04ホイールで拡大しても、ポインタの下の瞬間が動かず束が計算し直される波形

<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="ホイールで拡大しても、ポインタの下の瞬間が動かず束が計算し直される波形"></canvas>
  <p class="wf__status" data-role="status" aria-live="polite">拡大率</p>
  <button class="wf__btn" data-role="btn" type="button">一時停止</button>
  <p class="wf__caption">ホイールで拡大しても、ポインタの下の瞬間が動かず束が計算し直される波形</p>
</div>
</main>

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

.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: pan-y;
}

.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;
}

@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: #17141a;
  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: pan-y;
}

.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;
}

@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 = 43200;
const ZOOM_MIN = 1;
const ZOOM_MAX = 96;
const ZOOM_STEP = 1.5;
const VIEW_START = 0;
const COL_PX = 2;
const MID_Y = 142;
const HALF_Y = 78;
const SCRIPT_LEN = 420;
const KEY_PAN_PX = 24;
const TXT_ZOOM = '拡大率';
// 포인터 아래 표본 위치(anchorT)가 같은 화면 x(anchorPx)에 머물도록 시작점을 거꾸로 구한다
function viewStartFor(anchorT, anchorPx, span) {
    return clamp(anchorT - anchorPx / W * span, 0, SAMPLE_N - span);
}
function niceStep(raw) {
    const p = Math.pow(10, Math.floor(Math.log10(Math.max(1, raw))));
    const m = raw / p;
    return (m < 1.5 ? 1 : (m < 3.5 ? 2 : (m < 7.5 ? 5 : 10))) * p;
}
function makeZoomScene(h) {
    const sig = synth(SAMPLE_N, 4593);
    const nOv = Math.floor(W / 4);
    const ovLo = [];
    const ovHi = [];
    for (let c = 0; c < nOv; c += 1) {
        scanRange(sig, c * SAMPLE_N / nOv, (c + 1) * SAMPLE_N / nOv);
        ovLo.push(rangeLo);
        ovHi.push(rangeHi);
    }
    let zt = ZOOM_MIN;
    let z = ZOOM_MIN;
    let span = SAMPLE_N / ZOOM_MIN;
    let anchorPx = W / 2;
    let anchorT = VIEW_START + anchorPx / W * span;
    let start = VIEW_START;
    let hoverPx = W / 2;
    let k = 0;
    let fakeX = 330;
    let fakeDown = false;
    let drag = false;
    let lastX = 0;
    function recompute() {
        span = SAMPLE_N / z;
        start = viewStartFor(anchorT, anchorPx, span);
    }
    // 휠 한 칸 — 포인터가 가리키는 표본을 앵커로 잡고 목표 배율만 바꾼다
    function notch(dir, px) {
        const next = clamp(zt * (dir > 0 ? ZOOM_STEP : 1 / ZOOM_STEP), ZOOM_MIN, ZOOM_MAX);
        if (next === zt) {
            return false;
        }
        anchorT = start + px / W * span;
        anchorPx = px;
        zt = next;
        if (h.reduce) {
            z = zt;
            recompute();
        }
        return true;
    }
    function pan(dxPx) {
        anchorT = clamp(anchorT - dxPx / W * span, 0, SAMPLE_N);
        recompute();
    }
    h.listen(h.canvas, 'wheel', function (e) {
        const we = e;
        const px = h.local(we)[0];
        hoverPx = px;
        if (notch(we.deltaY < 0 ? 1 : -1, px)) {
            // 배율이 실제로 바뀔 때만 페이지 스크롤을 막는다
            e.preventDefault();
