03Foil Flakes That Fly Off Under Gravity

<main class="stage">
<div class="scv is-demo" id="scv">
  <div class="scv__card">
    <p class="scv__label">Scratch card</p>
    <div class="scv__zone" id="zone">
      <div class="scv__prize">
        <p class="scv__prizeTitle">Birthday coupon</p>
        <p class="scv__prizeSub">Flakes fly off with every scratch</p>
      </div>
      <canvas class="scv__foil" id="foil" width="280" height="150" aria-hidden="true"></canvas>
      <canvas class="scv__flakes" id="flakes" width="280" height="150" aria-hidden="true"></canvas>
    </div>
    <button type="button" class="scv__reveal" id="revealBtn">Reveal instantly</button>
    <p class="scv__live" id="live" aria-live="polite"></p>
  </div>
</div>
</main>

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

// 스크래치 카드 03 — spawnFlake() 가 긁는 지점마다 작은 조각을 만들고 stepFlakes() 가
// FLAKE_GRAVITY_PX_S2 로 낙하·회전을 적분한다. 조각 캔버스(scv__flakes)는 은박 캔버스 위에
// pointer-events:none 으로 겹쳐 긁기 입력을 가리지 않는다.

@include stage($stage-orange);

.scv { display: flex; justify-content: center; width: 100%; }
.scv__card {
  width: min(100%, 300px); background: $subject-blue-deep; color: $subject-cream;
  border-radius: $r-card; box-shadow: $shadow-raised; padding: $sp-4;
}
.scv__label { margin: 0 0 $sp-2; font-weight: 800; font-size: 12px; letter-spacing: .04em; }
.scv__zone {
  position: relative; border-radius: $r-control; overflow: hidden;
  aspect-ratio: 280 / 150; background: $stage-paper;
}
.scv__prize {
  position: absolute; inset: 0; display: flex; flex-direction: column; align-items: center;
  justify-content: center; gap: $sp-1; text-align: center; padding: $sp-2; z-index: 0;
}
.scv__prizeTitle { margin: 0; font-weight: 800; font-size: clamp(18px, 6vw, 22px); color: $subject-blue-deep; }
.scv__prizeSub { margin: 0; font-weight: 700; font-size: 11px; color: rgba(23, 20, 26, .68); }
.scv__foil { position: absolute; inset: 0; width: 100%; height: 100%; touch-action: none; z-index: 1; }
.scv__flakes { position: absolute; inset: 0; width: 100%; height: 100%; pointer-events: none; z-index: 2; }
.scv.is-open .scv__foil { visibility: hidden; }
.scv__reveal {
  margin-top: $sp-2; border: 0; cursor: pointer; background: $subject-cream; color: $subject-blue-deep;
  border-radius: $r-pill; font-family: inherit; font-weight: 800; font-size: 11px; padding: $sp-1 $sp-3; line-height: 1.3;
}
.scv__reveal:focus-visible { outline: 3px solid $stage-paper; outline-offset: 2px; }
.scv__live { margin: $sp-1 0 0; min-height: 1em; font-weight: 700; font-size: 10px; color: $subject-cream; }

@media (max-width: 340px) {
  .scv__card { padding: $sp-3; }
}

@media (max-height: 220px) {
  .stage { padding: $sp-2; }
  .scv__card { padding: $sp-2 $sp-3; }
  .scv__label { margin: 0 0 $sp-1; }
  .scv__zone { aspect-ratio: 280 / 88; }
  .scv__reveal { margin-top: $sp-1; }
  .scv__live { margin-top: $sp-1; min-height: .9em; }
}


@media (prefers-reduced-motion: reduce) {
  .scv { cursor: default; }
}

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);
}

.scv {
  display: flex;
  justify-content: center;
  width: 100%;
}

.scv__card {
  width: min(100%, 300px);
  background: #0a4fe8;
  color: #fff7e6;
  border-radius: 16px;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  padding: 16px;
}

