09Hero Ripple Scene Combining the Techniques Above

<main class="stage">
<div class="rv is-demo" id="rvRoot" tabindex="0">
  <canvas class="rv__canvas" id="rvCanvas" width="480" height="300"></canvas>
  <p class="rv__caption">Pointer ripples, ambient waves, and a reflection below all combine into one scene.</p>
</div>
</main>

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

.rv {
  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;
  cursor: crosshair;
  outline: none;
}

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

.rv__caption {
  position: absolute;
  left: $sp-3;
  bottom: $sp-3;
  max-width: 78%;
  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) {
  .rv__caption { font-size: 10px; padding: $sp-1 $sp-2; }
}

@media (prefers-reduced-motion: reduce) {
  .rv { cursor: pointer; }
}

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);
}

.rv {
  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);
  cursor: crosshair;
  outline: none;
}

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

.rv__caption {
  position: absolute;
  left: 12px;
  bottom: 12px;
  max-width: 78%;
  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) {
  .rv__caption {
    font-size: 10px;
    padding: 4px 8px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .rv {
    cursor: pointer;
  }
}

(function () {
  // 히어로 장면: 01(포인터 스플래시 2버퍼 파동식) + 02(사인파 잔물결 높이 필드) + 05(하단 반전 반사·sway) 세 기법을 한 캔버스에 합성한다.
  // 01: 포인터/가상 궤도가 splashAt 으로 grid 에 임펄스를 찍고 stepWave 로 전파한다.
  // 02: ambientHeight 다중 사인파가 배경 전체에 잔잔한 굴절을 계속 더한다.
  // 05: 수평선 아래는 위쪽을 상하 반전해 sway 오프셋과 알파 감쇠로 반사처럼 그린다.
  var root = document.getElementById('rvRoot');
  var canvas = document.getElementById('rvCanvas');
  var ctx = canvas.getContext('2d');
  var wrap = canvas.parentElement;

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

  function drawPhotoBase(pctx, w, h, seed) {
    var rand = seedRand(seed);
    var sky = pctx.createLinearGradient(0, 0, 0, h);
    sky.addColorStop(0, '#ffb877');
    sky.addColorStop(1, '#ffe9c2');
    pctx.fillStyle = sky;
    pctx.fillRect(0, 0, w, h);
    var sunX = w * 0.5, sunY = h * 0.28, sunR = h * 0.16;
    var glow = pctx.createRadialGradient(sunX, sunY, 0, sunX, sunY, sunR * 2.8);
    glow.addColorStop(0, 'rgba(255,240,210,.9)');
    glow.addColorStop(1, 'rgba(255,240,210,0)');
    pctx.fillStyle = glow;
    pctx.fillRect(0, 0, w, h);
    pctx.beginPath();
    pctx.arc(sunX, sunY, sunR, 0, Math.PI * 2);
    pctx.fillStyle = '#fff2d0';
    pctx.fill();
    var hillColors = ['#e08a4f', '#a5542c', '#5c2c16'];
    for (var i = 0; i < hillColors.length; i += 1) {
      var baseY = h * (0.42 + i * 0.05);
      pctx.beginPath();
      pctx.moveTo(0, h * 0.5);
      var step = Math.max(2, w / 24);
      for (var x = 0; x <= w; x += step) {
        var n = Math.sin(x * 0.06 + i * 2 + seed * 0.0003) * h * 0.03;
        pctx.lineTo(x, baseY + n);
      }
      pctx.lineTo(w, h * 0.5);
      pctx.closePath();
      pctx.fillStyle = hillColors[i];
      pctx.fill();
    }
    for (var k = 0; k < 40; k += 1) {
      var px = rand() * w, py = rand() * h * 0.45, r = rand() * 1.1 + 0.3;
      pctx.beginPath();
      pctx.arc(px, py, r, 0, Math.PI * 2);
      pctx.fillStyle = 'rgba(255,255,255,' + (0.1 + rand() * 0.2) + ')';
      pctx.fill();
    }
  }

  var CALC_W = 160, CALC_H = 100;
  var HORIZON = Math.round(CALC_H * 0.5);
  var RIPPLE_AMBIENT_WAVE_COUNT = 2;
  var HERO_SPLASH_DECAY_MS = 420;
  var SPLASH_AMP = -420;

