01Picker Whose Histogram Bars Recompute Height With Every Drag

<main class="stage">
<figure class="hg is-demo" id="hg">
  <figcaption class="hg__head">
    <span class="hg__title">Sample distribution by bucket</span>
    <span class="hg__stat" aria-hidden="true">Value <b class="hg__n" id="hg-val">50</b> · bucket <b class="hg__n" id="hg-bucket">6</b>/12</span>
  </figcaption>

  <div class="hg__zone">
    <svg class="hg__chart" id="chart" viewBox="0 0 480 200" preserveAspectRatio="none" role="img" aria-label="Bar chart of sample distribution across 12 buckets; only the bar for the bucket containing the value recomputes and rises.">
      <line class="hg__base" x1="0" y1="200" x2="480" y2="200"></line>
    </svg>
  </div>

  <div class="hg__track" id="track">
    <span class="hg__rail" aria-hidden="true"></span>
    <button class="hg__grab" id="grab" type="button" role="slider" aria-orientation="horizontal"
            aria-label="Choose value" aria-valuemin="0" aria-valuemax="100"
            aria-valuenow="50" aria-valuetext="Value 50, bucket 6/12">
      <svg class="hg__ic" viewBox="0 0 256 256" aria-hidden="true"><g fill="currentColor"><path d="M96 64v128a8 8 0 0 1-16 0V64a8 8 0 0 1 16 0m88 0v128a8 8 0 0 1-16 0V64a8 8 0 0 1 16 0" opacity=".2"/><path d="M188 32a8 8 0 0 0-8 8v176a8 8 0 0 0 16 0V40a8 8 0 0 0-8-8M76 32a8 8 0 0 0-8 8v176a8 8 0 0 0 16 0V40a8 8 0 0 0-8-8"/></g></svg>
    </button>
  </div>

  <p class="hg__hint">Drag on the bars or press the arrow keys — only the bar for the bucket containing that value recomputes.</p>

  <div class="sr">
    <span aria-live="polite" id="hg-live"></span>
    <table>
      <caption>Baseline height by bucket</caption>
      <thead><tr><th>Bucket</th><th>Baseline height</th></tr></thead>
      <tbody id="hg-table"></tbody>
    </table>
  </div>
</figure>
</main>

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

// 히스토그램 피커 — 드래그·키보드로 값(0~100)을 정하면 그 값이 속한 구간 하나만
// 목표 높이를 다시 계산해 올리고 나머지 11개는 기준 높이로 낮춘다. 어느 구간이
// 활성인지는 매 순간 바뀌는 정수라 선언형 keyframes 로 표현할 수 없어 rAF 루프가
// 직접 SVG rect 의 y·height 를 계산해 찍는다(@keyframes 0개, 395 캔버스 선례와 같은 이유).
// picker-graph-histogram-bucket-count(JS, BUCKET_COUNT)가 구간 개수를 정한다 — 변형 01 의 조정 대상.

$duration: $dur-loop;
$easing: $ease-lerp-settle;
$color: $subject-blue;

@include stage($stage-ink);

.sr {
  position: absolute; width: 1px; height: 1px; overflow: hidden;
  clip-path: inset(50%); white-space: nowrap;
}

.hg {
  box-sizing: border-box;
  width: min(424px, 92vw);
  margin: 0; padding: $sp-3;
  display: flex; flex-direction: column; gap: $sp-2;
  border-radius: $r-card;
  background: $stage-paper;
  box-shadow: $shadow-raised;
  color: $subject-ink;
}

.hg__head { display: flex; align-items: baseline; justify-content: space-between; gap: $sp-2; padding: 0 $sp-1; }
.hg__title { font-size: 13px; line-height: 18px; font-weight: 800; letter-spacing: .02em; }
.hg__stat { font-size: 12px; line-height: 18px; font-weight: 800; font-variant-numeric: tabular-nums; color: rgba($subject-ink, .62); }
.hg__n { color: $subject-blue-deep; }