            h.touch();
            h.refresh();
        }
    }, { passive: false });
    h.listen(h.canvas, 'pointerdown', function (e) {
        const pe = e;
        drag = true;
        lastX = h.local(pe)[0];
        h.canvas.setPointerCapture(pe.pointerId);
        h.touch();
    });
    h.listen(h.canvas, 'pointermove', function (e) {
        const x = h.local(e)[0];
        hoverPx = x;
        if (drag) {
            pan(x - lastX);
            lastX = x;
            h.touch();
            h.refresh();
        }
    });
    const drop = function () { drag = false; };
    h.listen(h.canvas, 'pointerup', drop);
    h.listen(h.canvas, 'pointercancel', drop);
    h.listen(h.canvas, 'keydown', function (e) {
        const key = e.key;
        let handled = true;
        if (key === '+' || key === '=') {
            notch(1, hoverPx);
        }
        else if (key === '-' || key === '_') {
            notch(-1, hoverPx);
        }
        else if (key === 'ArrowLeft') {
            pan(KEY_PAN_PX);
        }
        else if (key === 'ArrowRight') {
            pan(-KEY_PAN_PX);
        }
        else if (key === 'Home') {
            zt = ZOOM_MIN;
            anchorT = SAMPLE_N / 2;
            anchorPx = W / 2;
            if (h.reduce) {
                z = zt;
                recompute();
            }
        }
        else {
            handled = false;
        }
        if (handled) {
            e.preventDefault();
            h.touch();
            h.refresh();
        }
    });
    function script() {
        const j = k % SCRIPT_LEN;
        if (j === 0) {
            zt = ZOOM_MIN;
            anchorT = SAMPLE_N * 0.5;
            anchorPx = W / 2;
        }
        fakeDown = false;
        if (j < 12) {
            fakeX = 330;
        }
        else if (j < 56) {
            fakeX = 330;
            if ((j - 12) % 4 === 0) {
                notch(1, fakeX);
            }
        }
        else if (j >= 64 && j < 130) {
            fakeDown = true;
            fakeX = 330 - (j - 64) * 1.2;
            pan(-1.2);
        }
        else if (j >= 190 && j < 232) {
            fakeX = lerp(250, 120, (j - 190) / 42);
        }
        else if (j >= 240 && j < 312) {
            fakeX = 120;
            if ((j - 240) % 6 === 0) {
                notch(-1, fakeX);
            }
        }
        hoverPx = fakeX;
    }
    return {
        step() {
            k += 1;
            if (h.auto()) {
                script();
            }
            if (!h.reduce) {
                const r = zt / z;
                z = Math.abs(Math.log(r)) < 0.002 ? zt : z * Math.pow(r, 0.2);
                recompute();
            }
        },
        draw() {
            const ctx = h.ctx;
            paintBg(ctx, BG_TOP, BG_BOT);
            // 위쪽 개요 띠 — 전체 신호와 지금 보는 구간
            for (let c = 0; c < nOv; c += 1) {