.scv__label {
  margin: 0 0 8px;
  font-weight: 800;
  font-size: 12px;
  letter-spacing: 0.04em;
}

.scv__zone {
  position: relative;
  border-radius: 12px;
  overflow: hidden;
  aspect-ratio: 280/150;
  background: #ffffff;
}

.scv__prize {
  position: absolute;
  inset: 0;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 4px;
  text-align: center;
  padding: 8px;
  z-index: 0;
}

.scv__prizeTitle {
  margin: 0;
  font-weight: 800;
  font-size: clamp(18px, 6vw, 22px);
  color: #0a4fe8;
}

.scv__prizeSub {
  margin: 0;
  font-weight: 700;
  font-size: 11px;
  color: rgba(23, 20, 26, 0.68);
}

.scv__foil {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  touch-action: none;
  z-index: 1;
}

.scv__flakes {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  pointer-events: none;
  z-index: 2;
}

.scv.is-open .scv__foil {
  visibility: hidden;
}

.scv__reveal {
  margin-top: 8px;
  border: 0;
  cursor: pointer;
  background: #fff7e6;
  color: #0a4fe8;
  border-radius: 999px;
  font-family: inherit;
  font-weight: 800;
  font-size: 11px;
  padding: 4px 12px;
  line-height: 1.3;
}

.scv__reveal:focus-visible {
  outline: 3px solid #ffffff;
  outline-offset: 2px;
}

.scv__live {
  margin: 4px 0 0;
  min-height: 1em;
  font-weight: 700;
  font-size: 10px;
  color: #fff7e6;
}

@media (max-width: 340px) {
  .scv__card {
    padding: 12px;
  }
}
@media (max-height: 220px) {
  .stage {
    padding: 8px;
  }
  .scv__card {
    padding: 8px 12px;
  }
  .scv__label {
    margin: 0 0 4px;
  }
  .scv__zone {
    aspect-ratio: 280/88;
  }
  .scv__reveal {
    margin-top: 4px;
  }
  .scv__live {
    margin-top: 4px;
    min-height: 0.9em;
  }
}
@media (prefers-reduced-motion: reduce) {
  .scv {
    cursor: default;
  }
}

(function () {
  // 기법: 긁는 지점마다 spawnFlake() 로 작은 은박 조각을 만들어 중력(FLAKE_GRAVITY_PX_S2)과
  // 각속도를 준다. stepFlakes() 가 매 프레임 속도·회전을 적분해 조각이 카드 경계 밖으로
  // 튕겨 나가며 사라지게 한다 — 파티클 엔진 없이 배열 하나로 발생·낙하·소멸을 계산한다.
  var root = document.getElementById('scv');
  var zone = document.getElementById('zone');
  var foil = document.getElementById('foil');
  var ctx = foil.getContext('2d');
  var flakesCanvas = document.getElementById('flakes');
  var fctx = flakesCanvas.getContext('2d');
  var revealBtn = document.getElementById('revealBtn');
  var live = document.getElementById('live');

  var FW = foil.width, FH = foil.height;
  var SCRATCH_BRUSH_R = 15;
  var FLAKE_GRAVITY_PX_S2 = 400;
  var FLAKE_LIFE_MS = 900;

  function seedRand(seed) {
    var s = seed >>> 0;
    return function () { s = (s * 1664525 + 1013904223) >>> 0; return s / 4294967296; };
  }
  var foilRand = seedRand(424031);
  var flakeRand = seedRand(424032);

