06HSL sliders — a color picker that redraws track gradients whenever the hue value changes

<main class="stage">
<section class="panel">
  <div class="preview" id="preview"></div>
  <div class="row">
    <span class="rowLabel">Hue</span>
    <div class="track hueTrack" id="hTrack">
      <div class="thumb" id="hThumb" role="slider" aria-label="Hue" aria-valuemin="0" aria-valuemax="360" aria-valuenow="0"></div>
    </div>
  </div>
  <div class="row">
    <span class="rowLabel">Saturation</span>
    <div class="track" id="sTrack">
      <div class="thumb" id="sThumb" role="slider" aria-label="Saturation" aria-valuemin="0" aria-valuemax="100" aria-valuenow="0"></div>
    </div>
  </div>
  <div class="row">
    <span class="rowLabel">Lightness</span>
    <div class="track" id="lTrack">
      <div class="thumb" id="lThumb" role="slider" aria-label="Lightness" aria-valuemin="0" aria-valuemax="100" aria-valuenow="0"></div>
    </div>
  </div>
</section>
</main>

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

@include stage($stage-paper);

.panel {
  display: flex;
  flex-direction: column;
  align-items: stretch;
  gap: $sp-3;
  width: 100%;
  max-width: 220px;
}

.preview {
  height: 48px;
  border-radius: $r-card;
  box-shadow: $shadow-raised;
}

.row {
  display: flex;
  align-items: center;
  gap: $sp-2;
}

.rowLabel {
  flex: 0 0 auto;
  width: 30px;
  color: $subject-ink;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  font-weight: 500;
  font-size: 11px;
  line-height: 1.3;
}

.track {
  position: relative;
  flex: 1 1 auto;
  height: 10px;
  border-radius: $r-pill;
  background: rgba($subject-ink, .1);
  box-shadow: inset 0 0 0 1px rgba($subject-ink, .08);
}

.hueTrack {
  background: linear-gradient(
    to right,
    hsl(0, 100%, 50%), hsl(60, 100%, 50%), hsl(120, 100%, 50%),
    hsl(180, 100%, 50%), hsl(240, 100%, 50%), hsl(300, 100%, 50%), hsl(360, 100%, 50%)
  );
}

.thumb {
  position: absolute;
  top: 50%;
  left: 0;
  width: 16px;
  height: 16px;
  border-radius: $r-pill;
  background: $stage-paper;
  border: 2px solid $subject-blue;
  box-shadow: $shadow-press;
}

@media (max-width: 340px) {
  .panel { max-width: 168px; }
  .preview { height: 40px; }
  .rowLabel { width: 24px; font-size: 10px; }
}

@media (prefers-reduced-motion: reduce) {
  .thumb { transition: none; }
}

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);
}

.panel {
  display: flex;
  flex-direction: column;
  align-items: stretch;
  gap: 12px;
  width: 100%;
  max-width: 220px;
}

.preview {
  height: 48px;
  border-radius: 16px;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
}

.row {
  display: flex;
  align-items: center;
  gap: 8px;
}

.rowLabel {
  flex: 0 0 auto;
  width: 30px;
  color: #17141a;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  font-weight: 500;
  font-size: 11px;
  line-height: 1.3;
}

.track {
  position: relative;
  flex: 1 1 auto;
  height: 10px;
  border-radius: 999px;
  background: rgba(23, 20, 26, 0.1);
  box-shadow: inset 0 0 0 1px rgba(23, 20, 26, 0.08);
}

.hueTrack {
  background: linear-gradient(to right, hsl(0, 100%, 50%), hsl(60, 100%, 50%), hsl(120, 100%, 50%), hsl(180, 100%, 50%), hsl(240, 100%, 50%), hsl(300, 100%, 50%), hsl(0, 100%, 50%));
}

.thumb {
  position: absolute;
  top: 50%;
  left: 0;
  width: 16px;
  height: 16px;
  border-radius: 999px;
  background: #ffffff;
  border: 2px solid #2f6df6;
  box-shadow: 0 6px 12px rgba(23, 20, 26, 0.32);
}

