08Screen Transition Where a Tear-offset Value Locks Back Together

<main class="stage">
<div class="dt is-demo" id="dt">
  <p class="dt__hint"><span>Click or press Enter and the tear-offset value pulls the two halves apart then locks them back at 0</span></p>
  <div class="dt__panel" id="panel" tabindex="0" role="button" aria-label="Replay fullscreen menu transition where tear-offset value locks back together">
    <canvas class="dt__cv" id="cv" aria-hidden="true"></canvas>
  </div>
</div>
</main>

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

// 계산 겹(찢어짐 오프셋 렌더)은 index.html 의 PRECOMPUTE()/RENDER() 에 있다. 여기는 무대·레이아웃만.
$duration: $dur-loop;
$easing:   $ease-out;
$color:    $subject-blue-deep;

@include stage($stage-paper);

.dt {
  --scene-bar1: #{$subject-ink};
  --scene-bar2: #{$subject-blue};
  --scene-bar3: #{$subject-lilac};
  --accent: #{$color};
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: $sp-2;
  width: min(400px, 92vw);
}

.dt__hint {
  margin: 0;
  color: $subject-ink;
  font-size: 12px;
  font-weight: 500;
  line-height: 1.35;
  text-align: center;
}

.dt__panel {
  position: relative;
  width: 100%;
  height: 176px;
  border-radius: $r-card;
  overflow: hidden;
  cursor: pointer;
  box-shadow: 0 0 0 1px rgba($subject-ink, .14);
  transition: box-shadow $duration $easing;
}

.dt__panel:hover {
  box-shadow: 0 0 0 1px $color;
}

.dt__panel:focus-visible {
  outline: 2px solid $color;
  outline-offset: 2px;
}

.dt__cv {
  display: block;
  width: 100%;
  height: 100%;
}

@media (max-width: 340px) {
  .dt__hint { font-size: 11px; }
  .dt__panel, .dt__cv { height: 120px; }
}

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

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

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

.dt {
  --scene-bar1: #17141a;
  --scene-bar2: #2f6df6;
  --scene-bar3: #b9a0ff;
  --accent: #0a4fe8;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 8px;
  width: min(400px, 92vw);
}

.dt__hint {
  margin: 0;
  color: #17141a;
  font-size: 12px;
  font-weight: 500;
  line-height: 1.35;
  text-align: center;
}

.dt__panel {
  position: relative;
  width: 100%;
  height: 176px;
  border-radius: 16px;
  overflow: hidden;
  cursor: pointer;
  box-shadow: 0 0 0 1px rgba(23, 20, 26, 0.14);
  transition: box-shadow 2s ease-out;
}

.dt__panel:hover {
  box-shadow: 0 0 0 1px #0a4fe8;
}

.dt__panel:focus-visible {
  outline: 2px solid #0a4fe8;
  outline-offset: 2px;
}

.dt__cv {
  display: block;
  width: 100%;
  height: 100%;
}

@media (max-width: 340px) {
  .dt__hint {
    font-size: 11px;
  }
  .dt__panel, .dt__cv {
    height: 120px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .dt__panel {
    transition: none;
  }
}

(function () {
  var root = document.getElementById('dt');
  var panel = document.getElementById('panel');
  var cv = document.getElementById('cv');
  var ctx = cv.getContext('2d');
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  var isDemo = true;

  // 결정론 난수 — Math.random 을 쓰지 않는다. LCG(선형합동생성기) 하나로 장면을 만든다.
  function makeLcg(seed) {
    var s = seed >>> 0;
    return function () { s = (s * 1664525 + 1013904223) >>> 0; return s / 4294967296; };
  }

  var css = getComputedStyle(root);
  function tok(name, fb) { var v = css.getPropertyValue(name); return v ? (v.trim() || fb) : fb; }
  var BAR1 = tok('--scene-bar1', '#17141a');
  var BAR2 = tok('--scene-bar2', '#2f6df6');
  var BAR3 = tok('--scene-bar3', '#c9b8ff');

  var W = 0, H = 0, dpr = 1;
  var buf = document.createElement('canvas');
  var bctx = buf.getContext('2d');

