03재생 위치 한 줄이 기둥을 반 픽셀 단위로 갈라 지난 부분과 남은 부분의 색을 바꾸는 파형

<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="재생 위치 한 줄이 기둥을 반 픽셀 단위로 갈라 지난 부분과 남은 부분의 색을 바꾸는 파형" role="slider" aria-valuemin="0" aria-valuemax="6" aria-valuenow="0.5"></canvas>
  <p class="wf__status" data-role="status" aria-live="polite">재생 위치</p>
  <button class="wf__btn" data-role="btn" type="button">멈춤</button>
  <p class="wf__caption">재생 위치 한 줄이 기둥을 반 픽셀 단위로 갈라 지난 부분과 남은 부분의 색을 바꾸는 파형</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: 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: #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: 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 = '멈춤';
const BTN_PLAY = '재생';
const BTN_NEXT = '다음 순간';
// 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 PLAYHEAD_W = 2;
const PLAYED_HUE = 340;
const UNPLAYED_ALPHA = 0.28;
const SCRUB_EASE = 0.25;
const COL_PX = 6;
const COL_GAP = 2;
const DURATION_STEPS = 375;
const DURATION_S = 6;
const MID_Y = 128;
const HALF_Y = 80;
const KEY_SEEK = 0.0833;
const TXT_POS = '재생 위치';
// 재생 위치를 반 픽셀 단위로 맞춘다 — 기둥 안쪽에 떨어지면 그 기둥을 둘로 가른다
function halfPixel(px) {
    return Math.round(px * 2) / 2;
}
function makeSplitScene(h) {
    const sig = synth(SAMPLE_N, 4592);
    const nCols = Math.floor(W / COL_PX);
    const peaks = [];
    const lows = [];
    const per = SAMPLE_N / nCols;
    for (let c = 0; c < nCols; c += 1) {
        scanRange(sig, c * per, (c + 1) * per);
        lows.push(rangeLo);
        peaks.push(rangeHi);
    }
    let pos = 0.08;
    let target = pos;
    let dragging = false;
    let tick = 0;
    function setAria(force) {
        if (!force && tick % 30 !== 0) {
            return;
        }
        const sec = pos * DURATION_S;
        h.canvas.setAttribute('aria-valuenow', sec.toFixed(1));
        h.canvas.setAttribute('aria-valuetext', sec.toFixed(1) + ' / ' + DURATION_S.toFixed(1) + ' s');
    }
    function seek(next) {
        target = clamp(next, 0, 1);
        if (h.reduce) {
            pos = target;
        }
        h.touch();
        setAria(true);
        h.refresh();
    }
    h.listen(h.canvas, 'pointerdown', function (e) {
        const pe = e;
        dragging = true;
        h.canvas.setPointerCapture(pe.pointerId);
        seek(h.local(pe)[0] / W);
    });
    h.listen(h.canvas, 'pointermove', function (e) {
        if (dragging) {
            seek(h.local(e)[0] / W);
        }
    });
    const release = function () { dragging = false; };
    h.listen(h.canvas, 'pointerup', release);
    h.listen(h.canvas, 'pointercancel', release);
    h.listen(h.canvas, 'keydown', function (e) {
        const key = e.key;
        if (key === 'ArrowLeft') {
