01Damage-flash deplete toggle — when a value drops, the bar narrows first while a red afterglow trails behind, narrowing more slowly

<main class="stage">
<div class="gb is-demo" id="gb">
  <div class="gb__head">
    <span class="gb__label">HP</span>
    <span class="gb__value" id="gbValue">100 / 100</span>
  </div>
  <div class="gb__track" role="progressbar" aria-label="HP" aria-valuemin="0" aria-valuemax="100" aria-valuenow="100" id="gbTrack">
    <div class="gb__trail" id="gbTrail"></div>
    <div class="gb__fill" id="gbFill"></div>
    <div class="gb__flash" id="gbFlash"></div>
  </div>
  <button type="button" class="gb__hit" id="gbHit">Take Damage</button>
</div>
</main>

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

// 계산 겹: index.html loop() 이 매 프레임 잔상(trail) 값을 지수 평활로 본값에 수렴시키고
// 플래시는 감쇠 지수함수로 사그라든다 — 키프레임 반복이 아니라 시간 t 의 계산값이다.
@include stage($stage-ink);

.gb { width: 100%; max-width: 260px; background: $subject-cream; border-radius: $r-card; padding: $sp-5; box-shadow: $shadow-raised; box-sizing: border-box; }
.gb__head { display: flex; justify-content: space-between; align-items: baseline; margin-bottom: $sp-3; }
.gb__label { font-size: 12px; font-weight: 700; letter-spacing: .04em; color: rgba($subject-ink, .72); text-transform: uppercase; }
.gb__value { font-size: 15px; font-weight: 700; color: $subject-ink; }

.gb__track { position: relative; height: 18px; border-radius: $r-pill; background: rgba($subject-ink, .1); overflow: hidden; }
.gb__trail, .gb__fill {
  position: absolute; left: 0; top: 0; height: 100%; border-radius: $r-pill;
  will-change: width;
}
.gb__trail { background: $error; width: 100%; }
.gb__fill { background: $subject-blue-deep; width: 100%; z-index: 1; }
.gb__flash {
  position: absolute; inset: 0; border-radius: $r-pill;
  background: $subject-cream; opacity: 0; z-index: 2; pointer-events: none;
  will-change: opacity;
}

.gb__hit {
  margin-top: $sp-4; width: 100%; border: none; border-radius: $r-control;
  background: $subject-blue; color: $subject-cream;
  font-weight: 700; font-size: 13px; line-height: 1;
  padding: $sp-3 0; cursor: pointer;
}
.gb__hit:active { box-shadow: $shadow-press; }

@media (max-width: 340px) {
  .gb { max-width: 220px; padding: $sp-4; }
  .gb__track { height: 15px; }
  .gb__value { font-size: 13px; }
}

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

.gb {
  width: 100%;
  max-width: 260px;
  background: #fff7e6;
  border-radius: 16px;
  padding: 20px;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  box-sizing: border-box;
}

.gb__head {
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  margin-bottom: 12px;
}

.gb__label {
  font-size: 12px;
  font-weight: 700;
  letter-spacing: 0.04em;
  color: rgba(23, 20, 26, 0.72);
  text-transform: uppercase;
}

.gb__value {
  font-size: 15px;
  font-weight: 700;
  color: #17141a;
}

.gb__track {
  position: relative;
  height: 18px;
  border-radius: 999px;
  background: rgba(23, 20, 26, 0.1);
  overflow: hidden;
}

.gb__trail, .gb__fill {
  position: absolute;
  left: 0;
  top: 0;
  height: 100%;
  border-radius: 999px;
  will-change: width;
}

.gb__trail {
  background: #c2361a;
  width: 100%;
}

.gb__fill {
  background: #0a4fe8;
  width: 100%;
  z-index: 1;
}

.gb__flash {
  position: absolute;
  inset: 0;
  border-radius: 999px;
  background: #fff7e6;
  opacity: 0;
  z-index: 2;
  pointer-events: none;
  will-change: opacity;
}

.gb__hit {
  margin-top: 16px;
  width: 100%;
  border: none;
  border-radius: 12px;
  background: #2f6df6;
  color: #fff7e6;
  font-weight: 700;
  font-size: 13px;
  line-height: 1;
  padding: 12px 0;
  cursor: pointer;
}

.gb__hit:active {
  box-shadow: 0 6px 12px rgba(23, 20, 26, 0.32);
}

@media (max-width: 340px) {
  .gb {
    max-width: 220px;
    padding: 16px;
  }
  .gb__track {
    height: 15px;
  }
  .gb__value {
    font-size: 13px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .gb__flash {
    display: none;
  }
}