  function paintFoil() {
    ctx.globalCompositeOperation = 'source-over';
    ctx.clearRect(0, 0, FW, FH);
    var grad = ctx.createLinearGradient(0, 0, FW, FH);
    grad.addColorStop(0, '#d8863f');
    grad.addColorStop(.5, '#f3c98a');
    grad.addColorStop(1, '#c9752c');
    ctx.fillStyle = grad;
    ctx.fillRect(0, 0, FW, FH);
    ctx.strokeStyle = 'rgba(23,20,26,.16)';
    ctx.lineWidth = 1;
    for (var i = 0; i < 20; i += 1) {
      var x = foilRand() * FW, y = foilRand() * FH;
      ctx.beginPath();
      ctx.moveTo(x, y);
      ctx.lineTo(x + (foilRand() * 22 - 11), y + (foilRand() * 8 - 4));
      ctx.stroke();
    }
  }

  var flakes = [];
  function spawnFlake(x, y, vx, vy) {
    if (reduce) return;
    flakes.push({
      x: x, y: y, vx: vx, vy: vy,
      rot: flakeRand() * Math.PI * 2,
      angVel: (flakeRand() - .5) * 10,
      born: 0, size: 3 + flakeRand() * 3
    });
  }
  function stepFlakes(dtMs, nowMs) {
    var dtS = dtMs / 1000;
    var alive = [];
    for (var i = 0; i < flakes.length; i += 1) {
      var f = flakes[i];
      f.vy += FLAKE_GRAVITY_PX_S2 * dtS;
      f.x += f.vx * dtS;
      f.y += f.vy * dtS;
      f.rot += f.angVel * dtS;
      f.born += dtMs;
      if (f.born < FLAKE_LIFE_MS && f.x > -8 && f.x < FW + 8 && f.y < FH + 8) alive.push(f);
    }
    flakes = alive;
  }
  function drawFlakes() {
    fctx.clearRect(0, 0, FW, FH);
    for (var i = 0; i < flakes.length; i += 1) {
      var f = flakes[i];
      var fade = Math.max(0, 1 - f.born / FLAKE_LIFE_MS);
      fctx.save();
      fctx.translate(f.x, f.y);
      fctx.rotate(f.rot);
      fctx.fillStyle = 'rgba(243,201,138,' + fade + ')';
      fctx.fillRect(-f.size / 2, -f.size / 2, f.size, f.size);
      fctx.restore();
    }
  }

  function scratchAt(x, y, vx, vy) {
    ctx.globalCompositeOperation = 'destination-out';
    ctx.beginPath();
    ctx.arc(x, y, SCRATCH_BRUSH_R, 0, Math.PI * 2);
    ctx.fill();
    spawnFlake(x, y, vx, vy - 30);
    spawnFlake(x + (flakeRand() - .5) * 6, y + (flakeRand() - .5) * 6, -vx * .6, vy - 60);
  }

  function clearedRatio() {
    var data = ctx.getImageData(0, 0, FW, FH).data;
    var clear = 0, total = data.length / 4;
    for (var i = 3; i < data.length; i += 4) { if (data[i] < 40) clear += 1; }
    return clear / total;
  }

  var opened = false;
  function openCard() {
    if (opened) return;
    opened = true;
    ctx.globalCompositeOperation = 'destination-out';
    ctx.fillRect(0, 0, FW, FH);
    root.classList.add('is-open');
    live.textContent = 'The birthday coupon is revealed';
  }

  function pos(e) {
    var r = foil.getBoundingClientRect();
    return { x: (e.clientX - r.left) * (FW / r.width), y: (e.clientY - r.top) * (FH / r.height) };
  }

  paintFoil();
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  var dragging = false, lastPos = null;

  zone.addEventListener('pointerdown', function (e) {
    if (opened) return;
    root.classList.remove('is-demo');
    dragging = true;
    var p = pos(e);
    scratchAt(p.x, p.y, 0, 0);
    lastPos = p;
    if (zone.setPointerCapture) zone.setPointerCapture(e.pointerId);
  });
  zone.addEventListener('pointermove', function (e) {
    if (!dragging || opened) return;
    var p = pos(e);
    var vx = lastPos ? (p.x - lastPos.x) * 6 : 0;
    var vy = lastPos ? (p.y - lastPos.y) * 6 : 0;
    scratchAt(p.x, p.y, vx, vy);
    lastPos = p;
    if (clearedRatio() > .85) openCard();
  });
  window.addEventListener('pointerup', function () { dragging = false; lastPos = null; });

  revealBtn.addEventListener('click', function () { root.classList.remove('is-demo'); openCard(); });