@media (max-width: 340px) {
  .panel {
    max-width: 168px;
  }
  .preview {
    height: 40px;
  }
  .rowLabel {
    width: 24px;
    font-size: 10px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .thumb {
    transition: none;
  }
}

// HSL 슬라이더(06) — Hue 슬라이더 값이 바뀔 때마다 Saturation·Lightness 트랙의 배경 그라디언트를
// GRADIENT_STEPS  colors 정지점으로 다시 계산해 그린다. 실키·실서버 요청 없음.
(function () {
  var previewEl = document.getElementById('preview');
  var hTrack = document.getElementById('hTrack');
  var sTrack = document.getElementById('sTrack');
  var lTrack = document.getElementById('lTrack');
  var hThumb = document.getElementById('hThumb');
  var sThumb = document.getElementById('sThumb');
  var lThumb = document.getElementById('lThumb');
  if (!previewEl || !hTrack || !sTrack || !lTrack || !hThumb || !sThumb || !lThumb) return;
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  var CYCLE_MS = 3000;
  var TRACK_W = 156;
  var GRADIENT_STEPS = 20;

  function buildGradient(stopFn) {
    var stops = [];
    for (var i = 0; i < GRADIENT_STEPS; i++) {
      var ratio = i / (GRADIENT_STEPS - 1);
      stops.push(stopFn(ratio) + ' ' + (ratio * 100).toFixed(1) + '%');
    }
    return 'linear-gradient(to right, ' + stops.join(', ') + ')';
  }

  function setThumb(thumbEl, ratio) {
    var x = ratio * TRACK_W;
    thumbEl.style.transform = 'translate(calc(-50% + ' + x.toFixed(2) + 'px), -50%)';
  }

  function apply(t) {
    var p = t / CYCLE_MS;
    var hue = (p * 360) % 360;
    var sat = 55 + Math.sin(p * Math.PI * 2 * 1.3) * 35;
    var light = 50 + Math.sin(p * Math.PI * 2 * .9 + 1) * 25;

    setThumb(hThumb, hue / 360);
    setThumb(sThumb, sat / 100);
    setThumb(lThumb, light / 100);

    sTrack.style.background = buildGradient(function (r) {
      return 'hsl(' + hue.toFixed(1) + 'deg ' + (r * 100).toFixed(1) + '% 50%)';
    });
    lTrack.style.background = buildGradient(function (r) {
      return 'hsl(' + hue.toFixed(1) + 'deg ' + sat.toFixed(1) + '% ' + (r * 100).toFixed(1) + '%)';
    });
    previewEl.style.background = 'hsl(' + hue.toFixed(1) + 'deg ' + sat.toFixed(1) + '% ' + light.toFixed(1) + '%)';

    hThumb.setAttribute('aria-valuenow', String(Math.round(hue)));
    sThumb.setAttribute('aria-valuenow', String(Math.round(sat)));
    lThumb.setAttribute('aria-valuenow', String(Math.round(light)));
  }

  if (reduce) {
    apply(0);
    return;
  }

  var start = null;
  function loop(ts) {
    if (start === null) start = ts;
    var t = (ts - start) % CYCLE_MS;
    apply(t);
    requestAnimationFrame(loop);
  }
  requestAnimationFrame(loop);
})();

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

// HSL 슬라이더 — 색조 슬라이더 값이 바뀔 때마다 채도·명도 트랙의 배경 그라디언트를
// GRADIENT_STEPS 개 정지점으로 다시 계산해 그린다. 실키·실서버 요청 없음.
const CYCLE_MS = 3000;
const TRACK_W = 156;
const GRADIENT_STEPS = 20;

function buildGradient(stopFn: (ratio: number) => string) {
  const stops: string[] = [];
  for (let i = 0; i < GRADIENT_STEPS; i++) {
    const ratio = i / (GRADIENT_STEPS - 1);
    stops.push(`${stopFn(ratio)} ${(ratio * 100).toFixed(1)}%`);
  }
  return `linear-gradient(to right, ${stops.join(", ")})`;
}

