03낙하 높이 값이 쌓는 중력 블록 로더

<main class="stage">
<div class="ld" id="ld">
  <p class="ld__hint">
    <svg class="ld__ico" viewBox="0 0 256 256" aria-hidden="true"><g fill="currentColor"><path d="M232 56v56a8 8 0 0 1-16 0V91.3l-25.6 25.7A80 80 0 1 1 174 60a8 8 0 1 1-9 13.2A64 64 0 1 0 179.7 128H216a8 8 0 0 1 0 16h-56a8 8 0 0 1-8-8V80a8 8 0 0 1 16 0v20.7L192.7 76A80.1 80.1 0 0 0 64 128a8 8 0 0 1-16 0a96 96 0 0 1 163.6-68.3L224 71.3V56a8 8 0 0 1 8 8" opacity=".2"/><path d="M224 48a8 8 0 0 0-8 8v15.3l-11.7-11.6a96 96 0 1 0 27.6 51.6a8 8 0 0 0-15.8 2.5a80 80 0 1 1-23-43l-25.7 25.7A8 8 0 0 0 173 112h56a8 8 0 0 0 8-8V56a8 8 0 0 0-13-8"/></g></svg>
    <span>클릭하거나 스페이스바를 누르면 멈추거나 다시 갑니다</span>
  </p>
  <div class="ld__field" id="field" role="application" aria-label="중력 블록 쌓기 실험판" tabindex="0">
    <canvas class="ld__cv" id="cv"></canvas>
    <b class="ld__badge" aria-hidden="true"><span class="ld__badgeNum" id="pct">0%</span><span class="ld__badgeUnit">적재</span></b>
  </div>
</div>
</main>

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

// 중력 블록 로더 — 블록 8개를 하나씩 떨어뜨려 감쇠 상수(0.92)로 튕김을 줄이며 쌓는다.
// 움직임은 전부 캔버스 rAF 루프 안에 있다. CSS 는 무대·판·배지만 맡는다(@keyframes 0개 — 077 선례와 같은 이유).

$duration: $dur-loop;
$easing: $ease-pop;
$color: $subject-orange-deep;

@include stage($stage-orange);

.ld {
  --paper: #{$subject-cream};
  --ink: #{$subject-ink};
  --floor: #{rgba($subject-ink, .12)};
  --c1: #{$subject-blue};
  --c2: #{$subject-mint};
  --c3: #{$subject-pink};
  --c4: #{$subject-lilac};

  display: flex; flex-direction: column; gap: $sp-2;
  width: 100%; max-width: 424px;
}

.ld__hint {
  display: flex; align-items: center; gap: $sp-1; margin: 0;
  font-weight: 700; font-size: clamp(10px, 2.8vw, 12px); line-height: 1.35;
  color: $subject-ink;
}
.ld__ico { width: 16px; height: 16px; flex: 0 0 auto; color: $subject-orange-deep; }

.ld__field {
  position: relative; height: 208px;
  border-radius: $r-card; overflow: hidden;
  background: $subject-cream;
  box-shadow: inset 0 0 0 1px rgba($subject-ink, .16);
  cursor: pointer;
}
.ld__field:focus-visible { outline: 2px solid $subject-orange-deep; outline-offset: 2px; }

.ld__cv { display: block; width: 100%; height: 100%; }

.ld__badge {
  position: absolute; right: $sp-2; top: $sp-2;
  display: flex; align-items: baseline; gap: $sp-1;
  padding: $sp-1 $sp-2; border-radius: $r-pill;
  background: rgba($subject-ink, .78);
  color: $subject-cream; font-weight: 700; font-size: 11px;
}
.ld__badgeNum { font-size: 13px; color: $stage-yellow; }
.ld__badgeUnit { font-weight: 700; }

@media (max-width: 340px) {
  .ld { gap: $sp-1; }
  .ld__field { height: 124px; }
  .ld__badge { font-size: 10px; padding: 0 $sp-1; }
  .ld__badgeNum { font-size: 11px; }
}

// reduce — 루프를 시작하지 않고 진행률 62% 언저리에서 멈춘 한 장만 그린다.
@media (prefers-reduced-motion: reduce) {
  .ld.is-still .ld__field { cursor: default !important; }
  .ld.is-still .ld__badge { opacity: .92 !important; }
}

html, body {
  margin: 0;
  overflow: hidden;
}

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ff4d1f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.ld {
  --paper: #fff7e6;
  --ink: #17141a;
  --floor: rgba(23, 20, 26, 0.12);
  --c1: #2f6df6;
  --c2: #4cd4a6;
  --c3: #ff9ebb;
  --c4: #b9a0ff;
  display: flex;
  flex-direction: column;
  gap: 8px;
  width: 100%;
  max-width: 424px;
}