  // 격자 미리보기 — 같은 scratchAt() 경로를 스케줄로 호출해 조각을 계속 만든다
  var demoRand = seedRand(424033);
  var demoPath = [];
  (function buildDemoPath() {
    for (var i = 0; i < 22; i += 1) {
      demoPath.push({
        t: 230 + i * 82,
        x: (FW * 0.14) + (i % 6) * (FW * 0.15) + (demoRand() - .5) * 6,
        y: (FH * 0.24) + Math.floor(i / 6) * (FH * 0.26) + (demoRand() - .5) * 6,
        vx: (demoRand() - .5) * 90,
        vy: -40 - demoRand() * 40
      });
    }
  })();
  var DEMO_LOOP_MS = 3800;
  var demoStep = 0;

  function resetDemo() {
    opened = false;
    root.classList.remove('is-open');
    paintFoil();
    flakes = [];
    demoStep = 0;
  }
  function runDemo(tMod) {
    while (demoStep < demoPath.length && demoPath[demoStep].t <= tMod) {
      var p = demoPath[demoStep];
      scratchAt(p.x, p.y, p.vx, p.vy);
      demoStep += 1;
    }
    if (clearedRatio() > .85) openCard();
  }

  if (reduce) root.classList.remove('is-demo');
  var elapsed = 0, lastTs = null;
  function tick(ts) {
    if (lastTs === null) lastTs = ts;
    var dt = Math.min(ts - lastTs, 48);
    lastTs = ts;
    if (!reduce && root.classList.contains('is-demo')) {
      elapsed += dt;
      var tMod = elapsed % DEMO_LOOP_MS;
      if (tMod < dt) resetDemo();
      runDemo(tMod);
    }
    if (!reduce) stepFlakes(dt, elapsed);
    drawFlakes();
    requestAnimationFrame(tick);
  }
  requestAnimationFrame(tick);
})();

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

type Flake = { x: number; y: number; vx: number; vy: number; rot: number; angVel: number; born: number; size: number };

export default function ScratchCardRevealFlakeGravityParticle() {
  const rootRef = useRef<HTMLDivElement>(null);
  const zoneRef = useRef<HTMLDivElement>(null);
  const foilRef = useRef<HTMLCanvasElement>(null);
  const flakesRef = useRef<HTMLCanvasElement>(null);
  const revealBtnRef = useRef<HTMLButtonElement>(null);
  const liveRef = useRef<HTMLParagraphElement>(null);

  useEffect(() => {
    const root = rootRef.current;
    const zone = zoneRef.current;
    const foil = foilRef.current;
    const flakesCanvas = flakesRef.current;
    const revealBtn = revealBtnRef.current;
    const live = liveRef.current;
    if (!root || !zone || !foil || !flakesCanvas || !revealBtn || !live) return;
    const ctx = foil.getContext("2d");
    const fctx = flakesCanvas.getContext("2d");
    if (!ctx || !fctx) return;

    const FW = foil.width, FH = foil.height;
    const SCRATCH_BRUSH_R = 15;
    const FLAKE_GRAVITY_PX_S2 = 400;
    const FLAKE_LIFE_MS = 900;

    function seedRand(seed: number) {
      let s = seed >>> 0;
      return function () { s = (s * 1664525 + 1013904223) >>> 0; return s / 4294967296; };
    }
    const foilRand = seedRand(424031);
    const flakeRand = seedRand(424032);

