05切り出し区間のつまみが最も近いゼロ交差へ引き寄せられる区間ピッカー

<main class="stage">
<div class="wf is-demo" id="wfRoot">
  <canvas class="wf__canvas" data-role="canvas" width="480" height="300" tabindex="0" aria-label="切り出し区間のつまみが最も近いゼロ交差へ引き寄せられる区間ピッカー"></canvas>
  <div class="wf__handle" data-role="handle" role="slider" tabindex="0" aria-label="開始ハンドル" aria-valuemin="0" aria-valuemax="1919" aria-valuenow="221" style="left: 11.54%"></div>
  <div class="wf__handle" data-role="handle" role="slider" tabindex="0" aria-label="終了ハンドル" aria-valuemin="0" aria-valuemax="1919" aria-valuenow="1694" style="left: 88.25%"></div>
  <p class="wf__status" data-role="status" aria-live="polite">選択の長さ</p>
  <button class="wf__btn" data-role="btn" type="button">一時停止</button>
  <p class="wf__caption">切り出し区間のつまみが最も近いゼロ交差へ引き寄せられる区間ピッカー</p>
</div>
</main>

@use "../../../../site/static/demo-tokens" as *;
@include stage($stage-paper);

.wf {
  position: relative;
  width: min(92vw, calc(160vh - 12.8vw));
  aspect-ratio: 480 / 300;
  margin: 0 auto;
  border-radius: $r-card;
  overflow: hidden;
  box-shadow: $shadow-raised;
  background: $subject-ink;
}

.wf__canvas {
  display: block;
  width: 100%;
  height: 100%;
  touch-action: manipulation;
}

.wf__canvas:focus-visible {
  outline: 2px solid rgba(255, 255, 255, .85);
  outline-offset: -6px;
}

.wf__status {
  position: absolute;
  left: $sp-3;
  top: $sp-3;
  max-width: 62%;
  margin: 0;
  padding: $sp-1 $sp-3;
  border-radius: $r-pill;
  background: rgba(255, 255, 255, .85);
  color: $subject-ink;
  font-weight: 500;
  font-size: 11px;
  line-height: 1.4;
  pointer-events: none;
}

.wf__btn {
  position: absolute;
  right: $sp-3;
  bottom: $sp-3;
  margin: 0;
  padding: $sp-1 $sp-3;
  border: 0;
  border-radius: $r-pill;
  background: rgba(255, 255, 255, .85);
  color: $subject-ink;
  font: inherit;
  font-weight: 500;
  font-size: 12px;
  line-height: 1.4;
  cursor: pointer;
}

.wf__btn:focus-visible {
  outline: 2px solid #ffffff;
  outline-offset: 2px;
}

.wf__caption {
  position: absolute;
  left: $sp-3;
  bottom: $sp-3;
  max-width: 68%;
  margin: 0;
  padding: $sp-1 $sp-3;
  border-radius: $r-pill;
  background: rgba(255, 255, 255, .85);
  color: $subject-ink;
  font-weight: 500;
  font-size: 12px;
  line-height: 1.4;
  pointer-events: none;
}

.wf__handle {
  position: absolute;
  top: 12%;
  height: 76%;
  width: 6%;
  margin: 0;
  padding: 0;
  border: 0;
  background: transparent;
  transform: translateX(-50%);
  cursor: ew-resize;
  touch-action: none;
}

.wf__handle:focus-visible {
  outline: 2px solid $subject-ink;
  outline-offset: -2px;
  border-radius: $r-sm;
}

@media (max-width: 340px) {
  .wf__caption, .wf__btn { font-size: 10px; padding: $sp-1 $sp-2; }
  .wf__status { font-size: 10px; }
}

@media (prefers-reduced-motion: reduce) {
  .wf { cursor: default; }
}

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);
}

.wf {
  position: relative;
  width: min(92vw, 160vh - 12.8vw);
  aspect-ratio: 480/300;
  margin: 0 auto;
  border-radius: 16px;
  overflow: hidden;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  background: #17141a;
}

.wf__canvas {
  display: block;
  width: 100%;
  height: 100%;
  touch-action: manipulation;
}

.wf__canvas:focus-visible {
  outline: 2px solid rgba(255, 255, 255, 0.85);
  outline-offset: -6px;
}

.wf__status {
  position: absolute;
  left: 12px;
  top: 12px;
  max-width: 62%;
  margin: 0;
  padding: 4px 12px;
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.85);
  color: #17141a;
  font-weight: 500;
  font-size: 11px;
  line-height: 1.4;
  pointer-events: none;
}

.wf__btn {
  position: absolute;
  right: 12px;
  bottom: 12px;
  margin: 0;
  padding: 4px 12px;
  border: 0;
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.85);
  color: #17141a;
  font: inherit;
  font-weight: 500;
  font-size: 12px;
  line-height: 1.4;
  cursor: pointer;
}

.wf__btn:focus-visible {
  outline: 2px solid #ffffff;
  outline-offset: 2px;
}

.wf__caption {
  position: absolute;
  left: 12px;
  bottom: 12px;
  max-width: 68%;
  margin: 0;
  padding: 4px 12px;
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.85);
  color: #17141a;
  font-weight: 500;
  font-size: 12px;
  line-height: 1.4;
  pointer-events: none;
}

.wf__handle {
  position: absolute;
  top: 12%;
  height: 76%;
  width: 6%;
  margin: 0;
  padding: 0;
  border: 0;
  background: transparent;
  transform: translateX(-50%);
  cursor: ew-resize;
  touch-action: none;
}

.wf__handle:focus-visible {
  outline: 2px solid #17141a;
  outline-offset: -2px;
  border-radius: 8px;
}

@media (max-width: 340px) {
  .wf__caption, .wf__btn {
    font-size: 10px;
    padding: 4px 8px;
  }
  .wf__status {
    font-size: 10px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .wf {
    cursor: default;
  }
}