  var gridA = new Float32Array(CALC_W * CALC_H);
  var gridB = new Float32Array(CALC_W * CALC_H);
  var damping = Math.pow(0.02, 16 / HERO_SPLASH_DECAY_MS);

  function cellIndex(x, y) { return y * CALC_W + x; }
  function splashAt(gx, gy) {
    gx = Math.round(gx); gy = Math.round(gy);
    for (var dy = -1; dy <= 1; dy += 1) {
      for (var dx = -1; dx <= 1; dx += 1) {
        var x = gx + dx, y = gy + dy;
        if (x > 0 && x < CALC_W - 1 && y > 0 && y < HORIZON - 1) {
          gridA[cellIndex(x, y)] += SPLASH_AMP * (dx === 0 && dy === 0 ? 1 : 0.45);
        }
      }
    }
  }
  function stepWave() {
    for (var y = 1; y < HORIZON - 1; y += 1) {
      var row = y * CALC_W;
      for (var x = 1; x < CALC_W - 1; x += 1) {
        var i = row + x;
        var next = (gridA[i - 1] + gridA[i + 1] + gridA[i - CALC_W] + gridA[i + CALC_W]) / 2 - gridB[i];
        gridB[i] = next * damping;
      }
    }
    var t = gridA; gridA = gridB; gridB = t;
  }

  function ambientHeight(x, y, t) {
    var h = 0;
    for (var i = 0; i < RIPPLE_AMBIENT_WAVE_COUNT; i += 1) {
      var ang = (i / RIPPLE_AMBIENT_WAVE_COUNT) * Math.PI + 0.5;
      var freq = 0.05 + i * 0.021;
      var speed = 0.0017 + i * 0.0009;
      var amp = 4.5 / (i + 1);
      var dir = (i % 2 === 0) ? 1 : -1;
      h += amp * Math.sin(x * Math.cos(ang) * freq + y * Math.sin(ang) * freq + t * speed * dir);
    }
    return h;
  }

  var off = document.createElement('canvas');
  off.width = CALC_W; off.height = CALC_H;
  var octx = off.getContext('2d');
  drawPhotoBase(octx, CALC_W, CALC_H, 419091);
  var baseImg = octx.getImageData(0, 0, CALC_W, CALC_H);
  var baseBuf = baseImg.data;

  var out = document.createElement('canvas');
  out.width = CALC_W; out.height = CALC_H;
  var outCtx = out.getContext('2d');
  var outImg = outCtx.createImageData(CALC_W, CALC_H);
  var outBuf = outImg.data;

  function sampleBase(sx, sy) {
    sx = sx < 0 ? 0 : (sx > CALC_W - 1 ? CALC_W - 1 : sx);
    sy = sy < 0 ? 0 : (sy > HORIZON - 1 ? HORIZON - 1 : sy);
    var i = (Math.round(sy) * CALC_W + Math.round(sx)) * 4;
    return [baseBuf[i], baseBuf[i + 1], baseBuf[i + 2]];
  }

  function upperRGB(x, y, t) {
    var i = y * CALC_W + x;
    var hl = x > 0 ? gridA[i - 1] : gridA[i];
    var hr = x < CALC_W - 1 ? gridA[i + 1] : gridA[i];
    var hu = y > 0 ? gridA[i - CALC_W] : gridA[i];
    var hd = y < HORIZON - 1 ? gridA[i + CALC_W] : gridA[i];
    var amb = ambientHeight(x, y, t);
    var ambX = ambientHeight(x + 1, y, t) - ambientHeight(x - 1, y, t);
    var ambY = ambientHeight(x, y + 1, t) - ambientHeight(x, y - 1, t);
    var dx = (hr - hl) * 0.85 + ambX * 1.1;
    var dy = (hd - hu) * 0.85 + ambY * 1.1;
    var rgb = sampleBase(x + dx, y + dy);
    var shine = Math.max(-30, Math.min(55, (hu - hd) * 0.5 + amb * 4));
    return [
      Math.max(0, Math.min(255, rgb[0] + shine)),
      Math.max(0, Math.min(255, rgb[1] + shine)),
      Math.max(0, Math.min(255, rgb[2] + shine))
    ];
  }