.hg__zone { padding: 0 $sp-1; }
.hg__chart { display: block; width: 100%; height: 116px; overflow: visible; }
.hg__base { stroke: rgba($subject-ink, .16); stroke-width: 2; }

.hg__bar {
  fill: mix($subject-blue, $stage-paper, 58%);
  transition: none;
}
.hg__bar.is-active { fill: $subject-blue-deep; }

.hg__track {
  position: relative;
  height: 24px;
  margin: 0 $sp-1;
  border-radius: $r-pill;
  background: mix($subject-blue, $stage-paper, 14%);
}
.hg__rail {
  position: absolute; left: $sp-3; right: $sp-3; top: 50%;
  height: 3px; transform: translateY(-50%);
  border-radius: $r-pill;
  background: rgba($subject-ink, .18);
}
.hg__grab {
  position: absolute; top: 50%; left: 50%;
  width: 26px; height: 26px;
  margin: 0; padding: 0; border: 0; border-radius: 50%;
  display: grid; place-items: center;
  background: $subject-blue-deep;
  color: $stage-paper;
  transform: translate(-50%, -50%);
  cursor: ew-resize;
  touch-action: none;
}
.hg__grab:focus-visible { outline: 2px solid $subject-blue-deep; outline-offset: 2px; }
.hg__ic { width: 13px; height: 13px; }

.hg__hint { margin: 0; padding: 0 $sp-1; font-size: 11px; line-height: 16px; color: rgba($subject-ink, .62); }

@media (max-width: 340px) {
  .hg { padding: $sp-2; gap: $sp-1; }
  .hg__hint { display: none; }
  .hg__title { font-size: 12px; line-height: 16px; }
  .hg__stat { font-size: 11px; line-height: 16px; }
  .hg__chart { height: 108px; }
  .hg__grab { width: 22px; height: 22px; }
}

// reduce — rAF 루프를 시작하지 않는다. 드래그·키 입력은 여전히 currentH=targetH 를
// 즉시 맞추고 paint() 를 그 자리에서 한 번 호출해 화면에 반영한다(관성 lerp만 생략).
@media (prefers-reduced-motion: reduce) {
  .hg.is-still .hg__bar { transition: none !important; }
}

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);
}

.sr {
  position: absolute;
  width: 1px;
  height: 1px;
  overflow: hidden;
  clip-path: inset(50%);
  white-space: nowrap;
}

.hg {
  box-sizing: border-box;
  width: min(424px, 92vw);
  margin: 0;
  padding: 12px;
  display: flex;
  flex-direction: column;
  gap: 8px;
  border-radius: 16px;
  background: #ffffff;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  color: #17141a;
}

.hg__head {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 8px;
  padding: 0 4px;
}

.hg__title {
  font-size: 13px;
  line-height: 18px;
  font-weight: 800;
  letter-spacing: 0.02em;
}

.hg__stat {
  font-size: 12px;
  line-height: 18px;
  font-weight: 800;
  font-variant-numeric: tabular-nums;
  color: rgba(23, 20, 26, 0.62);
}

.hg__n {
  color: #0a4fe8;
}

.hg__zone {
  padding: 0 4px;
}

.hg__chart {
  display: block;
  width: 100%;
  height: 116px;
  overflow: visible;
}

.hg__base {
  stroke: rgba(23, 20, 26, 0.16);
  stroke-width: 2;
}

.hg__bar {
  fill: rgb(52.6901960784%, 66.7921568627%, 97.9529411765%);
  transition: none;
}

.hg__bar.is-active {
  fill: #0a4fe8;
}

.hg__track {
  position: relative;
  height: 24px;
  margin: 0 4px;
  border-radius: 999px;
  background: rgb(88.5803921569%, 91.9843137255%, 99.5058823529%);
}

.hg__rail {
  position: absolute;
  left: 12px;
  right: 12px;
  top: 50%;
  height: 3px;
  transform: translateY(-50%);
  border-radius: 999px;
  background: rgba(23, 20, 26, 0.18);
}