(function () {
const W = 480;
const H = 300;
const PI2 = Math.PI * 2;
const FIXED_DT = 16;
const IDLE_STEPS = 220;
const REDUCE_STEP_MS = 900;
const REDUCE_WARM_STEPS = 40;
const BTN_PAUSE = '一時停止';
const BTN_PLAY = '再生';
const BTN_NEXT = '次の瞬間';
// 파스텔 팔레트와 어두운 바탕 두 끝 색
const PINK = [255, 170, 196];
const MINT = [150, 226, 196];
const LILAC = [196, 176, 255];
const SKY_BLUE = [150, 214, 255];
const BUTTER = [255, 230, 150];
const CREAM = [255, 247, 230];
const INK = [23, 20, 26];
const BG_TOP = [24, 21, 40];
const BG_BOT = [48, 42, 78];
function clamp(v, lo, hi) { return v < lo ? lo : (v > hi ? hi : v); }
function lerp(a, b, k) { return a + (b - a) * k; }
function smooth(x) { const c = clamp(x, 0, 1); return c * c * (3 - 2 * c); }
function mix(a, b, k) { return [lerp(a[0], b[0], k), lerp(a[1], b[1], k), lerp(a[2], b[2], k)]; }
function rgba(c, a) { return 'rgba(' + Math.round(c[0]) + ',' + Math.round(c[1]) + ',' + Math.round(c[2]) + ',' + a.toFixed(3) + ')'; }
// 시드 고정 난수 — 같은 시드면 언제나 같은 수열 (선형 합동 방식)
function lcg(seed) {
    let s = seed >>> 0;
    return function () {
        s = (Math.imul(s, 1664525) + 1013904223) >>> 0;
        return s / 4294967296;
    };
}
// 정수 하나와 시드로 0 이상 1 미만의 값을 만드는 해시 (같은 입력은 늘 같은 값)
function hash1(i, seed) {
    let h = (Math.imul(i | 0, 374761393) + Math.imul(seed | 0, 668265263)) | 0;
    h = Math.imul(h ^ (h >>> 13), 1274126177);
    h ^= h >>> 16;
    return (h >>> 0) / 4294967296;
}
// 사인 두 개를 음절마다 갈아 끼우고 엔벨로프를 씌운 합성 신호 (소리는 재생하지 않고 수치만 만든다)
function synth(n, seed) {
    const rnd = lcg(seed);
    const out = new Float32Array(n);
    let i = 0;
    let p1 = 0;
    let p2 = 0;
    let peak = 0.0001;
    while (i < n) {
        const len = 1800 + Math.floor(rnd() * 4200);
        const amp = 0.18 + rnd() * 0.82;
        const rest = rnd() < 0.18;
        const f1 = 0.02 + rnd() * 0.09;
        const f2 = f1 * (1.5 + rnd());
        const stop = Math.min(n, i + len);
        for (let k = i; k < stop; k += 1) {
            const x = (k - i) / len;
            const env = Math.min(1, x / 0.06) * Math.pow(1 - x, 0.8);
            p1 += PI2 * f1;
            p2 += PI2 * f2;
            const tone = Math.sin(p1) * 0.7 + Math.sin(p2) * 0.3;
            const gain = rest ? 0.03 : amp * env;
            const v = gain * tone + (rnd() - 0.5) * 0.08 * (rest ? 0.4 : amp);
            out[k] = v;
            const a = Math.abs(v);
            if (a > peak) {
                peak = a;
            }
        }
        i = stop;
    }
    const norm = 0.92 / peak;
    for (let k = 0; k < n; k += 1) {
        out[k] *= norm;
    }
    return out;
}
// 표본 구간 [a, b) 의 최솟값과 최댓값 — 결과는 rangeLo, rangeHi 에 둔다
let rangeLo = 0;
let rangeHi = 0;
function scanRange(sig, a, b) {
    const from = Math.max(0, Math.floor(a));
    const to = Math.min(sig.length, Math.max(from + 1, Math.ceil(b)));
    let lo = 1e9;
    let hi = -1e9;
    for (let i = from; i < to; i += 1) {
        const v = sig[i];
        if (v < lo) {
            lo = v;
        }
        if (v > hi) {
            hi = v;
        }
    }
    if (lo > hi) {
        lo = 0;
        hi = 0;
    }
    rangeLo = lo;
    rangeHi = hi;
}
function paintBg(ctx, top, bot) {
    const g = ctx.createLinearGradient(0, 0, 0, H);
    g.addColorStop(0, rgba(top, 1));
    g.addColorStop(1, rgba(bot, 1));
    ctx.fillStyle = g;
    ctx.fillRect(0, 0, W, H);
}
// 가짜 포인터 — 시연 동안 손이 움직이는 것처럼 보이게 그린다
function drawCursor(ctx, x, y, down) {
    ctx.save();
    ctx.translate(x, y);
    ctx.beginPath();
    ctx.moveTo(0, 0);
    ctx.lineTo(0, 15);
    ctx.lineTo(4, 11.5);
    ctx.lineTo(7.5, 18);
    ctx.lineTo(10, 16.8);
    ctx.lineTo(6.6, 10.4);
    ctx.lineTo(11.5, 10.2);
    ctx.closePath();
    ctx.fillStyle = rgba(CREAM, 1);
    ctx.strokeStyle = rgba(INK, 1);
    ctx.lineWidth = 1.4;
    ctx.fill();
    ctx.stroke();
    if (down) {
        ctx.beginPath();
        ctx.arc(0, 0, 9, 0, PI2);
        ctx.strokeStyle = rgba(PINK, 0.9);
        ctx.lineWidth = 2;
        ctx.stroke();
    }
    ctx.restore();
}
function boot(root, make) {
    const canvasEl = root.querySelector('[data-role="canvas"]');
    const statusEl = root.querySelector('[data-role="status"]');
    const btnEl = root.querySelector('[data-role="btn"]');
    if (!(canvasEl instanceof HTMLCanvasElement) || !statusEl || !(btnEl instanceof HTMLButtonElement)) {
        return function () { };
    }
    const ctxOrNull = canvasEl.getContext('2d');
    if (!ctxOrNull) {
        return function () { };
    }
    const canvas = canvasEl;
    const ctx = ctxOrNull;
    const status = statusEl;
    const btn = btnEl;
    const reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
    const cleaners = [];
    let paused = false;
    let idle = IDLE_STEPS + 1;
    let clock = 0;
    let lastSayAt = -1e9;
    let lastText = status.textContent || '';
    let scene = null;
    let rafId = 0;
    let acc = 0;
    let lastTs = -1;
    function isAuto() { return !reduce && !paused && idle > IDLE_STEPS; }
    function sync() {
        const on = isAuto();
        if (root.classList.contains('is-demo') !== on) {
            root.classList.toggle('is-demo', on);
        }
    }
    function fit() {
        const r = canvas.getBoundingClientRect();
        const dpr = window.devicePixelRatio || 1;
        const cw = Math.max(1, Math.round(r.width * dpr));
        const ch = Math.max(1, Math.round(r.height * dpr));
        canvas.width = cw;
        canvas.height = ch;
        ctx.setTransform(cw / W, 0, 0, ch / H, 0, 0);
    }
    const host = {
        ctx,