                ctx.fillStyle = rgba(LILAC, 0.5);
                ctx.fillRect(c * 4, 40 - ovHi[c] * 5, 3, (ovHi[c] - ovLo[c]) * 5 + 1);
            }
            ctx.strokeStyle = rgba(BUTTER, 1);
            ctx.lineWidth = 1.5;
            ctx.strokeRect(start / SAMPLE_N * W, 31, Math.max(3, span / SAMPLE_N * W), 18);
            // 눈금
            const tickStep = niceStep(span / 7);
            ctx.font = '10px sans-serif';
            ctx.textAlign = 'center';
            for (let t = Math.ceil(start / tickStep) * tickStep; t < start + span; t += tickStep) {
                const x = (t - start) / span * W;
                ctx.fillStyle = rgba(CREAM, 0.16);
                ctx.fillRect(x, 56, 1, 178);
                ctx.fillStyle = rgba(CREAM, 0.7);
                ctx.fillText(String(Math.round(t)), x, 64);
            }
            ctx.fillStyle = rgba(CREAM, 0.16);
            ctx.fillRect(0, MID_Y, W, 1);
            const spp = span / W;
            if (spp >= 1.6) {
                // 묶음 단계 — 기둥마다 최대·최소
                const n = Math.floor(W / COL_PX);
                const per = span / n;
                for (let c = 0; c < n; c += 1) {
                    scanRange(sig, start + c * per, start + (c + 1) * per);
                    const loud = clamp(Math.max(rangeHi, -rangeLo), 0, 1);
                    ctx.fillStyle = rgba(mix(LILAC, PINK, loud), 0.9);
                    ctx.fillRect(c * COL_PX, MID_Y - rangeHi * HALF_Y, COL_PX - 0.5, Math.max(1, (rangeHi - rangeLo) * HALF_Y));
                }
            }
            else {
                // 표본 단계 — 표본마다 점과 선
                ctx.beginPath();
                const first = Math.floor(start);
                const last = Math.min(SAMPLE_N - 1, Math.ceil(start + span));
                for (let i = first; i <= last; i += 1) {
                    const x = (i - start) / span * W;
                    const y = MID_Y - sig[i] * HALF_Y;
                    if (i === first) {
                        ctx.moveTo(x, y);
                    }
                    else {
                        ctx.lineTo(x, y);
                    }
                }
                ctx.strokeStyle = rgba(MINT, 0.95);
                ctx.lineWidth = 1.4;
                ctx.stroke();
                ctx.fillStyle = rgba(PINK, 1);
                for (let i = first; i <= last; i += 1) {
                    ctx.beginPath();
                    ctx.arc((i - start) / span * W, MID_Y - sig[i] * HALF_Y, 1.8, 0, PI2);
                    ctx.fill();
                }
            }
            // 앵커 — 확대해도 이 선 아래 표본은 같은 자리에 있다
            ctx.fillStyle = rgba(BUTTER, 0.8);
            ctx.fillRect(anchorPx - 0.5, 56, 1.5, 178);
            if (h.auto() && !h.reduce) {
                drawCursor(ctx, fakeX, MID_Y + 6, fakeDown);
            }
            h.say(TXT_ZOOM + ': ' + z.toFixed(1) + ' x / ' + Math.round(span));
        }
    };
}

