Blender rigging

Expert rigging means the rig is specified by bone placement, proven by deformation under stress poses, and shaped around what the animator will actually use. The stance of every source expert: place joints precisely, generate or build the simplest mechanism that works, then pose it, measure it, render it and fix it before calling it done. If a sibling skill named here is missing from your available skills, ask the user to install it (npx skills add scenario-labs/skills --skill <name>); unattended, proceed from tool schemas and flag the gap.

REQUIRED BACKGROUND: scenario-blender-expert (execution channel, review loop, 5.2 API changes).

Module: scripts/bx_rig.py (tested on 5.2.1, headless and GUI). import sys; sys.path.append("<skills>/scenario-blender-rigging/scripts"); import bx_rig as R.

Stance (the expert delta)

• Placement is the specification. Joints sit in the center of the volume they move, not on the anatomical skeleton ("bones simulate bone, muscle and tissue"); knees and elbows get a slight pre-bend because the chain's curvature IS the IK plane; rolls put each hinge on one local axis so the animator uses one curve (CGDive; Demeter: the bend, not the roll, decided where his pole landed).
• The metarig is the source, the generated rig is disposable. Every fix goes into metarig bones, Rigify parameters or a post-generation script; regenerating keeps control names, so weights and animation survive (CGDive, Demeter, Ivan Cappiello).
• Automatic weights fail silently. parent_set returns FINISHED while a warning says bone heat failed; measure unweighted vertices and empty deform groups, and fall back to a voxel proxy plus Data Transfer (CGDive; verified). They also leak across the crotch and armpits: strip .L weights from the right half.
• Weights are judged in motion, firm beats mushy. Paint in pose or against a test animation; limit each seam to 2 or 3 bones ("bones fighting for influence"); slight intersection is better than rubbery transitions; rigid parts are assigned at 1.0, never painted (CGDive, Demeter, Dikko).
• Everything that deforms together gets weights from the same source, transferred and applied, so garments cannot drift while animating (Dikko, CGDive).
• Export decides the deformation tools. Four twist bones per segment instead of Preserve Volume; Preserve Volume, Corrective Smooth and B-bones are Blender-only, which is why Rigify segments its DEF bones (CGDive, Ivan).
• The animator is the client. Cut features nobody uses, restrict only what breaks the rig, keep automated bones hand-animatable (constraint plus child, Mix Add, Transformation instead of drivers), stop when fit for purpose (Wayne Dixon, Demeter, CGDive).
• Faces are per-character hybrids. There is no generic stylized face (Demeter); production faces mix joints, ribbons, shape keys and lattices (Rik Schutte).

Establish first

Input	Changes	Default when silent
Target: Blender render vs game/FBX	segmented DEF bones, max 4 influences, no Preserve Volume / Corrective Smooth / B-bone deformation	Blender-only keyframe animation
Character: biped, quadruped, mechanical, prop	metarig preset or custom samples; rigid islands	biped, Rigify
Face need and style	none / Rigify face / bones + shape keys + on-face controls	body rig + eye and jaw bones only
Fingers	Rigify Human (fingers + face) vs Basic Human	Basic Human (CGDive: first rig)
Pose, pieces, scale	T or A pose, separate eyes/teeth/clothes, real scale	measure; fix in the model check
Animator conventions	FK/IK defaults, side colors, finger controls	legs IK, arms FK, follow 0; left blue, right red (ask)

Choose the path

Rigify	Manual / scripted rig
Humans and animals with standard anatomy, many characters sharing controls, fast production-grade result	Unusual anatomy, mechanical parts, strict game-engine hierarchies, rigs that must stay small, or when the brief asks for a custom control scheme
add_metarig then fit_metarig, generate	new_bone, twist_chain, fk_ik_switch, ik_chain, foot_roll, make_def_layer, organize
Metarig types: arm exactly 3 bones, leg 4 + heel, spine 3+, super_copy 1 bone	DEF / MCH / CTRL: only DEF deforms, MCH is never animated, everything else is a control

