05Multi-Touch Scratching Where Each Finger Erases Its Own Path

<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">Exchange coupon</p>
        <p class="scv__prizeSub">Try scratching with several fingers at once</p>
      </div>
      <canvas class="scv__foil" id="foil" 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 05 — pointerdown 마다 e.pointerId 를 Map 키로 저장해 여러 포인터의
// 마지막 좌표를 독립적으로 추적한다. 한 손가락의 move 가 다른 손가락 좌표를 덮지 않는다.

@include stage($stage-ink);

.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.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: #17141a;
  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.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: pointerdown 마다 e.pointerId 를 키로 하는 Map 에 마지막 좌표를 저장해
  // 여러 포인터(멀티터치)가 서로를 덮어쓰지 않고 각자의 경로를 동시에 긁게 한다.
  var root = document.getElementById('scv');
  var zone = document.getElementById('zone');
  var foil = document.getElementById('foil');
  var ctx = foil.getContext('2d');
  var revealBtn = document.getElementById('revealBtn');
  var live = document.getElementById('live');

  var FW = foil.width, FH = foil.height;
  var SCRATCH_BRUSH_R = 14;

  function seedRand(seed) {
    var s = seed >>> 0;
    return function () { s = (s * 1664525 + 1013904223) >>> 0; return s / 4294967296; };
  }
  var foilRand = seedRand(424051);

  function paintFoil() {
    ctx.globalCompositeOperation = 'source-over';
    ctx.clearRect(0, 0, FW, FH);
    var grad = ctx.createLinearGradient(0, 0, FW, FH);
    grad.addColorStop(0, '#5b6cff');
    grad.addColorStop(.5, '#8f9bff');
    grad.addColorStop(1, '#3c46c9');
    ctx.fillStyle = grad;
    ctx.fillRect(0, 0, FW, FH);
    ctx.strokeStyle = 'rgba(23,20,26,.16)';
    ctx.lineWidth = 1;
    for (var i = 0; i < 18; i += 1) {
      var x = foilRand() * FW, y = foilRand() * FH;
      ctx.beginPath();
      ctx.moveTo(x, y);
      ctx.lineTo(x + (foilRand() * 20 - 10), y + (foilRand() * 8 - 4));
      ctx.stroke();
    }
  }

  function scratchAt(x, y) {
    ctx.globalCompositeOperation = 'destination-out';
    ctx.beginPath();
    ctx.arc(x, y, SCRATCH_BRUSH_R, 0, Math.PI * 2);
    ctx.fill();
  }
  function scratchLine(x0, y0, x1, y1) {
    var dx = x1 - x0, dy = y1 - y0;
    var dist = Math.max(1, Math.hypot(dx, dy));
    var steps = Math.max(1, Math.ceil(dist / 6));
    for (var i = 0; i <= steps; i += 1) {
      scratchAt(x0 + dx * (i / steps), y0 + dy * (i / steps));
    }
  }

  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 exchange 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 pointers = new Map(); // pointerId -> {x,y}

  zone.addEventListener('pointerdown', function (e) {
    if (opened) return;
    root.classList.remove('is-demo');
    var p = pos(e);
    pointers.set(e.pointerId, p);
    scratchAt(p.x, p.y);
    if (zone.setPointerCapture) zone.setPointerCapture(e.pointerId);
  });
  zone.addEventListener('pointermove', function (e) {
    if (opened || !pointers.has(e.pointerId)) return;
    var prev = pointers.get(e.pointerId);
    var p = pos(e);
    scratchLine(prev.x, prev.y, p.x, p.y);
    pointers.set(e.pointerId, p);
    if (clearedRatio() > .82) openCard();
  });
  function release(e) { pointers.delete(e.pointerId); }
  window.addEventListener('pointerup', release);
  window.addEventListener('pointercancel', release);

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

  // 데모 경로 두 개를 서로 다른 pointerId(9001·9002)로 흉내내 동시 긁기를 재현한다
  var demoRand = seedRand(424052);
  function buildPath(baseX, baseY, count) {
    var pts = [];
    for (var i = 0; i < count; i += 1) {
      pts.push({
        t: 240 + i * 96,
        x: baseX + (i % 4) * (FW * 0.12) + (demoRand() - .5) * 6,
        y: baseY + Math.floor(i / 4) * (FH * 0.2) + (demoRand() - .5) * 6
      });
    }
    return pts;
  }
  var pathA = buildPath(FW * 0.1, FH * 0.14, 12);
  var pathB = buildPath(FW * 0.52, FH * 0.5, 12);
  var DEMO_LOOP_MS = 4000;
  var stepA = 0, stepB = 0;
  var lastA = null, lastB = null;

  function resetDemo() {
    opened = false;
    root.classList.remove('is-open');
    paintFoil();
    stepA = 0; stepB = 0; lastA = null; lastB = null;
  }
  function advance(path, stepRef, lastRef, tMod) {
    var step = stepRef.v, last = lastRef.v;
    while (step < path.length && path[step].t <= tMod) {
      var p = path[step];
      if (last) scratchLine(last.x, last.y, p.x, p.y); else scratchAt(p.x, p.y);
      last = p;
      step += 1;
    }
    stepRef.v = step; lastRef.v = last;
  }
  function runDemo(tMod) {
    var sa = { v: stepA }, la = { v: lastA };
    var sb = { v: stepB }, lb = { v: lastB };
    advance(pathA, sa, la, tMod);
    advance(pathB, sb, lb, tMod);
    stepA = sa.v; lastA = la.v;
    stepB = sb.v; lastB = lb.v;
    if (clearedRatio() > .82) 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);
    }
    requestAnimationFrame(tick);
  }
  requestAnimationFrame(tick);
})();