  // 장면(풀스크린 메뉴 목록 자리) — 행·열 모두 색이 바뀌는 타일 결이라 가로 어긋남이 또렷이 드러난다.
  function paintScene(bc, w, h, seed) {
    var rng = makeLcg(seed);
    var barH = Math.max(10, h * 0.09);
    var chunkW = Math.max(8, w * 0.07);
    for (var y = 0; y < h; y += barH) {
      for (var x = 0; x < w; x += chunkW) {
        var v = rng();
        bc.fillStyle = v < 0.34 ? BAR1 : (v < 0.67 ? BAR2 : BAR3);
        bc.fillRect(x, y, chunkW + 1, barH + 1);
      }
    }
  }

  var SEED = 1027;
  var TEAR_OFFSET_MAX = 52;
  var data, outImg, iw, ih, tearY;

  function PRECOMPUTE() {
    iw = cv.width; ih = cv.height;
    data = bctx.getImageData(0, 0, iw, ih).data;
    outImg = ctx.createImageData(iw, ih);
    var rng = makeLcg(SEED + 3);
    tearY = Math.round(ih * (0.4 + rng() * 0.2));
  }

  function clampI(v, lo, hi) { return v < lo ? lo : (v > hi ? hi : v); }

  function RENDER(p) {
    var off = Math.round(TEAR_OFFSET_MAX * dpr * p);
    var o = outImg.data;
    for (var y = 0; y < ih; y++) {
      var dx = y < tearY ? off : -off;
      var base = y * iw;
      for (var x = 0; x < iw; x++) {
        var sx = clampI(x - dx, 0, iw - 1);
        var k = (base + x) * 4;
        var sk = (base + sx) * 4;
        o[k] = data[sk]; o[k + 1] = data[sk + 1]; o[k + 2] = data[sk + 2]; o[k + 3] = 255;
      }
    }
    ctx.putImageData(outImg, 0, 0);
  }

  function fit() {
    var r = panel.getBoundingClientRect();
    dpr = window.devicePixelRatio || 1;
    W = r.width; H = r.height;
    cv.width = Math.round(W * dpr); cv.height = Math.round(H * dpr);
    buf.width = cv.width; buf.height = cv.height;
    paintScene(bctx, buf.width, buf.height, SEED);
    PRECOMPUTE();
  }

  function human() { if (isDemo) { root.classList.remove('is-demo'); isDemo = false; } }

  var progress = 0, target = 0, playT0 = 0, playFrom = 0, playing = false;
  var PLAY_MS = 620;

  function easeInOut(t) { return t < 0.5 ? 2 * t * t : 1 - Math.pow(-2 * t + 2, 2) / 2; }

  function play() {
    human();
    playFrom = progress; target = progress < 0.5 ? 1 : 0;
    playT0 = 0; playing = true;
  }

  function stepPlay(now) {
    if (!playing) return;
    if (!playT0) playT0 = now;
    var t = Math.min(1, (now - playT0) / PLAY_MS);
    progress = playFrom + (target - playFrom) * easeInOut(t);
    if (t >= 1) { playing = false; progress = target; }
  }

  var DRIVE_PERIOD_MS = 2000;
  var driveStart = 0;
  function triangle(frac) { return frac < 0.5 ? frac * 2 : 2 - frac * 2; }
  function driveTick(now) {
    if (!driveStart) driveStart = now;
    if (isDemo) {
      var frac = ((now - driveStart) % DRIVE_PERIOD_MS) / DRIVE_PERIOD_MS;
      progress = triangle(frac);
    }
    requestAnimationFrame(driveTick);
  }

  function frame(now) {
    stepPlay(now);
    RENDER(progress);
    requestAnimationFrame(frame);
  }

  window.addEventListener('resize', fit);
  fit();

  if (reduce) {
    root.classList.add('is-still');
    progress = 0; RENDER(progress);
    panel.addEventListener('click', function () { human(); progress = progress < 0.5 ? 1 : 0; RENDER(progress); });
    panel.addEventListener('keydown', function (e) {
      if (e.key === 'Enter' || e.key === ' ') { e.preventDefault(); human(); progress = progress < 0.5 ? 1 : 0; RENDER(progress); }
    });
  } else {
    panel.addEventListener('click', play);
    panel.addEventListener('keydown', function (e) {
      if (e.key === 'Enter' || e.key === ' ') { e.preventDefault(); play(); }
    });
    requestAnimationFrame(frame);
    requestAnimationFrame(driveTick);
  }
})();