    function paintFoil() {
      ctx!.globalCompositeOperation = "source-over";
      ctx!.clearRect(0, 0, FW, FH);
      const grad = ctx!.createLinearGradient(0, 0, FW, FH);
      grad.addColorStop(0, "#d8863f");
      grad.addColorStop(.5, "#f3c98a");
      grad.addColorStop(1, "#c9752c");
      ctx!.fillStyle = grad;
      ctx!.fillRect(0, 0, FW, FH);
      ctx!.strokeStyle = "rgba(23,20,26,.16)";
      ctx!.lineWidth = 1;
      for (let i = 0; i < 20; i += 1) {
        const x = foilRand() * FW, y = foilRand() * FH;
        ctx!.beginPath();
        ctx!.moveTo(x, y);
        ctx!.lineTo(x + (foilRand() * 22 - 11), y + (foilRand() * 8 - 4));
        ctx!.stroke();
      }
    }

    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    let flakes: Flake[] = [];
    function spawnFlake(x: number, y: number, vx: number, vy: number) {
      if (reduce) return;
      flakes.push({
        x, y, vx, vy,
        rot: flakeRand() * Math.PI * 2,
        angVel: (flakeRand() - .5) * 10,
        born: 0, size: 3 + flakeRand() * 3
      });
    }
    function stepFlakes(dtMs: number) {
      const dtS = dtMs / 1000;
      const alive: Flake[] = [];
      for (let i = 0; i < flakes.length; i += 1) {
        const f = flakes[i];
        f.vy += FLAKE_GRAVITY_PX_S2 * dtS;
        f.x += f.vx * dtS;
        f.y += f.vy * dtS;
        f.rot += f.angVel * dtS;
        f.born += dtMs;
        if (f.born < FLAKE_LIFE_MS && f.x > -8 && f.x < FW + 8 && f.y < FH + 8) alive.push(f);
      }
      flakes = alive;
    }
    function drawFlakes() {
      fctx!.clearRect(0, 0, FW, FH);
      for (let i = 0; i < flakes.length; i += 1) {
        const f = flakes[i];
        const fade = Math.max(0, 1 - f.born / FLAKE_LIFE_MS);
        fctx!.save();
        fctx!.translate(f.x, f.y);
        fctx!.rotate(f.rot);
        fctx!.fillStyle = "rgba(243,201,138," + fade + ")";
        fctx!.fillRect(-f.size / 2, -f.size / 2, f.size, f.size);
        fctx!.restore();
      }
    }

    function scratchAt(x: number, y: number, vx: number, vy: number) {
      ctx!.globalCompositeOperation = "destination-out";
      ctx!.beginPath();
      ctx!.arc(x, y, SCRATCH_BRUSH_R, 0, Math.PI * 2);
      ctx!.fill();
      spawnFlake(x, y, vx, vy - 30);
      spawnFlake(x + (flakeRand() - .5) * 6, y + (flakeRand() - .5) * 6, -vx * .6, vy - 60);
    }

    function clearedRatio() {
      const data = ctx!.getImageData(0, 0, FW, FH).data;
      let clear = 0;
      const total = data.length / 4;
      for (let i = 3; i < data.length; i += 4) { if (data[i] < 40) clear += 1; }
      return clear / total;
    }

    let opened = false;
    function openCard() {
      if (opened) return;
      opened = true;
      ctx!.globalCompositeOperation = "destination-out";
      ctx!.fillRect(0, 0, FW, FH);
      root!.classList.add("is-open");
      live!.textContent = "생일 쿠폰이 열렸어요";
    }

    function pos(e: PointerEvent) {
      const r = foil!.getBoundingClientRect();
      return { x: (e.clientX - r.left) * (FW / r.width), y: (e.clientY - r.top) * (FH / r.height) };
    }

    paintFoil();
    let dragging = false;
    let lastPos: { x: number; y: number } | null = null;

