews with attribution.** CC-BY preview images are
   development-only and are not bundled with the game or its release packages.

## Consequences

### Positive

- The shipped library keeps one art direction, one skeleton and one audit gate.
- Crowd variety lands without a new runtime dependency or a second animation
  system.
- The licence position is simple: project-owned assets plus explicit CC-BY
  attribution where a preview or future asset requires it.
- The Quaternius evaluation removes a tempting but high-risk retarget from the
  critical path.

### Negative

- Procedural variation is still limited by the existing face and clothing
  vocabulary; four variants do not provide full age/body diversity.
- Quaternius' animation set remains unused unless a second rig path is approved.
- MakeHuman body-shape diversity is postponed.
- External previews add a small documentation footprint that must stay out of
  release packages.

## Alternatives considered

- **Retarget Quaternius onto the `npc_base` contract.** Rejected for now:
  welding brings the geometry inside budget, but the rest pose and body
  proportions differ enough that a contract rebuild would either distort the
  model or require a full proportion warp.
- **Use Quaternius' own rig and animations directly.** Deferred: attractive
  animation quality, but it adds a second skeleton/animation path and per-model
  gear offsets to `NpcAvatar`.
- **Use MakeHuman as the primary body source.** Rejected for this milestone: high
  polygon count, no rig in the base mesh and a separate authoring dependency.
- **Use Mixamo or Ready Player Me.** Rejected: service terms are not a simple
  free/open-source redistribution basis for shipped meshes.

## Amendment 2026-11-04

- The character budget is raised to **16,000 triangles / 16,000 glTF vertices** per character.
  The required 13 core bones remain; optional extra bones (fingers, face, toes) are allowed if
  they do not move the core rest positions. The low-poly fallback remains the fallback, not a
  second contract.
- MakeHuman is now an active local development pipeline (body retarget plus project-owned
  head/hands), while the procedural library remains the shipped path and CI fallback.
- Blender MCP is optional interactive tooling only; it is not a build, CI, test or runtime
  dependency. Setup is in [`docs/assets/asset-tooling.md#optional-interactive-blender-mcp`](../assets/asset-tooling.md#optional-interactive-blender-mcp).