        canvas,
        root,
        reduce,
        touch() {
            idle = 0;
            sync();
        },
        auto: isAuto,
        refresh() {
            if (scene) {
                scene.draw();
            }
        },
        say(text) {
            if (text === lastText) {
                return;
            }
            if (!reduce && clock - lastSayAt < 250) {
                return;
            }
            lastText = text;
            lastSayAt = clock;
            // 시연이 혼자 돌 때는 읽어 주지 않고, 사람이 만졌을 때만 알린다
            status.setAttribute('aria-live', isAuto() ? 'off' : 'polite');
            status.textContent = text;
        },
        local(e) {
            const r = canvas.getBoundingClientRect();
            return [clamp((e.clientX - r.left) * W / Math.max(1, r.width), 0, W), clamp((e.clientY - r.top) * H / Math.max(1, r.height), 0, H)];
        },
        listen(target, type, fn, opts) {
            target.addEventListener(type, fn, opts);
            cleaners.push(function () { target.removeEventListener(type, fn, opts); });
        }
    };
    function advance(ms) {
        if (!scene) {
            return;
        }
        const n = Math.max(1, Math.round(ms / FIXED_DT));
        for (let i = 0; i < n; i += 1) {
            idle += 1;
            clock += FIXED_DT;
            scene.step();
        }
    }
    function frame(ts) {
        if (lastTs < 0) {
            lastTs = ts;
        }
        const dt = Math.min(ts - lastTs, 160);
        lastTs = ts;
        if (!paused && scene) {
            acc += dt;
            while (acc >= FIXED_DT) {
                idle += 1;
                clock += FIXED_DT;
                scene.step();
                acc -= FIXED_DT;
            }
            sync();
            scene.draw();
        }
        rafId = requestAnimationFrame(frame);
    }
    scene = make(host);
    btn.textContent = reduce ? BTN_NEXT : BTN_PAUSE;
    fit();
    if (reduce) {
        root.classList.remove('is-demo');
        advance(REDUCE_WARM_STEPS * FIXED_DT);
    }
    scene.draw();
    host.listen(btn, 'click', function () {
        if (reduce) {
            advance(REDUCE_STEP_MS);
            host.refresh();
            return;
        }
        paused = !paused;
        btn.textContent = paused ? BTN_PLAY : BTN_PAUSE;
        sync();
    });
    host.listen(window, 'resize', function () {
        fit();
        host.refresh();
    });
    if (!reduce) {
        rafId = requestAnimationFrame(frame);
    }
    return function () {
        cancelAnimationFrame(rafId);
        for (let i = 0; i < cleaners.length; i += 1) {
            cleaners[i]();
        }
    };
}
const SAMPLE_N = 1920;
const SNAP_RADIUS = 6;
const HANDLE_W = 8;
const MIN_SPAN = 24;
const SNAP_EASE = 0.25;
const MID_Y = 138;
const HALF_Y = 74;
const SCRIPT_LEN = 360;
const START_A = 55.4;
const START_B = 423.6;
const TXT_SNAP = '引き寄せた距離';
const TXT_STAY = '半径内にゼロ交差なし';
const TXT_SPAN = '選択の長さ';
// 저주파 두 성분을 겹친 신호 — 영점 교차가 수십 픽셀 간격으로 나타난다
function lowSignal(n) {
    const out = new Float32Array(n);
    for (let i = 0; i < n; i += 1) {
        const a = Math.sin(PI2 * 0.0062 * i + 0.7) * 0.78;
        const b = Math.sin(PI2 * 0.0147 * i + 2.1) * 0.34;
        const c = Math.sin(PI2 * 0.0021 * i + 4.0) * 0.18;
        out[i] = clamp(a + b + c, -0.95, 0.95);
    }
    return out;
}
// 부호가 바뀌는 표본 사이를 직선으로 이어 영점 교차의 화면 x 를 구한다
function zeroCrossings(sig) {
    const xs = [];
    for (let i = 0; i < sig.length - 1; i += 1) {
        const a = sig[i];
        const b = sig[i + 1];
        if ((a < 0 && b >= 0) || (a >= 0 && b < 0)) {
            xs.push((i + a / (a - b)) / (sig.length - 1) * W);
        }
    }
    return xs;
}
// 놓은 자리 x 에서 반경 안의 가장 가까운 영점 교차로 — 없으면 제자리
function snapTarget(x, crossings, radius) {
    let best = x;
    let bestD = radius + 0.0001;
    for (let i = 0; i < crossings.length; i += 1) {
        const d = Math.abs(crossings[i] - x);
        if (d < bestD) {
            bestD = d;
            best = crossings[i];
        }
    }
    return best;
}
function makeTrimScene(h) {
    const sig = lowSignal(SAMPLE_N);
    const cross = zeroCrossings(sig);
    const hx = [START_A, START_B];
    const tx = [START_A, START_B];
    const els = [];
    const nodes = h.root.querySelectorAll('[data-role="handle"]');
    for (let i = 0; i < nodes.length; i += 1) {
        const node = nodes[i];
        if (node instanceof HTMLElement) {
            els.push(node);
        }
    }
    let active = -1;
    let k = 0;
    let fakeX = 200;
    let fakeY = 210;
    let fakeDown = false;
    let lastPull = -1;
    let msg = '';
    function limit(i, x) {
        return i === 0 ? clamp(x, 0, hx[1] - MIN_SPAN) : clamp(x, hx[0] + MIN_SPAN, W);
    }
    function release(i) {
        const want = limit(i, snapTarget(hx[i], cross, SNAP_RADIUS));
        lastPull = Math.abs(want - hx[i]);
        tx[i] = want;
        if (h.reduce) {
            hx[i] = want;
        }
        msg = lastPull < 0.05 ? TXT_STAY : TXT_SNAP + ': ' + lastPull.toFixed(1) + ' px';
    }
    function nextCross(i, dir) {
        let best = hx[i];
        let found = false;
        for (let c = 0; c < cross.length; c += 1) {
            const x = cross[c];
            if (dir > 0 && x > hx[i] + 0.5 && (!found || x < best)) {
                best = x;
                found = true;
            }
            if (dir < 0 && x < hx[i] - 0.5 && (!found || x > best)) {
                best = x;
                found = true;
            }
        }
        tx[i] = limit(i, best);
