ScrollZoomReveal

npx motionfoundry add scroll-zoom-reveal

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

1"use client";2 3import * as React from "react";4import styles from "../styles/scroll-zoom-reveal.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 ScrollZoomRevealProps {183  /** Headline revealed once the panel is full-bleed */184  title?: string;185  /** Supporting line under the headline */186  subtitle?: string;187  /** Caption shown before the zoom starts */188  caption?: string;189  /** First gradient color of the panel art */190  color1?: string;191  /** Second gradient color of the panel art */192  color2?: string;193  /** Initial panel size as a fraction of the viewport (0.2–0.9) */194  startScale?: number;195  /** Viewport height in px */196  height?: number;197  /** Viewport corner radius in px */198  borderRadius?: number;199  /** Interpolation factor per 60fps frame (0.05 = floaty, 0.3 = snappy) */200  lerp?: number;201  /** Multiplier applied to wheel / trackpad deltas */202  wheelMultiplier?: number;203  /** Enable smooth wheel scrolling (native scrolling when false or under reduced motion) */204  smooth?: boolean;205  /** Optional className merged onto the root */206  className?: string;207  /** Inline styles merged onto the root */208  style?: React.CSSProperties;209}210 211const easeInOutCubic = (t: number) => (t < 0.5 ? 4 * t * t * t : 1 - Math.pow(-2 * t + 2, 3) / 2);212const easeOutCubic = (t: number) => 1 - Math.pow(1 - t, 3);213 214export function ScrollZoomReveal({215  title = "Step into the frame",216  subtitle = "A small window grows into the whole world as you scroll.",217  caption = "Scroll to zoom",218  color1 = "#7c3aed",219  color2 = "#fb7185",220  startScale = 0.42,221  height = 380,222  borderRadius = 20,223  lerp = 0.1,224  wheelMultiplier = 1,225  smooth = true,226  className = "",227  style,228}: ScrollZoomRevealProps) {229  const reduced = usePrefersReducedMotion();230  const rootRef = React.useRef<HTMLDivElement>(null);231  const viewportRef = React.useRef<HTMLDivElement>(null);232  const s0 = clamp(startScale, 0.1, 1);233 234  const handleScroll = React.useCallback(235    (state: SmoothScrollState) => {236      const root = rootRef.current;237      if (!root) return;238      const p = state.progress;239      const expand = easeInOutCubic(clamp(p / 0.62, 0, 1));240      const k = s0 + (1 - s0) * expand;241      const reveal = easeOutCubic(clamp((p - 0.5) / 0.32, 0, 1));242      root.style.setProperty("--mf-szr-k", k.toFixed(4));243      root.style.setProperty("--mf-szr-e", expand.toFixed(4));244      root.style.setProperty("--mf-szr-t", reveal.toFixed(4));245      root.style.setProperty("--mf-szr-cap", clamp(1 - p / 0.22, 0, 1).toFixed(4));246    },247    [s0],248  );249 250  useSmoothScroll(viewportRef, { lerp, wheelMultiplier, smooth: smooth && !reduced, onScroll: handleScroll });251 252  const vars = {253    "--mf-szr-h": `${height}px`,254    "--mf-szr-r": `${borderRadius}px`,255    "--mf-szr-c1": color1,256    "--mf-szr-c2": color2,257    "--mf-szr-k": s0,258    ...style,259  } as React.CSSProperties;260 261  return (262    <div ref={rootRef} style={vars} className={`${styles.root} ${className}`.trim()}>263      <div ref={viewportRef} className={styles.viewport} tabIndex={0} role="region" aria-label={title}>264        <div className={styles.track} style={{ height: `${Math.round(height * 3.2)}px` }}>265          <div className={styles.stage}>266            <span aria-hidden="true" className={styles.caption}>267              {caption}268            </span>269            <div className={styles.panel}>270              <div aria-hidden="true" className={styles.art}>271                <span className={styles.sun} />272                <span className={styles.grid} />273                <span className={`${styles.ridge} ${styles.ridgeBack}`} />274                <span className={`${styles.ridge} ${styles.ridgeFront}`} />275              </div>276              <div className={styles.copy}>277                <h3 className={styles.title}>{title}</h3>278                <p className={styles.subtitle}>{subtitle}</p>279              </div>280            </div>281          </div>282        </div>283      </div>284    </div>285  );286}