            e.preventDefault();
            seek(pos - KEY_SEEK);
        }
        else if (key === 'ArrowRight') {
            e.preventDefault();
            seek(pos + KEY_SEEK);
        }
        else if (key === 'Home') {
            e.preventDefault();
            seek(0);
        }
        else if (key === 'End') {
            e.preventDefault();
            seek(1);
        }
    });
    return {
        step() {
            tick += 1;
            if (dragging) {
                pos += (target - pos) * SCRUB_EASE;
            }
            else {
                pos += 1 / DURATION_STEPS;
                if (pos >= 1) {
                    pos -= 1;
                }
                target = pos;
            }
            setAria(false);
        },
        draw() {
            const ctx = h.ctx;
            ctx.fillStyle = rgba(CREAM, 1);
            ctx.fillRect(0, 0, W, H);
            const played = 'hsl(' + PLAYED_HUE + ' 82% 66%)';
            const rest = rgba(INK, UNPLAYED_ALPHA);
            const ph = halfPixel(pos * W);
            for (let c = 0; c < nCols; c += 1) {
                const x0 = c * COL_PX;
                const x1 = x0 + COL_PX - COL_GAP;
                const top = MID_Y - Math.max(peaks[c], 0.02) * HALF_Y;
                const bot = MID_Y - Math.min(lows[c], -0.02) * HALF_Y;
                if (x1 <= ph) {
                    ctx.fillStyle = played;
                    ctx.fillRect(x0, top, x1 - x0, bot - top);
                }
                else if (x0 >= ph) {
                    ctx.fillStyle = rest;
                    ctx.fillRect(x0, top, x1 - x0, bot - top);
                }
                else {
                    // 재생 위치가 걸친 기둥 — 클립 영역 둘로 나눠 왼쪽은 진하게, 오른쪽은 옅게
                    ctx.save();
                    ctx.beginPath();
                    ctx.rect(x0, 0, ph - x0, H);
                    ctx.clip();
                    ctx.fillStyle = played;
                    ctx.fillRect(x0, top, x1 - x0, bot - top);
                    ctx.restore();
                    ctx.save();
                    ctx.beginPath();
                    ctx.rect(ph, 0, x1 - ph, H);
                    ctx.clip();
                    ctx.fillStyle = rest;
                    ctx.fillRect(x0, top, x1 - x0, bot - top);
                    ctx.restore();
                }
            }
            ctx.fillStyle = rgba(INK, 0.9);
            ctx.fillRect(ph - PLAYHEAD_W / 2, 36, PLAYHEAD_W, 188);
            ctx.beginPath();
            ctx.arc(ph, 36, 4, 0, PI2);
            ctx.fill();
            h.say(TXT_POS + ': ' + (pos * DURATION_S).toFixed(1) + ' / ' + DURATION_S.toFixed(1) + ' s');
        }
    };
}