import { useEffect, useRef } from "react";
import styles from "./DigitalTear.module.scss";

export default function DigitalTear() {
  const rootRef = useRef<HTMLDivElement | null>(null);
  const panelRef = useRef<HTMLDivElement | null>(null);
  const cvRef = useRef<HTMLCanvasElement | null>(null);

  useEffect(() => {
    const root = rootRef.current;
    const panel = panelRef.current;
    const cv = cvRef.current;
    if (!root || !panel || !cv) return;
    const ctx = cv.getContext("2d");
    if (!ctx) return;
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    let isDemo = true;

    // 결정론 난수 — Math.random 을 쓰지 않는다. LCG(선형합동생성기) 하나로 장면을 만든다.
    function makeLcg(seed: number) {
      let s = seed >>> 0;
      return function () {
        s = (s * 1664525 + 1013904223) >>> 0;
        return s / 4294967296;
      };
    }

    const css = getComputedStyle(root);
    function tok(name: string, fb: string) {
      const v = css.getPropertyValue(name);
      return v ? v.trim() || fb : fb;
    }
    const BAR1 = tok("--scene-bar1", "#17141a");
    const BAR2 = tok("--scene-bar2", "#2f6df6");
    const BAR3 = tok("--scene-bar3", "#c9b8ff");

    let W = 0;
    let H = 0;
    let dpr = 1;
    const buf = document.createElement("canvas");
    const bctx = buf.getContext("2d");
    if (!bctx) return;

    // 장면(풀스크린 메뉴 목록 자리) — 행·열 모두 색이 바뀌는 타일 결이라 가로 어긋남이 또렷이 드러난다.
    function paintScene(bc: CanvasRenderingContext2D, w: number, h: number, seed: number) {
      const rng = makeLcg(seed);
      const barH = Math.max(10, h * 0.09);
      const chunkW = Math.max(8, w * 0.07);
      for (let y = 0; y < h; y += barH) {
        for (let x = 0; x < w; x += chunkW) {
          const v = rng();
          bc.fillStyle = v < 0.34 ? BAR1 : v < 0.67 ? BAR2 : BAR3;
          bc.fillRect(x, y, chunkW + 1, barH + 1);
        }
      }
    }

    const SEED = 1027;
    const TEAR_OFFSET_MAX = 52;
    let data: Uint8ClampedArray | null = null;
    let outImg: ImageData | null = null;
    let iw = 0;
    let ih = 0;
    let tearY = 0;

    function PRECOMPUTE() {
      iw = cv!.width;
      ih = cv!.height;
      data = bctx!.getImageData(0, 0, iw, ih).data;
      outImg = ctx!.createImageData(iw, ih);
      const rng = makeLcg(SEED + 3);
      tearY = Math.round(ih * (0.4 + rng() * 0.2));
    }

    function clampI(v: number, lo: number, hi: number) {
      return v < lo ? lo : v > hi ? hi : v;
    }

    function RENDER(p: number) {
      const off = Math.round(TEAR_OFFSET_MAX * dpr * p);
      const o = outImg!.data;
      const d = data!;
      for (let y = 0; y < ih; y++) {
        const dx = y < tearY ? off : -off;
        const base = y * iw;
        for (let x = 0; x < iw; x++) {
          const sx = clampI(x - dx, 0, iw - 1);
          const k = (base + x) * 4;
          const sk = (base + sx) * 4;
          o[k] = d[sk];
          o[k + 1] = d[sk + 1];
          o[k + 2] = d[sk + 2];
          o[k + 3] = 255;
        }
      }
      ctx!.putImageData(outImg!, 0, 0);
    }

