Scenario Blender Animation

Blender animation (character and object)

Expert animation means every frame on screen is a choice: key poses the audience reads, holds and snaps placed by hand, spacing designed, arcs checked. The Blender Studio stance is to block stepped, spline late and in parts, and judge from the shot camera at real speed. An agent cannot scrub, so it measures instead: per-frame positions, spacing charts, arc checks, framing, an onion-skin image, a curve plot, and a playblast it actually looks at. 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). Shot planning, cameras and animatics belong to scenario-blender-previs-storyboard; building the rig to scenario-blender-rigging.

Toolkit: scripts/bx_anim.py (keying, blocking-to-spline, curve checks, measurement, staging, playblast light, knee-pop, flip and balance checks, onion-skin and curve images, one-object bouncing_ball; API in procedures.md, tested on 5.2.1) and bx_review.playblast.

Stance (the expert delta)

• Stay stepped long ("Blocking+"). Hjalti Hjalmarsson: juniors spline too early; computer in-betweens are "unintentional interpolated poses" that make notes hard. Keep adding hand-made breakdowns while stepped; splining is short and late.
• Never convert the whole blocking to Bezier. Rik Schutte: key every main control on every key pose, copy each pose to the end of its hold ("pillars"), then spline the body only; face and fingers stay stepped until their own pass. Measured on 5.2.1: the naive conversion drifted 84% of the next move across a hold, the pillars held at exactly 0.
• Snaps are authored. Rik: hold, then change pose in 2 to 3 frames; only big deliberate moves are left to interpolation. [added, measured] A contact inside continuous motion (a jump landing) is not a hold: pillaring it cut the body's speed at impact from 0.101 to 0.007 m per frame, a floaty landing.
• Odd frames, even gaps; breakdowns shape arcs and steer the eye. Alex Nagy: key poses on odd frames with even spacing so a true middle frame exists. The breakdown sets the arc first, the timing second; favoring it late leaves more travel for the last frames, and the fastest part draws the eye.
• The handle type is a timing decision. AUTO_CLAMPED keeps holds flat; AUTO overshoots between two equal keys (Alex uses it to push a pose or cushion a settle); VECTOR for hard hits, contacts and take-offs (Alex, Dillon Gu); FREE for burst spacing and exact arcs (Raymond Luc, Joey Carlino).
• Lead with one part, layer the rest. Rik blocks a torso-only rhythm pass first; Dillon leads body mechanics with the COG and acting with the head or eyes. Overlap goes into the blocking, and a head never turns on one axis only (Rik).
• Lip sync is rhythm before shapes. Rik: jaw first, stepped, opened big only on accents; off-sync is a missing preparation, not a global offset; M, B, P closed at least 2 frames and closed before the sound.
• Spacing is felt, arcs are checked, the shot must read. Raymond: the audience should feel spacing tricks, not see them. Pablo Fournier: arcs are the most important check (root, hands, feet, nose), in camera space. Hjalti (in scenario-blender-previs-storyboard): after each cut the eye must find one thing, so a subject lost in an empty frame fails however good the curves are.

Establish first

Workflow

1. Plan. Beat list with frames: every acting beat in order (Hjalti counts about 8 per shot), sub-beats notice, react, realize, respond (Rik), the leading part per beat. With audio, audio_envelope + accent_frames; hit a pose just before its audio peak (Alex). Start mid-action (Rik). GATE: beat table written.
2. Set up and stage the shot (P1, P18): fps, range, sound, passepartout 0.99, Simplify for previews. Place the camera, then staging_report(subject, frames) with the real render size: subject height, how much of the frame the action covers, entry, final pose margin. Playblast look: playblast_lighting(key_dir=(0, 0, 1)) (overhead key converted to Workbench's camera space: the shadow sits under the subject, the gap is its height, contact is where they meet), floor_slab, rotation_texture on anything that rolls. GATE: flags empty; shadow_frames visible in the air and touching at a contact; camera stills looked at.
3. Block A, key poses stepped. Strongest, longest-held pose first (Alex). Build each pose COG, feet (weight over the support foot, feet never twins, knees soft), hips, chest, head, arms. Pose in world terms with world_pose (rig axes are arbitrary), key with key_pose(..., keytype='EXTREME'), CONSTANT, all main controls. GATE: pose strip onion_skin(frames=keys, spread=...) shows clear silhouettes and contrast; balance_report margin >= 0 on held poses.
4. Blocking+ (still stepped). breakdown at the middle frame with per-part factors (COG dips, extremities delayed at 0.2 to 0.3, directed part favored late; after a take-off the body is ballistic, about 2/3 of the rise in 3 of 7 frames, and the feet must follow); ease_inbetweens for 20/80 (Pablo); overshoots and settles; overlap offsets; key types as a confidence map (Hjalti). GATE: stepped playblast approved; notes on intent stopped (Leo: none after Block B).
5. Spline the body with blocking_to_spline(rig, body_bones, transition=3, interpolate={...}): big moves and continuous contacts in interpolate; VECTOR on foot contacts and take-offs. GATE: hold_drift < 1e-5, overshoots only wanted settles, face still CONSTANT, motion_report without unintended constant spacing, ballistic_fit on the airborne COG with g_ratio near 1.0 and a small residual, limb_extension never above 1.0.
6. Re-inject energy (Leo: splining softens): timing accents, overshoots, desynchronized parts, offset_keys 1 to 2 frames per chain link (Dillon), head lag 2 to 3 frames in cycles (Joey), contacts that slide rather than glue (Rik). Fingers: little overlap, no bounce. GATE: arcs clean in camera pixels (to_camera(..., res=(w, h)), motion_report(dims=2)).
7. Face and lip sync, stepped (P6, P7): jaw rhythm, corners (never dead center), shapes from a pose library on the lower face minus the jaw, accents and asymmetry in small doses, tongue last, then spline the face. Eyes dart in 1 to 2 frames and lead the head; brows 3 to 10 frames (Rik). GATE: transitions meets those counts; accents clearly fewer than syllables.
8. Polish. foot_slip under 1 mm, lowest_point for penetration, rotation_flips empty (fix_rotation_flips), limb_extension under 0.99 wherever the leg should stay bent, smears 1 frame (Pablo), burst spacing only now (Raymond), subdivision on. GATE: critique.md rubric passes on the final playblast, onion skin and graph image.

Variants. Bouncing ball (P16, P18): bouncing_ball(obj=ANIM_ball, first_apex=-3, fit=False, ...) keys ONE object: exact parabolas under one gravity through whole-frame contacts, odd or even flights so small hops keep their height, squash on the contact frame and stretch along the velocity through a world-aligned squash modifier (the roll is never twisted), roll = distance / radius, constant-deceleration roll, a 6-frame hold. first_apex before start throws it in from off-screen. Weight mapping is [added]: tune by render. Walk (Joey, 30 fps): contact 0, down 5, passing 10, up 15, 40-frame cycle; heel curve straight during contact, root linear with REPEAT_OFFSET (P5). Jump: tests/code/blender-animation/test_rigify_jump.py is the worked example (Rigify human, blocking to spline).