02立ち上がりは速く戻りは遅い追従器が音量の輪郭をなめらかに塗る波形

<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="立ち上がりは速く戻りは遅い追従器が音量の輪郭をなめらかに塗る波形"></canvas>
  <p class="wf__status" data-role="status" aria-live="polite">二乗平均 / 輪郭</p>
  <button class="wf__btn" data-role="btn" type="button">一時停止</button>
  <p class="wf__caption">立ち上がりは速く戻りは遅い追従器が音量の輪郭をなめらかに塗る波形</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: 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;
}

@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: 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;
}

@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 ATTACK_K = 0.5;
const RELEASE_K = 0.06;
const RMS_WIN = 160;
const FILL_ALPHA = 0.55;
const COL_PX = 2;
const VIEW_SAMPLES = 14400;
const SLIDE_STEP = 60;
const WARM_COLS = 30;
const MID_Y = 140;
const HALF_Y = 84;
const VIS_GAIN = 1.5;
const TXT_ENV = '二乗平均 / 輪郭';
// 끝 위치 end 바로 앞 win 개 표본의 제곱평균 제곱근
function rmsAt(sig, end, win) {
    const to = clamp(Math.floor(end), 1, sig.length);
    const from = Math.max(0, to - win);
    let sum = 0;
    for (let i = from; i < to; i += 1) {
        sum += sig[i] * sig[i];
    }
    return Math.sqrt(sum / Math.max(1, to - from));
}
// 공격 계수와 해제 계수가 다른 지수 평활 — 오를 때는 빨리, 내릴 때는 천천히 따라간다
function followEnvelope(values, attackK, releaseK) {
    const out = [];
    let e = 0;
    for (let i = 0; i < values.length; i += 1) {
        const v = values[i];
        e += (v > e ? attackK : releaseK) * (v - e);
        out.push(e);
    }
    return out;
}
function makeEnvelopeScene(h) {
    const sig = synth(SAMPLE_N, 4591);
    let start = 0;
    let dir = 1;
    let k = 0;
    let cursorX = 200;
    function move(x) {
        cursorX = clamp(x, 0, W - 1);
        h.touch();
        h.refresh();
    }
    h.listen(h.canvas, 'pointermove', function (e) {
        move(h.local(e)[0]);
    });
    h.listen(h.canvas, 'keydown', function (e) {
        const key = e.key;
        if (key === 'ArrowLeft') {
            e.preventDefault();
            move(cursorX - 12);
        }
        else if (key === 'ArrowRight') {
            e.preventDefault();
            move(cursorX + 12);
        }
    });
    return {
        step() {
            k += 1;
            start += dir * SLIDE_STEP;
            if (start > SAMPLE_N - VIEW_SAMPLES) {
                start = SAMPLE_N - VIEW_SAMPLES;
                dir = -1;
            }
            else if (start < 0) {
                start = 0;
                dir = 1;
            }
            if (h.auto()) {
                cursorX = W * (0.5 + 0.4 * Math.sin(k * 0.03));
            }
        },
        draw() {
            const ctx = h.ctx;
            paintBg(ctx, BG_TOP, BG_BOT);
            const n = Math.floor(W / COL_PX);
            const per = VIEW_SAMPLES / n;
            const raw = [];
            for (let c = -WARM_COLS; c < n; c += 1) {
                raw.push(rmsAt(sig, start + (c + 1) * per, RMS_WIN));
            }
            const env = followEnvelope(raw, ATTACK_K, RELEASE_K);
            // 원래 최대·최소 기둥은 옅게 깔아 두고 그 위에 윤곽을 얹는다
            for (let c = 0; c < n; c += 1) {
                scanRange(sig, start + c * per, start + (c + 1) * per);
                ctx.fillStyle = rgba(LILAC, 0.42);
                ctx.fillRect(c * COL_PX, MID_Y - rangeHi * HALF_Y, COL_PX - 0.5, (rangeHi - rangeLo) * HALF_Y + 1);
            }
            ctx.beginPath();
            for (let c = 0; c < n; c += 1) {
                const y = MID_Y - Math.min(1, env[c + WARM_COLS] * VIS_GAIN) * HALF_Y;
                if (c === 0) {
                    ctx.moveTo(0, y);
                }
                else {
                    ctx.lineTo(c * COL_PX, y);
                }
            }
            for (let c = n - 1; c >= 0; c -= 1) {
                const y = MID_Y + Math.min(1, env[c + WARM_COLS] * VIS_GAIN) * HALF_Y;
                ctx.lineTo(c * COL_PX, y);
            }
            ctx.closePath();
            ctx.fillStyle = rgba(MINT, FILL_ALPHA);
            ctx.fill();
            ctx.strokeStyle = rgba(CREAM, 0.9);
            ctx.lineWidth = 1.5;
            ctx.stroke();
            // 순간 제곱평균 — 평활 전의 들쭉날쭉한 값
            ctx.beginPath();
            for (let c = 0; c < n; c += 1) {
                const y = MID_Y - Math.min(1, raw[c + WARM_COLS] * VIS_GAIN) * HALF_Y;
                if (c === 0) {
                    ctx.moveTo(0, y);
                }
                else {
                    ctx.lineTo(c * COL_PX, y);
                }
            }
            ctx.strokeStyle = rgba(SKY_BLUE, 0.95);
            ctx.lineWidth = 1;
            ctx.stroke();
            const cc = clamp(Math.floor(cursorX / COL_PX), 0, n - 1);
            ctx.fillStyle = rgba(BUTTER, 0.85);
            ctx.fillRect(cc * COL_PX, 40, 1.5, 200);
            h.say(TXT_ENV + ': ' + raw[cc + WARM_COLS].toFixed(2) + ' / ' + env[cc + WARM_COLS].toFixed(2));
        }
    };
}