.hg__grab {
  position: absolute;
  top: 50%;
  left: 50%;
  width: 26px;
  height: 26px;
  margin: 0;
  padding: 0;
  border: 0;
  border-radius: 50%;
  display: grid;
  place-items: center;
  background: #0a4fe8;
  color: #ffffff;
  transform: translate(-50%, -50%);
  cursor: ew-resize;
  touch-action: none;
}

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

.hg__ic {
  width: 13px;
  height: 13px;
}

.hg__hint {
  margin: 0;
  padding: 0 4px;
  font-size: 11px;
  line-height: 16px;
  color: rgba(23, 20, 26, 0.62);
}

@media (max-width: 340px) {
  .hg {
    padding: 8px;
    gap: 4px;
  }
  .hg__hint {
    display: none;
  }
  .hg__title {
    font-size: 12px;
    line-height: 16px;
  }
  .hg__stat {
    font-size: 11px;
    line-height: 16px;
  }
  .hg__chart {
    height: 108px;
  }
  .hg__grab {
    width: 22px;
    height: 22px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .hg.is-still .hg__bar {
    transition: none !important;
  }
}

// 실제 동작: pointerdown/move/up 과 keydown(화살표·Home·End) 이 Value(0~100)을 바꾸면
// 그 값이 속한 Bucket 하나만 목표 높이를 다시 계산해 올리고 나머지 11개는 기준 높이로 낮춘다.
// 매 프레임 rAF 루프가 현재 높이를 목표 높이로 관성 보간(lerp)한다 — CSS @keyframes 는
// 0개(어떤 구간이 지금 활성인지는 매 순간 바뀌는 정수라 선언형 keyframes 로 표현할 수 없다,
// 395 의 캔버스 rAF 선례와 같은 이유로 실시간 캡처 경로를 그대로 쓴다).
var root = document.getElementById('hg');
var chart = document.getElementById('chart');
var track = document.getElementById('track');
var grab = document.getElementById('grab');
var valEl = document.getElementById('hg-val');
var bucketEl = document.getElementById('hg-bucket');
var live = document.getElementById('hg-live');
var tableBody = document.getElementById('hg-table');

var BUCKET_COUNT = 12;                 // picker-graph-histogram-bucket-count — 변형 01 의 조정 대상
var BASE = [0.34, 0.52, 0.28, 0.61, 0.45, 0.72, 0.38, 0.55, 0.30, 0.48, 0.65, 0.42]; // 고정 표본(0~1, RNG 없음)
var PEAK_BOOST = 0.40;                 // 활성 구간에 더해지는 최대 여유 높이(0~1)
var LERP_RATE = 0.22;                  // 프레임마다 목표에 다가가는 Ratio — 관성
var AUTO_PERIOD = 1.5;                 // 자동 시연 한 바퀴(초)
var STEP = 5;                          // 키보드 한 번에 움직이는 Value
var CHART_H = 200;

var css = getComputedStyle(root);
function cssv(name) { return css.getPropertyValue(name).trim(); }

var currentH = BASE.slice();
var targetH = BASE.slice();
var value = 50;
var manual = false;
var autoT = 0;
var lastTs = 0;
var trackRect = null;
var rafId = 0;

function reduced() {
  return window.matchMedia && window.matchMedia('(prefers-reduced-motion: reduce)').matches;
}

function bucketOf(v) {
  var idx = Math.floor(v / 100 * BUCKET_COUNT);
  return Math.max(0, Math.min(BUCKET_COUNT - 1, idx));
}

function fracIn(v, bucket) {
  var raw = v / 100 * BUCKET_COUNT - bucket;
  return Math.max(0, Math.min(1, raw));
}