  function renderFrame(t) {
    var idx = 0;
    for (var y = 0; y < CALC_H; y += 1) {
      for (var x = 0; x < CALC_W; x += 1) {
        var rgb;
        if (y < HORIZON) {
          rgb = upperRGB(x, y, t);
        } else {
          var depth = y - HORIZON;
          var srcY = Math.max(0, HORIZON - 1 - depth);
          var sway = Math.sin(depth * 0.5 - t * 0.006) * 2.2 * (depth / (CALC_H - HORIZON));
          var refl = upperRGB(Math.max(0, Math.min(CALC_W - 1, Math.round(x + sway))), srcY, t);
          var alpha = Math.max(0.15, 1 - depth / (CALC_H - HORIZON) * 0.75);
          rgb = [refl[0] * alpha, refl[1] * alpha, refl[2] * alpha];
        }
        outBuf[idx] = rgb[0];
        outBuf[idx + 1] = rgb[1];
        outBuf[idx + 2] = rgb[2];
        outBuf[idx + 3] = 255;
        idx += 4;
      }
    }
  }

  var cw = 480, ch = 300;
  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;
    draw(lastElapsed);
  }

  var lastElapsed = 0;
  function draw(t) {
    lastElapsed = t;
    renderFrame(t);
    outCtx.putImageData(outImg, 0, 0);
    ctx.clearRect(0, 0, cw, ch);
    ctx.drawImage(out, 0, 0, CALC_W, CALC_H, 0, 0, cw, ch);
  }

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

  var pointerActive = false;
  var lastSplashMs = -9999;
  function toGrid(e) {
    var r = wrap.getBoundingClientRect();
    var t0 = (e.touches && e.touches[0]) ? e.touches[0] : e;
    return {
      x: (t0.clientX - r.left) / r.width * CALC_W,
      y: (t0.clientY - r.top) / r.height * HORIZON
    };
  }
  wrap.addEventListener('pointerdown', function (e) {
    pointerActive = true;
    var g = toGrid(e);
    splashAt(g.x, g.y);
    lastSplashMs = performance.now();
    if (reduce) draw(lastElapsed);
  });
  wrap.addEventListener('pointermove', function (e) {
    var g = toGrid(e);
    var now = performance.now();
    if (now - lastSplashMs > 100) {
      splashAt(g.x, g.y);
      lastSplashMs = now;
      if (reduce) draw(lastElapsed);
    }
  });
  wrap.addEventListener('pointerup', function () { pointerActive = false; });
  wrap.addEventListener('pointerleave', function () { pointerActive = false; });
  wrap.addEventListener('keydown', function (e) {
    if (e.key === 'Enter' || e.key === ' ') {
      e.preventDefault();
      splashAt(CALC_W / 2, HORIZON * 0.5);
      if (reduce) draw(lastElapsed);
    }
  });
  wrap.tabIndex = 0;

  var VIRTUAL_INTERVAL_MS = 520;
  var lastVirtualMs = -9999;
  function virtualPointerOrbit(t) {
    return {
      x: CALC_W * (0.28 + 0.44 * ((Math.sin(t * 0.0012) + 1) / 2)),
      y: HORIZON * (0.25 + 0.5 * ((Math.cos(t * 0.0017) + 1) / 2))
    };
  }

  var lastTs = null;
  var elapsed = 0;
  function tick(ts) {
    if (lastTs === null) lastTs = ts;
    var dt = ts - lastTs;
    lastTs = ts;
    if (playing) {
      elapsed += dt;
      if (!pointerActive && elapsed - lastVirtualMs > VIRTUAL_INTERVAL_MS) {
        var p = virtualPointerOrbit(elapsed);
        splashAt(p.x, p.y);
        lastVirtualMs = elapsed;
      }
      stepWave();
      draw(elapsed);
    }
    requestAnimationFrame(tick);
  }
  fit();
  window.addEventListener('resize', fit);
  splashAt(CALC_W * 0.5, HORIZON * 0.4);
  draw(elapsed);
  requestAnimationFrame(tick);
})();

