nehakanjamala/personal_website

Lottie Animation

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.

When to use

• Ship a designer's AE animation to web/iOS/Android/React Native
• Looping illustrations, onboarding, empty states, animated icons
• Scroll-driven or interaction-driven vector playback (hover, click, cursor)
• Runtime theming/recoloring instead of re-exporting per brand

Formats: .json vs .lottie

• .json — the raw Bodymovin output. Human-readable, larger.
• .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.

Prefer the dotLottie runtime for new work; use lottie-web only for legacy .json + SVG renderer needs.

Core workflow (web, dotLottie)

npm i @lottiefiles/dotlottie-web        # vanilla
npm i @lottiefiles/dotlottie-react      # React wrapper

Vanilla:

import { DotLottie } from "@lottiefiles/dotlottie-web";

const dotLottie = new DotLottie({
  canvas: document.querySelector("#lottie"),  // a <canvas> element
  src: "/hero.lottie",                         // or .json
  loop: true,
  autoplay: true,
  // speed: 1, mode: "forward" | "reverse" | "bounce", renderConfig: { autoResize: true }
});

React:

import { DotLottieReact } from "@lottiefiles/dotlottie-react";

function Hero() {
  return <DotLottieReact src="/hero.lottie" loop autoplay style={{ width: 320 }} />;
}

Capture the instance to control it:

const [dl, setDl] = useState(null);
<DotLottieReact src="/icon.lottie" dotLottieRefCallback={setDl} />;
// dl?.play(); dl?.pause(); dl?.setSpeed(2);

Playback control

dotLottie.play();
dotLottie.pause();
dotLottie.stop();
dotLottie.setSpeed(1.5);
dotLottie.setMode("bounce");        // forward | reverse | bounce | reverse-bounce
dotLottie.setFrame(42);             // jump to a frame
dotLottie.setSegment(30, 90);       // constrain playback to a frame range (e.g. a "loading" loop)

Events drive sequencing and UI:

dotLottie.addEventListener("load", () => { /* totalFrames now available */ });
dotLottie.addEventListener("complete", () => { /* non-looping playback finished */ });
dotLottie.addEventListener("frame", ({ currentFrame }) => { /* per-frame */ });

State-machine style (e.g. button that plays "checked" segment then idles): play a segment, listen for complete, then setSegment to the idle loop.

Scroll-driven Lottie (no GSAP needed)

Map scroll progress (0–1) to a frame. Pause autoplay and drive frames yourself.

const dotLottie = new DotLottie({ canvas, src: "/scroll.lottie", autoplay: false });
let total = 0;
dotLottie.addEventListener("load", () => { total = dotLottie.totalFrames; });

window.addEventListener("scroll", () => {
  const el = canvas.closest(".scrolly");
  const rect = el.getBoundingClientRect();
  const p = clamp(-rect.top / (rect.height - window.innerHeight), 0, 1); // 0..1 through the section
  dotLottie.setFrame(p * (total - 1));
}, { passive: true });

const clamp = (v, lo, hi) => Math.min(hi, Math.max(lo, v));

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.

Runtime theming / recoloring

Two paths:

• dotLottie themes: a .lottie can embed named color themes; switch with dotLottie.setTheme("dark") / loadTheme(...). Authored in LottieFiles tooling — no re-export to recolor.
• 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.

Mobile runtimes (parity)

• iOS — lottie-ios (LottieAnimationView): .play(), .currentProgress, .play(fromFrame:toFrame:).
• Android — lottie-android (LottieAnimationView / Compose LottieAnimation): setMinAndMaxFrame, progress.
• React Native — lottie-react-native (<LottieView source={...} progress={anim} />, drive progress with Animated).

The same .lottie/.json plays across all; segments and progress concepts match the web API.

Optimization

• Ship .lottie (zipped) over raw .json; lazy-load offscreen players and pause when not visible (IntersectionObserver → play/pause).
• 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.
• Keep AE comps small: fewer layers/keyframes, no large embedded rasters; flatten precomps where possible. File size tracks keyframe and path complexity, not duration.
• Recolor at runtime (themes) instead of exporting a file per brand/theme.

Deliver & verify (standalone HTML)

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.

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.

Output contract:

• One .html file: the runtime via CDN (@lottiefiles/dotlottie-web), the canvas, and autoplay:false so the frame is yours to drive.
• Include the seek harness so any frame can be frozen for a screenshot.

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:

<script>
  const dl = new DotLottie({ canvas, src: "/icon.lottie", autoplay: false });
  dl.addEventListener("load", () => {
    const t = new URLSearchParams(location.search).get("t");
    if (t !== null) dl.setFrame(parseFloat(t));      // freeze on frame N (lottie-web: anim.goToAndStop(N, true))
    else dl.play();
    console.log("totalFrames", dl.totalFrames);       // read for end-frame
    window.__ready = true;
  });
</script>

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:

npx playwright screenshot --wait-for-timeout=600 "file://$PWD/lottie.html?t=42" frame-mid.png

Before you finish:

1. Opens standalone — no console errors, CDN runtime and the .lottie/.json load.
2. ?t=N (setFrame/goToAndStop) freezes the correct, deterministic frame.
3. Screenshotted at first / mid / last frame — matches the brief, sharp, no clipping.
4. prefers-reduced-motion honored — don't autoplay a loop; show a static frame or offer a play control.
5. Easing is intentional — playback speed/segment chosen on purpose, motion baked in AE reads as designed.

Quick reference

Goal	Call
Play a range	setSegment(start, end)
Jump to frame	setFrame(n)
Reverse / bounce	`setMode("reverse"
Scroll-drive	autoplay:false + setFrame(p*totalFrames)
Theme swap	setTheme("dark")
Know length	totalFrames after load event
Declarative interactivity	@lottiefiles/lottie-interactivity

Reference files

• 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.