        if (h.reduce) {
            hx[i] = tx[i];
        }
    }
    for (let i = 0; i < els.length && i < 2; i += 1) {
        const el = els[i];
        const idx = i;
        h.listen(el, 'pointerdown', function (e) {
            const pe = e;
            active = idx;
            el.setPointerCapture(pe.pointerId);
            h.touch();
        });
        h.listen(el, 'pointermove', function (e) {
            if (active !== idx) {
                return;
            }
            const x = limit(idx, h.local(e)[0]);
            hx[idx] = x;
            tx[idx] = x;
            h.refresh();
        });
        const up = function () {
            if (active !== idx) {
                return;
            }
            active = -1;
            release(idx);
            h.refresh();
        };
        h.listen(el, 'pointerup', up);
        h.listen(el, 'pointercancel', up);
        h.listen(el, 'keydown', function (e) {
            const key = e.key;
            if (key === 'ArrowLeft' || key === 'ArrowRight') {
                e.preventDefault();
                nextCross(idx, key === 'ArrowRight' ? 1 : -1);
                h.touch();
                h.refresh();
            }
        });
    }
    function script() {
        const j = k % SCRIPT_LEN;
        fakeDown = false;
        if (j === 0) {
            hx[0] = START_A;
            tx[0] = START_A;
            hx[1] = START_B;
            tx[1] = START_B;
        }
        if (j < 20) {
            fakeX = lerp(200, START_A, smooth(j / 20));
            fakeY = lerp(210, MID_Y, smooth(j / 20));
        }
        else if (j < 60) {
            fakeDown = true;
            const x = lerp(START_A, 103.5, smooth((j - 20) / 40));
            hx[0] = limit(0, x);
            tx[0] = hx[0];
            fakeX = hx[0];
            fakeY = MID_Y;
            if (j === 59) {
                release(0);
            }
        }
        else if (j < 110) {
            fakeX = lerp(hx[0], START_B, smooth((j - 60) / 50));
        }
        else if (j < 150) {
            fakeDown = true;
            const x = lerp(START_B, 329, smooth((j - 110) / 40));
            hx[1] = limit(1, x);
            tx[1] = hx[1];
            fakeX = hx[1];
            if (j === 149) {
                release(1);
            }
        }
        else if (j < 200) {
            fakeX = lerp(tx[1], 250, smooth((j - 150) / 50));
            fakeY = lerp(MID_Y, 214, smooth((j - 150) / 50));
        }
    }
    return {
        step() {
            k += 1;
            if (h.auto()) {
                script();
            }
            for (let i = 0; i < 2; i += 1) {
                if (active === i || (h.auto() && fakeDown && ((k % SCRIPT_LEN) < 60 ? i === 0 : i === 1))) {
                    continue;
                }
                const d = tx[i] - hx[i];
                hx[i] = Math.abs(d) < 0.05 ? tx[i] : hx[i] + d * SNAP_EASE;
            }
        },
        draw() {
            const ctx = h.ctx;
            ctx.fillStyle = rgba(CREAM, 1);
            ctx.fillRect(0, 0, W, H);
            const a = hx[0];
            const b = hx[1];
            // 선택 구간 바탕
            ctx.fillStyle = rgba(MINT, 0.38);
            ctx.fillRect(a, 40, b - a, 196);
            // 흡착 반경 띠 — 끌고 있는 손잡이 둘레
            const grabbed = active >= 0 ? active : (h.auto() && fakeDown ? ((k % SCRIPT_LEN) < 60 ? 0 : 1) : -1);
            if (grabbed >= 0) {
                ctx.fillStyle = rgba(LILAC, 0.34);
                ctx.fillRect(hx[grabbed] - SNAP_RADIUS, 40, SNAP_RADIUS * 2, 196);
            }
            ctx.fillStyle = rgba(INK, 0.28);
            ctx.fillRect(0, MID_Y, W, 1);
            // 파형
            ctx.beginPath();
            for (let i = 0; i < SAMPLE_N; i += 4) {
                const x = i / (SAMPLE_N - 1) * W;
                const y = MID_Y - sig[i] * HALF_Y;
                if (i === 0) {
                    ctx.moveTo(x, y);
                }
                else {
                    ctx.lineTo(x, y);
                }
            }
            ctx.strokeStyle = rgba(INK, 0.9);
            ctx.lineWidth = 2;
            ctx.stroke();
            // 영점 교차 표시
            for (let i = 0; i < cross.length; i += 1) {
                ctx.beginPath();
                ctx.arc(cross[i], MID_Y, 3, 0, PI2);
                ctx.fillStyle = (cross[i] >= a - 0.5 && cross[i] <= b + 0.5) ? rgba(PINK, 1) : rgba(LILAC, 1);
                ctx.fill();
            }
            // 손잡이
            for (let i = 0; i < 2; i += 1) {
                const x = hx[i];
                ctx.fillStyle = rgba(INK, 0.95);
                ctx.fillRect(x - 1, 40, 2, 196);
                ctx.beginPath();
                ctx.roundRect(x - HANDLE_W / 2, 118, HANDLE_W, 40, 4);
                ctx.fillStyle = rgba(PINK, 1);
                ctx.fill();
                ctx.strokeStyle = rgba(INK, 0.95);
                ctx.lineWidth = 1.5;
                ctx.stroke();
                const el = els[i];
                if (el) {
                    el.style.left = (x / W * 100).toFixed(2) + '%';
                    const v = String(Math.round(x / W * (SAMPLE_N - 1)));
                    if (el.getAttribute('aria-valuenow') !== v) {
                        el.setAttribute('aria-valuenow', v);
                    }
                }
            }
            if (h.auto() && !h.reduce) {
                drawCursor(ctx, fakeX, fakeY, fakeDown);
            }
            h.say(msg !== '' && (active < 0) ? msg : TXT_SPAN + ': ' + Math.round((b - a) / W * SAMPLE_N));
        }
    };
}

