02Half-step precision fill — the filled value splits into a whole or half value depending on which half of a star's width the pointer falls in

<main class="stage">
<div class="sr is-demo" id="sr">
  <div class="sr__row" id="srRow">
    <span class="sr__star" data-i="0"><svg class="sr__base" viewBox="0 0 24 24"><path d="M12 .587l3.668 7.568 8.332 1.151-6.064 5.828 1.48 8.279L12 19.771l-7.416 3.642 1.48-8.279-6.064-5.828 8.332-1.151z"/></svg><span class="sr__fillclip" id="fc0"><svg class="sr__fill" viewBox="0 0 24 24"><path d="M12 .587l3.668 7.568 8.332 1.151-6.064 5.828 1.48 8.279L12 19.771l-7.416 3.642 1.48-8.279-6.064-5.828 8.332-1.151z"/></svg></span></span>
    <span class="sr__star" data-i="1"><svg class="sr__base" viewBox="0 0 24 24"><path d="M12 .587l3.668 7.568 8.332 1.151-6.064 5.828 1.48 8.279L12 19.771l-7.416 3.642 1.48-8.279-6.064-5.828 8.332-1.151z"/></svg><span class="sr__fillclip" id="fc1"><svg class="sr__fill" viewBox="0 0 24 24"><path d="M12 .587l3.668 7.568 8.332 1.151-6.064 5.828 1.48 8.279L12 19.771l-7.416 3.642 1.48-8.279-6.064-5.828 8.332-1.151z"/></svg></span></span>
    <span class="sr__star" data-i="2"><svg class="sr__base" viewBox="0 0 24 24"><path d="M12 .587l3.668 7.568 8.332 1.151-6.064 5.828 1.48 8.279L12 19.771l-7.416 3.642 1.48-8.279-6.064-5.828 8.332-1.151z"/></svg><span class="sr__fillclip" id="fc2"><svg class="sr__fill" viewBox="0 0 24 24"><path d="M12 .587l3.668 7.568 8.332 1.151-6.064 5.828 1.48 8.279L12 19.771l-7.416 3.642 1.48-8.279-6.064-5.828 8.332-1.151z"/></svg></span></span>
    <span class="sr__star" data-i="3"><svg class="sr__base" viewBox="0 0 24 24"><path d="M12 .587l3.668 7.568 8.332 1.151-6.064 5.828 1.48 8.279L12 19.771l-7.416 3.642 1.48-8.279-6.064-5.828 8.332-1.151z"/></svg><span class="sr__fillclip" id="fc3"><svg class="sr__fill" viewBox="0 0 24 24"><path d="M12 .587l3.668 7.568 8.332 1.151-6.064 5.828 1.48 8.279L12 19.771l-7.416 3.642 1.48-8.279-6.064-5.828 8.332-1.151z"/></svg></span></span>
    <span class="sr__star" data-i="4"><svg class="sr__base" viewBox="0 0 24 24"><path d="M12 .587l3.668 7.568 8.332 1.151-6.064 5.828 1.48 8.279L12 19.771l-7.416 3.642 1.48-8.279-6.064-5.828 8.332-1.151z"/></svg><span class="sr__fillclip" id="fc4"><svg class="sr__fill" viewBox="0 0 24 24"><path d="M12 .587l3.668 7.568 8.332 1.151-6.064 5.828 1.48 8.279L12 19.771l-7.416 3.642 1.48-8.279-6.064-5.828 8.332-1.151z"/></svg></span></span>
  </div>
  <div class="sr__readout" id="srReadout"><b id="srNum">0.0</b> / 5</div>
</div>
</main>

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

// 계산 겹: 별의 실제 렌더 폭(getBoundingClientRect)을 기준으로 포인터 위치가 왼쪽/오른쪽 절반
// 어디에 있는지를 나눠 정수 또는 .5 단위로만 값을 스냅한다 (valueFromX()).
@include stage($stage-ink);

.sr {
  display: grid;
  gap: $sp-5;
  place-items: center;
}

.sr__row {
  display: flex;
  gap: $sp-2;
  cursor: pointer;
}

.sr__star {
  position: relative;
  width: 44px;
  height: 44px;
}

.sr__base,
.sr__fill svg {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
}

.sr__base { fill: $subject-blue-light; opacity: .35; }

.sr__fillclip {
  position: absolute;
  inset: 0;
  width: 0%;
  overflow: hidden;
  transition: width $dur-instant $ease-out;
}

.sr__fill { fill: $subject-pink; }

.sr__readout {
  font: 600 20px/1.2 -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  color: $stage-paper;

  b { color: $subject-pink; font-variant-numeric: tabular-nums; }
}

@media (max-width: 340px) {
  .sr__star { width: 34px; height: 34px; }
  .sr__row { gap: $sp-1; }
  .sr__readout { font-size: 16px; }
}

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

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 {
  display: grid;
  gap: 20px;
  place-items: center;
}

.sr__row {
  display: flex;
  gap: 8px;
  cursor: pointer;
}

.sr__star {
  position: relative;
  width: 44px;
  height: 44px;
}

.sr__base,
.sr__fill svg {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
}

.sr__base {
  fill: #5b8cf8;
  opacity: 0.35;
}

.sr__fillclip {
  position: absolute;
  inset: 0;
  width: 0%;
  overflow: hidden;
  transition: width 140ms ease-out;
}

.sr__fill {
  fill: #ff9ebb;
}

.sr__readout {
  font: 600 20px/1.2 -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  color: #ffffff;
}
.sr__readout b {
  color: #ff9ebb;
  font-variant-numeric: tabular-nums;
}