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

type Pt = { x: number; y: number };

export default function ScratchCardRevealMultitouchPointer() {
  const rootRef = useRef<HTMLDivElement>(null);
  const zoneRef = useRef<HTMLDivElement>(null);
  const foilRef = 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 revealBtn = revealBtnRef.current;
    const live = liveRef.current;
    if (!root || !zone || !foil || !revealBtn || !live) return;
    const ctx = foil.getContext("2d");
    if (!ctx) return;

    const FW = foil.width, FH = foil.height;
    const SCRATCH_BRUSH_R = 14;

    function seedRand(seed: number) {
      let s = seed >>> 0;
      return function () { s = (s * 1664525 + 1013904223) >>> 0; return s / 4294967296; };
    }
    const foilRand = seedRand(424051);

    function paintFoil() {
      ctx!.globalCompositeOperation = "source-over";
      ctx!.clearRect(0, 0, FW, FH);
      const grad = ctx!.createLinearGradient(0, 0, FW, FH);
      grad.addColorStop(0, "#5b6cff");
      grad.addColorStop(.5, "#8f9bff");
      grad.addColorStop(1, "#3c46c9");
      ctx!.fillStyle = grad;
      ctx!.fillRect(0, 0, FW, FH);
      ctx!.strokeStyle = "rgba(23,20,26,.16)";
      ctx!.lineWidth = 1;
      for (let i = 0; i < 18; i += 1) {
        const x = foilRand() * FW, y = foilRand() * FH;
        ctx!.beginPath();
        ctx!.moveTo(x, y);
        ctx!.lineTo(x + (foilRand() * 20 - 10), y + (foilRand() * 8 - 4));
        ctx!.stroke();
      }
    }

    function scratchAt(x: number, y: number) {
      ctx!.globalCompositeOperation = "destination-out";
      ctx!.beginPath();
      ctx!.arc(x, y, SCRATCH_BRUSH_R, 0, Math.PI * 2);
      ctx!.fill();
    }
    function scratchLine(x0: number, y0: number, x1: number, y1: number) {
      const dx = x1 - x0, dy = y1 - y0;
      const dist = Math.max(1, Math.hypot(dx, dy));
      const steps = Math.max(1, Math.ceil(dist / 6));
      for (let i = 0; i <= steps; i += 1) scratchAt(x0 + dx * (i / steps), y0 + dy * (i / steps));
    }

    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 = "교환 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();
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    const pointers = new Map<number, Pt>();

    function onDown(e: PointerEvent) {
      if (opened) return;
      root!.classList.remove("is-demo");
      const p = pos(e);
      pointers.set(e.pointerId, p);
      scratchAt(p.x, p.y);
      zone!.setPointerCapture?.(e.pointerId);
    }
    function onMove(e: PointerEvent) {
      if (opened || !pointers.has(e.pointerId)) return;
      const prev = pointers.get(e.pointerId)!;
      const p = pos(e);
      scratchLine(prev.x, prev.y, p.x, p.y);
      pointers.set(e.pointerId, p);
      if (clearedRatio() > .82) openCard();
    }
    function release(e: PointerEvent) { pointers.delete(e.pointerId); }
    zone.addEventListener("pointerdown", onDown);
    zone.addEventListener("pointermove", onMove);
    window.addEventListener("pointerup", release);
    window.addEventListener("pointercancel", release);

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

    const demoRand = seedRand(424052);
    type DemoPt = { t: number; x: number; y: number };
    function buildPath(baseX: number, baseY: number, count: number) {
      const pts: DemoPt[] = [];
      for (let i = 0; i < count; i += 1) {
        pts.push({
          t: 240 + i * 96,
          x: baseX + (i % 4) * (FW * 0.12) + (demoRand() - .5) * 6,
          y: baseY + Math.floor(i / 4) * (FH * 0.2) + (demoRand() - .5) * 6
        });
      }
      return pts;
    }
    const pathA = buildPath(FW * 0.1, FH * 0.14, 12);
    const pathB = buildPath(FW * 0.52, FH * 0.5, 12);
    const DEMO_LOOP_MS = 4000;
    let stepA = 0, stepB = 0;
    let lastA: DemoPt | null = null, lastB: DemoPt | null = null;

    function resetDemo() {
      opened = false;
      root!.classList.remove("is-open");
      paintFoil();
      stepA = 0; stepB = 0; lastA = null; lastB = null;
    }
    function advance(path: DemoPt[], step: number, last: DemoPt | null, tMod: number): [number, DemoPt | null] {
      while (step < path.length && path[step].t <= tMod) {
        const p = path[step];
        if (last) scratchLine(last.x, last.y, p.x, p.y); else scratchAt(p.x, p.y);
        last = p;
        step += 1;
      }
      return [step, last];
    }
    function runDemo(tMod: number) {
      [stepA, lastA] = advance(pathA, stepA, lastA, tMod);
      [stepB, lastB] = advance(pathB, stepB, lastB, tMod);
      if (clearedRatio() > .82) 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);
      }
      raf = requestAnimationFrame(tick);
    }
    raf = requestAnimationFrame(tick);

    return () => {
      cancelAnimationFrame(raf);
      zone.removeEventListener("pointerdown", onDown);
      zone.removeEventListener("pointermove", onMove);
      window.removeEventListener("pointerup", release);
      window.removeEventListener("pointercancel", release);
      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}>교환 쿠폰</p>
              <p className={styles.scv__prizeSub}>손가락 여러 개로 동시에 긁어보세요</p>
            </div>
            <canvas className={styles.scv__foil} ref={foilRef} 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>
  );
}