02Page Flip Whose Shadow Is Computed Along the Fold Line

<main class="stage">
<div class="vd is-demo" id="vdRoot">
  <canvas class="vd__canvas" id="vdCanvas" width="480" height="300"></canvas>
  <p class="vd__caption">A Page Flip Whose Shadow Is Calculated Along the Fold Line</p>
</div>
</main>

@use "../../../../site/static/demo-tokens" as *;
@include stage($stage-yellow);

.vd {
  position: relative;
  width: min(92vw, calc(160vh - 12.8vw));
  aspect-ratio: 480 / 300;
  margin: 0 auto;
  border-radius: $r-card;
  overflow: hidden;
  box-shadow: $shadow-raised;
}

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

.vd__caption {
  position: absolute;
  left: $sp-3;
  bottom: $sp-3;
  max-width: 72%;
  margin: 0;
  padding: $sp-1 $sp-3;
  border-radius: $r-pill;
  background: rgba(255, 247, 230, .85);
  color: $subject-ink;
  font-weight: 500;
  font-size: 12px;
  line-height: 1.4;
  pointer-events: none;
}

@media (max-width: 340px) {
  .vd__caption { font-size: 10px; padding: $sp-1 $sp-2; }
}

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

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

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ffd23f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.vd {
  position: relative;
  width: min(92vw, 160vh - 12.8vw);
  aspect-ratio: 480/300;
  margin: 0 auto;
  border-radius: 16px;
  overflow: hidden;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
}

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

.vd__caption {
  position: absolute;
  left: 12px;
  bottom: 12px;
  max-width: 72%;
  margin: 0;
  padding: 4px 12px;
  border-radius: 999px;
  background: rgba(255, 247, 230, 0.85);
  color: #17141a;
  font-weight: 500;
  font-size: 12px;
  line-height: 1.4;
  pointer-events: none;
}

@media (max-width: 340px) {
  .vd__caption {
    font-size: 10px;
    padding: 4px 8px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .vd {
    cursor: default;
  }
}

(function () {
  var root = document.getElementById('vdRoot');
  var canvas = document.getElementById('vdCanvas');
  var ctx = canvas.getContext('2d');
  var wrap = canvas.parentElement;

  var LW = 320, LH = 200;
  var BOOK_L = 96, BOOK_T = 26, BOOK_R = 244, BOOK_B = 176;
  var FOLD_X = BOOK_L;
  var SCENE_BG = '#17141a';
  var BACK_PAGE = '#e7dcc2';
  var FRONT_PAGE = '#fff7e6';
  var FRONT_PAGE_BACK = '#caa96b';
  var LINE_COLOR = 'rgba(23,20,26,.28)';

  function seedRand(seed) {
    var s = seed >>> 0;
    return function () { s = (s * 1664525 + 1013904223) >>> 0; return s / 4294967296; };
  }
  var rand = seedRand(41302);

  function clamp(v, a, b) { return v < a ? a : (v > b ? b : v); }

  function drawLines(x, y, w, h, color) {
    ctx.strokeStyle = color;
    ctx.lineWidth = 1.4;
    for (var i = 0; i < 5; i += 1) {
      var ly = y + h * (0.18 + i * 0.16);
      ctx.beginPath();
      ctx.moveTo(x + w * 0.08, ly);
      ctx.lineTo(x + w * (0.92 - (i % 2) * 0.18), ly);
      ctx.stroke();
    }
  }

  var FLIP_MS = 900;
  var angle = 0;
  function flipAngle(tMs) {
    var p = (tMs % FLIP_MS) / FLIP_MS;                // 0→1, 2.2회/2초
    var w = p < 0.5 ? p * 2 : (1 - p) * 2;             // 삼각파
    return w * Math.PI;
  }

  function pageFlip() {
    var w = BOOK_R - BOOK_L, h = BOOK_B - BOOK_T;
    ctx.fillStyle = BACK_PAGE;
    ctx.fillRect(BOOK_L, BOOK_T, w, h);
    drawLines(BOOK_L, BOOK_T, w, h, LINE_COLOR);

    var c = Math.cos(angle);
    var frontFacing = c >= 0;
    var scaleW = Math.max(0.001, Math.abs(c)) * w;
    ctx.save();
    ctx.translate(FOLD_X, 0);
    ctx.scale(c === 0 ? 0.001 : c, 1);
    ctx.fillStyle = frontFacing ? FRONT_PAGE : FRONT_PAGE_BACK;
    ctx.fillRect(0, BOOK_T, w, h);
    if (frontFacing) drawLines(6, BOOK_T, w - 12, h, LINE_COLOR);
    ctx.restore();

