06限界を超えると抵抗が増して戻ってくる箱

<main class="stage">
<div class="rh is-demo" id="rh" data-demo="1">
  <div class="rh__panel" data-r="panel">
    <i class="rh__stripe"></i>
    <button class="rh__grip" data-r="grip" type="button" aria-label="サイズ変更つまみ"></button>
  </div>
  <i class="rh__limit" data-r="limit"></i>
  <p class="rh__meta"><span class="rh__tag">MAX</span> <b data-r="max">0</b> <span class="rh__tag">OVER</span> <b data-r="over">0</b></p>
  <i class="rh__cursor" data-r="cursor"></i>
</div>
</main>

@use "../../../../site/static/demo-tokens" as *;

// 핵심: 늘어난 양(--over)이 색과 줄무늬를 같이 끈다. 폭은 JS 스프링이 만든다.

@include stage($stage-ink);

.rh {
  position: relative;
  box-sizing: border-box;
  width: min(100%, 440px);
  height: min(252px, calc(100vh - 2 * clamp(8px, 4vw, 24px)));
  color: $subject-cream;
  font-size: 12px;
  line-height: 16px;
  font-weight: 600;
  user-select: none;
}
.rh b { font-weight: 800; font-variant-numeric: tabular-nums; }
.rh__tag { color: $tick-mute; letter-spacing: .5px; }
.rh__cursor {
  position: absolute;
  left: -10px;
  top: -10px;
  width: 20px;
  height: 20px;
  border-radius: 50%;
  background: $subject-cream;
  box-shadow: 0 0 0 3px rgba($subject-ink, .55), $shadow-press;
  opacity: 0;
  pointer-events: none;
  z-index: 6;
}
.rh[data-demo] .rh__cursor { opacity: 1; }
.rh button:focus-visible { outline: 3px solid $subject-pink; outline-offset: 2px; }
@media (prefers-reduced-motion: reduce) {
  .rh__cursor { display: none; }
}

.rh__panel {
  --over: 0;
  position: absolute;
  left: 0;
  top: 0;
  box-sizing: border-box;
  height: calc(100% - 24px);
  overflow: hidden;
  border-radius: $r-card;
  background: color-mix(in srgb, #{$subject-mint}, #{$subject-pink} calc(var(--over) * 100%));
}
.rh__stripe {
  position: absolute;
  inset: 0;
  opacity: var(--over);
  background: repeating-linear-gradient(90deg, transparent 0 10px, rgba($subject-ink, .18) 10px 12px);
}
.rh__grip {
  position: absolute;
  right: $sp-2;
  top: 50%;
  width: 12px;
  height: 64px;
  padding: 0;
  border: 0;
  border-radius: $r-pill;
  background: $subject-ink;
  transform: translateY(-50%);
  cursor: ew-resize;
  touch-action: none;
}
.rh__limit {
  position: absolute;
  left: 0;
  top: 0;
  height: calc(100% - 24px);
  border-left: 2px dashed $subject-cream;
  pointer-events: none;
}
.rh__meta { position: absolute; left: 0; bottom: 0; margin: 0; }

html, body {
  margin: 0;
  overflow: hidden;
}

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #17141a;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.rh {
  position: relative;
  box-sizing: border-box;
  width: min(100%, 440px);
  height: min(252px, 100vh - 2 * clamp(8px, 4vw, 24px));
  color: #fff7e6;
  font-size: 12px;
  line-height: 16px;
  font-weight: 600;
  user-select: none;
}

.rh b {
  font-weight: 800;
  font-variant-numeric: tabular-nums;
}

.rh__tag {
  color: #9a93a6;
  letter-spacing: 0.5px;
}

.rh__cursor {
  position: absolute;
  left: -10px;
  top: -10px;
  width: 20px;
  height: 20px;
  border-radius: 50%;
  background: #fff7e6;
  box-shadow: 0 0 0 3px rgba(23, 20, 26, 0.55), 0 6px 12px rgba(23, 20, 26, 0.32);
  opacity: 0;
  pointer-events: none;
  z-index: 6;
}