    boot(document.getElementById('wfRoot'), makeTrimScene);
})();

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

const W = 480;
const H = 300;
const PI2 = Math.PI * 2;
const FIXED_DT = 16;
const IDLE_STEPS = 220;
const REDUCE_STEP_MS = 900;
const REDUCE_WARM_STEPS = 40;
const BTN_PAUSE = '멈춤';
const BTN_PLAY = '재생';
const BTN_NEXT = '다음 순간';

type RGB = [number, number, number];

// 파스텔 팔레트와 어두운 바탕 두 끝 색
const PINK: RGB = [255, 170, 196];
const MINT: RGB = [150, 226, 196];
const LILAC: RGB = [196, 176, 255];
const SKY_BLUE: RGB = [150, 214, 255];
const BUTTER: RGB = [255, 230, 150];
const CREAM: RGB = [255, 247, 230];
const INK: RGB = [23, 20, 26];
const BG_TOP: RGB = [24, 21, 40];
const BG_BOT: RGB = [48, 42, 78];

interface Host {
    ctx: CanvasRenderingContext2D;
    canvas: HTMLCanvasElement;
    root: HTMLElement;
    reduce: boolean;
    touch(): void;
    auto(): boolean;
    refresh(): void;
    say(text: string): void;
    local(e: MouseEvent): [number, number];
    listen(target: EventTarget, type: string, fn: (e: Event) => void, opts?: AddEventListenerOptions): void;
}

interface Scene {
    step(): void;
    draw(): void;
}

function clamp(v: number, lo: number, hi: number): number { return v < lo ? lo : (v > hi ? hi : v); }
function lerp(a: number, b: number, k: number): number { return a + (b - a) * k; }
function smooth(x: number): number { const c = clamp(x, 0, 1); return c * c * (3 - 2 * c); }
function mix(a: RGB, b: RGB, k: number): RGB { return [lerp(a[0], b[0], k), lerp(a[1], b[1], k), lerp(a[2], b[2], k)]; }
function rgba(c: RGB, a: number): string { return 'rgba(' + Math.round(c[0]) + ',' + Math.round(c[1]) + ',' + Math.round(c[2]) + ',' + a.toFixed(3) + ')'; }

// 시드 고정 난수 — 같은 시드면 언제나 같은 수열 (선형 합동 방식)
function lcg(seed: number): () => number {
    let s = seed >>> 0;
    return function (): number {
        s = (Math.imul(s, 1664525) + 1013904223) >>> 0;
        return s / 4294967296;
    };
}

// 정수 하나와 시드로 0 이상 1 미만의 값을 만드는 해시 (같은 입력은 늘 같은 값)
function hash1(i: number, seed: number): number {
    let h = (Math.imul(i | 0, 374761393) + Math.imul(seed | 0, 668265263)) | 0;
    h = Math.imul(h ^ (h >>> 13), 1274126177);
    h ^= h >>> 16;
    return (h >>> 0) / 4294967296;
}

// 사인 두 개를 음절마다 갈아 끼우고 엔벨로프를 씌운 합성 신호 (소리는 재생하지 않고 수치만 만든다)
function synth(n: number, seed: number): Float32Array {
    const rnd = lcg(seed);
    const out = new Float32Array(n);
    let i = 0;
    let p1 = 0;
    let p2 = 0;
    let peak = 0.0001;
    while (i < n) {
        const len = 1800 + Math.floor(rnd() * 4200);
        const amp = 0.18 + rnd() * 0.82;
        const rest = rnd() < 0.18;
        const f1 = 0.02 + rnd() * 0.09;
        const f2 = f1 * (1.5 + rnd());
        const stop = Math.min(n, i + len);
        for (let k = i; k < stop; k += 1) {
            const x = (k - i) / len;
            const env = Math.min(1, x / 0.06) * Math.pow(1 - x, 0.8);
            p1 += PI2 * f1;
            p2 += PI2 * f2;
            const tone = Math.sin(p1) * 0.7 + Math.sin(p2) * 0.3;
            const gain = rest ? 0.03 : amp * env;
            const v = gain * tone + (rnd() - 0.5) * 0.08 * (rest ? 0.4 : amp);
            out[k] = v;
            const a = Math.abs(v);
            if (a > peak) { peak = a; }
        }
        i = stop;
    }
    const norm = 0.92 / peak;
    for (let k = 0; k < n; k += 1) { out[k] *= norm; }
    return out;
}