    var shadowW = 6 + Math.abs(Math.sin(angle)) * 46;
    var shadowA = 0.08 + Math.abs(Math.sin(angle)) * 0.34;
    var gx = FOLD_X + scaleW * (frontFacing ? 1 : -1);
    var dir = frontFacing ? -1 : 1;
    var g = ctx.createLinearGradient(gx, 0, gx + shadowW * dir, 0);
    g.addColorStop(0, 'rgba(0,0,0,' + shadowA + ')');
    g.addColorStop(1, 'rgba(0,0,0,0)');
    ctx.fillStyle = g;
    ctx.fillRect(Math.min(gx, gx + shadowW * dir), BOOK_T, shadowW, h);
  }

  function draw() {
    ctx.fillStyle = SCENE_BG;
    ctx.fillRect(0, 0, LW, LH);
    ctx.fillStyle = 'rgba(0,0,0,.3)';
    ctx.fillRect(BOOK_L - 6, BOOK_B + 3, BOOK_R - BOOK_L + 14, 6);
    ctx.strokeStyle = 'rgba(255,247,230,.5)';
    ctx.lineWidth = 2;
    ctx.beginPath(); ctx.moveTo(FOLD_X, BOOK_T - 4); ctx.lineTo(FOLD_X, BOOK_B + 4); ctx.stroke();
    pageFlip();
  }

  function update(dt, tMs) {
    if (reduce) return;
    angle = flipAngle(tMs);
  }

  var cw = 480, ch = 300, sx = 1, sy = 1;
  function fit() {
    var r = wrap.getBoundingClientRect();
    cw = Math.max(1, Math.round(r.width));
    ch = Math.max(1, Math.round(r.height));
    canvas.width = cw; canvas.height = ch;
    sx = cw / LW; sy = ch / LH;
    render();
  }
  function render() {
    ctx.setTransform(1, 0, 0, 1, 0, 0);
    ctx.clearRect(0, 0, cw, ch);
    ctx.save();
    ctx.scale(sx, sy);
    draw();
    ctx.restore();
  }

  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  var playing = !reduce;
  if (reduce) {
    root.classList.remove('is-demo');
    angle = Math.PI / 2;
  }

  var lastTs = null;
  function tick(ts) {
    if (lastTs === null) lastTs = ts;
    var dt = Math.min((ts - lastTs) / 1000, 0.05);
    lastTs = ts;
    if (playing) update(dt, ts);
    render();
    requestAnimationFrame(tick);
  }
  fit();
  window.addEventListener('resize', fit);
  render();
  if (playing) requestAnimationFrame(tick);
})();

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

export default function PageFlipShadowFoldLine() {
  const rootRef = useRef<HTMLDivElement>(null);
  const canvasRef = useRef<HTMLCanvasElement>(null);

  useEffect(() => {
    const root = rootRef.current;
    const canvas = canvasRef.current;
    if (!root || !canvas) return;
    const ctx = canvas.getContext("2d");
    if (!ctx) return;
    const wrap = canvas.parentElement as HTMLElement;

    const LW = 320, LH = 200;
    const BOOK_L = 96, BOOK_T = 26, BOOK_R = 244, BOOK_B = 176;
    const FOLD_X = BOOK_L;
    const SCENE_BG = "#17141a";
    const BACK_PAGE = "#e7dcc2";
    const FRONT_PAGE = "#fff7e6";
    const FRONT_PAGE_BACK = "#caa96b";
    const LINE_COLOR = "rgba(23,20,26,.28)";

    function seedRand(seed: number) {
      let s = seed >>> 0;
      return function () { s = (s * 1664525 + 1013904223) >>> 0; return s / 4294967296; };
    }
    const rand = seedRand(41302);

    function clamp(v: number, a: number, b: number): number { return v < a ? a : (v > b ? b : v); }

    function drawLines(x: number, y: number, w: number, h: number, color: string): void {
      ctx!.strokeStyle = color;
      ctx!.lineWidth = 1.4;
      for (let i = 0; i < 5; i += 1) {
        const ly = y + h * (0.18 + i * 0.16);
        ctx!.beginPath();
        ctx!.moveTo(x + w * 0.08, ly);
        ctx!.lineTo(x + w * (0.92 - (i % 2) * 0.18), ly);
        ctx!.stroke();
      }
    }