// Bucket 하나만 목표 높이를 다시 계산한다 — 나머지는 Baseline height 그대로
function recompute() {
  var b = bucketOf(value);
  var f = fracIn(value, b);
  for (var i = 0; i < BUCKET_COUNT; i++) {
    targetH[i] = BASE[i];
  }
  targetH[b] = Math.min(0.96, BASE[b] + PEAK_BOOST * (0.4 + 0.6 * f));
  return b;
}

function buildBars() {
  var gap = 6;
  var w = 480 / BUCKET_COUNT;
  for (var i = 0; i < BUCKET_COUNT; i++) {
    var r = document.createElementNS('http://www.w3.org/2000/svg', 'rect');
    r.setAttribute('class', 'hg__bar');
    r.setAttribute('x', String(i * w + gap / 2));
    r.setAttribute('width', String(Math.max(1, w - gap)));
    r.dataset.i = String(i);
    chart.appendChild(r);

    var tr = document.createElement('tr');
    var th = document.createElement('th');
    th.textContent = String(i + 1);
    var td = document.createElement('td');
    td.textContent = Math.round(BASE[i] * 100) + '%';
    tr.appendChild(th); tr.appendChild(td);
    tableBody.appendChild(tr);
  }
}

function paint() {
  var bars = chart.querySelectorAll('.hg__bar');
  var activeIdx = bucketOf(value);
  for (var i = 0; i < bars.length; i++) {
    var h = currentH[i] * CHART_H;
    bars[i].setAttribute('y', String(CHART_H - h));
    bars[i].setAttribute('height', String(h));
    bars[i].classList.toggle('is-active', i === activeIdx);
  }
  var rv = Math.round(value);
  valEl.textContent = String(rv);
  bucketEl.textContent = String(activeIdx + 1);
  grab.style.left = value + '%';
  grab.setAttribute('aria-valuenow', String(rv));
  var text = 'Value ' + rv + ', bucket ' + (activeIdx + 1) + '/12';
  grab.setAttribute('aria-valuetext', text);
}

function announce() {
  var activeIdx = bucketOf(value);
  live.textContent = 'Value ' + Math.round(value) + ', bucket ' + (activeIdx + 1) + '/12 recomputed';
}

function setValue(v, isManual) {
  value = Math.max(0, Math.min(100, v));
  if (isManual) {
    manual = true;
    root.classList.remove('is-demo');
  }
  recompute();
}

function fromPointer(clientX) {
  if (!trackRect) trackRect = track.getBoundingClientRect();
  var ratio = (clientX - trackRect.left) / trackRect.width;
  setValue(ratio * 100, true);
}

function onDown(e) {
  trackRect = track.getBoundingClientRect();
  if (grab.setPointerCapture) { try { grab.setPointerCapture(e.pointerId); } catch (err) {} }
  fromPointer(e.clientX);
  if (reduced()) { currentH = targetH.slice(); paint(); announce(); }
}
function onMove(e) {
  if (e.buttons === 0 && e.pointerType !== 'touch') { /* 버튼 안 눌렸으면 무시 */ }
  fromPointer(e.clientX);
  if (reduced()) { currentH = targetH.slice(); paint(); announce(); }
}
function onUp() { announce(); }

function onKey(e) {
  var map = { ArrowLeft: -STEP, ArrowDown: -STEP, ArrowRight: STEP, ArrowUp: STEP };
  if (e.key === 'Home') { setValue(0, true); e.preventDefault(); }
  else if (e.key === 'End') { setValue(100, true); e.preventDefault(); }
  else if (map[e.key] !== undefined) { setValue(value + map[e.key], true); e.preventDefault(); }
  else { return; }
  if (reduced()) { currentH = targetH.slice(); paint(); announce(); }
}

function onResize() {
  trackRect = track.getBoundingClientRect();
  if (reduced()) { paint(); }
}

function autoStep(dt) {
  autoT += dt;
  var omega = 2 * Math.PI / AUTO_PERIOD;
  var v = 50 + 46 * Math.sin(autoT * omega);
  value = v;
  recompute();
}