.rh[data-demo] .rh__cursor {
  opacity: 1;
}

.rh button:focus-visible {
  outline: 3px solid #ff9ebb;
  outline-offset: 2px;
}

@media (prefers-reduced-motion: reduce) {
  .rh__cursor {
    display: none;
  }
}
.rh__panel {
  --over: 0;
  position: absolute;
  left: 0;
  top: 0;
  box-sizing: border-box;
  height: calc(100% - 24px);
  overflow: hidden;
  border-radius: 16px;
  background: color-mix(in srgb, #4cd4a6, #ff9ebb calc(var(--over) * 100%));
}

.rh__stripe {
  position: absolute;
  inset: 0;
  opacity: var(--over);
  background: repeating-linear-gradient(90deg, transparent 0 10px, rgba(23, 20, 26, 0.18) 10px 12px);
}

.rh__grip {
  position: absolute;
  right: 8px;
  top: 50%;
  width: 12px;
  height: 64px;
  padding: 0;
  border: 0;
  border-radius: 999px;
  background: #17141a;
  transform: translateY(-50%);
  cursor: ew-resize;
  touch-action: none;
}

.rh__limit {
  position: absolute;
  left: 0;
  top: 0;
  height: calc(100% - 24px);
  border-left: 2px dashed #fff7e6;
  pointer-events: none;
}

