2d_character_rigging v1.0.0

name: 2d_character_rigging description: Rig 2D characters for animation: joint and pivot placement, deformer basics, mouth and hand sets, turnaround requirements, and testing the rig with extreme poses before animation starts. Triggers on rig a character, build a puppet, set pivots, add deformers or bones, make a mouth chart or hand set, or check if a rig is ready to animate.

2D Character Rigging

Purpose

Turn finished character artwork into a rig an animator can pose without the artwork tearing, sliding, or drifting off model. The method is tool neutral. It maps to pegs and deformers in Toon Boom Harmony, bones and constraints in Spine, Smart Bones and switch layers in Moho, bones in Duik for After Effects, puppet pins in After Effects, and warp and rotation deformers in Live2D Cubism.

A rig is not done when it moves. It is done when it survives extreme poses, returns cleanly to its default pose, and every mouth, hand, and view the script needs already exists.

Workflow

1. Gate the artwork on the turnaround. Do not rig from a single drawing. Require the five view turnaround and the construction lines described in references/turnaround-and-artwork-prep.md. Check that eyes, chin, shoulders, waist, hips, knees, and ankles line up across views, that arms sit in a relaxed default pose rather than a folded or dynamic pose, and that every part that moves on its own is on its own layer or drawing. If a view is missing, rig only the views that exist and list the missing view as a blocker for any shot that turns that far.

1. Split the artwork for movement, not for looks. Name parts by side and function: torso, pelvis, head, jaw, upper_arm_L, forearm_L, hand_L, and the same for legs, hair sections, and clothing that must lag behind the body. Extend artwork hidden under joints by a rounded overlap so a bent elbow or knee does not open a gap. Number repeating pieces, such as hair tufts, in turnaround order so each piece keeps its identity through a turn.

1. Place pivots at the center of articulation. Follow references/pivot-and-hierarchy.md. Put the shoulder pivot at the center of the shoulder joint, the elbow at the center of the elbow, and so on for wrist, hip, knee, ankle, neck, and waist. Put the master control between the feet at ground level so the whole character moves without an offset surprise. Test each pivot alone: rotate one joint a full swing and watch whether the part stays attached. A part that orbits or slides has a pivot in the wrong place, no matter how good it looks at rest.

1. Build the hierarchy from the ground up. Parent order is pelvis as body root, spine to chest to neck to head, chest to shoulder to upper arm to forearm to hand, pelvis to thigh to shin to foot to toe. Keep controllers separate from artwork. In Harmony keep pegs above deformer chains, not under them. In Live2D nest deformers so broad motion sits above fine motion: body above head, head above face groups, face groups above pupils and lashes. See the full hierarchy tables for the simple and complex worked rigs in references/worked-rigs.md.

1. Choose the motion tool per part. Use a plain pivot or bone for stiff parts that only rotate, such as a robot arm segment or a prop. Use a bone chain with inverse kinematics for legs and for arms that must plant a hand on a surface. Use a curve or mesh deformer for parts that bend through their length, such as a spine, a tail, a soft arm, hair, or clothing. Use a warp deformer for squash, stretch, and head turn cheating in Live2D style rigs. Use a switch set, not a deformer, for mouths and hands. The decision table and per tool notes are in references/deformers-and-ik.md.

1. Fix the joints that deform badly. A rotating elbow made from two stiff pieces shows a gap or a sharp fold. Fix it in this order: add overlap artwork, add a patch or glue joint, add a curve deformer over the joint, then add a corrective pose driven by the joint angle. In Moho that corrective is a Smart Bone action. In Spine it is weight painting plus a second bone influence at the joint. In Harmony it is an envelope deformer plus an auto patch. In Live2D it is glue between neighboring meshes. Never hide a bad joint by telling animators to avoid the pose.

1. Build the mouth set from phoneme groups, not the alphabet. Ship the ten drawing set in references/mouth-and-hand-sets.md, based on the Preston Blair groups: rest, A I, E, O, U, M B P, F V, W Q, C D G K N R S T Th Y Z, and L. Add three expression mouths the character uses often, usually smile closed, frown closed, and open shout or laugh, in the character own style. Draw each mouth at front and three quarter angles if the head turns. Keep the mouth pivot at one anchor point across all drawings so swaps do not jump.