function frame(ts) {
  if (!lastTs) lastTs = ts;
  var dt = Math.min(0.05, (ts - lastTs) / 1000);
  lastTs = ts;
  if (!manual) { autoStep(dt); }
  for (var i = 0; i < BUCKET_COUNT; i++) {
    currentH[i] += (targetH[i] - currentH[i]) * LERP_RATE;
  }
  paint();
  rafId = requestAnimationFrame(frame);
}

buildBars();
recompute();

grab.addEventListener('pointerdown', onDown);
grab.addEventListener('pointermove', onMove);
grab.addEventListener('pointerup', onUp);
track.addEventListener('pointerdown', function (e) {
  trackRect = track.getBoundingClientRect();
  fromPointer(e.clientX);
  if (reduced()) { currentH = targetH.slice(); paint(); announce(); }
});
grab.addEventListener('keydown', onKey);
window.addEventListener('resize', onResize);

if (reduced()) {
  root.classList.add('is-still');
  currentH = targetH.slice();
  paint();
} else {
  rafId = requestAnimationFrame(frame);
}

// HistogramBarsLive — vanilla 판(run/398/demo/01-picker-graph-histogram-bars-live/index.html) 의 React 포트.
// 드래그·키보드로 값(0~100)을 정하면 그 값이 속한 구간 하나만 목표 높이를 다시 계산해 올리고
// 나머지 11개는 기준 높이로 낮춘다. 매 프레임 rAF 루프가 현재 높이를 목표 높이로 관성 보간(lerp)한다.
import { useEffect, useRef } from "react";
import styles from "./HistogramBarsLive.module.scss";

type Box<T> = { current: T };
type KeyEvt = { key: string; preventDefault(): void };
type PtrEvt = { clientX: number; clientY: number; pointerId: number; buttons?: number; pointerType?: string };

const BUCKET_COUNT = 12;                 // picker-graph-histogram-bucket-count — 변형 01 의 조정 대상
const BASE = [0.34, 0.52, 0.28, 0.61, 0.45, 0.72, 0.38, 0.55, 0.30, 0.48, 0.65, 0.42]; // 고정 표본(0~1, RNG 없음)
const PEAK_BOOST = 0.40;
const LERP_RATE = 0.22;
const AUTO_PERIOD = 1.5;
const STEP = 5;
const CHART_H = 200;
const GAP = 6;
const BAR_W = 480 / BUCKET_COUNT;

export default function HistogramBarsLive() {
  const rootRef = useRef<HTMLElement | null>(null);
  const chartRef = useRef<SVGSVGElement | null>(null);
  const trackRef = useRef<HTMLDivElement | null>(null);
  const grabRef = useRef<HTMLButtonElement | null>(null);
  const valRef = useRef<HTMLElement | null>(null);
  const bucketRef = useRef<HTMLElement | null>(null);
  const liveRef = useRef<HTMLSpanElement | null>(null);
  const barRefs = useRef(new Array(BUCKET_COUNT).fill(null)) as Box<(SVGRectElement | null)[]>;

  const currentH = useRef(BASE.slice()) as Box<number[]>;
  const targetH = useRef(BASE.slice()) as Box<number[]>;
  const value = useRef(50) as Box<number>;
  const manual = useRef(false) as Box<boolean>;
  const autoT = useRef(0) as Box<number>;
  const lastTs = useRef(0) as Box<number>;
  const trackRect = useRef<DOMRect | null>(null) as Box<DOMRect | null>;
  const rafId = useRef(0) as Box<number>;

  function reduced(): boolean {
    return window.matchMedia("(prefers-reduced-motion: reduce)").matches;
  }

  function bucketOf(v: number): number {
    const idx = Math.floor((v / 100) * BUCKET_COUNT);
    return Math.max(0, Math.min(BUCKET_COUNT - 1, idx));
  }

  function fracIn(v: number, bucket: number): number {
    const raw = (v / 100) * BUCKET_COUNT - bucket;
    return Math.max(0, Math.min(1, raw));
  }