// 표본 구간 [a, b) 의 최솟값과 최댓값 — 결과는 rangeLo, rangeHi 에 둔다
let rangeLo = 0;
let rangeHi = 0;
function scanRange(sig: Float32Array, a: number, b: number): void {
    const from = Math.max(0, Math.floor(a));
    const to = Math.min(sig.length, Math.max(from + 1, Math.ceil(b)));
    let lo = 1e9;
    let hi = -1e9;
    for (let i = from; i < to; i += 1) {
        const v = sig[i];
        if (v < lo) { lo = v; }
        if (v > hi) { hi = v; }
    }
    if (lo > hi) { lo = 0; hi = 0; }
    rangeLo = lo;
    rangeHi = hi;
}

function paintBg(ctx: CanvasRenderingContext2D, top: RGB, bot: RGB): void {
    const g = ctx.createLinearGradient(0, 0, 0, H);
    g.addColorStop(0, rgba(top, 1));
    g.addColorStop(1, rgba(bot, 1));
    ctx.fillStyle = g;
    ctx.fillRect(0, 0, W, H);
}

// 가짜 포인터 — 시연 동안 손이 움직이는 것처럼 보이게 그린다
function drawCursor(ctx: CanvasRenderingContext2D, x: number, y: number, down: boolean): void {
    ctx.save();
    ctx.translate(x, y);
    ctx.beginPath();
    ctx.moveTo(0, 0);
    ctx.lineTo(0, 15);
    ctx.lineTo(4, 11.5);
    ctx.lineTo(7.5, 18);
    ctx.lineTo(10, 16.8);
    ctx.lineTo(6.6, 10.4);
    ctx.lineTo(11.5, 10.2);
    ctx.closePath();
    ctx.fillStyle = rgba(CREAM, 1);
    ctx.strokeStyle = rgba(INK, 1);
    ctx.lineWidth = 1.4;
    ctx.fill();
    ctx.stroke();
    if (down) {
        ctx.beginPath();
        ctx.arc(0, 0, 9, 0, PI2);
        ctx.strokeStyle = rgba(PINK, 0.9);
        ctx.lineWidth = 2;
        ctx.stroke();
    }
    ctx.restore();
}

function boot(root: HTMLElement, make: (h: Host) => Scene): () => void {
    const canvasEl = root.querySelector('[data-role="canvas"]');
    const statusEl = root.querySelector('[data-role="status"]');
    const btnEl = root.querySelector('[data-role="btn"]');
    if (!(canvasEl instanceof HTMLCanvasElement) || !statusEl || !(btnEl instanceof HTMLButtonElement)) {
        return function (): void { /* 필요한 요소가 없으면 아무것도 하지 않는다 */ };
    }
    const ctxOrNull = canvasEl.getContext('2d');
    if (!ctxOrNull) {
        return function (): void { /* 2d 문맥이 없으면 아무것도 하지 않는다 */ };
    }
    const canvas: HTMLCanvasElement = canvasEl;
    const ctx: CanvasRenderingContext2D = ctxOrNull;
    const status: Element = statusEl;
    const btn: HTMLButtonElement = btnEl;
    const reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
    const cleaners: Array<() => void> = [];
    let paused = false;
    let idle = IDLE_STEPS + 1;
    let clock = 0;
    let lastSayAt = -1e9;
    let lastText = status.textContent || '';
    let scene: Scene | null = null;
    let rafId = 0;
    let acc = 0;
    let lastTs = -1;

    function isAuto(): boolean { return !reduce && !paused && idle > IDLE_STEPS; }
    function sync(): void {
        const on = isAuto();
        if (root.classList.contains('is-demo') !== on) {
            root.classList.toggle('is-demo', on);
        }
    }
    function fit(): void {
        const r = canvas.getBoundingClientRect();
        const dpr = window.devicePixelRatio || 1;
        const cw = Math.max(1, Math.round(r.width * dpr));
        const ch = Math.max(1, Math.round(r.height * dpr));
        canvas.width = cw;
        canvas.height = ch;
        ctx.setTransform(cw / W, 0, 0, ch / H, 0, 0);
    }
    const host: Host = {
        ctx,
        canvas,
        root,
        reduce,
        touch(): void {
            idle = 0;
            sync();
        },
        auto: isAuto,
        refresh(): void {
            if (scene) { scene.draw(); }
        },
        say(text: string): void {
            if (text === lastText) { return; }
            if (!reduce && clock - lastSayAt < 250) { return; }
            lastText = text;
            lastSayAt = clock;
            // 시연이 혼자 돌 때는 읽어 주지 않고, 사람이 만졌을 때만 알린다
            status.setAttribute('aria-live', isAuto() ? 'off' : 'polite');
            status.textContent = text;
        },
        local(e: MouseEvent): [number, number] {
            const r = canvas.getBoundingClientRect();
            return [clamp((e.clientX - r.left) * W / Math.max(1, r.width), 0, W), clamp((e.clientY - r.top) * H / Math.max(1, r.height), 0, H)];
        },
        listen(target: EventTarget, type: string, fn: (e: Event) => void, opts?: AddEventListenerOptions): void {
            target.addEventListener(type, fn, opts);
            cleaners.push(function (): void { target.removeEventListener(type, fn, opts); });
        }
    };
    function advance(ms: number): void {
        if (!scene) { return; }
        const n = Math.max(1, Math.round(ms / FIXED_DT));
        for (let i = 0; i < n; i += 1) {
            idle += 1;
            clock += FIXED_DT;
            scene.step();
        }
    }
    function frame(ts: number): void {
        if (lastTs < 0) { lastTs = ts; }
        const dt = Math.min(ts - lastTs, 160);
        lastTs = ts;
        if (!paused && scene) {
            acc += dt;
            while (acc >= FIXED_DT) {
                idle += 1;
                clock += FIXED_DT;
                scene.step();
                acc -= FIXED_DT;
            }
            sync();
            scene.draw();
        }
        rafId = requestAnimationFrame(frame);
    }
    scene = make(host);
    btn.textContent = reduce ? BTN_NEXT : BTN_PAUSE;
    fit();
    if (reduce) {
        root.classList.remove('is-demo');
        advance(REDUCE_WARM_STEPS * FIXED_DT);
    }
    scene.draw();
    host.listen(btn, 'click', function (): void {
        if (reduce) {
            advance(REDUCE_STEP_MS);
            host.refresh();
            return;
        }
        paused = !paused;
        btn.textContent = paused ? BTN_PLAY : BTN_PAUSE;
        sync();
    });
    host.listen(window, 'resize', function (): void {
        fit();
        host.refresh();
    });
    if (!reduce) {
        rafId = requestAnimationFrame(frame);
    }
    return function (): void {
        cancelAnimationFrame(rafId);
        for (let i = 0; i < cleaners.length; i += 1) { cleaners[i](); }
    };
}

