Scenario Maya Deformation

Maya deformation (character TD)

Expert deformation is decided before the first weight: joint pivots and edge loops set what skinning can do. Weights are then built region by region, judged in motion at extremes with numbers and renders, and every fault is fixed where it originates. Stance: block rigid, diagnose, smooth and shape, correct what weights cannot, and keep everything regenerable as data. 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-maya-expert (execution channel, review loop, 2027 version traps).

Module scripts/mx_skin.py: weights IO, region blocking, masks, mirror, transfer, ROM generator, deformation metrics, correctives, Skin Tools wrappers. Status (2026-09-24): its pure-Python half ran offline (test_mx_skin_offline.py, all pass); every Maya call is not yet run in Maya (tests: tests/code/maya-deformation/run_all.sh, via mx_run.py). import sys; sys.path.insert(0, "<skills>/scenario-maya-deformation/scripts"); import mx_skin as S

Stance (the expert delta)

• Raw blocked weights are a rig test. Assign every vertex 100% to its closest joint and pose: it "should look relatively close to your expected final result"; if not, fix pivots, placement or loops first. Smoothing a rig fault away: "don't do this in production" (Makauskas). Loops running along the wrist or ankle are the modeler's fault; volume loss at a clean elbow is the rig's (antCGi).
• Fill the region, art-direct in the mask. One layer per decision: twist joints get an even fill, the shape of shrug, shoulder and elbow lives in the mask, so re-smoothing twists never breaks the elbow (Jao). "Mask is not an actual influence", it is the layer's alpha (Makauskas). Headless, S.block_regions composites the same stack and writes once.
• Judge in motion, one motion per test. Calisthenics: keys every 10 frames, a pose on every second key, back to bind between, never bend and lower together (Makauskas); extreme and "weird" poses expose errors. ML pose data: one joint at a time in about 30 degree steps (Widup).
• Smoothing is not free. Sparse fingers lose volume: smooth the middle loops, then Sharpen (Makauskas). Measured here [added]: smoothing a 110 degree elbow cut stretch from 3.9x to 1.5x but collapsed the inner elbow (edge ratio 0.19). Deep bends need correctives, not more smoothing.
• Skin Tools layers are an authoring state. While layers exist, Maya blocks the classic paint, mirror, copy, hammer, set-max-influences and normalize tools; Delete Skin Layers keeps the evaluated weights and is the handoff step (Help). "It's still a normal Maya skin in the end" (Jao).
• Choose the corrective's space before sculpting. Pre-deformation is "like fixing the original character's mesh" and holds in other poses; post-deformation fixes one posed result, in Transform Space when one joint owns the fix (faster, bounded by that joint's envelope) or Tangent Space when it follows the surface across joints (Help; the cross-joint reading is [added]). Extremes first, then in-betweens (Help). Engines: secondary joints driven by swing-twist pose fractions, each assigned to its LODs (Rudy).
• Read the joint the rig actually moves. Bind joints driven by IK/FK constraints or an offsetParentMatrix blend are posed through their controls. Pose Editor: create the interpolator without neutral poses, add the controller's driving attributes in Driver Settings, then Add Neutral Poses; Euler Twist when a wrist twists about the forearm (Help). Node readers use dagLocalMatrix, since an OPM drive leaves rotate at 0 [added].
• Face: budget first, joints for rotation. Ask for the joint and shape budget first; a neutral with lips slightly parted made skinning "night and day easier" (Burton). Eyes, lids and jaw stay on joints even in shape faces, and split shapes must sum exactly to their master (antCGi). The ML Deformer learns what you feed it: skin joints in the Control Collector, Delta Mush removed first, pose coverage over network size (Widup).

Establish first

Workflow

1. Intake gates. mx_validate.validate(profile="model"), mx_audit.verdict(r, symmetric=True), S.bind_precheck(mesh, joints, method). GATE: no error lines, joints inside, transform frozen, no non-deformer history, X symmetry; face: lips apart, eye joint at the eyeball center (Burton).
2. Bind, explicitly. S.bind(mesh, joints, method, skin_method=0, normalize=1): pass every flag, since cmds and UI defaults differ and the Help contradicts itself on normalizeWeights. GATE: S.weights_verdict(S.audit_weights(...)) clean; S.export_weights_json backup (OpenMaya writes are not undoable).
3. Block and diagnose. S.block_regions with closest-bone regions, no smoothing; key calisthenics (S.rom_schedule, S.key_rom); S.deformation_test; S.pose_snapshots then mx_review.review headless and look. GATE: raw poses read close to the goal; faults go back to scenario-maya-rigging (pivots) or scenario-maya-retopology-uv (loops) with numbers and images.
4. Regions, twists, masks. Order: torso, clavicle and shoulder, upper arm, forearm, hand, thumb, fingers, head and neck, legs, feet (Makauskas). Twist chains as even ramps, masks as ranges along bones; with the API, S.st_add_region_layer and S.st_flood. Tune mask ranges, not vertices. GATE: audit clean, warnings shrink pose by pose, worst poses looked at.
5. Mirror and shells. S.mirror_skin (or the Skin Tools Mirror tab); clothing and accessories take the body under them (S.copy_nearest, S.remap_by_closest, volume smoothing limited to the shell). GATE: mirror error < 0.01, nothing unmatched, no penetration at rest.
6. Full ROM. Sections at mid-forearm and mid-upper-arm, bone volumes, folds, cross talk, rigid soles, clothing penetration; then combined "weird" poses and animator-style play; a GUI playblast when a session exists. GATE: no error:, every warn: fixed or explained, references/critique.md at 2 or more.
7. Correctives. Candy wrapper: twist distribution, then DQ or weight-blended skinning. Deep bends: pick pre or post and the target space (stance), check S.joint_drive(joint) and pose through the controls when it is driven, then S.solve_pre_corrective from a posed sculpt plus S.corrective_driver, or the Pose Editor in the GUI (controller-driven order above; extremes first; Regularization from 0.01). GATE: 0 at rest, 1 at the pose reached through the controls, residual < 1e-3 cm; ROM rerun.
8. Face, if in scope. Shapes through the split generator (S.split_targets, S.add_split_targets), or a joint face with a zero rest pose (Burton); squash under tweaks as two clusters (multi=True, UV Pin reading cluster 1, group inverse into bindPreMatrix). GATE: split error < 1e-5, counts within budget, double-transform test passes.
9. Finalize. S.delete_skin_layers, S.prune_and_limit to the target cap, ROM rerun, weights JSON (plus layers JSON), mx_validate.validate(profile="rig"), a new saved version.