.ld__hint {
  display: flex;
  align-items: center;
  gap: 4px;
  margin: 0;
  font-weight: 700;
  font-size: clamp(10px, 2.8vw, 12px);
  line-height: 1.35;
  color: #17141a;
}

.ld__ico {
  width: 16px;
  height: 16px;
  flex: 0 0 auto;
  color: #c93000;
}

.ld__field {
  position: relative;
  height: 208px;
  border-radius: 16px;
  overflow: hidden;
  background: #fff7e6;
  box-shadow: inset 0 0 0 1px rgba(23, 20, 26, 0.16);
  cursor: pointer;
}

.ld__field:focus-visible {
  outline: 2px solid #c93000;
  outline-offset: 2px;
}

.ld__cv {
  display: block;
  width: 100%;
  height: 100%;
}

.ld__badge {
  position: absolute;
  right: 8px;
  top: 8px;
  display: flex;
  align-items: baseline;
  gap: 4px;
  padding: 4px 8px;
  border-radius: 999px;
  background: rgba(23, 20, 26, 0.78);
  color: #fff7e6;
  font-weight: 700;
  font-size: 11px;
}

.ld__badgeNum {
  font-size: 13px;
  color: #ffd23f;
}

.ld__badgeUnit {
  font-weight: 700;
}

@media (max-width: 340px) {
  .ld {
    gap: 4px;
  }
  .ld__field {
    height: 124px;
  }
  .ld__badge {
    font-size: 10px;
    padding: 0 4px;
  }
  .ld__badgeNum {
    font-size: 11px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .ld.is-still .ld__field {
    cursor: default !important;
  }
  .ld.is-still .ld__badge {
    opacity: 0.92 !important;
  }
}

// 중력 블록 로더 — 블록 8개를 위에서 하나씩 중력 가속도로 떨어뜨리고, 바닥에 닿을 때마다
// 튕기는 높이를 감쇠 상수(gravity-bounce-damping = 0.92, 훅 고정)로 줄여 쌓인 블록 수가 진행률이 된다.
var root = document.getElementById('ld');
var field = document.getElementById('field');
var cv = document.getElementById('cv');
var ctx = cv.getContext('2d');
var pctEl = document.getElementById('pct');

var css = getComputedStyle(root);
var PAPER = css.getPropertyValue('--paper').trim();
var FLOOR = css.getPropertyValue('--floor').trim();
var C1 = css.getPropertyValue('--c1').trim();
var C2 = css.getPropertyValue('--c2').trim();
var C3 = css.getPropertyValue('--c3').trim();
var C4 = css.getPropertyValue('--c4').trim();
var PALETTE = [C1, C2, C3, C4];

var BLOCKS = 8;
var GRAVITY = 1700;                 // px/s^2 — 캔버스 규모에 맞춘 중력 가속도
var DAMPING = 0.92;                 // 튕김 감쇠 상수(훅 고정값) — gravity-bounce-damping
var DROP_INTERVAL = 0.3;            // 블록 사이 낙하 시작 간격(초)
var REST_V = 40;                    // 이 속도 밑으로 떨어지면 멈춘 것으로 본다
var LOOP = BLOCKS * DROP_INTERVAL + 0.5;

var W = 0, H = 0, dpr = 1, blockH = 0, blockW = 0, margin = 0;
var blocks = [];

function resetBlocks() {
  blocks = [];
  for (var i = 0; i < BLOCKS; i++) blocks.push({ y: -blockH, vy: 0, state: 'waiting' });
}

function fit() {
  var r = field.getBoundingClientRect();
  dpr = window.devicePixelRatio || 1;
  W = r.width; H = r.height;
  cv.width = Math.round(W * dpr); cv.height = Math.round(H * dpr);
  ctx.setTransform(dpr, 0, 0, dpr, 0, 0);
  blockH = (H - 10) / (BLOCKS + 1.4);
  blockW = Math.min(W * 0.42, blockH * 2.6);
  margin = (H - 10) - BLOCKS * blockH;
  resetBlocks();
}

