03Hover Ripple That Reveals a Second Image

<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">On hover, a ripple spreads and a second image underneath gradually appears along the wave.</p>
</div>
</main>

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

.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: pointer;
  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: #ff4d1f;
  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: pointer;
  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 () {
  // 기법: 호버 시작점에서 시간에 비례해 자라는 파동 반경으로 두 절차적 "사진" A·B 를 마스크 블렌드한다.
  // 반경 경계띠 안에서는 sin 오프셋으로 픽셀을 살짝 밀어 물결 전선이 지나가는 것처럼 보이게 한다.
  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, palette) {
    var rand = seedRand(seed);
    var sky = pctx.createLinearGradient(0, 0, 0, h);
    sky.addColorStop(0, palette[0]);
    sky.addColorStop(1, palette[1]);
    pctx.fillStyle = sky;
    pctx.fillRect(0, 0, w, h);
    var sunX = w * 0.68, sunY = h * 0.26, sunR = h * 0.15;
    var glow = pctx.createRadialGradient(sunX, sunY, 0, sunX, sunY, sunR * 2.5);
    glow.addColorStop(0, palette[2]);
    glow.addColorStop(1, 'rgba(255,255,255,0)');
    pctx.fillStyle = glow;
    pctx.fillRect(0, 0, w, h);
    pctx.beginPath();
    pctx.arc(sunX, sunY, sunR, 0, Math.PI * 2);
    pctx.fillStyle = palette[3];
    pctx.fill();
    for (var i = 0; i < palette[4].length; i += 1) {
      var baseY = h * (0.5 + i * 0.14);
      pctx.beginPath();
      pctx.moveTo(0, h);
      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 * 0.04 + Math.sin(x * 0.15 + i) * h * 0.018;
        pctx.lineTo(x, baseY + n);
      }
      pctx.lineTo(w, h);
      pctx.closePath();
      pctx.fillStyle = palette[4][i];
      pctx.fill();
    }
    for (var k = 0; k < 50; k += 1) {
      var px = rand() * w, py = rand() * h * 0.5, r = rand() * 1.2 + 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 WAVE_FRONT_SPEED = 0.11;
  var WAVE_BAND = 10;

  function makeBase(seed, palette) {
    var c = document.createElement('canvas');
    c.width = CALC_W; c.height = CALC_H;
    var cx = c.getContext('2d');
    drawPhotoBase(cx, CALC_W, CALC_H, seed, palette);
    return cx.getImageData(0, 0, CALC_W, CALC_H).data;
  }

  var bufA = makeBase(419031, ['#bfe3ff', '#fff3da', 'rgba(255,247,225,.9)', '#ffe27a', ['#8fd0c7', '#4a9d8f', '#215a56']]);
  var bufB = makeBase(419032, ['#3a2154', '#8a4fae', 'rgba(255,214,247,.7)', '#ffd6f7', ['#5c3a7a', '#2f1f4a', '#160f28']]);

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

  var origin = { x: CALC_W * 0.5, y: CALC_H * 0.5 };
  var radius = 0;
  var target = 0;

  function renderFrame(t) {
    var maxR = Math.sqrt(CALC_W * CALC_W + CALC_H * CALC_H);
    var idx = 0;
    for (var y = 0; y < CALC_H; y += 1) {
      for (var x = 0; x < CALC_W; x += 1) {
        var dx0 = x - origin.x, dy0 = y - origin.y;
        var dist = Math.sqrt(dx0 * dx0 + dy0 * dy0);
        var band = Math.sin(dist * 0.35 - t * 0.01);
        var mix = 1 - Math.max(0, Math.min(1, (dist - (radius - WAVE_BAND)) / WAVE_BAND));
        var rippled = dist + band * (mix > 0.02 && mix < 0.98 ? 2.4 : 0);
        var a = sampleAt(bufA, x + band * 0.6, y);
        var b = sampleAt(bufB, x - band * 0.6, y);
        var m = mix;
        outBuf[idx] = a[0] + (b[0] - a[0]) * m;
        outBuf[idx + 1] = a[1] + (b[1] - a[1]) * m;
        outBuf[idx + 2] = a[2] + (b[2] - a[2]) * m;
        outBuf[idx + 3] = 255;
        idx += 4;
        void rippled; void maxR;
      }
    }
  }

