08Color-temperature track — interpolating hue and saturation from the value ratio

<main class="stage">
<div class="ct" id="ct">
  <p class="ct__hint">Converts the value ratio into an HSL color every frame, tinting the track and thumb from cool blue to warm orange</p>
  <div class="ct__wrap" id="ctWrap" role="img" aria-label="Scene of a slider whose color temperature shifts from blue to orange with the value">
    <input class="ct__range" id="ctRange" type="range" min="0" max="100" step="1" value="50" aria-label="Color temperature">
  </div>
  <p class="ct__meta"><b class="ct__tag" id="ctHue">hue 122</b><span class="ct__unit">HSL interpolation</span></p>
</div>
</main>

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

// 색온도 그라디언트(08, 아이디어형·기능색) — 색 자체가 값을 나타내는 편이라
// hue 는 JS 가 매 프레임 계산해 --hue·--sat 커스텀 프로퍼티로 넘긴다. 트랙·썸은
// hsl(var(--hue) var(--sat)% L%) 로 그 값을 그대로 그린다 — 정적 토큰이 아니다.

$duration: $dur-quick;
$easing: $ease-out;
$color: $subject-blue-deep;

@include stage($stage-paper);

$track-h: 8px;
$thumb-d: 20px;

.ct {
  display: flex; flex-direction: column; align-items: center; gap: $sp-3;
  width: 100%; max-width: 360px;
}

.ct__hint {
  margin: 0; font-weight: 700; font-size: clamp(10px, 2.8vw, 12px); line-height: 1.35;
  color: $subject-ink; text-align: center;
}

.ct__wrap {
  position: relative; width: 100%; height: 40px;
  display: flex; align-items: center;
  --pct: 50; --hue: 165; --sat: 66;
}

.ct__range {
  appearance: none; -webkit-appearance: none;
  width: 100%; height: $thumb-d; margin: 0; background: transparent;
}
.ct__range:focus-visible { outline: 2px solid $subject-ink; outline-offset: 4px; border-radius: $r-pill; }

.ct__range::-webkit-slider-runnable-track {
  height: $track-h; border-radius: $r-pill;
  background: linear-gradient(
    to right,
    hsl(calc(var(--hue) * 1deg) calc(var(--sat) * 1%) 50%) calc(var(--pct) * 1%),
    rgba($subject-ink, .14) calc(var(--pct) * 1%)
  );
}
.ct__range::-webkit-slider-thumb {
  appearance: none; -webkit-appearance: none;
  width: $thumb-d; height: $thumb-d; border-radius: 50%;
  background: hsl(calc(var(--hue) * 1deg) calc(var(--sat) * 1%) 50%);
  box-shadow: $shadow-press;
  margin-top: calc(($track-h - $thumb-d) / 2);
}
.ct__range::-moz-range-track {
  height: $track-h; border-radius: $r-pill; background: rgba($subject-ink, .14);
}
.ct__range::-moz-range-progress {
  height: $track-h; border-radius: $r-pill;
  background: hsl(calc(var(--hue) * 1deg) calc(var(--sat) * 1%) 50%);
}
.ct__range::-moz-range-thumb {
  width: $thumb-d; height: $thumb-d; border: 0; border-radius: 50%;
  background: hsl(calc(var(--hue) * 1deg) calc(var(--sat) * 1%) 50%);
  box-shadow: $shadow-press;
}

.ct__meta { margin: 0; font-size: clamp(9px, 2.4vw, 11px); color: rgba($subject-ink, .82); }
.ct__tag { font-weight: 700; color: $color; font-variant-numeric: tabular-nums; margin-right: $sp-1; }
.ct__unit { color: rgba($subject-ink, .72); }

@media (max-width: 340px) {
  .ct { gap: $sp-2; max-width: 280px; }
  .ct__hint { font-size: 8px; }
  .ct__meta { font-size: 7px; }
}

@media (prefers-reduced-motion: reduce) {
  .ct__range { 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);
}

.ct {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 12px;
  width: 100%;
  max-width: 360px;
}

.ct__hint {
  margin: 0;
  font-weight: 700;
  font-size: clamp(10px, 2.8vw, 12px);
  line-height: 1.35;
  color: #17141a;
  text-align: center;
}

.ct__wrap {
  position: relative;
  width: 100%;
  height: 40px;
  display: flex;
  align-items: center;
  --pct: 50;
  --hue: 165;
  --sat: 66;
}

.ct__range {
  appearance: none;
  -webkit-appearance: none;
  width: 100%;
  height: 20px;
  margin: 0;
  background: transparent;
}

.ct__range:focus-visible {
  outline: 2px solid #17141a;
  outline-offset: 4px;
  border-radius: 999px;
}