var lastSec = null, cycleIndex = -1;

function step(sec) {
  if (lastSec === null) lastSec = sec;
  var dt = Math.min(0.05, Math.max(0, sec - lastSec));
  lastSec = sec;
  var ci = Math.floor(sec / LOOP);
  if (ci !== cycleIndex) { resetBlocks(); cycleIndex = ci; }
  var t = sec - ci * LOOP;
  var settled = 0;
  for (var i = 0; i < BLOCKS; i++) {
    var b = blocks[i];
    if (b.state === 'waiting') {
      if (t >= i * DROP_INTERVAL) { b.state = 'falling'; b.y = -blockH; b.vy = 0; }
    }
    if (b.state === 'falling') {
      b.vy += GRAVITY * dt;
      b.y += b.vy * dt;
      var floorY = (H - margin) - (i + 1) * blockH;
      if (b.y >= floorY) {
        b.y = floorY;
        b.vy = -b.vy * DAMPING;
        if (Math.abs(b.vy) < REST_V) { b.state = 'settled'; b.vy = 0; }
      }
    }
    if (b.state === 'settled') settled++;
  }
  return settled;
}

function draw(sec) {
  var settled = step(sec);
  ctx.clearRect(0, 0, W, H);
  ctx.fillStyle = PAPER;
  ctx.fillRect(0, 0, W, H);

  ctx.fillStyle = FLOOR;
  ctx.fillRect(0, H - margin, W, margin);

  var cx = W * 0.5;
  var r = 6;
  for (var i = 0; i < BLOCKS; i++) {
    var b = blocks[i];
    if (b.state === 'waiting') continue;
    var x = cx - blockW / 2;
    var y = b.y;
    ctx.fillStyle = PALETTE[i % PALETTE.length];
    ctx.beginPath();
    ctx.moveTo(x + r, y);
    ctx.arcTo(x + blockW, y, x + blockW, y + blockH, r);
    ctx.arcTo(x + blockW, y + blockH, x, y + blockH, r);
    ctx.arcTo(x, y + blockH, x, y, r);
    ctx.arcTo(x, y, x + blockW, y, r);
    ctx.closePath();
    ctx.fill();
  }

  var pct = Math.round(settled / BLOCKS * 100);
  pctEl.textContent = pct + '%';
}

var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
var paused = false;
var t0 = 0;
var raf = 0;

function togglePause() {
  paused = !paused;
  root.classList.toggle('is-paused', paused);
}
function restart() {
  t0 = performance.now();
  lastSec = null; cycleIndex = -1;
  resetBlocks();
  draw(0);
}

field.addEventListener('click', function () { togglePause(); });
field.addEventListener('keydown', function (e) {
  if (e.key === ' ' || e.key === 'Enter') { e.preventDefault(); togglePause(); }
  else if (e.key === 'r' || e.key === 'R') { e.preventDefault(); restart(); }
});
window.addEventListener('resize', function () {
  fit();
  if (paused || reduce) draw(((performance.now() - t0) / 1000));
});

function frame(now) {
  if (!paused) draw((now - t0) / 1000);
  raf = requestAnimationFrame(frame);
}

t0 = performance.now();
fit();
if (reduce) {
  root.classList.add('is-still');
  draw(LOOP * 0.62);
} else {
  raf = requestAnimationFrame(frame);
}

// GravityDrop — vanilla 판(run/395/demo/03-canvas-loader-gravity-drop-stack-height/index.html) 의 React 포트.
// 블록 8개를 하나씩 떨어뜨려 감쇠 상수(0.92, 훅 고정)로 튕김을 줄이며 쌓는다. 쌓인 블록 수가 진행률.
import { useEffect, useRef } from "react";
import type { CSSProperties } from "react";
import styles from "./GravityDrop.module.scss";