Workflow

1. Model check. R.model_check([body, *parts], fix=True): transforms applied (shape keys included), feet on Z=0, centered on X, facing -Y, about 1.8 m for an adult human. Apply Mirror modifiers or keep their mirror object. GATE: model_check(...)["problems"] == [].
2. Landmarks. lm = R.landmarks(body, eyes=eyes): cross-sections find crotch, hips, ankle, neck, armpit, wrist; eye centers from the eye mesh; nose tip and chin from the face profile. Override any joint with overrides={...}. GATE: joint order sane, lm["notes"] empty or explained.
3. Fit. Rigify: meta = R.add_metarig("basic"|"human"), R.fit_metarig(meta, lm) (joints as shared points, pre-bends, hinge rolls, left side symmetrized; hands and face by similarity, coarse). Manual: build the deform skeleton with new_bone from the same landmarks. GATE: R.check_metarig(meta, body) == [] AND R.placement_sheet([body, eyes], out, arm_obj=meta, views=("front","right","top")) looked at; zoom the head with center=, size=.
4. Face (Rigify Human). Fit, then R.upgrade_face(meta) (irreversible; eyelid follow Z 0.3, bottom lip 0.9, Overwrite Widget Meshes on). Stylized hero face: bones for jaw, eyes, tongue plus shape keys instead (stage 7).
5. Generate or build. rig, err = R.generate(meta); err is the first Rigify error line naming the bone ("Cannot connect chain - bone position is disjoint", "Expected 2 eye corners"): fix the metarig, regenerate. Manual: twist chains, FK/IK layers with settings properties, IK with solved pole angle, foot roll, symmetrize, mirror_drivers, make_def_layer, organize, widgets. GATE (manual): static_cycles == [], cycle_check() == [], root_test < 1e-4, FK and IK coincide at rest, pole error < 1e-3.
6. Bind. rep = R.bind(rig, body, garments=[shirt, pants], rigid={eyes: None, teeth: "DEF-teeth.T"}): auto weights, verification, proxy fallback, cross-side strip, garment transfer (applied), rigid islands, clean and normalize, Armature after Mirror and before Subdivision. GATE: rep["ok"], unweighted == 0, no non-deform groups; for export max_influences=4.
7. Range of motion. dr = R.deformation_report(rig, [body, *garments], R.RIGIFY_POSES), R.flag_report(dr), then R.pose_sheet(...) and R.joint_sheet(...) close-ups and LOOK at them. GATE: no leaks, no unexplained collapse, renders acceptable at armpit, elbow, wrist twist, groin, knee, collar.
8. Fix, in this order. Placement or roll problems: back to the metarig and regenerate. Weights: targeted data edits (strip_opposite_side, assign_rigid, smooth_weights with a vertex mask, clean_weights). Volume at deep bends: corrective shape keys (volume_restore_targets, corrective_from_targets, corrective_driver). Blender-only candy wrapper: preserve_volume_mask. Re-run stage 7 after every fix; re-check earlier poses (CGDive).
9. Usability and delivery. Controls visible with In Front off, widgets, side colors, MCH/DEF hidden, at least one Rigify UI row, rig_ui.py needs Auto Run in a GUI, switches exactly 0 or 1, rest pose clean, test action removed. Report numbers, renders and what was not verified.

Numbers

Value	Relative to	Source
Knee/elbow pre-bend 1 to 3 deg (fit: 1.2% of limb length, 2.7 deg); check 1 to 15	chain in the bend view	CGDive; check [added]
4 twist bones, Copy Rotation 1.0 / 0.66 / 0.33 / 0.1 (thigh 0.05)	from the driving end	CGDive
IK chain length 2; IK Stretch 0.1; lock IK Y/Z on shin and forearm	IK bone	Wayne, CGDive
Foot roll: heel X [-90, 0], toe X [0, 90], inside/outside Z one-sided	pivot local, roll 0, pointing up	CGDive (verified)
Weight brush Add, strength 0.1 to 0.2, Auto Normalize; seams Mix 0.5 at strength 1	Weight Paint	CGDive
Clean near-zero weights before blurring (Demeter); limit 0.001 (CGDive), 0.01 in bind [added]; 4 influences for games	per vertex	Demeter, CGDive
Eyelid follow 0.15 (bone face); Rigify eyelid follow Z 0.3 (default 0.7); jaw bottom lip 0.9; mouth corners follow jaw 0.5	face	CGDive
Palm 0.5 / 0.25; elbow plate 0.2 of forearm rotation	Copy Rotation Local, Mix Add	CGDive
Finger curl: Transformation Scale Z 0..1 to Rot Z 90..0 deg, Extrapolate	finger control	CGDive
Action constraint: keys frames 1 and 10, LINEAR, max = measured control travel	control local Y	CGDive, Demeter
Shoulder test range about 20 to 30 deg of clavicle raise	anatomy	CGDive
Face: about 16 Stop Staring shapes; 52 ARKit for mocap	shape keys	CGDive
Proxy voxel H/180, then H/90, H/45	character height	[added, verified]
Collapse < 0.85, bulge > 1.25 (joint band), leak > 0.001 H, strain 0.5 to 1.6	rest	[added]

