Add web animation skills (iart-ai/web-animation-skills)
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01GYeokZtSmqg42ZGWsLXX2C
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---
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name: lottie-animation
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description: This skill should be used when the user asks to "add a Lottie animation", "play a .lottie or .json animation", "integrate a Bodymovin/After Effects animation on web or mobile", "control Lottie playback / segments", "make a scroll-driven Lottie", "recolor a Lottie at runtime", or "export an AE animation to Lottie". Covers dotLottie/lottie-web integration, playback control, interactivity, theming, and the AE export checklist.
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version: 0.1.0
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---
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# Lottie Animation
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The bridge from After Effects to product: vector animation shipped as JSON (or zipped `.lottie`), tiny and resolution-independent, played by a runtime on web, iOS, Android, and React Native. This skill covers integrating, controlling, and exporting Lottie.
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## When to use
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- Ship a designer's AE animation to web/iOS/Android/React Native
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- Looping illustrations, onboarding, empty states, animated icons
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- Scroll-driven or interaction-driven vector playback (hover, click, cursor)
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- Runtime theming/recoloring instead of re-exporting per brand
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## Formats: .json vs .lottie
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- `.json` — the raw Bodymovin output. Human-readable, larger.
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- `.lottie` — a zipped container (often 60–80% smaller) that can bundle multiple animations, images, and theming. Preferred for shipping. Player: `@lottiefiles/dotlottie-web` (modern, canvas + WASM) supersedes the older `lottie-web`.
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Prefer the **dotLottie** runtime for new work; use `lottie-web` only for legacy `.json` + SVG renderer needs.
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## Core workflow (web, dotLottie)
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```bash
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npm i @lottiefiles/dotlottie-web # vanilla
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npm i @lottiefiles/dotlottie-react # React wrapper
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```
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Vanilla:
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```js
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import { DotLottie } from "@lottiefiles/dotlottie-web";
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const dotLottie = new DotLottie({
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canvas: document.querySelector("#lottie"), // a <canvas> element
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src: "/hero.lottie", // or .json
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loop: true,
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autoplay: true,
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// speed: 1, mode: "forward" | "reverse" | "bounce", renderConfig: { autoResize: true }
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});
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```
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React:
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```jsx
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import { DotLottieReact } from "@lottiefiles/dotlottie-react";
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function Hero() {
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return <DotLottieReact src="/hero.lottie" loop autoplay style={{ width: 320 }} />;
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}
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```
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Capture the instance to control it:
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```jsx
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const [dl, setDl] = useState(null);
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<DotLottieReact src="/icon.lottie" dotLottieRefCallback={setDl} />;
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// dl?.play(); dl?.pause(); dl?.setSpeed(2);
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```
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## Playback control
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```js
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dotLottie.play();
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dotLottie.pause();
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dotLottie.stop();
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dotLottie.setSpeed(1.5);
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dotLottie.setMode("bounce"); // forward | reverse | bounce | reverse-bounce
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dotLottie.setFrame(42); // jump to a frame
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dotLottie.setSegment(30, 90); // constrain playback to a frame range (e.g. a "loading" loop)
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```
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Events drive sequencing and UI:
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```js
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dotLottie.addEventListener("load", () => { /* totalFrames now available */ });
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dotLottie.addEventListener("complete", () => { /* non-looping playback finished */ });
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dotLottie.addEventListener("frame", ({ currentFrame }) => { /* per-frame */ });
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```
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State-machine style (e.g. button that plays "checked" segment then idles): play a segment, listen for `complete`, then `setSegment` to the idle loop.
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## Scroll-driven Lottie (no GSAP needed)
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Map scroll progress (0–1) to a frame. Pause autoplay and drive frames yourself.
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```js
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const dotLottie = new DotLottie({ canvas, src: "/scroll.lottie", autoplay: false });
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let total = 0;
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dotLottie.addEventListener("load", () => { total = dotLottie.totalFrames; });
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window.addEventListener("scroll", () => {
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const el = canvas.closest(".scrolly");
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const rect = el.getBoundingClientRect();
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const p = clamp(-rect.top / (rect.height - window.innerHeight), 0, 1); // 0..1 through the section
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dotLottie.setFrame(p * (total - 1));
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}, { passive: true });
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const clamp = (v, lo, hi) => Math.min(hi, Math.max(lo, v));
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```
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For richer interaction (hover-to-play, click toggles, cursor-follow) without writing the wiring, use `@lottiefiles/lottie-interactivity`, which maps `scroll`, `hover`, `click`, `play`, and `cursor` modes to frame ranges declaratively.
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## Runtime theming / recoloring
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Two paths:
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- **dotLottie themes**: a `.lottie` can embed named color themes; switch with `dotLottie.setTheme("dark")` / `loadTheme(...)`. Authored in LottieFiles tooling — no re-export to recolor.