@media (max-width: 340px) {
  .sr__star {
    width: 34px;
    height: 34px;
  }
  .sr__row {
    gap: 4px;
  }
  .sr__readout {
    font-size: 16px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .sr__fillclip {
    transition: none;
  }
}

(function () {
  var root = document.getElementById('sr');
  var row = document.getElementById('srRow');
  var stars = Array.prototype.slice.call(row.querySelectorAll('.sr__star'));
  var clips = stars.map(function (s) { return s.querySelector('.sr__fillclip'); });
  var numEl = document.getElementById('srNum');
  var STAR_W = 44;
  var value = 0;

  // 계산 겹: 각 별의 실제 렌더 폭(getBoundingClientRect)을 기준으로 포인터가 왼쪽 절반에 있는지
  // 오른쪽 절반에 있는지를 나눠, 정수 또는 .5 단위로만 값을 스냅한다.
  function valueFromX(clientX) {
    for (var i = 0; i < stars.length; i++) {
      var r = stars[i].getBoundingClientRect();
      if (clientX < r.left) return i;
      if (clientX <= r.right) {
        var half = r.left + r.width / 2;
        return clientX < half ? i + 0.5 : i + 1;
      }
    }
    return stars.length;
  }

  function paint(v) {
    stars.forEach(function (s, idx) {
      var starVal = Math.max(0, Math.min(1, v - idx));
      clips[idx].style.width = (starVal * 100).toFixed(0) + '%';
    });
    numEl.textContent = v.toFixed(1);
  }

  function setFromPointer(clientX) {
    value = valueFromX(clientX);
    paint(value);
  }

  row.addEventListener('pointermove', function (e) {
    root.classList.remove('is-demo'); stopAutoplay();
    setFromPointer(e.clientX);
  });
  row.addEventListener('click', function (e) { setFromPointer(e.clientX); });

  paint(value);

  // 자동 루프: 반 칸 단위(0.5)로 값을 끝까지 올렸다 처음으로 되돌리는 것을 반복한다.
  var steps = [0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5];
  var step = 0;
  var autoTimer = null;
  function autoTick() { paint(steps[step]); value = steps[step]; step = (step + 1) % steps.length; }
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  function stopAutoplay() { if (autoTimer) { clearInterval(autoTimer); autoTimer = null; } }
  if (!reduce) { autoTimer = setInterval(autoTick, 260); autoTick(); }
})();

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

const STAR_PATH =
  "M12 .587l3.668 7.568 8.332 1.151-6.064 5.828 1.48 8.279L12 19.771l-7.416 3.642 1.48-8.279-6.064-5.828 8.332-1.151z";

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

  useEffect(() => {
    const root = rootRef.current;
    if (!root) return;
    const row = root.querySelector<HTMLDivElement>(`.${styles.row}`);
    const numEl = root.querySelector<HTMLElement>(`.${styles.num}`);
    if (!row || !numEl) return;
    const stars = Array.prototype.slice.call(
      row.querySelectorAll(`.${styles.star}`)
    ) as HTMLElement[];
    const clips = stars.map((s) => s.querySelector<HTMLElement>(`.${styles.fillclip}`)!);
    let value = 0;

    // 계산 겹: 각 별의 실제 렌더 폭(getBoundingClientRect)을 기준으로 포인터가 왼쪽 절반에 있는지
    // 오른쪽 절반에 있는지를 나눠, 정수 또는 .5 단위로만 값을 스냅한다.
    function valueFromX(clientX: number) {
      for (let i = 0; i < stars.length; i++) {
        const r = stars[i].getBoundingClientRect();
        if (clientX < r.left) return i;
        if (clientX <= r.right) {
          const half = r.left + r.width / 2;
          return clientX < half ? i + 0.5 : i + 1;
        }
      }
      return stars.length;
    }

    function paint(v: number) {
      stars.forEach((_s, idx) => {
        const starVal = Math.max(0, Math.min(1, v - idx));
        clips[idx].style.width = (starVal * 100).toFixed(0) + "%";
      });
      numEl!.textContent = v.toFixed(1);
    }

    function setFromPointer(clientX: number) {
      value = valueFromX(clientX);
      paint(value);
    }

    function onMove(e: PointerEvent) {
      stopAutoplay();
      setFromPointer(e.clientX);
    }
    function onClick(e: MouseEvent) { setFromPointer(e.clientX); }
    row.addEventListener("pointermove", onMove);
    row.addEventListener("click", onClick);

    paint(value);

    // 자동 루프: 반 칸 단위(0.5)로 값을 끝까지 올렸다 처음으로 되돌리는 것을 반복한다.
    const steps = [0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5];
    let step = 0;
    let autoTimer: number | null = null;
    function autoTick() { paint(steps[step]); value = steps[step]; step = (step + 1) % steps.length; }
    function stopAutoplay() { if (autoTimer !== null) { window.clearInterval(autoTimer); autoTimer = null; } }
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    if (!reduce) { autoTimer = window.setInterval(autoTick, 260); autoTick(); }

    return () => {
      stopAutoplay();
      row.removeEventListener("pointermove", onMove);
      row.removeEventListener("click", onClick);
    };
  }, []);

  return (
    <div ref={rootRef} className={styles.stage}>
      <div className={styles.sr}>
        <div className={styles.row}>
          {[0, 1, 2, 3, 4].map((i) => (
            <span key={i} className={styles.star}>
              <svg className={styles.base} viewBox="0 0 24 24"><path d={STAR_PATH} /></svg>
              <span className={styles.fillclip}>
                <svg className={styles.fill} viewBox="0 0 24 24"><path d={STAR_PATH} /></svg>
              </span>
            </span>
          ))}
        </div>
        <div className={styles.readout}><b className={styles.num}>0.0</b> / 5</div>
      </div>
    </div>
  );
}