1. Build the hand set the production will actually pose. Minimum set per hand: relaxed, open flat, fist, point with index, grip for holding a prop, and thumbs up or the character signature gesture if the script uses it. Draw left and right versions, do not mirror a hand that wears a ring, glove mark, or scar. Put hands in a switch group parented to the forearm end, or attach them past a kinematic output so a deforming arm does not deform the hand drawing itself.

1. Add secondary controls last. Hair, ears, tails, jewelry, loose clothing, and props get their own small chains or deformers parented to the part they follow. Keep them off the main controls so an animator can pose the body without fighting lag controls. For Live2D and game rigs add the standard parameter list and physics only after the manual pose test passes. A rig that only looks alive with physics on is hiding a pivot problem.

1. Run the extreme pose test before handoff. Work through every pose on assets/pose-test-sheet.md, or generate a sheet for a custom rig with scripts/rig_check.py. The sheet covers joint limits, a walk contact pose, a deep crouch, arms overhead, a full head turn, every mouth and hand, and a reset check. Score each pose pass, fix, or fail with a note. A fail on any load bearing pose, foot plant, hand plant, head turn, or reset means the rig goes back to rigging, not to animation.

1. Reset, rename, and lock the default. Return every control to zero and confirm the character matches the turnaround front view exactly. In Harmony that is the reset all controls check. In other tools it is clearing all transforms and parameters to default. Name every control in the agreed scheme, hide build layers, lock artwork layers that animators should not edit, and save a separate rig file. Never hand off the only copy.

Output Contract

Deliver all of the following:

• Rig file in the target tool, with named hierarchy, pivots placed per references/pivot-and-hierarchy.md, and a default pose that matches the turnaround front view on reset.
• Turnaround check: list of views received, views missing, and any construction line mismatches found, with the shot impact of each missing view.
• Mouth set: the ten phoneme group drawings plus expression mouths, named mouth_rest, mouth_AI, mouth_E, mouth_O, mouth_U, mouth_MBP, mouth_FV, mouth_WQ, mouth_CD, mouth_L, at each head angle the rig supports.
• Hand set: at least six hands per side, named hand_<side>_<pose>, in a switch group that does not deform with the arm.
• Pose test sheet: completed copy of assets/pose-test-sheet.md with pass, fix, or fail per pose, the fix applied for every fix score, and a retest result.
• Rig spec and validation: a JSON spec following assets/rig-spec.example.json, validated with python3 scripts/rig_check.py spec.json --sheet out.md. Report the validator output. A rig with missing mouths, missing hands, or untested poses fails validation.
• Animator note: one short page listing the main controls, any pose the rig cannot do, and the correct way to turn the head or plant a foot in this rig.

Operating Rules

1. Pivot first, deformer second. Most rig complaints that look like deformer problems are pivot problems. Recheck pivot position before adding mesh density, weights, or correctives.
2. Never rig a peg or child control under a deformer that should not move it. In Harmony use a kinematic output to pass position and angle to a hand or prop without deforming its drawing. In other tools use the equivalent pass through or separate parent.
3. Use as few pins, points, and bones as the motion needs. After Effects puppet guidance and Spine weight practice agree on this: extra pins and vertices over constrain the mesh, slow the rig, and create lumps. Add density only where a test pose shows a fold.
4. Mouths blend, they do not hop. Blair dialogue practice stresses continuous mouth movement, with wider shapes placed before vowels and fewer jumps in fast speech. Build in between mouth shapes or interpolated switches for fast talkers instead of snapping between extremes on every syllable.
5. Do not invent joint limits. Angle limits depend on the character design, species, and costume. Set limits from the pose test on that character, record the tested values in the rig spec, and leave untested ranges marked untested.
6. Separate views need separate checks. A rig built for front view will not turn to profile by deformer alone unless it was built for that turn with three quarter and profile artwork or a modeled head turn. State the supported turn range in the animator note.
7. If the pose test fails, do not publish the rig as ready. Fix it in the same pass, or hand it back labeled as a work in progress with the failed poses listed. A rig labeled ready that fails on a walk cycle costs more than a late rig.