const SAMPLE_N = 1920;
const SNAP_RADIUS = 6;
const HANDLE_W = 8;
const MIN_SPAN = 24;
const SNAP_EASE = 0.25;
const MID_Y = 138;
const HALF_Y = 74;
const SCRIPT_LEN = 360;
const START_A = 55.4;
const START_B = 423.6;
const TXT_SNAP = '끌려간 거리';
const TXT_STAY = '반경 안에 영점 교차 없음';
const TXT_SPAN = '선택 길이';

// 저주파 두 성분을 겹친 신호 — 영점 교차가 수십 픽셀 간격으로 나타난다
function lowSignal(n: number): Float32Array {
    const out = new Float32Array(n);
    for (let i = 0; i < n; i += 1) {
        const a = Math.sin(PI2 * 0.0062 * i + 0.7) * 0.78;
        const b = Math.sin(PI2 * 0.0147 * i + 2.1) * 0.34;
        const c = Math.sin(PI2 * 0.0021 * i + 4.0) * 0.18;
        out[i] = clamp(a + b + c, -0.95, 0.95);
    }
    return out;
}

// 부호가 바뀌는 표본 사이를 직선으로 이어 영점 교차의 화면 x 를 구한다
function zeroCrossings(sig: Float32Array): number[] {
    const xs: number[] = [];
    for (let i = 0; i < sig.length - 1; i += 1) {
        const a = sig[i];
        const b = sig[i + 1];
        if ((a < 0 && b >= 0) || (a >= 0 && b < 0)) {
            xs.push((i + a / (a - b)) / (sig.length - 1) * W);
        }
    }
    return xs;
}

// 놓은 자리 x 에서 반경 안의 가장 가까운 영점 교차로 — 없으면 제자리
function snapTarget(x: number, crossings: number[], radius: number): number {
    let best = x;
    let bestD = radius + 0.0001;
    for (let i = 0; i < crossings.length; i += 1) {
        const d = Math.abs(crossings[i] - x);
        if (d < bestD) {
            bestD = d;
            best = crossings[i];
        }
    }
    return best;
}