  function recompute(): number {
    const b = bucketOf(value.current);
    const f = fracIn(value.current, b);
    for (let i = 0; i < BUCKET_COUNT; i++) targetH.current[i] = BASE[i];
    targetH.current[b] = Math.min(0.96, BASE[b] + PEAK_BOOST * (0.4 + 0.6 * f));
    return b;
  }

  function paint(): void {
    const activeIdx = bucketOf(value.current);
    const bars = barRefs.current;
    for (let i = 0; i < bars.length; i++) {
      const r = bars[i];
      if (!r) continue;
      const h = currentH.current[i] * CHART_H;
      r.setAttribute("y", String(CHART_H - h));
      r.setAttribute("height", String(h));
      r.classList.toggle("is-active", i === activeIdx);
    }
    const rv = Math.round(value.current);
    if (valRef.current) valRef.current.textContent = String(rv);
    if (bucketRef.current) bucketRef.current.textContent = String(activeIdx + 1);
    const grab = grabRef.current;
    if (grab) {
      grab.style.left = value.current + "%";
      grab.setAttribute("aria-valuenow", String(rv));
      grab.setAttribute("aria-valuetext", "값 " + rv + ", 구간 " + (activeIdx + 1) + "/12");
    }
  }

  function announce(): void {
    const activeIdx = bucketOf(value.current);
    if (liveRef.current) {
      liveRef.current.textContent = "값 " + Math.round(value.current) + ", 구간 " + (activeIdx + 1) + "/12로 다시 계산됨";
    }
  }

  function setValue(v: number, isManual: boolean): void {
    value.current = Math.max(0, Math.min(100, v));
    if (isManual) {
      manual.current = true;
      rootRef.current?.classList.remove("is-demo");
    }
    recompute();
  }

  function fromPointer(clientX: number): void {
    if (!trackRect.current && trackRef.current) trackRect.current = trackRef.current.getBoundingClientRect();
    const rect = trackRect.current;
    if (!rect) return;
    const ratio = (clientX - rect.left) / rect.width;
    setValue(ratio * 100, true);
  }

  function reflectNow(): void {
    currentH.current = targetH.current.slice();
    paint();
    announce();
  }

  function onDown(e: PtrEvt): void {
    if (trackRef.current) trackRect.current = trackRef.current.getBoundingClientRect();
    const grab = grabRef.current;
    if (grab && typeof grab.setPointerCapture === "function") {
      try { grab.setPointerCapture(e.pointerId); } catch { /* 캡처 실패는 치명적이지 않다 */ }
    }
    fromPointer(e.clientX);
    if (reduced()) reflectNow();
  }
  function onMove(e: PtrEvt): void {
    fromPointer(e.clientX);
    if (reduced()) reflectNow();
  }
  function onUp(): void {
    announce();
  }
  function onTrackDown(e: PtrEvt): void {
    if (trackRef.current) trackRect.current = trackRef.current.getBoundingClientRect();
    fromPointer(e.clientX);
    if (reduced()) reflectNow();
  }

  function onKey(e: KeyEvt): void {
    const map: Record<string, number> = { ArrowLeft: -STEP, ArrowDown: -STEP, ArrowRight: STEP, ArrowUp: STEP };
    if (e.key === "Home") { setValue(0, true); e.preventDefault(); }
    else if (e.key === "End") { setValue(100, true); e.preventDefault(); }
    else if (map[e.key] !== undefined) { setValue(value.current + map[e.key], true); e.preventDefault(); }
    else { return; }
    if (reduced()) reflectNow();
  }

  function onResize(): void {
    if (trackRef.current) trackRect.current = trackRef.current.getBoundingClientRect();
    if (reduced()) paint();
  }

  function autoStep(dt: number): void {
    autoT.current += dt;
    const omega = (2 * Math.PI) / AUTO_PERIOD;
    value.current = 50 + 46 * Math.sin(autoT.current * omega);
    recompute();
  }