export default function ColorPickerHslSliders() {
  const previewRef = useRef<HTMLDivElement>(null);
  const sTrackRef = useRef<HTMLDivElement>(null);
  const lTrackRef = useRef<HTMLDivElement>(null);
  const hThumbRef = useRef<HTMLDivElement>(null);
  const sThumbRef = useRef<HTMLDivElement>(null);
  const lThumbRef = useRef<HTMLDivElement>(null);

  useEffect(() => {
    const preview = previewRef.current;
    const sTrack = sTrackRef.current;
    const lTrack = lTrackRef.current;
    const hThumb = hThumbRef.current;
    const sThumb = sThumbRef.current;
    const lThumb = lThumbRef.current;
    if (!preview || !sTrack || !lTrack || !hThumb || !sThumb || !lThumb) return;
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;

    function setThumb(thumbEl: HTMLDivElement, ratio: number) {
      const x = ratio * TRACK_W;
      thumbEl.style.transform = `translate(calc(-50% + ${x.toFixed(2)}px), -50%)`;
    }

    function apply(t: number) {
      const p = t / CYCLE_MS;
      const hue = (p * 360) % 360;
      const sat = 55 + Math.sin(p * Math.PI * 2 * 1.3) * 35;
      const light = 50 + Math.sin(p * Math.PI * 2 * .9 + 1) * 25;

      setThumb(hThumb!, hue / 360);
      setThumb(sThumb!, sat / 100);
      setThumb(lThumb!, light / 100);

      sTrack!.style.background = buildGradient((r) => `hsl(${hue.toFixed(1)}deg ${(r * 100).toFixed(1)}% 50%)`);
      lTrack!.style.background = buildGradient((r) => `hsl(${hue.toFixed(1)}deg ${sat.toFixed(1)}% ${(r * 100).toFixed(1)}%)`);
      preview!.style.background = `hsl(${hue.toFixed(1)}deg ${sat.toFixed(1)}% ${light.toFixed(1)}%)`;

      hThumb!.setAttribute("aria-valuenow", String(Math.round(hue)));
      sThumb!.setAttribute("aria-valuenow", String(Math.round(sat)));
      lThumb!.setAttribute("aria-valuenow", String(Math.round(light)));
    }

    if (reduce) {
      apply(0);
      return;
    }

    let start: number | null = null;
    let raf = 0;
    function loop(ts: number) {
      if (start === null) start = ts;
      const t = (ts - start) % CYCLE_MS;
      apply(t);
      raf = requestAnimationFrame(loop);
    }
    raf = requestAnimationFrame(loop);
    return () => cancelAnimationFrame(raf);
  }, []);

  return (
    <div className={styles.stage}>
      <section className={styles.panel}>
        <div className={styles.preview} ref={previewRef} />
        <div className={styles.row}>
          <span className={styles.rowLabel}>색조</span>
          <div className={`${styles.track} ${styles.hueTrack}`}>
            <div className={styles.thumb} ref={hThumbRef} role="slider" aria-label="색조" aria-valuemin={0} aria-valuemax={360} aria-valuenow={0} />
          </div>
        </div>
        <div className={styles.row}>
          <span className={styles.rowLabel}>채도</span>
          <div className={styles.track} ref={sTrackRef}>
            <div className={styles.thumb} ref={sThumbRef} role="slider" aria-label="채도" aria-valuemin={0} aria-valuemax={100} aria-valuenow={0} />
          </div>
        </div>
        <div className={styles.row}>
          <span className={styles.rowLabel}>명도</span>
          <div className={styles.track} ref={lTrackRef}>
            <div className={styles.thumb} ref={lThumbRef} role="slider" aria-label="명도" aria-valuemin={0} aria-valuemax={100} aria-valuenow={0} />
          </div>
        </div>
      </section>
    </div>
  );
}