    function onDown(e: PointerEvent) {
      if (opened) return;
      root!.classList.remove("is-demo");
      dragging = true;
      const p = pos(e);
      scratchAt(p.x, p.y, 0, 0);
      lastPos = p;
      zone!.setPointerCapture?.(e.pointerId);
    }
    function onMove(e: PointerEvent) {
      if (!dragging || opened) return;
      const p = pos(e);
      const vx = lastPos ? (p.x - lastPos.x) * 6 : 0;
      const vy = lastPos ? (p.y - lastPos.y) * 6 : 0;
      scratchAt(p.x, p.y, vx, vy);
      lastPos = p;
      if (clearedRatio() > .85) openCard();
    }
    function onUp() { dragging = false; lastPos = null; }
    zone.addEventListener("pointerdown", onDown);
    zone.addEventListener("pointermove", onMove);
    window.addEventListener("pointerup", onUp);

    function onReveal() { root!.classList.remove("is-demo"); openCard(); }
    revealBtn.addEventListener("click", onReveal);

    const demoRand = seedRand(424033);
    type DemoPt = { t: number; x: number; y: number; vx: number; vy: number };
    const demoPath: DemoPt[] = [];
    for (let i = 0; i < 22; i += 1) {
      demoPath.push({
        t: 230 + i * 82,
        x: (FW * 0.14) + (i % 6) * (FW * 0.15) + (demoRand() - .5) * 6,
        y: (FH * 0.24) + Math.floor(i / 6) * (FH * 0.26) + (demoRand() - .5) * 6,
        vx: (demoRand() - .5) * 90,
        vy: -40 - demoRand() * 40
      });
    }
    const DEMO_LOOP_MS = 3800;
    let demoStep = 0;

    function resetDemo() {
      opened = false;
      root!.classList.remove("is-open");
      paintFoil();
      flakes = [];
      demoStep = 0;
    }
    function runDemo(tMod: number) {
      while (demoStep < demoPath.length && demoPath[demoStep].t <= tMod) {
        const p = demoPath[demoStep];
        scratchAt(p.x, p.y, p.vx, p.vy);
        demoStep += 1;
      }
      if (clearedRatio() > .85) openCard();
    }

    if (reduce) root.classList.remove("is-demo");
    let elapsed = 0;
    let lastTs: number | null = null;
    let raf = 0;
    function tick(ts: number) {
      if (lastTs === null) lastTs = ts;
      const dt = Math.min(ts - lastTs, 48);
      lastTs = ts;
      if (!reduce && root!.classList.contains("is-demo")) {
        elapsed += dt;
        const tMod = elapsed % DEMO_LOOP_MS;
        if (tMod < dt) resetDemo();
        runDemo(tMod);
      }
      if (!reduce) stepFlakes(dt);
      drawFlakes();
      raf = requestAnimationFrame(tick);
    }
    raf = requestAnimationFrame(tick);

    return () => {
      cancelAnimationFrame(raf);
      zone.removeEventListener("pointerdown", onDown);
      zone.removeEventListener("pointermove", onMove);
      window.removeEventListener("pointerup", onUp);
      revealBtn.removeEventListener("click", onReveal);
    };
  }, []);

  return (
    <main className={styles.stage}>
      <div className={`${styles.scv} is-demo`} ref={rootRef}>
        <div className={styles.scv__card}>
          <p className={styles.scv__label}>스크래치 카드</p>
          <div className={styles.scv__zone} ref={zoneRef}>
            <div className={styles.scv__prize}>
              <p className={styles.scv__prizeTitle}>생일 쿠폰</p>
              <p className={styles.scv__prizeSub}>긁을 때마다 조각이 튀어 나가요</p>
            </div>
            <canvas className={styles.scv__foil} ref={foilRef} width={280} height={150} aria-hidden="true" />
            <canvas className={styles.scv__flakes} ref={flakesRef} width={280} height={150} aria-hidden="true" />
          </div>
          <button type="button" className={styles.scv__reveal} ref={revealBtnRef}>한 번에 보기</button>
          <p className={styles.scv__live} ref={liveRef} aria-live="polite"></p>
        </div>
      </div>
    </main>
  );
}