  function frame(ts: number): void {
    if (!lastTs.current) lastTs.current = ts;
    const dt = Math.min(0.05, (ts - lastTs.current) / 1000);
    lastTs.current = ts;
    if (!manual.current) autoStep(dt);
    for (let i = 0; i < BUCKET_COUNT; i++) {
      currentH.current[i] += (targetH.current[i] - currentH.current[i]) * LERP_RATE;
    }
    paint();
    rafId.current = requestAnimationFrame(frame);
  }

  useEffect(() => {
    recompute();
    window.addEventListener("resize", onResize);
    if (reduced()) {
      rootRef.current?.classList.add("is-still");
      reflectNow();
    } else {
      rafId.current = requestAnimationFrame(frame);
    }
    return () => {
      window.removeEventListener("resize", onResize);
      cancelAnimationFrame(rafId.current);
    };
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, []);

  return (
    <main className={styles.stage}>
      <figure className={styles.hg + " is-demo"} ref={rootRef}>
        <figcaption className={styles.head}>
          <span className={styles.title}>구간별 표본 분포</span>
          <span className={styles.stat} aria-hidden="true">값 <b className={styles.n} ref={valRef}>50</b> · 구간 <b className={styles.n} ref={bucketRef}>6</b>/12</span>
        </figcaption>

        <div className={styles.zone}>
          <svg
            className={styles.chart}
            ref={chartRef}
            viewBox="0 0 480 200"
            preserveAspectRatio="none"
            role="img"
            aria-label="구간 12개 표본 분포 막대그래프, 값이 속한 구간의 막대만 다시 계산되어 올라간다"
          >
            <line className={styles.base} x1="0" y1="200" x2="480" y2="200" />
            {BASE.map((_, i) => (
              <rect
                key={i}
                className={styles.bar}
                ref={(el: SVGRectElement | null) => { barRefs.current[i] = el; }}
                x={i * BAR_W + GAP / 2}
                width={Math.max(1, BAR_W - GAP)}
              />
            ))}
          </svg>
        </div>

        <div className={styles.track} ref={trackRef} onPointerDown={onTrackDown}>
          <span className={styles.rail} aria-hidden="true" />
          <button
            className={styles.grab}
            ref={grabRef}
            type="button"
            role="slider"
            aria-orientation="horizontal"
            aria-label="값 고르기"
            aria-valuemin={0}
            aria-valuemax={100}
            aria-valuenow={50}
            aria-valuetext="값 50, 구간 6/12"
            onPointerDown={onDown}
            onPointerMove={onMove}
            onPointerUp={onUp}
            onKeyDown={onKey}
          >
            <svg className={styles.ic} viewBox="0 0 256 256" aria-hidden="true"><g fill="currentColor"><path d="M96 64v128a8 8 0 0 1-16 0V64a8 8 0 0 1 16 0m88 0v128a8 8 0 0 1-16 0V64a8 8 0 0 1 16 0" opacity=".2" /><path d="M188 32a8 8 0 0 0-8 8v176a8 8 0 0 0 16 0V40a8 8 0 0 0-8-8M76 32a8 8 0 0 0-8 8v176a8 8 0 0 0 16 0V40a8 8 0 0 0-8-8" /></g></svg>
          </button>
        </div>

        <p className={styles.hint}>막대 위를 드래그하거나 화살표키를 누르면 그 값이 속한 구간의 막대만 다시 계산됩니다</p>

        <div className={styles.sr}>
          <span aria-live="polite" ref={liveRef} />
          <table>
            <caption>구간별 기준 높이</caption>
            <thead><tr><th>구간</th><th>기준 높이</th></tr></thead>
            <tbody>
              {BASE.map((b, i) => (
                <tr key={i}><th>{i + 1}</th><td>{Math.round(b * 100)}%</td></tr>
              ))}
            </tbody>
          </table>
        </div>
      </figure>
    </main>
  );
}