---
name: rigc-face
description: Author a face on plain Spine data with rigc — a blink, a gaze shift, a breathing portrait and a head turn a few degrees off axis, built from deform timelines and per-part parallax. Use when the request is a talking or living portrait, a standing character, an expression or a head turn, such as "rig this face", "make the portrait blink and look around" or "turn the head". Not for Live2D file conversion, cutting a face illustration into parts, or VTuber-style real-time face tracking.
license: MIT
compatibility: Requires Bun 1.2 or later and the npm package rig-c.
---

# Face — a turn, a gaze and a blink

Load this when the request is a **head rather than a body**: a drawn face that
breathes, blinks, moves its eyes and turns a few degrees off axis. Every rule below
is owned by [FACE.md](https://github.com/rig-c/core/blob/main/docs/FACE.md); this file says when to open it and what
it will not do for you.

📖 **A failure line ends with the command that prints its row of the guide** —
` (see rigc guide <RULE>)`. Run that command first, before reading anything else:
it prints that rule's row of the shipped guide and nothing else. `rigc guide §<n>`
(and `§<n>.<m>`, `§<n>.<m>.<k>`) prints the section's heading, own prose and
subsection index from `docs/AUTHORING.md`; add `--all` to include subsection
bodies. A leaf prints its full text either way. Sizes describe full ledger spans;
`--all` with a rule name is refused, exit 2. A compile error points at its stable
`CE_` code row. `rigc guide §5.1.<k>` prints a numbered compile-error group of
at most 30,000 UTF-8 bytes, and `rigc guide §5.1` prints the introduction and
index within that same limit; only legacy uncoded library errors point at `§5.1`.

## Non-negotiables

- **Validation is never bypassed.** `build` writes nothing on a red gate, and there
  is no flag that changes that — AUTHORING §0.
- **The compiler never invents a value.** A `deform` key states every vertex it
  moves; the geometry a turn implies is evaluated by you and written into the spec,
  never inferred by the compiler — AUTHORING §4 and FACE §1.
- **The validator's messages are the instructions.** Read each named failure as the
  pointer to the file that has to change — AUTHORING §5.

## What this guide will not do

A `deform` key's own geometry is measured now.
`A39_DEFORM_KEEPS_TRIANGLE_WINDING` refuses a key that folds a mesh inside out —
per key, per interpolated span between two keys, per frame and per skin — and
names the reversed triangles with their signed areas. `invariants.deformMayFold`
in the rig spec is the one declared exemption, so reach for it when the slot
folds on purpose and never to quiet a refusal you have not read. It is an
**archetype** rule: a `--profile spine` build prints `PROF` for it and says
nothing about the fold, so author under `--profile rig-play`.

What `A39` still cannot say is whether the projection was the right one —
nothing measures whether 12° was the angle the shot wanted. FACE §9.2 is that
demonstration, three builds with one of them refused, and §9.3 is the
differential audit and the three limits it does not lift.

## Read, in this order

1. [AUTHORING.md](https://github.com/rig-c/core/blob/main/docs/AUTHORING.md) — the `deform` timeline field by field
   and what rigc refuses in it (§4), the failure map (§5–§6), the editor's
   conventions (§10).
2. [MOTION.md](https://github.com/rig-c/core/blob/main/docs/MOTION.md) — timing, easing and the offset table (§3),
   candidates and the ballot (§4–§5). A blink and a gaze are ordinary motion work.
3. [FACE.md](https://github.com/rig-c/core/blob/main/docs/FACE.md) — the face's own geometry: the closed form every
   number in a turn comes from (§1), the hierarchy underneath (§3), what
   foreshortens (§5), and the deform audit gap (§9).
4. Then [RIGGING.md](https://github.com/rig-c/core/blob/main/docs/RIGGING.md) for the hierarchy as a general rule
   rather than this closed form, and [INGEST.md](https://github.com/rig-c/core/blob/main/docs/INGEST.md) if the head
   arrived as a compiled skeleton.

Every guide linked here is in the installed package at `node_modules/rig-c/docs/`,
which is the copy that matches the rigc you run; the links go to the repository's
`main`. Inside the Claude Code plugin the same files are at `${CLAUDE_PLUGIN_ROOT}/docs/`.

The install line and the build → validate → render → check loop are in the `rigc`
skill.