(function () {
  var HP_MAX = 100;
  // 계산 겹 상수: 시드 고정 전투 이벤트 배열 — [발생시각ms, 피해량]
  var EVENTS = [[300, 24], [1100, 18], [2000, 28], [2900, 12]];
  var CYCLE = 3800; // ms, 자동 루프 한 바퀴
  var LERP_RATE = 0.006; // 계산 겹: 잔상이 본값을 따라가는 지수 평활 상수(프레임 독립)
  var FLASH_TAU = 70; // ms, 플래시 감쇠 시간상수
  var HIT_LIST = [24, 18, 28, 12, 20]; // 클릭(실사용자) 피해량 순환
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  var gb = document.getElementById('gb');
  var track = document.getElementById('gbTrack');
  var fill = document.getElementById('gbFill');
  var trailEl = document.getElementById('gbTrail');
  var flashEl = document.getElementById('gbFlash');
  var valueEl = document.getElementById('gbValue');
  var hitBtn = document.getElementById('gbHit');

  var isDemo = true;
  var mainHP = HP_MAX;
  var trailHP = HP_MAX;
  var flashStart = -9999;
  var appliedIdx = 0;
  var cycleStart = 0;
  var lastTs = 0;
  var hitIdx = 0;

  function render() {
    var mp = Math.max(0, Math.min(100, mainHP));
    var tp = Math.max(0, Math.min(100, trailHP));
    fill.style.width = mp.toFixed(2) + '%';
    trailEl.style.width = tp.toFixed(2) + '%';
    track.setAttribute('aria-valuenow', String(Math.round(mp)));
    valueEl.textContent = Math.round(mp) + ' / ' + HP_MAX;
  }

  function applyHit(dmg, ts) {
    trailHP = mainHP; // 잔상은 피해 직전 값에서 출발해 뒤늦게 따라간다
    mainHP = Math.max(0, mainHP - dmg);
    flashStart = ts;
  }

  function human() {
    if (isDemo) { gb.classList.remove('is-demo'); isDemo = false; }
  }

  function onHit() {
    human();
    var now = performance.now();
    if (mainHP <= 0) {
      mainHP = HP_MAX; trailHP = HP_MAX; flashStart = -9999;
    } else {
      applyHit(HIT_LIST[hitIdx % HIT_LIST.length], now);
      hitIdx++;
    }
    render();
  }

  hitBtn.addEventListener('click', onHit);
  hitBtn.addEventListener('keydown', function (ev) {
    if (ev.key !== 'Enter' && ev.key !== ' ') return;
    ev.preventDefault();
    onHit();
  });

  function loop(ts) {
    if (!cycleStart) { cycleStart = ts; lastTs = ts; }
    var dt = ts - lastTs;
    lastTs = ts;
    var elapsed = ts - cycleStart;

    if (isDemo) {
      if (elapsed >= CYCLE) {
        cycleStart = ts;
        elapsed = 0;
        appliedIdx = 0;
        mainHP = HP_MAX;
        trailHP = HP_MAX;
        flashStart = -9999;
      }
      while (appliedIdx < EVENTS.length && elapsed >= EVENTS[appliedIdx][0]) {
        applyHit(EVENTS[appliedIdx][1], ts);
        appliedIdx++;
      }
    }

    // 계산 겹: 잔상 지수 평활 — dt(ms) 에 독립적으로 같은 반감기를 유지
    trailHP += (mainHP - trailHP) * (1 - Math.exp(-LERP_RATE * dt));
    var flash = Math.max(0, Math.exp(-(ts - flashStart) / FLASH_TAU));
    flashEl.style.opacity = flash < 0.02 ? '0' : flash.toFixed(3);

    render();
    requestAnimationFrame(loop);
  }

  if (!reduce) {
    requestAnimationFrame(loop);
  } else {
    render();
  }
})();

import { useEffect, useRef, useState } from 'react';
import styles from './GaugeBarDamageFlash.module.scss';

type Box<T> = { current: T };

const HP_MAX = 100;
// 계산 겹 상수: 시드 고정 전투 이벤트 배열 — [발생시각ms, 피해량]
const EVENTS: [number, number][] = [[300, 24], [1100, 18], [2000, 28], [2900, 12]];
const CYCLE = 3800; // ms, 자동 루프 한 바퀴
const LERP_RATE = 0.006; // 계산 겹: 잔상이 본값을 따라가는 지수 평활 상수(프레임 독립)
const FLASH_TAU = 70; // ms, 플래시 감쇠 시간상수
const HIT_LIST = [24, 18, 28, 12, 20]; // 클릭(실사용자) 피해량 순환