.ct__range::-webkit-slider-runnable-track {
  height: 8px;
  border-radius: 999px;
  background: linear-gradient(to right, hsl(calc(var(--hue) * 1deg), calc(var(--sat) * 1%), 50%) calc(var(--pct) * 1%), rgba(23, 20, 26, 0.14) calc(var(--pct) * 1%));
}

.ct__range::-webkit-slider-thumb {
  appearance: none;
  -webkit-appearance: none;
  width: 20px;
  height: 20px;
  border-radius: 50%;
  background: hsl(calc(var(--hue) * 1deg), calc(var(--sat) * 1%), 50%);
  box-shadow: 0 6px 12px rgba(23, 20, 26, 0.32);
  margin-top: -6px;
}

.ct__range::-moz-range-track {
  height: 8px;
  border-radius: 999px;
  background: rgba(23, 20, 26, 0.14);
}

.ct__range::-moz-range-progress {
  height: 8px;
  border-radius: 999px;
  background: hsl(calc(var(--hue) * 1deg), calc(var(--sat) * 1%), 50%);
}

.ct__range::-moz-range-thumb {
  width: 20px;
  height: 20px;
  border: 0;
  border-radius: 50%;
  background: hsl(calc(var(--hue) * 1deg), calc(var(--sat) * 1%), 50%);
  box-shadow: 0 6px 12px rgba(23, 20, 26, 0.32);
}

.ct__meta {
  margin: 0;
  font-size: clamp(9px, 2.4vw, 11px);
  color: rgba(23, 20, 26, 0.82);
}

.ct__tag {
  font-weight: 700;
  color: #0a4fe8;
  font-variant-numeric: tabular-nums;
  margin-right: 4px;
}

.ct__unit {
  color: rgba(23, 20, 26, 0.72);
}

@media (max-width: 340px) {
  .ct {
    gap: 8px;
    max-width: 280px;
  }
  .ct__hint {
    font-size: 8px;
  }
  .ct__meta {
    font-size: 7px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .ct__range {
    transition: none;
  }
}

// Color temperature 그라디언트(08, 아이디어형) — 값 비율(0~1)을 hue 로 선형 보간한다.
// 차가운 파랑(HUE_COLD=210) → 따뜻한 주황(HUE_WARM=28). 매 프레임 --hue·--sat
// CSS 커스텀 프로퍼티를 갱신해 트랙 채움색과 썸 배경이 값과 함께 실시간으로
// 물든다. CSS @keyframes 는 없다 — 색은 매 프레임 계산으로 나온다.
(function () {
  var root = document.getElementById('ct');
  var wrap = document.getElementById('ctWrap');
  var range = document.getElementById('ctRange');
  var hueEl = document.getElementById('ctHue');
  if (!root || !wrap || !range || !hueEl) return;

  var MIN = 0, MAX = 100;
  var HUE_COLD = 210, HUE_WARM = 28;
  var SAT_MIN = 55, SAT_MAX = 78;
  var TAU = 0.14;

  function paint(v) {
    var ratio = (v - MIN) / (MAX - MIN);
    var hue = HUE_COLD + (HUE_WARM - HUE_COLD) * ratio;
    var sat = SAT_MIN + (SAT_MAX - SAT_MIN) * ratio;
    wrap.style.setProperty('--pct', (ratio * 100).toFixed(2));
    wrap.style.setProperty('--hue', hue.toFixed(1));
    wrap.style.setProperty('--sat', sat.toFixed(1));
    hueEl.textContent = 'hue ' + Math.round(hue);
    range.setAttribute('aria-valuenow', String(Math.round(v)));
  }

  var current = 50;
  paint(current);

  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  var playing = true;
  function stop() { playing = false; }
  range.addEventListener('pointerdown', stop);
  range.addEventListener('keydown', stop);
  range.addEventListener('input', function () { current = Number(range.value); paint(current); });

  var targets = [50, 5, 92, 18, 78, 50];
  var seg = 0, segFrom = current;
  var SEG_MS = 400;
  var segStart = performance.now();

  if (reduce) {
    current = targets[0];
    range.value = String(current);
    paint(current);
  } else {
    (function step(now) {
      if (playing) {
        var elapsed = now - segStart;
        if (elapsed >= SEG_MS) {
          seg = (seg + 1) % targets.length;
          segStart = now; elapsed = 0; segFrom = current;
        }
        var target = targets[seg];
        var t = elapsed / 1000;
        var k = 1 - Math.exp(-t / TAU);
        current = segFrom + (target - segFrom) * k;
        range.value = String(Math.round(current));
        paint(current);
      }
      requestAnimationFrame(step);
    })(segStart);
  }
})();