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

import { useEffect, useRef } from "react";
import styles from "./WfWheelZoomPointerAnchorLod.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 = 43200;
const ZOOM_MIN = 1;
const ZOOM_MAX = 96;
const ZOOM_STEP = 1.5;
const VIEW_START = 0;
const COL_PX = 2;
const MID_Y = 142;
const HALF_Y = 78;
const SCRIPT_LEN = 420;
const KEY_PAN_PX = 24;
const TXT_ZOOM = '확대 배율';

// 포인터 아래 표본 위치(anchorT)가 같은 화면 x(anchorPx)에 머물도록 시작점을 거꾸로 구한다
function viewStartFor(anchorT: number, anchorPx: number, span: number): number {
    return clamp(anchorT - anchorPx / W * span, 0, SAMPLE_N - span);
}

function niceStep(raw: number): number {
    const p = Math.pow(10, Math.floor(Math.log10(Math.max(1, raw))));
    const m = raw / p;
    return (m < 1.5 ? 1 : (m < 3.5 ? 2 : (m < 7.5 ? 5 : 10))) * p;
}

function makeZoomScene(h: Host): Scene {
    const sig = synth(SAMPLE_N, 4593);
    const nOv = Math.floor(W / 4);
    const ovLo: number[] = [];
    const ovHi: number[] = [];
    for (let c = 0; c < nOv; c += 1) {
        scanRange(sig, c * SAMPLE_N / nOv, (c + 1) * SAMPLE_N / nOv);
        ovLo.push(rangeLo);
        ovHi.push(rangeHi);
    }
    let zt = ZOOM_MIN;
    let z = ZOOM_MIN;
    let span = SAMPLE_N / ZOOM_MIN;
    let anchorPx = W / 2;
    let anchorT = VIEW_START + anchorPx / W * span;
    let start = VIEW_START;
    let hoverPx = W / 2;
    let k = 0;
    let fakeX = 330;
    let fakeDown = false;
    let drag = false;
    let lastX = 0;
    function recompute(): void {
        span = SAMPLE_N / z;
        start = viewStartFor(anchorT, anchorPx, span);
    }
    // 휠 한 칸 — 포인터가 가리키는 표본을 앵커로 잡고 목표 배율만 바꾼다
    function notch(dir: number, px: number): boolean {
        const next = clamp(zt * (dir > 0 ? ZOOM_STEP : 1 / ZOOM_STEP), ZOOM_MIN, ZOOM_MAX);
        if (next === zt) { return false; }
        anchorT = start + px / W * span;
        anchorPx = px;
        zt = next;
        if (h.reduce) {
            z = zt;
            recompute();
        }
        return true;
    }
    function pan(dxPx: number): void {
        anchorT = clamp(anchorT - dxPx / W * span, 0, SAMPLE_N);
        recompute();
    }
    h.listen(h.canvas, 'wheel', function (e: Event): void {
        const we = e as WheelEvent;
        const px = h.local(we)[0];
        hoverPx = px;
        if (notch(we.deltaY < 0 ? 1 : -1, px)) {
            // 배율이 실제로 바뀔 때만 페이지 스크롤을 막는다
            e.preventDefault();
            h.touch();
            h.refresh();
        }
    }, { passive: false });
    h.listen(h.canvas, 'pointerdown', function (e: Event): void {
        const pe = e as PointerEvent;
        drag = true;
        lastX = h.local(pe)[0];
        h.canvas.setPointerCapture(pe.pointerId);
        h.touch();
    });
    h.listen(h.canvas, 'pointermove', function (e: Event): void {
        const x = h.local(e as PointerEvent)[0];
        hoverPx = x;
        if (drag) {
            pan(x - lastX);
            lastX = x;
            h.touch();
            h.refresh();
        }
    });
    const drop = function (): void { drag = false; };
    h.listen(h.canvas, 'pointerup', drop);
    h.listen(h.canvas, 'pointercancel', drop);
    h.listen(h.canvas, 'keydown', function (e: Event): void {
        const key = (e as KeyboardEvent).key;
        let handled = true;
        if (key === '+' || key === '=') { notch(1, hoverPx); }
        else if (key === '-' || key === '_') { notch(-1, hoverPx); }
        else if (key === 'ArrowLeft') { pan(KEY_PAN_PX); }
        else if (key === 'ArrowRight') { pan(-KEY_PAN_PX); }
        else if (key === 'Home') { zt = ZOOM_MIN; anchorT = SAMPLE_N / 2; anchorPx = W / 2; if (h.reduce) { z = zt; recompute(); } }
        else { handled = false; }
        if (handled) {
            e.preventDefault();
            h.touch();
            h.refresh();
        }
    });
    function script(): void {
        const j = k % SCRIPT_LEN;
        if (j === 0) { zt = ZOOM_MIN; anchorT = SAMPLE_N * 0.5; anchorPx = W / 2; }
        fakeDown = false;
        if (j < 12) { fakeX = 330; }
        else if (j < 56) {
            fakeX = 330;
            if ((j - 12) % 4 === 0) { notch(1, fakeX); }