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

// 히어로 장면: 01(포인터 스플래시 2버퍼 파동식) + 02(사인파 잔물결 높이 필드) + 05(하단 반전 반사·sway) 세 기법을 한 캔버스에 합성한다.
// 01: 포인터/가상 궤도가 splashAt 으로 grid 에 임펄스를 찍고 stepWave 로 전파한다.
// 02: ambientHeight 다중 사인파가 배경 전체에 잔잔한 굴절을 계속 더한다.
// 05: 수평선 아래는 위쪽을 상하 반전해 sway 오프셋과 알파 감쇠로 반사처럼 그린다.
export default function RippleCanvasHeroScene() {
  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") as CanvasRenderingContext2D;
    const wrap = canvas.parentElement as HTMLElement;

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

    function drawPhotoBase(pctx: CanvasRenderingContext2D, w: number, h: number, seed: number) {
      const rand = seedRand(seed);
      const sky = pctx.createLinearGradient(0, 0, 0, h);
      sky.addColorStop(0, "#ffb877");
      sky.addColorStop(1, "#ffe9c2");
      pctx.fillStyle = sky;
      pctx.fillRect(0, 0, w, h);
      const sunX = w * 0.5, sunY = h * 0.28, sunR = h * 0.16;
      const glow = pctx.createRadialGradient(sunX, sunY, 0, sunX, sunY, sunR * 2.8);
      glow.addColorStop(0, "rgba(255,240,210,.9)");
      glow.addColorStop(1, "rgba(255,240,210,0)");
      pctx.fillStyle = glow;
      pctx.fillRect(0, 0, w, h);
      pctx.beginPath();
      pctx.arc(sunX, sunY, sunR, 0, Math.PI * 2);
      pctx.fillStyle = "#fff2d0";
      pctx.fill();
      const hillColors = ["#e08a4f", "#a5542c", "#5c2c16"];
      for (let i = 0; i < hillColors.length; i += 1) {
        const baseY = h * (0.42 + i * 0.05);
        pctx.beginPath();
        pctx.moveTo(0, h * 0.5);
        const step = Math.max(2, w / 24);
        for (let x = 0; x <= w; x += step) {
          const n = Math.sin(x * 0.06 + i * 2 + seed * 0.0003) * h * 0.03;
          pctx.lineTo(x, baseY + n);
        }
        pctx.lineTo(w, h * 0.5);
        pctx.closePath();
        pctx.fillStyle = hillColors[i];
        pctx.fill();
      }
      for (let k = 0; k < 40; k += 1) {
        const px = rand() * w, py = rand() * h * 0.45, r = rand() * 1.1 + 0.3;
        pctx.beginPath();
        pctx.arc(px, py, r, 0, Math.PI * 2);
        pctx.fillStyle = "rgba(255,255,255," + (0.1 + rand() * 0.2) + ")";
        pctx.fill();
      }
    }

    const CALC_W = 160, CALC_H = 100;
    const HORIZON = Math.round(CALC_H * 0.5);
    const RIPPLE_AMBIENT_WAVE_COUNT = 2;
    const HERO_SPLASH_DECAY_MS = 420;
    const SPLASH_AMP = -420;

    let gridA = new Float32Array(CALC_W * CALC_H);
    let gridB = new Float32Array(CALC_W * CALC_H);
    const damping = Math.pow(0.02, 16 / HERO_SPLASH_DECAY_MS);

    function cellIndex(x: number, y: number) { return y * CALC_W + x; }
    function splashAt(gx: number, gy: number) {
      gx = Math.round(gx); gy = Math.round(gy);
      for (let dy = -1; dy <= 1; dy += 1) {
        for (let dx = -1; dx <= 1; dx += 1) {
          const x = gx + dx, y = gy + dy;
          if (x > 0 && x < CALC_W - 1 && y > 0 && y < HORIZON - 1) {
            gridA[cellIndex(x, y)] += SPLASH_AMP * (dx === 0 && dy === 0 ? 1 : 0.45);
          }
        }
      }
    }
    function stepWave() {
      for (let y = 1; y < HORIZON - 1; y += 1) {
        const row = y * CALC_W;
        for (let x = 1; x < CALC_W - 1; x += 1) {
          const i = row + x;
          const next = (gridA[i - 1] + gridA[i + 1] + gridA[i - CALC_W] + gridA[i + CALC_W]) / 2 - gridB[i];
          gridB[i] = next * damping;
        }
      }
      const t = gridA; gridA = gridB; gridB = t;
    }