    function fit() {
      const r = panel!.getBoundingClientRect();
      dpr = window.devicePixelRatio || 1;
      W = r.width;
      H = r.height;
      cv!.width = Math.round(W * dpr);
      cv!.height = Math.round(H * dpr);
      buf.width = cv!.width;
      buf.height = cv!.height;
      paintScene(bctx!, buf.width, buf.height, SEED);
      PRECOMPUTE();
    }

    function human() {
      if (isDemo) {
        root!.classList.remove("is-demo");
        isDemo = false;
      }
    }

    let progress = 0;
    let target = 0;
    let playT0 = 0;
    let playFrom = 0;
    let playing = false;
    const PLAY_MS = 620;

    function easeInOut(t: number) {
      return t < 0.5 ? 2 * t * t : 1 - Math.pow(-2 * t + 2, 2) / 2;
    }

    function play() {
      human();
      playFrom = progress;
      target = progress < 0.5 ? 1 : 0;
      playT0 = 0;
      playing = true;
    }

    function stepPlay(now: number) {
      if (!playing) return;
      if (!playT0) playT0 = now;
      const t = Math.min(1, (now - playT0) / PLAY_MS);
      progress = playFrom + (target - playFrom) * easeInOut(t);
      if (t >= 1) {
        playing = false;
        progress = target;
      }
    }

    const DRIVE_PERIOD_MS = 2000;
    let driveStart = 0;
    let rafFrame = 0;
    let rafDrive = 0;

    function triangle(frac: number) {
      return frac < 0.5 ? frac * 2 : 2 - frac * 2;
    }

    function driveTick(now: number) {
      if (!driveStart) driveStart = now;
      if (isDemo) {
        const frac = ((now - driveStart) % DRIVE_PERIOD_MS) / DRIVE_PERIOD_MS;
        progress = triangle(frac);
      }
      rafDrive = requestAnimationFrame(driveTick);
    }

    function frame(now: number) {
      stepPlay(now);
      RENDER(progress);
      rafFrame = requestAnimationFrame(frame);
    }

    function onClick() {
      play();
    }
    function onKeyDown(e: Event) {
      const ke = e as KeyboardEvent;
      if (ke.key === "Enter" || ke.key === " ") {
        ke.preventDefault();
        play();
      }
    }
    function onClickReduce() {
      human();
      progress = progress < 0.5 ? 1 : 0;
      RENDER(progress);
    }
    function onKeyDownReduce(e: Event) {
      const ke = e as KeyboardEvent;
      if (ke.key === "Enter" || ke.key === " ") {
        ke.preventDefault();
        human();
        progress = progress < 0.5 ? 1 : 0;
        RENDER(progress);
      }
    }

    window.addEventListener("resize", fit);
    fit();

    if (reduce) {
      root.classList.add("is-still");
      progress = 0;
      RENDER(progress);
      panel.addEventListener("click", onClickReduce);
      panel.addEventListener("keydown", onKeyDownReduce);
    } else {
      panel.addEventListener("click", onClick);
      panel.addEventListener("keydown", onKeyDown);
      rafFrame = requestAnimationFrame(frame);
      rafDrive = requestAnimationFrame(driveTick);
    }

    return () => {
      window.removeEventListener("resize", fit);
      cancelAnimationFrame(rafFrame);
      cancelAnimationFrame(rafDrive);
      if (reduce) {
        panel.removeEventListener("click", onClickReduce);
        panel.removeEventListener("keydown", onKeyDownReduce);
      } else {
        panel.removeEventListener("click", onClick);
        panel.removeEventListener("keydown", onKeyDown);
      }
    };
  }, []);

  return (
    <main className={styles.stage}>
      <div className={`${styles.root} is-demo`} ref={rootRef}>
        <p className={styles.hint}>
          <span>클릭하거나 Enter 를 누르면 찢어짐 오프셋 값이 두 조각을 어긋나게 했다가 0 으로 맞물립니다</span>
        </p>
        <div
          className={styles.panel}
          ref={panelRef}
          tabIndex={0}
          role="button"
          aria-label="찢어짐 오프셋 값이 맞물리는 풀스크린 메뉴 전환 다시 재생"
        >
          <canvas className={styles.cv} ref={cvRef} aria-hidden="true" />
        </div>
      </div>
    </main>
  );
}