.rh__meta {
  position: absolute;
  left: 0;
  bottom: 0;
  margin: 0;
}

(function () {
    const root = document.getElementById("rh");
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    let demo = !reduce;
    let raf = 0;
    let t0 = -1;
    let last = -1;
    const offs = [];
    function q(sel) {
        return root.querySelector(sel);
    }
    function clamp(v, lo, hi) {
        return Math.max(lo, Math.min(hi, v));
    }
    function seg(t, a, b) {
        const c = clamp((t - a) / (b - a), 0, 1);
        return c * c * (3 - 2 * c);
    }
    function on(el, type, fn) {
        el.addEventListener(type, fn);
        offs.push(() => el.removeEventListener(type, fn));
    }
    function stopDemo() {
        demo = false;
        root.removeAttribute("data-demo");
        root.classList.remove("is-demo");
    }
    function pos(e) {
        const r = root.getBoundingClientRect();
        return { x: e.clientX - r.left, y: e.clientY - r.top };
    }
    function spring(x, v, to, k, c, dt) {
        const n = Math.max(1, Math.ceil(dt / 0.008));
        const h = dt / n;
        for (let i = 0; i < n; i += 1) {
            v += (-k * (x - to) - c * v) * h;
            x += v * h;
        }
        return [x, v];
    }
    function sync() {
        if (reduce) {
            snap();
            render();
        }
    }
    // 기법: 한계(MAX_RATIO) 넘은 만큼을 제곱근으로 눌러 저항을 만든다 - 더 끌수록 같은 거리에서 덜 늘어난다.
    // 놓으면 목표는 한계선이고, 감쇠비 0.35 의 스프링이 한계선을 지나쳤다 돌아오며 진동한다.
    const MAX_RATIO = 0.64;
    const RESIST = 5;
    const SPRING_BACK = 16;
    const MIN_W = 56;
    const panel = q("[data-r=panel]");
    const grip = q("[data-r=grip]");
    const limit = q("[data-r=limit]");
    const maxEl = q("[data-r=max]");
    const overEl = q("[data-r=over]");
    const cursor = q("[data-r=cursor]");
    let w = 0;
    let vw = 0;
    let target = 0;
    let raw = 0;
    let px = 0;
    let py = 0;
    let gx = 0;
    let grabW = 0;
    let dragging = false;
    let ready = false;
    function maxW() { return root.clientWidth * MAX_RATIO; }
    function stretch(r) {
        const m = maxW();
        return r <= m ? r : m + RESIST * Math.sqrt(r - m);
    }
    function init() {
        if (ready)
            return;
        ready = true;
        target = raw = w = root.clientWidth * 0.4;
    }
    function release() {
        if (!dragging)
            return;
        dragging = false;
        target = Math.min(raw, maxW());
    }
    function userTakes() {
        stopDemo();
        dragging = false;
        init();
    }
    function script(now) {
        const W = root.clientWidth;
        const ph = now % 2000;
        const was = dragging;
        const r0 = W * 0.4;
        dragging = false;
        if (ph >= 200 && ph < 1000) {
            dragging = true;
            raw = r0 + (W - r0) * seg(ph, 200, 700);
        }
        else if (ph >= 1400 && ph < 1960) {
            dragging = true;
            if (!was)
                grabW = w;
            raw = grabW + (r0 - grabW) * seg(ph, 1400, 1960);
        }
        if (was && !dragging) {
            dragging = true;
            release();
        }
        px = (dragging ? raw : w) - 8;
        py = root.clientHeight * 0.5;
        gx = 8;
    }
    function snap() {
        init();
        w = target;
        vw = 0;
    }
    function step(dt, now) {
        init();
        if (demo)
            script(now);
        if (dragging) {
            if (!demo)
                raw = clamp(px + gx, MIN_W, root.clientWidth);
            target = clamp(stretch(raw), MIN_W, root.clientWidth);
            const a = spring(w, vw, target, 1600, 80, dt);
            w = a[0];
            vw = a[1];
        }
        else {
            const a = spring(w, vw, target, SPRING_BACK * SPRING_BACK, 2 * 0.35 * SPRING_BACK, dt);
            w = a[0];
            vw = a[1];
        }
    }
    function render() {
        const m = maxW();
        const over = Math.max(0, w - m);
        const span = Math.max(1, RESIST * Math.sqrt(Math.max(1, root.clientWidth - m)));
        panel.style.width = w.toFixed(1) + "px";
        panel.style.setProperty("--over", clamp(over / span, 0, 1).toFixed(3));
        limit.style.transform = "translateX(" + m.toFixed(1) + "px)";
        maxEl.textContent = String(Math.round(m));
        overEl.textContent = String(Math.round(over));
        cursor.style.transform = "translate(" + px.toFixed(1) + "px," + py.toFixed(1) + "px)";
    }
    on(grip, "pointerdown", (e) => {
        userTakes();
        grip.setPointerCapture(e.pointerId);
        const p = pos(e);
        px = p.x;
        py = p.y;
        gx = w - p.x;
        raw = w;
        dragging = true;
    });
    on(grip, "pointermove", (e) => {
        if (!dragging)
            return;
        px = pos(e).x;
        raw = clamp(px + gx, MIN_W, root.clientWidth);
        if (reduce) {
            target = clamp(Math.min(stretch(raw), maxW()), MIN_W, root.clientWidth);
            sync();
        }
    });
    on(grip, "pointerup", release);
    on(grip, "pointercancel", release);
    on(grip, "keydown", (e) => {
        if (e.key !== "ArrowLeft" && e.key !== "ArrowRight")
            return;
        e.preventDefault();
        userTakes();
        target = clamp(target + (e.key === "ArrowRight" ? 16 : -16), MIN_W, maxW());
        sync();
    });
    function frame(ts) {
        if (t0 < 0) {
            t0 = ts;
            last = ts;
        }
        const dt = Math.min(0.05, (ts - last) / 1000);
        last = ts;
        step(dt, ts - t0);
        render();
        raf = requestAnimationFrame(frame);
    }
    if (reduce) {
        stopDemo();
        snap();
        render();
    }
    else {
        raf = requestAnimationFrame(frame);
    }
    return () => {
        cancelAnimationFrame(raf);
        offs.forEach((f) => f());
    };
})();