    function ambientHeight(x: number, y: number, t: number) {
      let h = 0;
      for (let i = 0; i < RIPPLE_AMBIENT_WAVE_COUNT; i += 1) {
        const ang = (i / RIPPLE_AMBIENT_WAVE_COUNT) * Math.PI + 0.5;
        const freq = 0.05 + i * 0.021;
        const speed = 0.0017 + i * 0.0009;
        const amp = 4.5 / (i + 1);
        const dir = (i % 2 === 0) ? 1 : -1;
        h += amp * Math.sin(x * Math.cos(ang) * freq + y * Math.sin(ang) * freq + t * speed * dir);
      }
      return h;
    }

    const off = document.createElement("canvas");
    off.width = CALC_W; off.height = CALC_H;
    const octx = off.getContext("2d") as CanvasRenderingContext2D;
    drawPhotoBase(octx, CALC_W, CALC_H, 419091);
    const baseBuf = octx.getImageData(0, 0, CALC_W, CALC_H).data;

    const out = document.createElement("canvas");
    out.width = CALC_W; out.height = CALC_H;
    const outCtx = out.getContext("2d") as CanvasRenderingContext2D;
    const outImg = outCtx.createImageData(CALC_W, CALC_H);
    const outBuf = outImg.data;

    function sampleBase(sx: number, sy: number): [number, number, number] {
      sx = sx < 0 ? 0 : (sx > CALC_W - 1 ? CALC_W - 1 : sx);
      sy = sy < 0 ? 0 : (sy > HORIZON - 1 ? HORIZON - 1 : sy);
      const i = (Math.round(sy) * CALC_W + Math.round(sx)) * 4;
      return [baseBuf[i], baseBuf[i + 1], baseBuf[i + 2]];
    }

    function upperRGB(x: number, y: number, t: number): [number, number, number] {
      const i = y * CALC_W + x;
      const hl = x > 0 ? gridA[i - 1] : gridA[i];
      const hr = x < CALC_W - 1 ? gridA[i + 1] : gridA[i];
      const hu = y > 0 ? gridA[i - CALC_W] : gridA[i];
      const hd = y < HORIZON - 1 ? gridA[i + CALC_W] : gridA[i];
      const amb = ambientHeight(x, y, t);
      const ambX = ambientHeight(x + 1, y, t) - ambientHeight(x - 1, y, t);
      const ambY = ambientHeight(x, y + 1, t) - ambientHeight(x, y - 1, t);
      const dx = (hr - hl) * 0.85 + ambX * 1.1;
      const dy = (hd - hu) * 0.85 + ambY * 1.1;
      const rgb = sampleBase(x + dx, y + dy);
      const shine = Math.max(-30, Math.min(55, (hu - hd) * 0.5 + amb * 4));
      return [
        Math.max(0, Math.min(255, rgb[0] + shine)),
        Math.max(0, Math.min(255, rgb[1] + shine)),
        Math.max(0, Math.min(255, rgb[2] + shine))
      ];
    }

    function renderFrame(t: number) {
      let idx = 0;
      for (let y = 0; y < CALC_H; y += 1) {
        for (let x = 0; x < CALC_W; x += 1) {
          let rgb: [number, number, number];
          if (y < HORIZON) {
            rgb = upperRGB(x, y, t);
          } else {
            const depth = y - HORIZON;
            const srcY = Math.max(0, HORIZON - 1 - depth);
            const sway = Math.sin(depth * 0.5 - t * 0.006) * 2.2 * (depth / (CALC_H - HORIZON));
            const refl = upperRGB(Math.max(0, Math.min(CALC_W - 1, Math.round(x + sway))), srcY, t);
            const alpha = Math.max(0.15, 1 - depth / (CALC_H - HORIZON) * 0.75);
            rgb = [refl[0] * alpha, refl[1] * alpha, refl[2] * alpha];
          }
          outBuf[idx] = rgb[0];
          outBuf[idx + 1] = rgb[1];
          outBuf[idx + 2] = rgb[2];
          outBuf[idx + 3] = 255;
          idx += 4;
        }
      }
    }

    let cw = 480, ch = 300;
    let lastElapsed = 0;
    function draw(t: number) {
      lastElapsed = t;
      renderFrame(t);
      outCtx.putImageData(outImg, 0, 0);
      ctx.clearRect(0, 0, cw, ch);
      ctx.drawImage(out, 0, 0, CALC_W, CALC_H, 0, 0, cw, ch);
    }

    function fit() {
      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;
      draw(lastElapsed);
    }

