05固定シードのノイズでぎざぎざに切った破れ紙の境目

<main class="stage">
<div class="dv is-demo" id="dvRoot">
  <div class="dv__paper" role="separator">
    <div class="dv__sheet" id="dvSheet"></div>
  </div>
  <div class="dv__bar">
  <button class="dv__btn" id="dvBtn" type="button">もう一度破る</button>
  <p class="dv__meta"><span class="dv__tag">TORN_SEED</span> <b id="dvSeed">0</b></p>
  </div>
</div>
</main>

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

// 핵심: 시드 고정 노이즈로 높이를 정한 꼭짓점을 clip-path polygon 으로 이어 종이 아래 경계를 찢는다.

$sheet-color: $subject-pink;
$base-color: $subject-mint;

@include stage($stage-ink);

.dv {
  width: min(100%, 360px);
  display: grid;
  gap: $sp-2;
}

.dv__paper {
  box-sizing: border-box;
  height: 100px;
  border-radius: $r-card;
  background: $base-color;
  overflow: hidden;
}

.dv__sheet {
  height: 100px;
  background: $sheet-color;
  clip-path: polygon(0 0, 100% 0, 100% 58px, 0 58px);
}

.dv__bar {
  box-sizing: border-box;
  width: 100%;
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: $sp-2 $sp-3;
}

.dv__btn {
  box-sizing: border-box;
  height: 40px;
  padding: 0 $sp-5;
  border: 0;
  border-radius: $r-control;
  background: $subject-lilac;
  color: $subject-ink;
  font-family: inherit;
  font-size: 14px;
  font-weight: 700;
  line-height: 20px;
  cursor: pointer;
}
.dv__btn:focus-visible { outline: 3px solid $stage-paper; outline-offset: 3px; }

.dv__meta {
  margin: 0;
  display: flex;
  align-items: baseline;
  gap: $sp-2;
  font-size: 12px;
  line-height: 16px;
  color: rgba($stage-paper, .78);
}
.dv__tag { font-weight: 700; letter-spacing: .08em; }
.dv__meta b { font-variant-numeric: tabular-nums; color: $stage-paper; }

@media (prefers-reduced-motion: reduce) {
  .dv__btn { transition: none; }
}

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);
}

.dv {
  width: min(100%, 360px);
  display: grid;
  gap: 8px;
}

.dv__paper {
  box-sizing: border-box;
  height: 100px;
  border-radius: 16px;
  background: #4cd4a6;
  overflow: hidden;
}

.dv__sheet {
  height: 100px;
  background: #ff9ebb;
  clip-path: polygon(0 0, 100% 0, 100% 58px, 0 58px);
}

.dv__bar {
  box-sizing: border-box;
  width: 100%;
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 8px 12px;
}

.dv__btn {
  box-sizing: border-box;
  height: 40px;
  padding: 0 20px;
  border: 0;
  border-radius: 12px;
  background: #b9a0ff;
  color: #17141a;
  font-family: inherit;
  font-size: 14px;
  font-weight: 700;
  line-height: 20px;
  cursor: pointer;
}

.dv__btn:focus-visible {
  outline: 3px solid #ffffff;
  outline-offset: 3px;
}

.dv__meta {
  margin: 0;
  display: flex;
  align-items: baseline;
  gap: 8px;
  font-size: 12px;
  line-height: 16px;
  color: rgba(255, 255, 255, 0.78);
}

.dv__tag {
  font-weight: 700;
  letter-spacing: 0.08em;
}

.dv__meta b {
  font-variant-numeric: tabular-nums;
  color: #ffffff;
}

@media (prefers-reduced-motion: reduce) {
  .dv__btn {
    transition: none;
  }
}

(function () {
  // 기법: 직접 구현한 시드 난수(mulberry32)로 값 표를 한 번 만들고, 큰 굴곡(4칸마다 보간)과 칸별 잔떨림을 섞어 꼭짓점 높이를 정한다.
  // 같은 TORN_SEED 이면 새로고침해도 같은 모양이다. 찢김은 왼쪽에서 오른쪽으로 progress 만큼 진행한다.
  var TORN_SEED = 20261008;
  var TORN_STEP = 9;
  var TORN_AMP = 20;
  var BASE_Y = 48;
  var START_MS = 200;
  var TEAR_MS = 1400;
  var CYCLE_MS = 2000;

  var root = document.getElementById('dvRoot');
  var sheet = document.getElementById('dvSheet');
  var btn = document.getElementById('dvBtn');
  var seedEl = document.getElementById('dvSeed');
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  function mulberry32(seed) {
    var a = seed >>> 0;
    return function () {
      a = (a + 0x6D2B79F5) >>> 0;
      var t = a;
      t = Math.imul(t ^ (t >>> 15), t | 1);
      t ^= t + Math.imul(t ^ (t >>> 7), t | 61);
      return ((t ^ (t >>> 14)) >>> 0) / 4294967296;
    };
  }
  var rand = mulberry32(TORN_SEED);
  var table = [];
  var i;
  for (i = 0; i < 256; i += 1) table.push(rand());

  function smooth(t) { return t * t * (3 - 2 * t); }
  function noiseAt(k) {
    var big = k / 4;
    var i0 = Math.floor(big);
    var f = smooth(big - i0);
    var coarse = table[i0 % 256] * (1 - f) + table[(i0 + 1) % 256] * f;
    var fine = table[(k * 7 + 3) % 256];
    return 0.65 * coarse + 0.35 * fine;
  }