    const FLIP_MS = 900;
    let angle = 0;
    function flipAngle(tMs: number): number {
      const p = (tMs % FLIP_MS) / FLIP_MS;
      const w = p < 0.5 ? p * 2 : (1 - p) * 2;
      return w * Math.PI;
    }

    function pageFlip(): void {
      const w = BOOK_R - BOOK_L, h = BOOK_B - BOOK_T;
      ctx!.fillStyle = BACK_PAGE;
      ctx!.fillRect(BOOK_L, BOOK_T, w, h);
      drawLines(BOOK_L, BOOK_T, w, h, LINE_COLOR);

      const c = Math.cos(angle);
      const frontFacing = c >= 0;
      const scaleW = Math.max(0.001, Math.abs(c)) * w;
      ctx!.save();
      ctx!.translate(FOLD_X, 0);
      ctx!.scale(c === 0 ? 0.001 : c, 1);
      ctx!.fillStyle = frontFacing ? FRONT_PAGE : FRONT_PAGE_BACK;
      ctx!.fillRect(0, BOOK_T, w, h);
      if (frontFacing) drawLines(6, BOOK_T, w - 12, h, LINE_COLOR);
      ctx!.restore();

      const shadowW = 6 + Math.abs(Math.sin(angle)) * 46;
      const shadowA = 0.08 + Math.abs(Math.sin(angle)) * 0.34;
      const gx = FOLD_X + scaleW * (frontFacing ? 1 : -1);
      const dir = frontFacing ? -1 : 1;
      const g = ctx!.createLinearGradient(gx, 0, gx + shadowW * dir, 0);
      g.addColorStop(0, "rgba(0,0,0," + shadowA + ")");
      g.addColorStop(1, "rgba(0,0,0,0)");
      ctx!.fillStyle = g;
      ctx!.fillRect(Math.min(gx, gx + shadowW * dir), BOOK_T, shadowW, h);
    }

    function draw(): void {
      ctx!.fillStyle = SCENE_BG;
      ctx!.fillRect(0, 0, LW, LH);
      ctx!.fillStyle = "rgba(0,0,0,.3)";
      ctx!.fillRect(BOOK_L - 6, BOOK_B + 3, BOOK_R - BOOK_L + 14, 6);
      ctx!.strokeStyle = "rgba(255,247,230,.5)";
      ctx!.lineWidth = 2;
      ctx!.beginPath(); ctx!.moveTo(FOLD_X, BOOK_T - 4); ctx!.lineTo(FOLD_X, BOOK_B + 4); ctx!.stroke();
      pageFlip();
    }

    function update(dt: number, tMs: number): void {
      if (reduce) return;
      angle = flipAngle(tMs);
    }

    let cw = 480, ch = 300, sx = 1, sy = 1;
    function fit(): void {
      const r = wrap.getBoundingClientRect();
      cw = Math.max(1, Math.round(r.width));
      ch = Math.max(1, Math.round(r.height));
      canvas!.width = cw; canvas!.height = ch;
      sx = cw / LW; sy = ch / LH;
      render();
    }
    function render(): void {
      ctx!.setTransform(1, 0, 0, 1, 0, 0);
      ctx!.clearRect(0, 0, cw, ch);
      ctx!.save();
      ctx!.scale(sx, sy);
      draw();
      ctx!.restore();
    }

    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    const playing = !reduce;
    if (reduce) {
      root.classList.remove("is-demo");
      angle = Math.PI / 2;
    }

    let lastTs: number | null = null;
    let raf = 0;
    function tick(ts: number): void {
      if (lastTs === null) lastTs = ts;
      const dt = Math.min((ts - lastTs) / 1000, 0.05);
      lastTs = ts;
      if (playing) update(dt, ts);
      render();
      raf = requestAnimationFrame(tick);
    }
    fit();
    window.addEventListener("resize", fit);
    render();
    if (playing) raf = requestAnimationFrame(tick);

    return () => {
      cancelAnimationFrame(raf);
      window.removeEventListener("resize", fit);
    };
  }, []);

  return (
    <main className={styles.stage}>
      <div className={`${styles.vd} is-demo`} ref={rootRef}>
        <canvas className={styles.vd__canvas} ref={canvasRef} width={480} height={300} />
        <p className={styles.vd__caption}>접힘선을 따라 그림자가 계산되는 페이지 플립</p>
      </div>
    </main>
  );
}