ScrollTimeline

npx motionfoundry add scroll-timeline

1import { ScrollTimeline } from "@motionfoundry/ui";2 3export function Example() {4  return (5    <ScrollTimeline />6  );7}

1"use client";2 3import * as React from "react";4import styles from "../styles/scroll-timeline.module.css";5 6interface SmoothScrollState {7  /** Current scrollTop of the viewport in px */8  scroll: number;9  /** Maximum scrollTop in px */10  limit: number;11  /** scroll / limit, 0..1 */12  progress: number;13  /** Signed scroll velocity in px per 60fps frame */14  velocity: number;15}16 17interface SmoothScrollOptions {18  lerp: number;19  wheelMultiplier: number;20  smooth: boolean;21  onScroll?: (state: SmoothScrollState) => void;22}23 24const clamp = (v: number, min: number, max: number) => Math.min(max, Math.max(min, v));25 26function usePrefersReducedMotion(): boolean {27  const [reduced, setReduced] = React.useState(false);28  React.useEffect(() => {29    const mq = window.matchMedia("(prefers-reduced-motion: reduce)");30    const update = () => setReduced(mq.matches);31    update();32    mq.addEventListener("change", update);33    return () => mq.removeEventListener("change", update);34  }, []);35  return reduced;36}37 38/** True when a nested scrollable element under the pointer can still scroll in the wheel direction. */39function nestedCanScroll(node: EventTarget | null, root: HTMLElement, dy: number): boolean {40  let el: Element | null = node instanceof Element ? node : null;41  while (el && el !== root) {42    if (el instanceof HTMLElement) {43      if (el.dataset.mfScrollPrevent !== undefined) return true;44      const overflowY = window.getComputedStyle(el).overflowY;45      if ((overflowY === "auto" || overflowY === "scroll") && el.scrollHeight > el.clientHeight + 1) {46        const canMove = dy < 0 ? el.scrollTop > 0 : el.scrollTop + el.clientHeight < el.scrollHeight - 1;47        if (canMove) return true;48      }49    }50    el = el.parentElement;51  }52  return false;53}54 55/**56 * Self-contained smooth scroller for an overflow container. Wheel input updates a target57 * position; a rAF loop eases the real scrollTop toward it (frame-rate independent lerp) and58 * stops once settled. Touch, keyboard and scrollbar drags stay native. At the top/bottom edge59 * wheel events are released so the page keeps scrolling.60 */61function useSmoothScroll(62  containerRef: React.RefObject<HTMLElement | null>,63  { lerp, wheelMultiplier, smooth, onScroll }: SmoothScrollOptions,64): React.RefObject<SmoothScrollState> {65  const stateRef = React.useRef<SmoothScrollState>({ scroll: 0, limit: 0, progress: 0, velocity: 0 });66  const callbackRef = React.useRef(onScroll);67  React.useEffect(() => {68    callbackRef.current = onScroll;69  }, [onScroll]);70 71  React.useEffect(() => {72    const el = containerRef.current;73    if (!el) return;74    const ease = clamp(Number.isFinite(lerp) ? lerp : 0.1, 0.01, 1);75    const multiplier = Number.isFinite(wheelMultiplier) ? wheelMultiplier : 1;76    let target = el.scrollTop;77    let current = target;78    let raf = 0;79    let lastTime = 0;80    let lastNative = el.scrollTop;81    let lastNativeTime = 0;82    let settleTimer: ReturnType<typeof setTimeout> | undefined;83 84    const getLimit = () => Math.max(0, el.scrollHeight - el.clientHeight);85 86    const emit = (velocity: number) => {87      const limit = getLimit();88      const scroll = clamp(el.scrollTop, 0, limit);89      lastNative = el.scrollTop;90      const s = stateRef.current;91      s.scroll = scroll;92      s.limit = limit;93      s.progress = limit > 0 ? scroll / limit : 0;94      s.velocity = velocity;95      callbackRef.current?.