// RubberBandLimit - vanilla 판(06-rh-rubber-band-limit) 의 React 포트. 같은 계산을 useEffect 안에서 돌린다.
import { useEffect, useRef } from "react";
import styles from "./RubberBandLimit.module.scss";

export default function RubberBandLimit() {
  const rootRef = useRef<HTMLDivElement | null>(null);

  useEffect(() => {
    const rootEl = rootRef.current;
    if (!rootEl) return;
    const root: HTMLElement = rootEl;
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    let demo = !reduce;
    let raf = 0;
    let t0 = -1;
    let last = -1;
    const offs: Array<() => void> = [];

    function q<T extends Element>(sel: string): T {
      return root.querySelector(sel) as T;
    }
    function clamp(v: number, lo: number, hi: number): number {
      return Math.max(lo, Math.min(hi, v));
    }
    function seg(t: number, a: number, b: number): number {
      const c = clamp((t - a) / (b - a), 0, 1);
      return c * c * (3 - 2 * c);
    }
    function on(el: EventTarget, type: string, fn: (e: any) => void): void {
      el.addEventListener(type, fn);
      offs.push(() => el.removeEventListener(type, fn));
    }
    function stopDemo(): void {
      demo = false;
      root.removeAttribute("data-demo");
      root.classList.remove("is-demo");
    }
    function pos(e: PointerEvent): { x: number; y: number } {
      const r = root.getBoundingClientRect();
      return { x: e.clientX - r.left, y: e.clientY - r.top };
    }
    function spring(x: number, v: number, to: number, k: number, c: number, dt: number): number[] {
      const n = Math.max(1, Math.ceil(dt / 0.008));
      const h = dt / n;
      for (let i = 0; i < n; i += 1) {
        v += (-k * (x - to) - c * v) * h;
        x += v * h;
      }
      return [x, v];
    }
    function sync(): void {
      if (reduce) {
        snap();
        render();
      }
    }

    // 기법: 한계(MAX_RATIO) 넘은 만큼을 제곱근으로 눌러 저항을 만든다 - 더 끌수록 같은 거리에서 덜 늘어난다.
    // 놓으면 목표는 한계선이고, 감쇠비 0.35 의 스프링이 한계선을 지나쳤다 돌아오며 진동한다.
    const MAX_RATIO = 0.64;
    const RESIST = 5;
    const SPRING_BACK = 16;
    const MIN_W = 56;
    const panel = q<HTMLElement>("[data-r=panel]");
    const grip = q<HTMLElement>("[data-r=grip]");
    const limit = q<HTMLElement>("[data-r=limit]");
    const maxEl = q<HTMLElement>("[data-r=max]");
    const overEl = q<HTMLElement>("[data-r=over]");
    const cursor = q<HTMLElement>("[data-r=cursor]");
    let w = 0;
    let vw = 0;
    let target = 0;
    let raw = 0;
    let px = 0;
    let py = 0;
    let gx = 0;
    let grabW = 0;
    let dragging = false;
    let ready = false;

    function maxW(): number { return root.clientWidth * MAX_RATIO; }

    function stretch(r: number): number {
      const m = maxW();
      return r <= m ? r : m + RESIST * Math.sqrt(r - m);
    }

    function init(): void {
      if (ready) return;
      ready = true;
      target = raw = w = root.clientWidth * 0.4;
    }

    function release(): void {
      if (!dragging) return;
      dragging = false;
      target = Math.min(raw, maxW());
    }

    function userTakes(): void {
      stopDemo();
      dragging = false;
      init();
    }

    function script(now: number): void {
      const W = root.clientWidth;
      const ph = now % 2000;
      const was = dragging;
      const r0 = W * 0.4;
      dragging = false;
      if (ph >= 200 && ph < 1000) {
        dragging = true;
        raw = r0 + (W - r0) * seg(ph, 200, 700);
      } else if (ph >= 1400 && ph < 1960) {
        dragging = true;
        if (!was) grabW = w;
        raw = grabW + (r0 - grabW) * seg(ph, 1400, 1960);
      }
      if (was && !dragging) { dragging = true; release(); }
      px = (dragging ? raw : w) - 8;
      py = root.clientHeight * 0.5;
      gx = 8;
    }