// RangeSliderColorTemperatureGradient — vanilla 판(run/334/demo/08-range-slider-color-temperature-gradient/index.html)
// 의 React 포트. 값 비율(0~1)을 hue 로 선형 보간한다: 차가운 파랑(HUE_COLD=210) → 따뜻한
// 주황(HUE_WARM=28). 매 프레임 --hue·--sat CSS 커스텀 프로퍼티를 갱신해 트랙 채움색과
// 썸 배경이 값과 함께 실시간으로 물든다. CSS @keyframes 는 없다 — 색은 매 프레임 계산으로 나온다.
import { useEffect, useRef } from "react";
import type { CSSProperties } from "react";
import styles from "./RangeSliderColorTemperatureGradient.module.scss";

export type RangeSliderColorTemperatureGradientProps = {
  duration?: string;
  easing?: string;
  color?: string;
};

type Vars = CSSProperties & { "--duration"?: string; "--easing"?: string; "--color"?: string };
type Box<T> = { current: T };

const HINT = "값 비율을 HSL 색상으로 매 프레임 환산해 트랙과 썸을 차가운 파랑에서 따뜻한 주황으로 물들입니다";
const ARIA_SCENE = "값에 따라 색온도가 파랑에서 주황으로 바뀌는 슬라이더 장면";
const LABEL_RANGE = "색온도";
const UNIT = "HSL 보간";

export default function RangeSliderColorTemperatureGradient({
  duration = "220ms",
  easing = "ease-out",
  color = "#0a4fe8"
}: RangeSliderColorTemperatureGradientProps) {
  const rootRef = useRef<HTMLDivElement | null>(null);
  const wrapRef = useRef<HTMLDivElement | null>(null);
  const rangeRef = useRef<HTMLInputElement | null>(null);
  const hueRef = useRef<HTMLElement | null>(null);
  const rafRef = useRef(0) as Box<number>;

  useEffect(() => {
    const root = rootRef.current;
    const wrap = wrapRef.current;
    const range = rangeRef.current;
    const hueEl = hueRef.current;
    if (!root || !wrap || !range || !hueEl) return;

    const MIN = 0, MAX = 100;
    const HUE_COLD = 210, HUE_WARM = 28;
    const SAT_MIN = 55, SAT_MAX = 78;
    const TAU = 0.14;

    function paint(v: number): void {
      const ratio = (v - MIN) / (MAX - MIN);
      const hue = HUE_COLD + (HUE_WARM - HUE_COLD) * ratio;
      const sat = SAT_MIN + (SAT_MAX - SAT_MIN) * ratio;
      wrap!.style.setProperty("--pct", (ratio * 100).toFixed(2));
      wrap!.style.setProperty("--hue", hue.toFixed(1));
      wrap!.style.setProperty("--sat", sat.toFixed(1));
      hueEl!.textContent = "hue " + Math.round(hue);
      range!.setAttribute("aria-valuenow", String(Math.round(v)));
    }

    let current = 50;
    paint(current);

    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;

    let playing = true;
    const stop = (): void => {
      playing = false;
    };
    const onInput = (): void => {
      current = Number(range.value);
      paint(current);
    };

    range.addEventListener("pointerdown", stop);
    range.addEventListener("keydown", stop);
    range.addEventListener("input", onInput);

    const targets = [50, 5, 92, 18, 78, 50];
    let seg = 0, segFrom = current;
    const SEG_MS = 400;
    let segStart = performance.now();

    if (reduce) {
      current = targets[0];
      range.value = String(current);
      paint(current);
    } else {
      const step = (now: number): void => {
        if (playing) {
          let elapsed = now - segStart;
          if (elapsed >= SEG_MS) {
            seg = (seg + 1) % targets.length;
            segStart = now;
            elapsed = 0;
            segFrom = current;
          }
          const target = targets[seg];
          const t = elapsed / 1000;
          const k = 1 - Math.exp(-t / TAU);
          current = segFrom + (target - segFrom) * k;
          range.value = String(Math.round(current));
          paint(current);
        }
        rafRef.current = requestAnimationFrame(step);
      };
      step(segStart);
    }

    return () => {
      range.removeEventListener("pointerdown", stop);
      range.removeEventListener("keydown", stop);
      range.removeEventListener("input", onInput);
      cancelAnimationFrame(rafRef.current);
    };
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, []);

  return (
    <main className={styles.stage}>
      <div
        className={styles.ct}
        ref={rootRef}
        style={{ "--duration": duration, "--easing": easing, "--color": color } as Vars}
      >
        <p className={styles.hint}>{HINT}</p>
        <div className={styles.wrap} ref={wrapRef} role="img" aria-label={ARIA_SCENE}>
          <input
            className={styles.range}
            ref={rangeRef}
            type="range"
            min={0}
            max={100}
            step={1}
            defaultValue={50}
            aria-label={LABEL_RANGE}
          />
        </div>
        <p className={styles.meta}>
          <b className={styles.tag} ref={hueRef}>hue 122</b>
          <span className={styles.unit}>{UNIT}</span>
        </p>
      </div>
    </main>
  );
}