(s);96    };97 98    const tick = (time: number) => {99      const dt = lastTime ? Math.min(64, Math.max(1, time - lastTime)) : 16.667;100      lastTime = time;101      const limit = getLimit();102      target = clamp(target, 0, limit);103      if (Math.abs(el.scrollTop - current) > 2) {104        // Something else moved the viewport (scrollbar drag, keyboard, touch): hand control back.105        current = target = el.scrollTop;106        raf = 0;107        lastTime = 0;108        emit(0);109        return;110      }111      const prev = current;112      const frames = dt / 16.667;113      current += (target - current) * (1 - Math.pow(1 - ease, frames));114      if (Math.abs(target - current) < 0.35) current = target;115      el.scrollTop = current;116      emit((current - prev) / frames);117      if (current === target) {118        raf = 0;119        lastTime = 0;120        emit(0);121        return;122      }123      raf = requestAnimationFrame(tick);124    };125 126    const onWheel = (event: WheelEvent) => {127      if (event.ctrlKey || event.defaultPrevented) return;128      if (Math.abs(event.deltaX) > Math.abs(event.deltaY)) return;129      let dy = event.deltaY;130      if (event.deltaMode === 1) dy *= 16;131      else if (event.deltaMode === 2) dy *= el.clientHeight;132      dy *= multiplier;133      if (dy === 0 || nestedCanScroll(event.target, el, dy)) return;134      const limit = getLimit();135      if (!raf) current = target = el.scrollTop;136      // Release to native scrolling at the edges so the page is never trapped.137      if ((dy < 0 && target <= 0) || (dy > 0 && target >= limit - 0.5)) return;138      event.preventDefault();139      target = clamp(target + dy, 0, limit);140      if (!raf) {141        lastTime = 0;142        raf = requestAnimationFrame(tick);143      }144    };145 146    const onNativeScroll = () => {147      if (raf) return;148      const top = el.scrollTop;149      const delta = top - lastNative;150      if (delta === 0) return;151      const now = performance.now();152      const dt = lastNativeTime ? clamp(now - lastNativeTime, 8, 100) : 16.667;153      lastNativeTime = now;154      current = target = top;155      emit(delta / (dt / 16.667));156      if (settleTimer) clearTimeout(settleTimer);157      settleTimer = setTimeout(() => {158        lastNativeTime = 0;159        emit(0);160      }, 90);161    };162 163    if (smooth) el.addEventListener("wheel", onWheel, { passive: false });164    el.addEventListener("scroll", onNativeScroll, { passive: true });165    const ro = new ResizeObserver(() => emit(stateRef.current.velocity));166    ro.observe(el);167    if (el.firstElementChild) ro.observe(el.firstElementChild);168    emit(0);169 170    return () => {171      if (smooth) el.removeEventListener("wheel", onWheel);172      el.removeEventListener("scroll", onNativeScroll);173      ro.disconnect();174      if (raf) cancelAnimationFrame(raf);175      if (settleTimer) clearTimeout(settleTimer);176    };177  }, [containerRef, lerp, wheelMultiplier, smooth]);178 179  return stateRef;180}181 182export interface ScrollTimelineProps {183  /** Milestone titles, one per timeline entry */184  items?: string[];185  /** Optional description per milestone (matched by index) */186  descriptions?: string[];187  /** Heading shown above the timeline */188  title?: string;189  /** Accent color for the drawn line and active dots */190  accentColor?: string;191  /** Viewport height in px */192  height?: number;193  /** Viewport corner radius in px */194  borderRadius?: number;195  /** Interpolation factor per 60fps frame (0.05 = floaty, 0.3 = snappy) */196  lerp?: number;197  /** Multiplier applied to wheel / trackpad deltas */198  wheelMultiplier?: number;199  /** Enable smooth wheel scrolling (native scrolling when false or under reduced motion) */200  smooth?: boolean;201  /** Optional className merged onto the root */202  className?: string;203  /** Inline styles merged onto the root */204  style?: React.CSSProperties;205}206 207const DEFAULT_ITEMS = [208  "Idea on a napkin",209  "First prototype",210  "Private beta",211  "Public launch",212  "10k teams onboard",213  "What comes next",214];215 216const DEFAULT_DESCRIPTIONS = [217  "A late-night sketch of a motion library that stays out of the way.",218  "Twelve components, one rAF loop, zero dependencies beyond React.",219  "Forty studios stress-test every easing curve and edge case.",220  "Docs, playground and CLI ship the same afternoon.",221  "Teams across product, marketing and games build with it daily.",222  "Scroll-driven scenes, physics and a visual timeline editor.",223];224 225/** Fraction of the viewport height where the line tip sits. */226const ANCHOR = 0.6;227 228export function ScrollTimeline({229  items = DEFAULT_ITEMS,230  descriptions = DEFAULT_DESCRIPTIONS,231  title = "How we got here",232  accentColor = "#34d399",233  height = 380,234  borderRadius = 20,235  lerp = 0.1,236  wheelMultiplier = 1,237  smooth = true,238  className = "",239  style,240}: ScrollTimelineProps) {241  const reduced = usePrefersReducedMotion();242  const rootRef = React.useRef<HTMLDivElement>(null);243  const viewportRef = React.useRef<HTMLDivElement>(null);244  const listRef = React.useRef<HTMLDivElement>(null);245  const itemRefs = React.useRef<(HTMLLIElement | null)[]>([]);246  const geometryRef = React.useRef({ listTop: 0, listHeight: 1, dots: [] as number[] });247  const stateRef = React.useRef({ scroll: 0, progress: 0, viewport: 0 });248  const total = items.length;249 250  const apply = React.useCallback(() => {251    const root = rootRef.current;252    if (!root) return;253    const { listTop, listHeight, dots } = geometryRef.current;254    const { scroll, progress, viewport } = stateRef.current;255    const anchor = progress >= 0.999 ? Number.POSITIVE_INFINITY : scroll + viewport * ANCHOR - listTop;256    const fill = clamp(anchor / listHeight, 0, 1);257    root.style.setProperty("--mf-st-fill", fill.toFixed(4));258    for (let i = 0; i < total; i++) {259      const item = itemRefs.current[i];260      if (!item) continue;261      const active = anchor >= (dots[i] ?? 0);262      if ((item.dataset.active === "true") !== active) item.dataset.active = active ? "true" : "false";263    }264  }, [total]);265 266  const handleScroll = React.useCallback(267    (state: SmoothScrollState) => {268      stateRef.current.scroll = state.scroll;269      stateRef.current.progress = state.progress;270      apply();271    },272    [apply],273  );274 275  useSmoothScroll(viewportRef, { lerp, wheelMultiplier, smooth: smooth && !reduced, onScroll: handleScroll });276 277  React.useEffect(() => {278    const list = listRef.current;279    const viewport = viewportRef.current;280    if (!list || !viewport) return;281    const measure = () => {282      geometryRef.current = {283        listTop: list.offsetTop,284        listHeight: Math.max(1, list.offsetHeight),285        dots: itemRefs.current.slice(0, total).map((node) => (node ? node.offsetTop + 22 : 0)),286      };287      stateRef.current.viewport = viewport.clientHeight;288      apply();289    };290    measure();291    const ro = new ResizeObserver(measure);292    ro.observe(list);293    ro.observe(viewport);294    return () => ro.disconnect();295  }, [total, apply]);296 297  const vars = {298    "--mf-st-h": `${height}px`,299    "--mf-st-r": `${borderRadius}px`,300    "--mf-st-accent": accentColor,301    ...style,302  } as React.CSSProperties;303 304  return (305    <div ref={rootRef} style={vars} className={`${styles.root} ${className}`.trim()}>306      <div ref={viewportRef} className={styles.viewport} tabIndex={0} role="region" aria-label={title}>307        <div className={styles.content}>308          <header className={styles.header}>309            <span className={styles.kicker}>Timeline</span>310            <h3 className={styles.title}>{title}</h3>311          </header>312          <div ref={listRef} className={styles.timeline}>313            <span aria-hidden="true" className={styles.line}>314              <span className={styles.lineFill} />315            </span>316            <ol className={styles.list}>317              {items.map((item, i) => (318                <li319                  key={`${item}-${i}`}320                  ref={(node) => {321                    itemRefs.current[i] = node;322                  }}323                  className={styles.item}324                >325                  <span aria-hidden="true" className={styles.dot} />326                  <div className={styles.card}>327                    <span className={styles.step}>{`Milestone ${String(i + 1).padStart(2, "0")}`}</span>328                    <span className={styles.itemTitle}>{item}</span>329                    {descriptions[i] && <p className={styles.description}>{descriptions[i]}</p>}330                  </div>331                </li>332              ))}333            </ol>334          </div>335        </div>336      </div>337    </div>338  );339}