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

    let pointerActive = false;
    let lastSplashMs = -9999;
    function toGrid(e: PointerEvent) {
      const r = wrap.getBoundingClientRect();
      return {
        x: (e.clientX - r.left) / r.width * CALC_W,
        y: (e.clientY - r.top) / r.height * HORIZON
      };
    }
    function onPointerDown(e: PointerEvent) {
      pointerActive = true;
      const g = toGrid(e);
      splashAt(g.x, g.y);
      lastSplashMs = performance.now();
      if (reduce) draw(lastElapsed);
    }
    function onPointerMove(e: PointerEvent) {
      const g = toGrid(e);
      const now = performance.now();
      if (now - lastSplashMs > 100) {
        splashAt(g.x, g.y);
        lastSplashMs = now;
        if (reduce) draw(lastElapsed);
      }
    }
    function onPointerUp() { pointerActive = false; }
    function onPointerLeave() { pointerActive = false; }
    function onKeyDown(e: KeyboardEvent) {
      if (e.key === "Enter" || e.key === " ") {
        e.preventDefault();
        splashAt(CALC_W / 2, HORIZON * 0.5);
        if (reduce) draw(lastElapsed);
      }
    }
    wrap.addEventListener("pointerdown", onPointerDown);
    wrap.addEventListener("pointermove", onPointerMove);
    wrap.addEventListener("pointerup", onPointerUp);
    wrap.addEventListener("pointerleave", onPointerLeave);
    wrap.addEventListener("keydown", onKeyDown);
    wrap.tabIndex = 0;

    const VIRTUAL_INTERVAL_MS = 520;
    let lastVirtualMs = -9999;
    function virtualPointerOrbit(t: number) {
      return {
        x: CALC_W * (0.28 + 0.44 * ((Math.sin(t * 0.0012) + 1) / 2)),
        y: HORIZON * (0.25 + 0.5 * ((Math.cos(t * 0.0017) + 1) / 2))
      };
    }

    let lastTs: number | null = null;
    let elapsed = 0;
    let raf = 0;
    function tick(ts: number) {
      if (lastTs === null) lastTs = ts;
      const dt = ts - lastTs;
      lastTs = ts;
      if (playing) {
        elapsed += dt;
        if (!pointerActive && elapsed - lastVirtualMs > VIRTUAL_INTERVAL_MS) {
          const p = virtualPointerOrbit(elapsed);
          splashAt(p.x, p.y);
          lastVirtualMs = elapsed;
        }
        stepWave();
        draw(elapsed);
      }
      raf = requestAnimationFrame(tick);
    }
    fit();
    window.addEventListener("resize", fit);
    splashAt(CALC_W * 0.5, HORIZON * 0.4);
    draw(elapsed);
    raf = requestAnimationFrame(tick);

    return () => {
      cancelAnimationFrame(raf);
      window.removeEventListener("resize", fit);
      wrap.removeEventListener("pointerdown", onPointerDown);
      wrap.removeEventListener("pointermove", onPointerMove);
      wrap.removeEventListener("pointerup", onPointerUp);
      wrap.removeEventListener("pointerleave", onPointerLeave);
      wrap.removeEventListener("keydown", onKeyDown);
    };
  }, []);

  return (
    <main className={styles.stage}>
      <div className={`${styles.rv} is-demo`} ref={rootRef} tabIndex={0}>
        <canvas className={styles.rv__canvas} ref={canvasRef} width={480} height={300} />
        <p className={styles.rv__caption}>포인터 물결과 잔잔한 파동, 아래쪽 반사까지 한 장면 안에서 합쳐 보여준다</p>
      </div>
    </main>
  );
}