    function snap(): void {
      init();
      w = target;
      vw = 0;
    }

    function step(dt: number, now: number): void {
      init();
      if (demo) script(now);
      if (dragging) {
        if (!demo) raw = clamp(px + gx, MIN_W, root.clientWidth);
        target = clamp(stretch(raw), MIN_W, root.clientWidth);
        const a = spring(w, vw, target, 1600, 80, dt);
        w = a[0];
        vw = a[1];
      } else {
        const a = spring(w, vw, target, SPRING_BACK * SPRING_BACK, 2 * 0.35 * SPRING_BACK, dt);
        w = a[0];
        vw = a[1];
      }
    }

    function render(): void {
      const m = maxW();
      const over = Math.max(0, w - m);
      const span = Math.max(1, RESIST * Math.sqrt(Math.max(1, root.clientWidth - m)));
      panel.style.width = w.toFixed(1) + "px";
      panel.style.setProperty("--over", clamp(over / span, 0, 1).toFixed(3));
      limit.style.transform = "translateX(" + m.toFixed(1) + "px)";
      maxEl.textContent = String(Math.round(m));
      overEl.textContent = String(Math.round(over));
      cursor.style.transform = "translate(" + px.toFixed(1) + "px," + py.toFixed(1) + "px)";
    }

    on(grip, "pointerdown", (e: PointerEvent) => {
      userTakes();
      grip.setPointerCapture(e.pointerId);
      const p = pos(e);
      px = p.x;
      py = p.y;
      gx = w - p.x;
      raw = w;
      dragging = true;
    });
    on(grip, "pointermove", (e: PointerEvent) => {
      if (!dragging) return;
      px = pos(e).x;
      raw = clamp(px + gx, MIN_W, root.clientWidth);
      if (reduce) { target = clamp(Math.min(stretch(raw), maxW()), MIN_W, root.clientWidth); sync(); }
    });
    on(grip, "pointerup", release);
    on(grip, "pointercancel", release);
    on(grip, "keydown", (e: KeyboardEvent) => {
      if (e.key !== "ArrowLeft" && e.key !== "ArrowRight") return;
      e.preventDefault();
      userTakes();
      target = clamp(target + (e.key === "ArrowRight" ? 16 : -16), MIN_W, maxW());
      sync();
    });

    function frame(ts: number): void {
      if (t0 < 0) {
        t0 = ts;
        last = ts;
      }
      const dt = Math.min(0.05, (ts - last) / 1000);
      last = ts;
      step(dt, ts - t0);
      render();
      raf = requestAnimationFrame(frame);
    }
    if (reduce) {
      stopDemo();
      snap();
      render();
    } else {
      raf = requestAnimationFrame(frame);
    }
    return () => {
      cancelAnimationFrame(raf);
      offs.forEach((f) => f());
    };

  }, []);

  return (
    <main className={styles["stage"]}>
      <div ref={rootRef} className={styles["rh"] + " is-demo"} data-demo="1">
        <div className={styles["rh__panel"]} data-r="panel">
          <i className={styles["rh__stripe"]}></i>
          <button className={styles["rh__grip"]} data-r="grip" type="button" aria-label="크기 조절 손잡이"></button>
        </div>
        <i className={styles["rh__limit"]} data-r="limit"></i>
        <p className={styles["rh__meta"]}><span className={styles["rh__tag"]}>MAX</span> <b data-r="max">0</b> <span className={styles["rh__tag"]}>OVER</span> <b data-r="over">0</b></p>
        <i className={styles["rh__cursor"]} data-r="cursor"></i>
      </div>
    </main>
  );
}