  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 hovering = false;
  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 * CALC_H
    };
  }
  function startReveal(e) {
    hovering = true;
    if (e) origin = toGrid(e);
    target = Math.sqrt(CALC_W * CALC_W + CALC_H * CALC_H);
    if (reduce) draw(lastElapsed);
  }
  function endReveal() {
    hovering = false;
    target = 0;
    if (reduce) draw(lastElapsed);
  }
  wrap.addEventListener('pointerenter', startReveal);
  wrap.addEventListener('pointermove', function (e) { if (hovering) origin = toGrid(e); });
  wrap.addEventListener('pointerleave', endReveal);
  wrap.addEventListener('focus', function () { startReveal(null); origin = { x: CALC_W * 0.5, y: CALC_H * 0.5 }; });
  wrap.addEventListener('blur', endReveal);

  var VIRTUAL_CYCLE_MS = 1900;
  function virtualHover(t) {
    var phase = (t % VIRTUAL_CYCLE_MS) / VIRTUAL_CYCLE_MS;
    return phase < 0.55;
  }

  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 (!hovering) {
        var on = virtualHover(elapsed);
        target = on ? Math.sqrt(CALC_W * CALC_W + CALC_H * CALC_H) : 0;
        if (on) {
          origin.x = CALC_W * (0.3 + 0.4 * ((Math.sin(elapsed * 0.0007) + 1) / 2));
          origin.y = CALC_H * (0.3 + 0.4 * ((Math.cos(elapsed * 0.0011) + 1) / 2));
        }
      }
      var maxR = Math.sqrt(CALC_W * CALC_W + CALC_H * CALC_H);
      var step = WAVE_FRONT_SPEED * dt * (maxR / 20);
      if (radius < target) radius = Math.min(target, radius + step);
      else if (radius > target) radius = Math.max(target, radius - step);
      draw(elapsed);
    }
    requestAnimationFrame(tick);
  }
  fit();
  window.addEventListener('resize', fit);
  draw(elapsed);
  requestAnimationFrame(tick);
})();

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

export default function RippleCanvasHoverReveal() {
  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, palette: [string, string, string, string, string[]]) {
      const rand = seedRand(seed);
      const sky = pctx.createLinearGradient(0, 0, 0, h);
      sky.addColorStop(0, palette[0]);
      sky.addColorStop(1, palette[1]);
      pctx.fillStyle = sky;
      pctx.fillRect(0, 0, w, h);
      const sunX = w * 0.68, sunY = h * 0.26, sunR = h * 0.15;
      const glow = pctx.createRadialGradient(sunX, sunY, 0, sunX, sunY, sunR * 2.5);
      glow.addColorStop(0, palette[2]);
      glow.addColorStop(1, "rgba(255,255,255,0)");
      pctx.fillStyle = glow;
      pctx.fillRect(0, 0, w, h);
      pctx.beginPath();
      pctx.arc(sunX, sunY, sunR, 0, Math.PI * 2);
      pctx.fillStyle = palette[3];
      pctx.fill();
      const bands = palette[4];
      for (let i = 0; i < bands.length; i += 1) {
        const baseY = h * (0.5 + i * 0.14);
        pctx.beginPath();
        pctx.moveTo(0, h);
        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 * 0.04 + Math.sin(x * 0.15 + i) * h * 0.018;
          pctx.lineTo(x, baseY + n);
        }
        pctx.lineTo(w, h);
        pctx.closePath();
        pctx.fillStyle = bands[i];
        pctx.fill();
      }
      for (let k = 0; k < 50; k += 1) {
        const px = rand() * w, py = rand() * h * 0.5, r = rand() * 1.2 + 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 WAVE_FRONT_SPEED = 0.11;
    const WAVE_BAND = 10;

    function makeBase(seed: number, palette: [string, string, string, string, string[]]) {
      const c = document.createElement("canvas");
      c.width = CALC_W; c.height = CALC_H;
      const cx = c.getContext("2d") as CanvasRenderingContext2D;
      drawPhotoBase(cx, CALC_W, CALC_H, seed, palette);
      return cx.getImageData(0, 0, CALC_W, CALC_H).data;
    }

    const bufA = makeBase(419031, ["#bfe3ff", "#fff3da", "rgba(255,247,225,.9)", "#ffe27a", ["#8fd0c7", "#4a9d8f", "#215a56"]]);
    const bufB = makeBase(419032, ["#3a2154", "#8a4fae", "rgba(255,214,247,.7)", "#ffd6f7", ["#5c3a7a", "#2f1f4a", "#160f28"]]);