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

import { useEffect, useRef } from "react";
import styles from "./WfPlayheadSubpixelPlayedSplit.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 PLAYHEAD_W = 2;
const PLAYED_HUE = 340;
const UNPLAYED_ALPHA = 0.28;
const SCRUB_EASE = 0.25;
const COL_PX = 6;
const COL_GAP = 2;
const DURATION_STEPS = 375;
const DURATION_S = 6;
const MID_Y = 128;
const HALF_Y = 80;
const KEY_SEEK = 0.0833;
const TXT_POS = '재생 위치';

// 재생 위치를 반 픽셀 단위로 맞춘다 — 기둥 안쪽에 떨어지면 그 기둥을 둘로 가른다
function halfPixel(px: number): number {
    return Math.round(px * 2) / 2;
}

function makeSplitScene(h: Host): Scene {
    const sig = synth(SAMPLE_N, 4592);
    const nCols = Math.floor(W / COL_PX);
    const peaks: number[] = [];
    const lows: number[] = [];
    const per = SAMPLE_N / nCols;
    for (let c = 0; c < nCols; c += 1) {
        scanRange(sig, c * per, (c + 1) * per);
        lows.push(rangeLo);
        peaks.push(rangeHi);
    }
    let pos = 0.08;
    let target = pos;
    let dragging = false;
    let tick = 0;
    function setAria(force: boolean): void {
        if (!force && tick % 30 !== 0) { return; }
        const sec = pos * DURATION_S;
        h.canvas.setAttribute('aria-valuenow', sec.toFixed(1));
        h.canvas.setAttribute('aria-valuetext', sec.toFixed(1) + ' / ' + DURATION_S.toFixed(1) + ' s');
    }
    function seek(next: number): void {
        target = clamp(next, 0, 1);
        if (h.reduce) { pos = target; }
        h.touch();
        setAria(true);
        h.refresh();
    }
    h.listen(h.canvas, 'pointerdown', function (e: Event): void {
        const pe = e as PointerEvent;
        dragging = true;
        h.canvas.setPointerCapture(pe.pointerId);
        seek(h.local(pe)[0] / W);
    });
    h.listen(h.canvas, 'pointermove', function (e: Event): void {
        if (dragging) { seek(h.local(e as PointerEvent)[0] / W); }
    });
    const release = function (): void { dragging = false; };
    h.listen(h.canvas, 'pointerup', release);
    h.listen(h.canvas, 'pointercancel', release);
    h.listen(h.canvas, 'keydown', function (e: Event): void {
        const key = (e as KeyboardEvent).key;
        if (key === 'ArrowLeft') { e.preventDefault(); seek(pos - KEY_SEEK); }
        else if (key === 'ArrowRight') { e.preventDefault(); seek(pos + KEY_SEEK); }
        else if (key === 'Home') { e.preventDefault(); seek(0); }
        else if (key === 'End') { e.preventDefault(); seek(1); }
    });
    return {
        step(): void {
            tick += 1;
            if (dragging) {
                pos += (target - pos) * SCRUB_EASE;
            }
            else {
                pos += 1 / DURATION_STEPS;
                if (pos >= 1) { pos -= 1; }
                target = pos;
            }
            setAria(false);
        },
        draw(): void {
            const ctx = h.ctx;
            ctx.fillStyle = rgba(CREAM, 1);
            ctx.fillRect(0, 0, W, H);
            const played = 'hsl(' + PLAYED_HUE + ' 82% 66%)';
            const rest = rgba(INK, UNPLAYED_ALPHA);
            const ph = halfPixel(pos * W);
            for (let c = 0; c < nCols; c += 1) {
                const x0 = c * COL_PX;
                const x1 = x0 + COL_PX - COL_GAP;
                const top = MID_Y - Math.max(peaks[c], 0.02) * HALF_Y;
                const bot = MID_Y - Math.min(lows[c], -0.02) * HALF_Y;
                if (x1 <= ph) {
                    ctx.fillStyle = played;
                    ctx.fillRect(x0, top, x1 - x0, bot - top);
                }
                else if (x0 >= ph) {
                    ctx.fillStyle = rest;
                    ctx.fillRect(x0, top, x1 - x0, bot - top);
                }
                else {
                    // 재생 위치가 걸친 기둥 — 클립 영역 둘로 나눠 왼쪽은 진하게, 오른쪽은 옅게
                    ctx.save();
                    ctx.beginPath();
                    ctx.rect(x0, 0, ph - x0, H);
                    ctx.clip();
                    ctx.fillStyle = played;
                    ctx.fillRect(x0, top, x1 - x0, bot - top);
                    ctx.restore();
                    ctx.save();
                    ctx.beginPath();
                    ctx.rect(ph, 0, x1 - ph, H);
                    ctx.clip();
                    ctx.fillStyle = rest;
                    ctx.fillRect(x0, top, x1 - x0, bot - top);
                    ctx.restore();
                }
            }
            ctx.fillStyle = rgba(INK, 0.9);
            ctx.fillRect(ph - PLAYHEAD_W / 2, 36, PLAYHEAD_W, 188);
            ctx.beginPath();
            ctx.arc(ph, 36, 4, 0, PI2);
            ctx.fill();
            h.say(TXT_POS + ': ' + (pos * DURATION_S).toFixed(1) + ' / ' + DURATION_S.toFixed(1) + ' s');
        }
    };
}

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

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

  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="재생 위치 한 줄이 기둥을 반 픽셀 단위로 갈라 지난 부분과 남은 부분의 색을 바꾸는 파형" role="slider" aria-valuemin={0} aria-valuemax={6} aria-valuenow={0.5} />
        <p className={styles.status} data-role="status" aria-live="polite">재생 위치</p>
        <button className={styles.btn} data-role="btn" type="button">멈춤</button>
        <p className={styles.caption}>재생 위치 한 줄이 기둥을 반 픽셀 단위로 갈라 지난 부분과 남은 부분의 색을 바꾸는 파형</p>
      </div>
    </main>
  );
}