04Open-book Gutter That Darkens by Its Bend Curvature

<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">An Open-book Scene Darkened by the Gutter's Curvature</p>
</div>
</main>

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

.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: #ffffff;
  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 CENTER = LW / 2;
  var PAGE_T = 26, PAGE_B = 176;
  var HALF_W = 108;
  var SCENE_BG = '#17141a';
  var PAPER = '#fff7e6';
  var BEND_MAX_RAD = Math.PI / 180 * 26;
  var PERIOD_MS = 1000;

  function seedRand(seed) {
    var s = seed >>> 0;
    return function () { s = (s * 1664525 + 1013904223) >>> 0; return s / 4294967296; };
  }
  var rand = seedRand(41304);

  function clamp(v, a, b) { return v < a ? a : (v > b ? b : v); }
  function shadeHex(hex, f) {
    var r = parseInt(hex.slice(1, 3), 16), g = parseInt(hex.slice(3, 5), 16), b = parseInt(hex.slice(5, 7), 16);
    r = clamp(Math.round(r * f), 0, 255); g = clamp(Math.round(g * f), 0, 255); b = clamp(Math.round(b * f), 0, 255);
    return 'rgb(' + r + ',' + g + ',' + b + ')';
  }

  var bendAngle = 0;
  function gutterBend(tMs) {
    return BEND_MAX_RAD * (0.5 - 0.5 * Math.cos(2 * Math.PI * tMs / PERIOD_MS));
  }

  function drawLines(x, y, w, h) {
    ctx.strokeStyle = 'rgba(23,20,26,.22)';
    ctx.lineWidth = 1.2;
    for (var i = 0; i < 5; i += 1) {
      var ly = y + h * (0.16 + i * 0.17);
      ctx.beginPath(); ctx.moveTo(x, ly); ctx.lineTo(x + w, ly); ctx.stroke();
    }
  }

  function drawPageSide(sign) {
    var strip = 4, h = PAGE_B - PAGE_T;
    for (var dx = 0; dx <= HALF_W; dx += strip) {
      var t = dx / HALF_W;                             // 0=골 · 1=바깥 가장자리
      var curveTheta = (1 - t) * bendAngle;             // 골에 가까울수록 곡률이 크다
      var comp = Math.sin(curveTheta) * 12;             // 골 쪽으로 눌리는 폭(px)
      var x = CENTER + sign * (dx - comp);
      var shade = 1 - (1 - t) * (bendAngle / BEND_MAX_RAD) * 0.42;
      ctx.fillStyle = shadeHex(PAPER, shade);
      ctx.fillRect(sign > 0 ? x : x - strip, PAGE_T, strip + 1, h);
    }
  }

  function draw() {
    ctx.fillStyle = SCENE_BG;
    ctx.fillRect(0, 0, LW, LH);
    ctx.fillStyle = 'rgba(0,0,0,.3)';
    ctx.fillRect(CENTER - HALF_W - 6, PAGE_B + 3, HALF_W * 2 + 12, 6);

    drawPageSide(-1);
    drawPageSide(1);
    drawLines(CENTER - HALF_W + 8, PAGE_T, HALF_W - 16, PAGE_B - PAGE_T);
    drawLines(CENTER + 8, PAGE_T, HALF_W - 16, PAGE_B - PAGE_T);

    var gutterA = 0.12 + (bendAngle / BEND_MAX_RAD) * 0.42;
    var gutterW = 8 + (bendAngle / BEND_MAX_RAD) * 20;
    var g = ctx.createLinearGradient(CENTER - gutterW, 0, CENTER + gutterW, 0);
    g.addColorStop(0, 'rgba(0,0,0,0)');
    g.addColorStop(0.5, 'rgba(0,0,0,' + gutterA + ')');
    g.addColorStop(1, 'rgba(0,0,0,0)');
    ctx.fillStyle = g;
    ctx.fillRect(CENTER - gutterW, PAGE_T, gutterW * 2, PAGE_B - PAGE_T);
  }

  function update(dt, tMs) {
    if (reduce) return;
    bendAngle = gutterBend(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'); bendAngle = BEND_MAX_RAD * 0.6; }

