Motion Doctrine (Gateway) Read this before composing any animation. It decides WHAT happens at every seam and how every scene performs; the technique skills implement it. These rules supersede generic / upstream motion guidance. The failure this prevents: scenes authored in isolation — the eye's momentum dies at every cut, and scenes wobble in place between entry and exit. Route map Decision (this skill) Implementation skill Seam transition choice + parameters + code cut the curve §1–5 (the catalog) Text / element entry cascades cut the curve §6 (waterfall entry) In scene group repositioning (no cut) cut the curve §7 (nudge curve) Cursor led action / scene kickoff / morph ignition oversized cursor Seam render mechanics / white flash guard seam craft Product launch / explainer / caption work overlays text beat economics , brand faithful , captions overlay on top of the upstream skill Authoring order: vector ledger ( ledger.json ) → STAMP the master seams from it ( scripts/seam stamp.mjs ledger ledger.json write index.html ) → sustained motion route per phase → carriers and causes → build comps → VERIFY ( scripts/seam gate.mjs ). Hand author only Tier A morphs/match cuts; stamped seams pass the gate by construction. Part 1 — The Seam Law The Vector Law How Scene A exits determines how Scene B enters: same axis, same direction, matched speed, cut mid motion on both sides. 1. Axis — x stays x, y stays y, Z stays Z. Never trade axes across a cut. 2. Direction — never mirror. On Z, direction = the SIGN of scale change: growing = push (camera forward), shrinking = pull (camera back). A receding exit answered by a grow from small entry is a mirrored vector — the most common violation, because grow from small is the default element entrance. 3. Speed — entry initial velocity ≈ exit final velocity, via mirrored eases (exit power4.in + entry power4.out , same distance and duration; the incoming side picks up ≥50% through the notional path). Mechanics in cut the curve . 4. Phase — the cut lands mid motion on BOTH sides. Settling to rest before the cut, or starting from rest after it, is a dead beat. The Current Every film picks ONE dominant direction (house default: LEFT). Every ordinary seam uses it. Other vectors are RESERVED — spending one means something: Vector Meaning The current (LEFT) "next beat" — neutral forward progress Upward elevation — a conclusion or reveal rises above what came before Z forward (zoom through) pushing deeper into the same thought Z backward (inverse zoom) ARRIVAL — something bigger lands Scale burst (explode out) leaving a world — a surface blasts past camera Never run consecutive seams in opposing directions — ping pong reads as an error. A direction change needs a visible cause (click / bounce / impact) or a chapter boundary. The Vector Ledger Write it before authoring any master timeline — as ledger.json at the project root (schema: references/seam gate.md ). One row per seam: cut time, exit and entry vectors (axis + signed direction; Z rows carry the scale sign), selectors, technique. Exit and entry must match; if a row mismatches, fix the plan, not the easing. The verifier checks row consistency statically before any runtime sampling. Carriers The eye follows objects, not abstractions. The strongest seams hand a concrete carrier across the cut at matched position AND velocity: a cursor mid path, a container that shrinks/docks into the next layout, a mark that flies into its exact slot, the word group of a waterfall cut. With no natural carrier, the scene heroes carry it (partial travel + early fade, entry mid flight). Never a crossfade — it has no carrier at all. Causal Motion Chain motion so each move is visibly launched by the last: click → squash → release spring → flight → impact → recoil → reveal. Effects start ON the causing frame — same timeline position, never "shortly after." Reactions scale with implied mass: big elements rebound slower, small ones snap. A force is a license to change direction; an uncaused flip is a ping pong. The Seam Gate (build gate — run the verifier, exit 0 or the seam is not done) The script (usage + ledger schema: references/seam gate.md ) numerically enforces, per seam: ledger row consistency, exit still moving at the cut, entry mid flight (never from rest), measured direction = ledger direction, entry/exit speed match (WARN), zero overlap (one side visible per frame — the cut is not a dissolve), the Z sign rule (d(scale)/dt same sign both sides; the incoming scene's own entrances are scanned for sign fighting), and carrier rect continuity with ancestor scale included. Use seam gate.mjs probe t <cut to find each seam's true carrier selectors when authoring the ledger. Rules the script cannot check — still yours: 1. Edits re open the seam. Any change to a scene's first/last ~1s (including re timing to new VO) invalidates that boundary's audit — re run the verifier. 2. Audio is the clock. Re time scenes to the VO's real word timestamps; never rush a read to fit a slot. A VO regen re opens its seams. 3. Clip gating gotcha (the usual cause of a zero overlap FAIL): a clip whose data start precedes its entry tween is un hidden at its initial opacity — set initial autoAlpha: 0 AND data start = the cut time, never earlier. Part 2 — Performance (the scene keeps performing) No idle wobble Idle sine loops (breathe, float, drift, glow pulse) are BANNED as sustained motion — they read as "the video is waiting." A scene that finishes entering with seconds left is a planning bug: add story, not wobble. Every phase between entry and exit is owned by one of these routes (name the route in the plan): Route What it is Staged reveals Hold content back; pay it off on narration beats — the frame keeps gaining information (default for ≥2 content groups) Camera with intent A mapped scale+pan path: establish wide → travel → arrive on the subject Sequenced UI life The product behaves over time: progress advances, highlights step, counts tick Animated sequences Elements act out a beat: a card files into a stack, an item gets dragged, a result assembles Cursor led action An oversized cursor walks the eye to a trigger; its CLICK ignites the next beat ( oversized cursor ) Test: pause at any second — something meaningful must be mid flight (a reveal landing, the camera traveling, the UI doing what the narration says). Stillness before climax Schedule a 0.3–0.75s pause between the major action and its result — the dramatic comma. A scene that jumps straight from action to result loses it. Timing intents Single entry ≤ ~800ms; longer buildup = multi element stagger, not one slow element. Exit ≈ 75% of entry. Exception: cut the curve inverts this (entry ~127% of exit). Total stagger ≤ 500ms; with 8+ elements, tighten per item delay or stagger the first few. Forbidden eases: bounce.out / elastic.out . Entry overshoot back.out(1.4–1.7) is fine. Similar elements share one ease+duration intent — never a unique pair per element. Transition vocabulary Use only 2–3 inter scene transitions per film and repeat them; the default boundary is cut the curve in the current's direction . Hand written shared element morphs ( intent: morph ) don't count against the budget. Anti Patterns Don't Instead Author each scene's entrance in isolation Write the vector ledger first Crossfade between scenes Cut the curve in the current's direction Exit completes, THEN the scene changes Cut mid motion on both sides Entry starts from rest after a cut Enter ≥50% through the notional path Inverse zoom exit → grow from small entry (or push → oversized retraction) Match the scale velocity sign (Seam Gate 7) Incoming scene's own pop in intro under a Z seam handoff Hold its opening frame composed, or match the sign Idle wobble / breathe / float to fill time Assign a sustained motion route; or add story Direction flip without a cause Spend a force, or keep the current Reserved vectors used as variety Default to the current; spend them on meaning Reaction a few frames after its cause Same frame ignition Action jumps straight to result Schedule stillness before climax (0.3–0.75s)

motion-doctrine