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- **Manual color override**: load the JSON, walk `layers[].shapes[]` and patch `c.k` color arrays (normalized 0–1 RGBA), then init the player with the modified object. Brittle (depends on layer structure) — prefer themes or CSS-driven SVG-renderer (`lottie-web` `rendererSettings`) when you must restyle by class.
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## Mobile runtimes (parity)
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- iOS — `lottie-ios` (`LottieAnimationView`): `.play()`, `.currentProgress`, `.play(fromFrame:toFrame:)`.
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- Android — `lottie-android` (`LottieAnimationView` / Compose `LottieAnimation`): `setMinAndMaxFrame`, `progress`.
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- React Native — `lottie-react-native` (`<LottieView source={...} progress={anim} />`, drive `progress` with `Animated`).
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The same `.lottie`/`.json` plays across all; segments and progress concepts match the web API.
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## Optimization
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- Ship `.lottie` (zipped) over raw `.json`; lazy-load offscreen players and pause when not visible (`IntersectionObserver` → `play`/`pause`).
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- Prefer the canvas/WASM dotLottie renderer for many simultaneous animations; SVG renderer (lottie-web) is fine for one crisp icon but costs more DOM for complex files.
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- Keep AE comps small: fewer layers/keyframes, no large embedded rasters; flatten precomps where possible. File size tracks keyframe and path complexity, not duration.
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- Recolor at runtime (themes) instead of exporting a file per brand/theme.
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## Deliver & verify (standalone HTML)
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> **Packaged helper** (`scripts/`): `scripts/seek-shot.sh anim.html 0 1.5 3` freezes the `?t=N` harness and screenshots each moment; `scripts/contact-sheet.sh sheet.png frame-*.png` tiles them for one-glance review. See `scripts/README.md`.
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For a self-contained Lottie demo (looping illustration, animated icon, empty state) the deliverable is **one HTML file that opens directly in a browser** — the dotLottie/lottie-web runtime from CDN, a `<canvas>`, and your `.lottie`/`.json` (a relative file or a data URL). No build step. One file is the right tier for shipping a player; don't reach for a bundler.
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**Output contract:**
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- One `.html` file: the runtime via CDN (`@lottiefiles/dotlottie-web`), the canvas, and `autoplay:false` so the frame is yours to drive.
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- Include the seek harness so any frame can be frozen for a screenshot.
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**Seek harness — freeze an exact frame.** `?t=N` jumps to a frame and holds it so a screenshot lands on a still, deterministic frame. Lottie's playhead is in frames, so stop on the frame directly:
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```html
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<script>
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const dl = new DotLottie({ canvas, src: "/icon.lottie", autoplay: false });
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dl.addEventListener("load", () => {
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const t = new URLSearchParams(location.search).get("t");
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if (t !== null) dl.setFrame(parseFloat(t)); // freeze on frame N (lottie-web: anim.goToAndStop(N, true))
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else dl.play();
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console.log("totalFrames", dl.totalFrames); // read for end-frame
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window.__ready = true;
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});
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</script>
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```
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**Verify loop — render → freeze → screenshot → check:** open the file at first / mid / last frame (`?t=0`, `?t=<total/2>`, `?t=<total-1>`; read `totalFrames` from the console), screenshot each, and check **fidelity** (colors/theme correct, segment loops where intended) plus **artifacts** (canvas blurry from missing `autoResize`/DPR, clipped composition, FOUC before the file loads, jank). Any headless tool works:
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```bash
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npx playwright screenshot --wait-for-timeout=600 "file://$PWD/lottie.html?t=42" frame-mid.png
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```
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**Before you finish:**
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1. Opens standalone — no console errors, CDN runtime and the `.lottie`/`.json` load.
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2. `?t=N` (`setFrame`/`goToAndStop`) freezes the correct, deterministic frame.
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3. Screenshotted at first / mid / last frame — matches the brief, sharp, no clipping.
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4. `prefers-reduced-motion` honored — don't `autoplay` a loop; show a static frame or offer a play control.
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5. Easing is intentional — playback speed/segment chosen on purpose, motion baked in AE reads as designed.
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## Quick reference
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| Goal | Call |
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|------|------|
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| Play a range | `setSegment(start, end)` |
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| Jump to frame | `setFrame(n)` |
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| Reverse / bounce | `setMode("reverse"|"bounce")` |
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| Scroll-drive | `autoplay:false` + `setFrame(p*totalFrames)` |
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| Theme swap | `setTheme("dark")` |
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| Know length | `totalFrames` after `load` event |
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| Declarative interactivity | `@lottiefiles/lottie-interactivity` |
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## Reference files
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- `references/integration-and-export.md` — full dotLottie-web + React setup and event/segment control, `lottie-interactivity` mode configs, scroll/cursor patterns, runtime theming details, and the complete After Effects → Bodymovin export checklist with the list of unsupported AE features and how to work around them.
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