  var progress = 0;
  function paint() {
    var count = Math.max(8, Math.ceil(sheet.clientWidth / TORN_STEP));
    var pts = ['0 0', '100% 0'];
    var edge = [];
    for (var k = 0; k <= count; k += 1) {
      var xr = k / count;
      var y = xr <= progress ? BASE_Y + TORN_AMP * noiseAt(k) : BASE_Y + TORN_AMP * 0.5;
      edge.push((xr * 100).toFixed(2) + '% ' + y.toFixed(1) + 'px');
    }
    edge.reverse();
    sheet.style.clipPath = 'polygon(' + pts.concat(edge).join(',') + ')';
  }
  function stopDemo() { root.classList.remove('is-demo'); }

  var restartAt = null;
  btn.addEventListener('click', function () {
    stopDemo();
    if (reduce) { progress = 1; paint(); return; }
    restartAt = -1;
  });

  var t0 = null;
  function tick(ts) {
    if (t0 === null) t0 = ts;
    var local = null;
    if (restartAt === -1) restartAt = ts;
    if (root.classList.contains('is-demo')) local = (ts - t0) % CYCLE_MS;
    else if (restartAt !== null) local = ts - restartAt;
    if (local !== null) {
      progress = Math.min(1, Math.max(0, (local - START_MS) / TEAR_MS));
      paint();
    }
    requestAnimationFrame(tick);
  }

  seedEl.textContent = String(TORN_SEED);
  if (reduce) {
    stopDemo();
    progress = 1;
    paint();
  } else {
    paint();
    requestAnimationFrame(tick);
  }
})();

// TornEdge — vanilla 판(05-divl-torn-edge-seeded-noise) 의 React 포트.
// 직접 구현한 시드 난수로 꼭짓점 높이를 정해 clip-path polygon 으로 종이 아래 경계를 찢는다. 같은 시드는 같은 모양이다.
import { useEffect, useRef } from "react";
import styles from "./TornEdge.module.scss";

type Box<T> = { current: T };

const TORN_SEED = 20261008;
const TORN_STEP = 9;
const TORN_AMP = 20;
const BASE_Y = 48;
const START_MS = 200;
const TEAR_MS = 1400;
const CYCLE_MS = 2000;

function mulberry32(seed: number): () => number {
  let a = seed >>> 0;
  return () => {
    a = (a + 0x6d2b79f5) >>> 0;
    let t = a;
    t = Math.imul(t ^ (t >>> 15), t | 1);
    t ^= t + Math.imul(t ^ (t >>> 7), t | 61);
    return ((t ^ (t >>> 14)) >>> 0) / 4294967296;
  };
}

const smooth = (t: number): number => t * t * (3 - 2 * t);

export default function TornEdge() {
  const sheetRef = useRef<HTMLDivElement | null>(null) as Box<HTMLDivElement | null>;
  const btnRef = useRef<HTMLButtonElement | null>(null) as Box<HTMLButtonElement | null>;

  useEffect(() => {
    const sheet = sheetRef.current;
    const btn = btnRef.current;
    if (!sheet || !btn) return;
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    const rand = mulberry32(TORN_SEED);
    const table: number[] = [];
    for (let i = 0; i < 256; i += 1) table.push(rand());
    const noiseAt = (k: number): number => {
      const big = k / 4;
      const i0 = Math.floor(big);
      const f = smooth(big - i0);
      const coarse = table[i0 % 256] * (1 - f) + table[(i0 + 1) % 256] * f;
      const fine = table[(k * 7 + 3) % 256];
      return 0.65 * coarse + 0.35 * fine;
    };

    let demo = !reduce;
    let progress = reduce ? 1 : 0;
    let restartAt: number | null = null;
    let t0: number | null = null;
    let raf = 0;

    const paint = (): void => {
      const count = Math.max(8, Math.ceil(sheet.clientWidth / TORN_STEP));
      const edge: string[] = [];
      for (let k = 0; k <= count; k += 1) {
        const xr = k / count;
        const y = xr <= progress ? BASE_Y + TORN_AMP * noiseAt(k) : BASE_Y + TORN_AMP * 0.5;
        edge.push((xr * 100).toFixed(2) + "% " + y.toFixed(1) + "px");
      }
      edge.reverse();
      sheet.style.clipPath = "polygon(" + ["0 0", "100% 0"].concat(edge).join(",") + ")";
    };
    const onClick = (): void => {
      demo = false;
      if (reduce) {
        progress = 1;
        paint();
        return;
      }
      restartAt = -1;
    };
    btn.addEventListener("click", onClick);

    function tick(ts: number): void {
      if (t0 === null) t0 = ts;
      let local: number | null = null;
      if (restartAt === -1) restartAt = ts;
      if (demo) local = (ts - t0) % CYCLE_MS;
      else if (restartAt !== null) local = ts - restartAt;
      if (local !== null) {
        progress = Math.min(1, Math.max(0, (local - START_MS) / TEAR_MS));
        paint();
      }
      raf = requestAnimationFrame(tick);
    }

    paint();
    if (!reduce) raf = requestAnimationFrame(tick);
    return () => {
      cancelAnimationFrame(raf);
      btn.removeEventListener("click", onClick);
    };
  }, []);

  return (
    <div className={styles.dv}>
      <div className={styles.paper} role="separator">
        <div className={styles.sheet} ref={sheetRef} />
      </div>
      <div className={styles.bar}>
        <button className={styles.btn} ref={btnRef} type="button">다시 찢기</button>
        <p className={styles.meta}>
          <span className={styles.tag}>TORN_SEED</span> <b>{TORN_SEED}</b>
        </p>
      </div>
    </div>
  );
}