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

import { useEffect, useRef } from "react";
import styles from "./WfRmsEnvelopeAttackReleaseFill.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 ATTACK_K = 0.5;
const RELEASE_K = 0.06;
const RMS_WIN = 160;
const FILL_ALPHA = 0.55;
const COL_PX = 2;
const VIEW_SAMPLES = 14400;
const SLIDE_STEP = 60;
const WARM_COLS = 30;
const MID_Y = 140;
const HALF_Y = 84;
const VIS_GAIN = 1.5;
const TXT_ENV = '제곱평균 / 윤곽';

// 끝 위치 end 바로 앞 win 개 표본의 제곱평균 제곱근
function rmsAt(sig: Float32Array, end: number, win: number): number {
    const to = clamp(Math.floor(end), 1, sig.length);
    const from = Math.max(0, to - win);
    let sum = 0;
    for (let i = from; i < to; i += 1) { sum += sig[i] * sig[i]; }
    return Math.sqrt(sum / Math.max(1, to - from));
}

// 공격 계수와 해제 계수가 다른 지수 평활 — 오를 때는 빨리, 내릴 때는 천천히 따라간다
function followEnvelope(values: number[], attackK: number, releaseK: number): number[] {
    const out: number[] = [];
    let e = 0;
    for (let i = 0; i < values.length; i += 1) {
        const v = values[i];
        e += (v > e ? attackK : releaseK) * (v - e);
        out.push(e);
    }
    return out;
}