export default function GaugeBarDamageFlash() {
  const fillRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const trailRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const flashRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const trackRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const isDemoRef = useRef(true) as unknown as Box<boolean>;
  const [isDemo, setIsDemo] = useState(true);
  const [value, setValue] = useState(HP_MAX);

  const mainHPRef = useRef(HP_MAX) as unknown as Box<number>;
  const trailHPRef = useRef(HP_MAX) as unknown as Box<number>;
  const flashStartRef = useRef(-9999) as unknown as Box<number>;
  const hitIdxRef = useRef(0) as unknown as Box<number>;

  function human() {
    isDemoRef.current = false;
    setIsDemo(false);
  }

  function applyHit(dmg: number, ts: number) {
    trailHPRef.current = mainHPRef.current; // 잔상은 피해 직전 값에서 출발해 뒤늦게 따라간다
    mainHPRef.current = Math.max(0, mainHPRef.current - dmg);
    flashStartRef.current = ts;
  }

  function render() {
    const mp = Math.max(0, Math.min(100, mainHPRef.current));
    const tp = Math.max(0, Math.min(100, trailHPRef.current));
    const fill = fillRef.current;
    const trail = trailRef.current;
    const track = trackRef.current;
    if (fill) fill.style.width = mp.toFixed(2) + '%';
    if (trail) trail.style.width = tp.toFixed(2) + '%';
    if (track) track.setAttribute('aria-valuenow', String(Math.round(mp)));
    setValue(Math.round(mp));
  }

  useEffect(() => {
    const reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
    let cycleStart = 0;
    let lastTs = 0;
    let appliedIdx = 0;
    let rafId = 0;

    function loop(ts: number) {
      if (!cycleStart) { cycleStart = ts; lastTs = ts; }
      const dt = ts - lastTs;
      lastTs = ts;
      let elapsed = ts - cycleStart;

      if (isDemoRef.current) {
        if (elapsed >= CYCLE) {
          cycleStart = ts;
          elapsed = 0;
          appliedIdx = 0;
          mainHPRef.current = HP_MAX;
          trailHPRef.current = HP_MAX;
          flashStartRef.current = -9999;
        }
        while (appliedIdx < EVENTS.length && elapsed >= EVENTS[appliedIdx][0]) {
          applyHit(EVENTS[appliedIdx][1], ts);
          appliedIdx++;
        }
      }

      // 계산 겹: 잔상 지수 평활 — dt(ms) 에 독립적으로 같은 반감기를 유지
      trailHPRef.current += (mainHPRef.current - trailHPRef.current) * (1 - Math.exp(-LERP_RATE * dt));
      const flash = Math.max(0, Math.exp(-(ts - flashStartRef.current) / FLASH_TAU));
      const flashEl = flashRef.current;
      if (flashEl) flashEl.style.opacity = flash < 0.02 ? '0' : flash.toFixed(3);

      render();
      rafId = requestAnimationFrame(loop);
    }

    if (!reduce) {
      rafId = requestAnimationFrame(loop);
    } else {
      render();
    }
    return () => cancelAnimationFrame(rafId);
  }, []);

  function onHit() {
    human();
    const now = performance.now();
    if (mainHPRef.current <= 0) {
      mainHPRef.current = HP_MAX;
      trailHPRef.current = HP_MAX;
      flashStartRef.current = -9999;
    } else {
      applyHit(HIT_LIST[hitIdxRef.current % HIT_LIST.length], now);
      hitIdxRef.current++;
    }
    render();
  }

  function onKeyDown(e: { key: string; preventDefault: () => void }) {
    if (e.key !== 'Enter' && e.key !== ' ') return;
    e.preventDefault();
    onHit();
  }

  return (
    <div className={`${styles.gb} ${isDemo ? styles.isDemo : ''}`}>
      <div className={styles.gbHead}>
        <span className={styles.gbLabel}>HP</span>
        <span className={styles.gbValue}>{value} / {HP_MAX}</span>
      </div>
      <div
        className={styles.gbTrack}
        role="progressbar"
        aria-label="HP"
        aria-valuemin={0}
        aria-valuemax={100}
        aria-valuenow={value}
        ref={trackRef}
      >
        <div className={styles.gbTrail} ref={trailRef} />
        <div className={styles.gbFill} ref={fillRef} />
        <div className={styles.gbFlash} ref={flashRef} />
      </div>
      <button type="button" className={styles.gbHit} onClick={onHit} onKeyDown={onKeyDown}>
        피해 입기
      </button>
    </div>
  );
}