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

type Vars = CSSProperties & { "--duration"?: string; "--easing"?: string; "--color"?: string };
type Box<T> = { current: T };
type KeyEvt = { key: string; preventDefault(): void };
type BlockState = "waiting" | "falling" | "settled";
type BlockT = { y: number; vy: number; state: BlockState };

const BLOCKS = 8;
const GRAVITY = 1700;
const DAMPING = 0.92;               // 튕김 감쇠 상수(훅 고정값) — gravity-bounce-damping
const DROP_INTERVAL = 0.3;
const REST_V = 40;
const LOOP = BLOCKS * DROP_INTERVAL + 0.5;
const FIELD_LABEL = "중력 블록 쌓기 실험판";

export default function GravityDrop({
  duration = "2.9s",
  easing = "cubic-bezier(.2, 1.4, .4, 1)",     // vanilla $easing: $ease-pop
  color = "#c93000",                           // vanilla $color: $subject-orange-deep
}: GravityDropProps) {
  const rootRef = useRef<HTMLDivElement | null>(null);
  const fieldRef = useRef<HTMLDivElement | null>(null);
  const cvRef = useRef<HTMLCanvasElement | null>(null);
  const ctxRef = useRef<CanvasRenderingContext2D | null>(null);
  const pctRef = useRef<HTMLSpanElement | null>(null);
  const sizeRef = useRef({ w: 0, h: 0, dpr: 1, blockH: 0, blockW: 0, margin: 0 }) as Box<{ w: number; h: number; dpr: number; blockH: number; blockW: number; margin: number }>;
  const blocksRef = useRef<BlockT[]>([]) as Box<BlockT[]>;
  const timeRef = useRef({ last: null as number | null, cycle: -1 }) as Box<{ last: number | null; cycle: number }>;
  const pausedRef = useRef(false) as Box<boolean>;
  const t0Ref = useRef(0) as Box<number>;
  const rafRef = useRef(0) as Box<number>;
  const vars: Vars = { "--duration": duration, "--easing": easing, "--color": color };

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

  function resetBlocks(): void {
    const blockH = sizeRef.current.blockH;
    const list: BlockT[] = [];
    for (let i = 0; i < BLOCKS; i++) list.push({ y: -blockH, vy: 0, state: "waiting" });
    blocksRef.current = list;
  }

  function fit(): void {
    const field = fieldRef.current;
    const cv = cvRef.current;
    if (!field || !cv) return;
    const r = field.getBoundingClientRect();
    const dpr = window.devicePixelRatio || 1;
    const size = sizeRef.current;
    size.w = r.width; size.h = r.height; size.dpr = dpr;
    cv.width = Math.round(r.width * dpr);
    cv.height = Math.round(r.height * dpr);
    const ctx = ctxRef.current;
    if (ctx) ctx.setTransform(dpr, 0, 0, dpr, 0, 0);
    size.blockH = (r.height - 10) / (BLOCKS + 1.4);
    size.blockW = Math.min(r.width * 0.42, size.blockH * 2.6);
    size.margin = (r.height - 10) - BLOCKS * size.blockH;
    resetBlocks();
  }

  function step(sec: number): number {
    const time = timeRef.current;
    if (time.last === null) time.last = sec;
    const dt = Math.min(0.05, Math.max(0, sec - time.last));
    time.last = sec;
    const ci = Math.floor(sec / LOOP);
    if (ci !== time.cycle) { resetBlocks(); time.cycle = ci; }
    const t = sec - ci * LOOP;
    const size = sizeRef.current;
    const list = blocksRef.current;
    let settled = 0;
    for (let i = 0; i < BLOCKS; i++) {
      const b = list[i];
      if (b.state === "waiting") {
        if (t >= i * DROP_INTERVAL) { b.state = "falling"; b.y = -size.blockH; b.vy = 0; }
      }
      if (b.state === "falling") {
        b.vy += GRAVITY * dt;
        b.y += b.vy * dt;
        const floorY = (size.h - size.margin) - (i + 1) * size.blockH;
        if (b.y >= floorY) {
          b.y = floorY;
          b.vy = -b.vy * DAMPING;
          if (Math.abs(b.vy) < REST_V) { b.state = "settled"; b.vy = 0; }
        }
      }
      if (b.state === "settled") settled++;
    }
    return settled;
  }

  function draw(sec: number): void {
    const ctx = ctxRef.current;
    const root = rootRef.current;
    if (!ctx || !root) return;
    const settled = step(sec);
    const size = sizeRef.current;
    const W = size.w, H = size.h;
    const cssv = (n: string) => getComputedStyle(root).getPropertyValue(n).trim();
    const PAPER = cssv("--paper"), FLOOR = cssv("--floor");
    const PALETTE = [cssv("--c1"), cssv("--c2"), cssv("--c3"), cssv("--c4")];

    ctx.clearRect(0, 0, W, H);
    ctx.fillStyle = PAPER;
    ctx.fillRect(0, 0, W, H);
    ctx.fillStyle = FLOOR;
    ctx.fillRect(0, H - size.margin, W, size.margin);