        }
        else if (j >= 64 && j < 130) {
            fakeDown = true;
            fakeX = 330 - (j - 64) * 1.2;
            pan(-1.2);
        }
        else if (j >= 190 && j < 232) {
            fakeX = lerp(250, 120, (j - 190) / 42);
        }
        else if (j >= 240 && j < 312) {
            fakeX = 120;
            if ((j - 240) % 6 === 0) { notch(-1, fakeX); }
        }
        hoverPx = fakeX;
    }
    return {
        step(): void {
            k += 1;
            if (h.auto()) { script(); }
            if (!h.reduce) {
                const r = zt / z;
                z = Math.abs(Math.log(r)) < 0.002 ? zt : z * Math.pow(r, 0.2);
                recompute();
            }
        },
        draw(): void {
            const ctx = h.ctx;
            paintBg(ctx, BG_TOP, BG_BOT);
            // 위쪽 개요 띠 — 전체 신호와 지금 보는 구간
            for (let c = 0; c < nOv; c += 1) {
                ctx.fillStyle = rgba(LILAC, 0.5);
                ctx.fillRect(c * 4, 40 - ovHi[c] * 5, 3, (ovHi[c] - ovLo[c]) * 5 + 1);
            }
            ctx.strokeStyle = rgba(BUTTER, 1);
            ctx.lineWidth = 1.5;
            ctx.strokeRect(start / SAMPLE_N * W, 31, Math.max(3, span / SAMPLE_N * W), 18);
            // 눈금
            const tickStep = niceStep(span / 7);
            ctx.font = '10px sans-serif';
            ctx.textAlign = 'center';
            for (let t = Math.ceil(start / tickStep) * tickStep; t < start + span; t += tickStep) {
                const x = (t - start) / span * W;
                ctx.fillStyle = rgba(CREAM, 0.16);
                ctx.fillRect(x, 56, 1, 178);
                ctx.fillStyle = rgba(CREAM, 0.7);
                ctx.fillText(String(Math.round(t)), x, 64);
            }
            ctx.fillStyle = rgba(CREAM, 0.16);
            ctx.fillRect(0, MID_Y, W, 1);
            const spp = span / W;
            if (spp >= 1.6) {
                // 묶음 단계 — 기둥마다 최대·최소
                const n = Math.floor(W / COL_PX);
                const per = span / n;
                for (let c = 0; c < n; c += 1) {
                    scanRange(sig, start + c * per, start + (c + 1) * per);
                    const loud = clamp(Math.max(rangeHi, -rangeLo), 0, 1);
                    ctx.fillStyle = rgba(mix(LILAC, PINK, loud), 0.9);
                    ctx.fillRect(c * COL_PX, MID_Y - rangeHi * HALF_Y, COL_PX - 0.5, Math.max(1, (rangeHi - rangeLo) * HALF_Y));
                }
            }
            else {
                // 표본 단계 — 표본마다 점과 선
                ctx.beginPath();
                const first = Math.floor(start);
                const last = Math.min(SAMPLE_N - 1, Math.ceil(start + span));
                for (let i = first; i <= last; i += 1) {
                    const x = (i - start) / span * W;
                    const y = MID_Y - sig[i] * HALF_Y;
                    if (i === first) { ctx.moveTo(x, y); } else { ctx.lineTo(x, y); }
                }
                ctx.strokeStyle = rgba(MINT, 0.95);
                ctx.lineWidth = 1.4;
                ctx.stroke();
                ctx.fillStyle = rgba(PINK, 1);
                for (let i = first; i <= last; i += 1) {
                    ctx.beginPath();
                    ctx.arc((i - start) / span * W, MID_Y - sig[i] * HALF_Y, 1.8, 0, PI2);
                    ctx.fill();
                }
            }
            // 앵커 — 확대해도 이 선 아래 표본은 같은 자리에 있다
            ctx.fillStyle = rgba(BUTTER, 0.8);
            ctx.fillRect(anchorPx - 0.5, 56, 1.5, 178);
            if (h.auto() && !h.reduce) { drawCursor(ctx, fakeX, MID_Y + 6, fakeDown); }
            h.say(TXT_ZOOM + ': ' + z.toFixed(1) + ' x / ' + Math.round(span));
        }
    };
}

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

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

  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="휠로 확대해도 포인터 아래 순간이 제자리에 머물고 묶음이 다시 계산되는 파형" />
        <p className={styles.status} data-role="status" aria-live="polite">확대 배율</p>
        <button className={styles.btn} data-role="btn" type="button">멈춤</button>
        <p className={styles.caption}>휠로 확대해도 포인터 아래 순간이 제자리에 머물고 묶음이 다시 계산되는 파형</p>
      </div>
    </main>
  );
}