    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 sampleAt(buf: Uint8ClampedArray, sx: number, sy: number): [number, number, number] {
      sx = sx < 0 ? 0 : (sx > CALC_W - 1 ? CALC_W - 1 : sx);
      sy = sy < 0 ? 0 : (sy > CALC_H - 1 ? CALC_H - 1 : sy);
      const i = (Math.round(sy) * CALC_W + Math.round(sx)) * 4;
      return [buf[i], buf[i + 1], buf[i + 2]];
    }

    let origin = { x: CALC_W * 0.5, y: CALC_H * 0.5 };
    let radius = 0;
    let target = 0;

    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) {
          const dx0 = x - origin.x, dy0 = y - origin.y;
          const dist = Math.sqrt(dx0 * dx0 + dy0 * dy0);
          const band = Math.sin(dist * 0.35 - t * 0.01);
          const mix = 1 - Math.max(0, Math.min(1, (dist - (radius - WAVE_BAND)) / WAVE_BAND));
          const a = sampleAt(bufA, x + band * 0.6, y);
          const b = sampleAt(bufB, x - band * 0.6, y);
          const m = mix;
          outBuf[idx] = a[0] + (b[0] - a[0]) * m;
          outBuf[idx + 1] = a[1] + (b[1] - a[1]) * m;
          outBuf[idx + 2] = a[2] + (b[2] - a[2]) * m;
          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 hovering = false;
    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 * CALC_H
      };
    }
    function startReveal(e: PointerEvent | null) {
      hovering = true;
      if (e) origin = toGrid(e);
      target = Math.sqrt(CALC_W * CALC_W + CALC_H * CALC_H);
      if (reduce) draw(lastElapsed);
    }
    function endReveal() {
      hovering = false;
      target = 0;
      if (reduce) draw(lastElapsed);
    }
    function onPointerMove(e: PointerEvent) { if (hovering) origin = toGrid(e); }
    function onFocus() { startReveal(null); origin = { x: CALC_W * 0.5, y: CALC_H * 0.5 }; }
    wrap.addEventListener("pointerenter", startReveal as EventListener);
    wrap.addEventListener("pointermove", onPointerMove);
    wrap.addEventListener("pointerleave", endReveal);
    wrap.addEventListener("focus", onFocus);
    wrap.addEventListener("blur", endReveal);

    const VIRTUAL_CYCLE_MS = 1900;
    function virtualHover(t: number) {
      const phase = (t % VIRTUAL_CYCLE_MS) / VIRTUAL_CYCLE_MS;
      return phase < 0.55;
    }

    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 (!hovering) {
          const on = virtualHover(elapsed);
          target = on ? Math.sqrt(CALC_W * CALC_W + CALC_H * CALC_H) : 0;
          if (on) {
            origin.x = CALC_W * (0.3 + 0.4 * ((Math.sin(elapsed * 0.0007) + 1) / 2));
            origin.y = CALC_H * (0.3 + 0.4 * ((Math.cos(elapsed * 0.0011) + 1) / 2));
          }
        }
        const maxR = Math.sqrt(CALC_W * CALC_W + CALC_H * CALC_H);
        const step = WAVE_FRONT_SPEED * dt * (maxR / 20);
        if (radius < target) radius = Math.min(target, radius + step);
        else if (radius > target) radius = Math.max(target, radius - step);
        draw(elapsed);
      }
      raf = requestAnimationFrame(tick);
    }
    fit();
    window.addEventListener("resize", fit);
    draw(elapsed);
    raf = requestAnimationFrame(tick);

    return () => {
      cancelAnimationFrame(raf);
      window.removeEventListener("resize", fit);
      wrap.removeEventListener("pointerenter", startReveal as EventListener);
      wrap.removeEventListener("pointermove", onPointerMove);
      wrap.removeEventListener("pointerleave", endReveal);
      wrap.removeEventListener("focus", onFocus);
      wrap.removeEventListener("blur", endReveal);
    };
  }, []);

  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}>호버하면 물결이 퍼지면서 밑에 깔린 두 번째 이미지가 파동을 따라 서서히 드러난다</p>
      </div>
    </main>
  );
}