function makeEnvelopeScene(h: Host): Scene {
    const sig = synth(SAMPLE_N, 4591);
    let start = 0;
    let dir = 1;
    let k = 0;
    let cursorX = 200;
    function move(x: number): void {
        cursorX = clamp(x, 0, W - 1);
        h.touch();
        h.refresh();
    }
    h.listen(h.canvas, 'pointermove', function (e: Event): void {
        move(h.local(e as PointerEvent)[0]);
    });
    h.listen(h.canvas, 'keydown', function (e: Event): void {
        const key = (e as KeyboardEvent).key;
        if (key === 'ArrowLeft') {
            e.preventDefault();
            move(cursorX - 12);
        }
        else if (key === 'ArrowRight') {
            e.preventDefault();
            move(cursorX + 12);
        }
    });
    return {
        step(): void {
            k += 1;
            start += dir * SLIDE_STEP;
            if (start > SAMPLE_N - VIEW_SAMPLES) {
                start = SAMPLE_N - VIEW_SAMPLES;
                dir = -1;
            }
            else if (start < 0) {
                start = 0;
                dir = 1;
            }
            if (h.auto()) {
                cursorX = W * (0.5 + 0.4 * Math.sin(k * 0.03));
            }
        },
        draw(): void {
            const ctx = h.ctx;
            paintBg(ctx, BG_TOP, BG_BOT);
            const n = Math.floor(W / COL_PX);
            const per = VIEW_SAMPLES / n;
            const raw: number[] = [];
            for (let c = -WARM_COLS; c < n; c += 1) {
                raw.push(rmsAt(sig, start + (c + 1) * per, RMS_WIN));
            }
            const env = followEnvelope(raw, ATTACK_K, RELEASE_K);
            // 원래 최대·최소 기둥은 옅게 깔아 두고 그 위에 윤곽을 얹는다
            for (let c = 0; c < n; c += 1) {
                scanRange(sig, start + c * per, start + (c + 1) * per);
                ctx.fillStyle = rgba(LILAC, 0.42);
                ctx.fillRect(c * COL_PX, MID_Y - rangeHi * HALF_Y, COL_PX - 0.5, (rangeHi - rangeLo) * HALF_Y + 1);
            }
            ctx.beginPath();
            for (let c = 0; c < n; c += 1) {
                const y = MID_Y - Math.min(1, env[c + WARM_COLS] * VIS_GAIN) * HALF_Y;
                if (c === 0) { ctx.moveTo(0, y); } else { ctx.lineTo(c * COL_PX, y); }
            }
            for (let c = n - 1; c >= 0; c -= 1) {
                const y = MID_Y + Math.min(1, env[c + WARM_COLS] * VIS_GAIN) * HALF_Y;
                ctx.lineTo(c * COL_PX, y);
            }
            ctx.closePath();
            ctx.fillStyle = rgba(MINT, FILL_ALPHA);
            ctx.fill();
            ctx.strokeStyle = rgba(CREAM, 0.9);
            ctx.lineWidth = 1.5;
            ctx.stroke();
            // 순간 제곱평균 — 평활 전의 들쭉날쭉한 값
            ctx.beginPath();
            for (let c = 0; c < n; c += 1) {
                const y = MID_Y - Math.min(1, raw[c + WARM_COLS] * VIS_GAIN) * HALF_Y;
                if (c === 0) { ctx.moveTo(0, y); } else { ctx.lineTo(c * COL_PX, y); }
            }
            ctx.strokeStyle = rgba(SKY_BLUE, 0.95);
            ctx.lineWidth = 1;
            ctx.stroke();
            const cc = clamp(Math.floor(cursorX / COL_PX), 0, n - 1);
            ctx.fillStyle = rgba(BUTTER, 0.85);
            ctx.fillRect(cc * COL_PX, 40, 1.5, 200);
            h.say(TXT_ENV + ': ' + raw[cc + WARM_COLS].toFixed(2) + ' / ' + env[cc + WARM_COLS].toFixed(2));
        }
    };
}

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

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

  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="공격은 빠르고 해제는 느린 추종기가 소리 크기 윤곽을 매끈하게 채우는 파형" />
        <p className={styles.status} data-role="status" aria-live="polite">제곱평균 / 윤곽</p>
        <button className={styles.btn} data-role="btn" type="button">멈춤</button>
        <p className={styles.caption}>공격은 빠르고 해제는 느린 추종기가 소리 크기 윤곽을 매끈하게 채우는 파형</p>
      </div>
    </main>
  );
}