    const cx = W * 0.5;
    const r = 6;
    const list = blocksRef.current;
    for (let i = 0; i < BLOCKS; i++) {
      const b = list[i];
      if (b.state === "waiting") continue;
      const x = cx - size.blockW / 2;
      const y = b.y;
      ctx.fillStyle = PALETTE[i % PALETTE.length];
      ctx.beginPath();
      ctx.moveTo(x + r, y);
      ctx.arcTo(x + size.blockW, y, x + size.blockW, y + size.blockH, r);
      ctx.arcTo(x + size.blockW, y + size.blockH, x, y + size.blockH, r);
      ctx.arcTo(x, y + size.blockH, x, y, r);
      ctx.arcTo(x, y, x + size.blockW, y, r);
      ctx.closePath();
      ctx.fill();
    }

    const pct = Math.round(settled / BLOCKS * 100);
    if (pctRef.current) pctRef.current.textContent = pct + "%";
  }

  function togglePause(): void {
    pausedRef.current = !pausedRef.current;
    const root = rootRef.current;
    if (root) root.classList.toggle("is-paused", pausedRef.current);
  }

  function restart(): void {
    t0Ref.current = performance.now();
    timeRef.current.last = null;
    timeRef.current.cycle = -1;
    resetBlocks();
    draw(0);
  }

  function onKey(e: KeyEvt): void {
    if (e.key === " " || e.key === "Enter") { e.preventDefault(); togglePause(); }
    else if (e.key === "r" || e.key === "R") { e.preventDefault(); restart(); }
  }

  function onClick(): void {
    togglePause();
  }

  function onResize(): void {
    fit();
    if (pausedRef.current || reduced()) draw((performance.now() - t0Ref.current) / 1000);
  }

  function frame(now: number): void {
    if (!pausedRef.current) draw((now - t0Ref.current) / 1000);
    rafRef.current = requestAnimationFrame(frame);
  }

  useEffect(() => {
    const cv = cvRef.current;
    if (!cv) return;
    ctxRef.current = cv.getContext("2d");
    if (!ctxRef.current) return;
    t0Ref.current = performance.now();
    fit();
    window.addEventListener("resize", onResize);
    if (reduced()) {
      const root = rootRef.current;
      if (root) root.classList.add("is-still");
      draw(LOOP * 0.62);
    } else {
      rafRef.current = requestAnimationFrame(frame);
    }
    return () => {
      window.removeEventListener("resize", onResize);
      cancelAnimationFrame(rafRef.current);
    };
  }, []);

  return (
    <main className={styles.stage}>
      <div className={styles.root} ref={rootRef} style={vars}>
        <p className={styles.hint}>
          <svg className={styles.ico} viewBox="0 0 256 256" aria-hidden="true"><g fill="currentColor"><path d="M232 56v56a8 8 0 0 1-16 0V91.3l-25.6 25.7A80 80 0 1 1 174 60a8 8 0 1 1-9 13.2A64 64 0 1 0 179.7 128H216a8 8 0 0 1 0 16h-56a8 8 0 0 1-8-8V80a8 8 0 0 1 16 0v20.7L192.7 76A80.1 80.1 0 0 0 64 128a8 8 0 0 1-16 0a96 96 0 0 1 163.6-68.3L224 71.3V56a8 8 0 0 1 8 8" opacity=".2"/><path d="M224 48a8 8 0 0 0-8 8v15.3l-11.7-11.6a96 96 0 1 0 27.6 51.6a8 8 0 0 0-15.8 2.5a80 80 0 1 1-23-43l-25.7 25.7A8 8 0 0 0 173 112h56a8 8 0 0 0 8-8V56a8 8 0 0 0-13-8"/></g></svg>
          <span>클릭하거나 스페이스바를 누르면 멈추거나 다시 갑니다</span>
        </p>
        <div
          className={styles.field}
          ref={fieldRef}
          role="application"
          aria-label={FIELD_LABEL}
          tabIndex={0}
          onClick={onClick}
          onKeyDown={onKey}
        >
          <canvas className={styles.cv} ref={cvRef}></canvas>
          <b className={styles.badge} aria-hidden="true"><span className={styles.badgeNum} ref={pctRef}>0%</span><span className={styles.badgeUnit}>적재</span></b>
        </div>
      </div>
    </main>
  );
}