function makeTrimScene(h: Host): Scene {
    const sig = lowSignal(SAMPLE_N);
    const cross = zeroCrossings(sig);
    const hx = [START_A, START_B];
    const tx = [START_A, START_B];
    const els: HTMLElement[] = [];
    const nodes = h.root.querySelectorAll('[data-role="handle"]');
    for (let i = 0; i < nodes.length; i += 1) {
        const node = nodes[i];
        if (node instanceof HTMLElement) { els.push(node); }
    }
    let active = -1;
    let k = 0;
    let fakeX = 200;
    let fakeY = 210;
    let fakeDown = false;
    let lastPull = -1;
    let msg = '';
    function limit(i: number, x: number): number {
        return i === 0 ? clamp(x, 0, hx[1] - MIN_SPAN) : clamp(x, hx[0] + MIN_SPAN, W);
    }
    function release(i: number): void {
        const want = limit(i, snapTarget(hx[i], cross, SNAP_RADIUS));
        lastPull = Math.abs(want - hx[i]);
        tx[i] = want;
        if (h.reduce) { hx[i] = want; }
        msg = lastPull < 0.05 ? TXT_STAY : TXT_SNAP + ': ' + lastPull.toFixed(1) + ' px';
    }
    function nextCross(i: number, dir: number): void {
        let best = hx[i];
        let found = false;
        for (let c = 0; c < cross.length; c += 1) {
            const x = cross[c];
            if (dir > 0 && x > hx[i] + 0.5 && (!found || x < best)) { best = x; found = true; }
            if (dir < 0 && x < hx[i] - 0.5 && (!found || x > best)) { best = x; found = true; }
        }
        tx[i] = limit(i, best);
        if (h.reduce) { hx[i] = tx[i]; }
    }
    for (let i = 0; i < els.length && i < 2; i += 1) {
        const el = els[i];
        const idx = i;
        h.listen(el, 'pointerdown', function (e: Event): void {
            const pe = e as PointerEvent;
            active = idx;
            el.setPointerCapture(pe.pointerId);
            h.touch();
        });
        h.listen(el, 'pointermove', function (e: Event): void {
            if (active !== idx) { return; }
            const x = limit(idx, h.local(e as PointerEvent)[0]);
            hx[idx] = x;
            tx[idx] = x;
            h.refresh();
        });
        const up = function (): void {
            if (active !== idx) { return; }
            active = -1;
            release(idx);
            h.refresh();
        };
        h.listen(el, 'pointerup', up);
        h.listen(el, 'pointercancel', up);
        h.listen(el, 'keydown', function (e: Event): void {
            const key = (e as KeyboardEvent).key;
            if (key === 'ArrowLeft' || key === 'ArrowRight') {
                e.preventDefault();
                nextCross(idx, key === 'ArrowRight' ? 1 : -1);
                h.touch();
                h.refresh();
            }
        });
    }
    function script(): void {
        const j = k % SCRIPT_LEN;
        fakeDown = false;
        if (j === 0) {
            hx[0] = START_A; tx[0] = START_A; hx[1] = START_B; tx[1] = START_B;
        }
        if (j < 20) {
            fakeX = lerp(200, START_A, smooth(j / 20));
            fakeY = lerp(210, MID_Y, smooth(j / 20));
        }
        else if (j < 60) {
            fakeDown = true;
            const x = lerp(START_A, 103.5, smooth((j - 20) / 40));
            hx[0] = limit(0, x);
            tx[0] = hx[0];
            fakeX = hx[0];
            fakeY = MID_Y;
            if (j === 59) { release(0); }
        }
        else if (j < 110) {
            fakeX = lerp(hx[0], START_B, smooth((j - 60) / 50));
        }
        else if (j < 150) {
            fakeDown = true;
            const x = lerp(START_B, 329, smooth((j - 110) / 40));
            hx[1] = limit(1, x);
            tx[1] = hx[1];
            fakeX = hx[1];
            if (j === 149) { release(1); }
        }
        else if (j < 200) {
            fakeX = lerp(tx[1], 250, smooth((j - 150) / 50));
            fakeY = lerp(MID_Y, 214, smooth((j - 150) / 50));
        }
    }
    return {
        step(): void {
            k += 1;
            if (h.auto()) { script(); }
            for (let i = 0; i < 2; i += 1) {
                if (active === i || (h.auto() && fakeDown && ((k % SCRIPT_LEN) < 60 ? i === 0 : i === 1))) { continue; }
                const d = tx[i] - hx[i];
                hx[i] = Math.abs(d) < 0.05 ? tx[i] : hx[i] + d * SNAP_EASE;
            }
        },
        draw(): void {
            const ctx = h.ctx;
            ctx.fillStyle = rgba(CREAM, 1);
            ctx.fillRect(0, 0, W, H);
            const a = hx[0];
            const b = hx[1];
            // 선택 구간 바탕
            ctx.fillStyle = rgba(MINT, 0.38);
            ctx.fillRect(a, 40, b - a, 196);
            // 흡착 반경 띠 — 끌고 있는 손잡이 둘레
            const grabbed = active >= 0 ? active : (h.auto() && fakeDown ? ((k % SCRIPT_LEN) < 60 ? 0 : 1) : -1);
            if (grabbed >= 0) {
                ctx.fillStyle = rgba(LILAC, 0.34);
                ctx.fillRect(hx[grabbed] - SNAP_RADIUS, 40, SNAP_RADIUS * 2, 196);
            }
            ctx.fillStyle = rgba(INK, 0.28);
            ctx.fillRect(0, MID_Y, W, 1);
            // 파형
            ctx.beginPath();
            for (let i = 0; i < SAMPLE_N; i += 4) {
                const x = i / (SAMPLE_N - 1) * W;
                const y = MID_Y - sig[i] * HALF_Y;
                if (i === 0) { ctx.moveTo(x, y); } else { ctx.lineTo(x, y); }
            }
            ctx.strokeStyle = rgba(INK, 0.9);
            ctx.lineWidth = 2;
            ctx.stroke();
            // 영점 교차 표시
            for (let i = 0; i < cross.length; i += 1) {
                ctx.beginPath();
                ctx.arc(cross[i], MID_Y, 3, 0, PI2);
                ctx.fillStyle = (cross[i] >= a - 0.5 && cross[i] <= b + 0.5) ? rgba(PINK, 1) : rgba(LILAC, 1);
                ctx.fill();
            }
            // 손잡이
            for (let i = 0; i < 2; i += 1) {
                const x = hx[i];
                ctx.fillStyle = rgba(INK, 0.95);
                ctx.fillRect(x - 1, 40, 2, 196);
                ctx.beginPath();
                ctx.roundRect(x - HANDLE_W / 2, 118, HANDLE_W, 40, 4);
                ctx.fillStyle = rgba(PINK, 1);
                ctx.fill();
                ctx.strokeStyle = rgba(INK, 0.95);
                ctx.lineWidth = 1.5;
                ctx.stroke();
                const el = els[i];
                if (el) {
                    el.style.left = (x / W * 100).toFixed(2) + '%';
                    const v = String(Math.round(x / W * (SAMPLE_N - 1)));
                    if (el.getAttribute('aria-valuenow') !== v) { el.setAttribute('aria-valuenow', v); }
                }
            }
            if (h.auto() && !h.reduce) { drawCursor(ctx, fakeX, fakeY, fakeDown); }
            h.say(msg !== '' && (active < 0) ? msg : TXT_SPAN + ': ' + Math.round((b - a) / W * SAMPLE_N));
        }
    };
}

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

  useEffect(() => {
    const root = rootRef.current;
    if (!root) return;
    return boot(root, makeTrimScene);
  }, []);

  return (
    <main className={styles.stage}>
      <div className={`${styles.wf} is-demo`} ref={rootRef}>
        <canvas className={styles.canvas} data-role="canvas" width={480} height={300} tabIndex={0} aria-label="자를 구간의 손잡이가 가장 가까운 영점 교차로 끌려가 붙는 구간 선택기" />
        <div className={styles.handle} data-role="handle" role="slider" tabIndex={0} aria-label="시작 손잡이" aria-valuemin={0} aria-valuemax={1919} aria-valuenow={221} style={{ left: "11.54%" }} />
        <div className={styles.handle} data-role="handle" role="slider" tabIndex={0} aria-label="끝 손잡이" aria-valuemin={0} aria-valuemax={1919} aria-valuenow={1694} style={{ left: "88.25%" }} />
        <p className={styles.status} data-role="status" aria-live="polite">선택 길이</p>
        <button className={styles.btn} data-role="btn" type="button">멈춤</button>
        <p className={styles.caption}>자를 구간의 손잡이가 가장 가까운 영점 교차로 끌려가 붙는 구간 선택기</p>
      </div>
    </main>
  );
}