  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 "./BookOpenGutterBendShade.module.scss";

export default function BookOpenGutterBendShade() {
  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 CENTER = LW / 2;
    const PAGE_T = 26, PAGE_B = 176;
    const HALF_W = 108;
    const SCENE_BG = "#17141a";
    const PAPER = "#fff7e6";
    const BEND_MAX_RAD = (Math.PI / 180) * 26;
    const PERIOD_MS = 1000;

    function seedRand(seed: number) {
      let s = seed >>> 0;
      return function () { s = (s * 1664525 + 1013904223) >>> 0; return s / 4294967296; };
    }
    const rand = seedRand(41304);

    function clamp(v: number, a: number, b: number): number { return v < a ? a : (v > b ? b : v); }
    function shadeHex(hex: string, f: number): string {
      let r = parseInt(hex.slice(1, 3), 16), g = parseInt(hex.slice(3, 5), 16), b = parseInt(hex.slice(5, 7), 16);
      r = clamp(Math.round(r * f), 0, 255); g = clamp(Math.round(g * f), 0, 255); b = clamp(Math.round(b * f), 0, 255);
      return "rgb(" + r + "," + g + "," + b + ")";
    }

    let bendAngle = 0;
    function gutterBend(tMs: number): number {
      return BEND_MAX_RAD * (0.5 - 0.5 * Math.cos((2 * Math.PI * tMs) / PERIOD_MS));
    }

    function drawLines(x: number, y: number, w: number, h: number): void {
      ctx!.strokeStyle = "rgba(23,20,26,.22)";
      ctx!.lineWidth = 1.2;
      for (let i = 0; i < 5; i += 1) {
        const ly = y + h * (0.16 + i * 0.17);
        ctx!.beginPath(); ctx!.moveTo(x, ly); ctx!.lineTo(x + w, ly); ctx!.stroke();
      }
    }

    function drawPageSide(sign: number): void {
      const strip = 4, h = PAGE_B - PAGE_T;
      for (let dx = 0; dx <= HALF_W; dx += strip) {
        const t = dx / HALF_W;
        const curveTheta = (1 - t) * bendAngle;
        const comp = Math.sin(curveTheta) * 12;
        const x = CENTER + sign * (dx - comp);
        const shade = 1 - (1 - t) * (bendAngle / BEND_MAX_RAD) * 0.42;
        ctx!.fillStyle = shadeHex(PAPER, shade);
        ctx!.fillRect(sign > 0 ? x : x - strip, PAGE_T, strip + 1, h);
      }
    }

    function draw(): void {
      ctx!.fillStyle = SCENE_BG;
      ctx!.fillRect(0, 0, LW, LH);
      ctx!.fillStyle = "rgba(0,0,0,.3)";
      ctx!.fillRect(CENTER - HALF_W - 6, PAGE_B + 3, HALF_W * 2 + 12, 6);

      drawPageSide(-1);
      drawPageSide(1);
      drawLines(CENTER - HALF_W + 8, PAGE_T, HALF_W - 16, PAGE_B - PAGE_T);
      drawLines(CENTER + 8, PAGE_T, HALF_W - 16, PAGE_B - PAGE_T);

      const gutterA = 0.12 + (bendAngle / BEND_MAX_RAD) * 0.42;
      const gutterW = 8 + (bendAngle / BEND_MAX_RAD) * 20;
      const g = ctx!.createLinearGradient(CENTER - gutterW, 0, CENTER + gutterW, 0);
      g.addColorStop(0, "rgba(0,0,0,0)");
      g.addColorStop(0.5, "rgba(0,0,0," + gutterA + ")");
      g.addColorStop(1, "rgba(0,0,0,0)");
      ctx!.fillStyle = g;
      ctx!.fillRect(CENTER - gutterW, PAGE_T, gutterW * 2, PAGE_B - PAGE_T);
    }

    function update(dt: number, tMs: number): void {
      if (reduce) return;
      bendAngle = gutterBend(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"); bendAngle = BEND_MAX_RAD * 0.6; }

    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}>책 중심 골 곡률로 어두워지는 펼침 장면</p>
      </div>
    </main>
  );
}