Quality gates

Code (all in bx_rig): check_metarig, weight_report (unweighted, empty_major, non_deform_groups, over4, sum_dev, mirror_err), deformation_report + flag_report (strain, joint volume bands, cross-side leak, new self-intersections via bx_audit), static_cycles, cycle_check, root_test, twist_angles, solve_pole_angle, rigid_check.

Visual: placement sheet (front, right, top; head zoom) before generating; pose sheet of RIGIFY_POSES (front, right, three-quarter); joint close-ups (arm joints front/top/three-quarter, others front/right/three-quarter) at every flagged pose. Look for armpit collapse, pointy or pinched elbows and knees, candy-wrapper wrists, groin and butt volume, collar clipping, garments sliding or intersecting, teeth and eyes lagging, widgets hidden inside the mesh. Numbers passed while a render showed broken arms or crease spikes during testing: always open the render. Rubric: references/critique.md.

Common mistakes

Mistake	What it looks like	Fix
Metarig scale or pose not applied	generated rig differs in size or pose	apply scale, Apply Pose as Rest Pose
Neck moved without the spine tip	"bone position is disjoint"	move joints as units (move_points)
Straight knee or elbow	IK bends sideways or backward	pre-bend in the bend view
Parented to the metarig	mesh follows nothing useful	bind to the generated rig
Heat failure unnoticed	mesh does not move	weight_report; proxy route
Armature below Subdivision, or before Mirror	slow; mirrored half copies the posed half	armature_first
Left thigh weights on the right leg	opposite side moves	strip_opposite_side
Eyes and teeth auto-weighted	drift, poke through	assign_rigid
Live Data Transfer on clothes	weights change while animating	apply it
Driver on an animatable bone	channel cannot be keyed	Transformation or Copy Rotation Mix Add
Inherit Rotation off for isolation	root rotation breaks the limb	follow bones (World Copy Loc/Rot/Scale)
IK target parented inside its chain	jitter, flips	clear parent; static_cycles
Re-parenting a connected bone	head jumps to the new parent's tail	reparent clears use_connect first
Symmetrize expected to copy drivers; .L.001 names	right side dead	mirror_drivers; side_of
IK/FK left at 0.86	mixed, unreadable deformation	exactly 0 or 1

Blender 5.2 notes

• Rigify ships disabled on factory startup (enable_rigify); the Human metarig still has the legacy face (upgrade it); Overwrite Widget Meshes still defaults off.
• Bone collections and per-bone colors replace layers and bone groups; edit_bones.new() joins no collection; pose selection is pose.bones[n].select.
• parent_set appends the Armature modifier last; weight operators (vertex_group_smooth, _clean) need Weight Paint mode headless; bx_rig does clean, normalize and limit on data instead.
• shape_key_add leaves new keys at value 1.0 in 5.2.1: set 0 before driving [verified]. VertexGroup.remove with out-of-range indices crashes 5.2.1 [verified].
• Setting a parent's tail moves a connected child's head; EditBone.transform on a connected group double-moves shared ends [verified]: use transform_bones.
• Python drivers start with keys (0,0),(1,1); remap them (remap_driver). Action constraints pick the action slot automatically. Only Insert Available is on by default; keyframe_insert from Python is unaffected.
• Custom shapes: Affect Gizmo (use_transform_at_custom_shape), Use As Pivot (use_transform_around_custom_shape). 5.2 adds Duplicate and Rename and Add Bone align Axes.

References

• references/procedures.md: full tested code for each stage and the test script behind it; load before writing rig code.
• references/expert-notes.md: judgment by expert (placement, Rigify internals, weighting, mechanisms, faces) with timestamps; load when a decision is not covered above.
• references/critique.md: the review rubric; load at every gate.
• references/sources.md: videos, experts, best timestamps.