08우산 뒤로는 가려지는 빗줄기

<main class="stage">
<div class="rn is-demo" id="rnRoot">
  <canvas class="rn__canvas" id="rnCanvas" width="480" height="300"></canvas>
  <p class="rn__caption">우산 모양의 경계 안에 빗줄기 좌표가 들어오는지 매 프레임 판정해, 경계 안쪽에 들어온 부분만 그리지 않아 우산이 실제로 비를 막는 것처럼 보인다</p>
</div>
</main>

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

.rn {
  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;
  background: #eef1ef;
}

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

.rn__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(23, 20, 26, .78);
  color: $subject-cream;
  font-weight: 500;
  font-size: 12px;
  line-height: 1.4;
  pointer-events: none;
}

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

@media (prefers-reduced-motion: reduce) {
  .rn { 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);
}

.rn {
  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);
  background: #eef1ef;
}

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

.rn__caption {
  position: absolute;
  left: 12px;
  bottom: 12px;
  max-width: 78%;
  margin: 0;
  padding: 4px 12px;
  border-radius: 999px;
  background: rgba(23, 20, 26, 0.78);
  color: #fff7e6;
  font-weight: 500;
  font-size: 12px;
  line-height: 1.4;
  pointer-events: none;
}

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

(function () {
  // 기법: umbrellaOcclusion() 이 타원 돔 방정식으로 각 빗줄기 점이 우산 안인지 매 프레임 판정한다.
  // 안에 들면 그 줄기를 지우고 대신 UMBRELLA_BOUNCE_COUNT 개의 튐 방울을 돔 표면에서 바깥으로 쏘아
  // 포물선으로 떨어뜨린다(umbrellaBounce) — 우산 밖 줄기는 그냥 통과해 바닥까지 떨어진다.
  var root = document.getElementById('rnRoot');
  var canvas = document.getElementById('rnCanvas');
  var ctx = canvas.getContext('2d');
  var wrap = canvas.parentElement;

  var CALC_W = 160, CALC_H = 100;
  var UMBRELLA_RADIUS_PX = 34;
  var UMBRELLA_HEIGHT_PX = 16;
  var UMBRELLA_BOUNCE_COUNT = 5;
  var UMBRELLA_SWAY_PX = 6;
  var UMBRELLA_SWAY_PERIOD_MS = 4200;
  var UMBRELLA_BOUNCE_GRAVITY = 240;
  var RAIN_STREAK_COUNT = 80;

  function seedRand(seed) {
    var s = seed >>> 0;
    return function () { s = (s * 1664525 + 1013904223) >>> 0; return s / 4294967296; };
  }
  var rRand = seedRand(431081);

  var umbY = 58, umbBaseX = CALC_W / 2;

  var streaks = [];
  for (var i = 0; i < RAIN_STREAK_COUNT; i += 1) {
    streaks.push({ x: rRand() * CALC_W, y: rRand() * CALC_H, speed: 110 + rRand() * 80, thick: 0.6 + rRand() * 1 });
  }
  var bounces = [];

  function umbrellaOcclusion(x, y, umbX) {
    var dx = (x - umbX) / UMBRELLA_RADIUS_PX;
    if (Math.abs(dx) > 1) return false;
    var edgeY = umbY - UMBRELLA_HEIGHT_PX * Math.sqrt(Math.max(0, 1 - dx * dx));
    return y >= edgeY && y <= umbY;
  }

  function umbrellaBounce(x, y, umbX) {
    var dx = (x - umbX) / UMBRELLA_RADIUS_PX;
    var nx = dx;
    for (var i = 0; i < UMBRELLA_BOUNCE_COUNT; i += 1) {
      var spread = (rRand() - 0.5) * 40;
      bounces.push({
        x: x,
        y: y,
        vx: nx * (40 + rRand() * 30) + spread,
        vy: -(30 + rRand() * 40),
        born: 0,
        life: 380 + rRand() * 200
      });
    }
  }

  function stepSim(dtS, nowMs) {
    var umbX = umbBaseX + Math.sin((nowMs / UMBRELLA_SWAY_PERIOD_MS) * Math.PI * 2) * UMBRELLA_SWAY_PX;
    for (var i = 0; i < streaks.length; i += 1) {
      var s = streaks[i];
      var prevY = s.y;
      s.y += s.speed * dtS;
      if (!(prevY >= umbY) && umbrellaOcclusion(s.x, s.y, umbX)) {
        umbrellaBounce(s.x, umbY - 1, umbX);
        s.y = -4 - rRand() * 10;
        s.x = rRand() * CALC_W;
      }
      if (s.y > CALC_H + 4) { s.y = -4 - rRand() * 6; s.x = rRand() * CALC_W; }
    }
    for (var b = bounces.length - 1; b >= 0; b -= 1) {
      var p = bounces[b];
      p.born += dtS * 1000;
      p.vy += UMBRELLA_BOUNCE_GRAVITY * dtS;
      p.x += p.vx * dtS;
      p.y += p.vy * dtS;
      if (p.born > p.life) bounces.splice(b, 1);
    }
  }

  var cw = 480, ch = 300, elapsedGlobal = 0;
  function draw(nowMs) {
    var sx = cw / CALC_W, sy = ch / CALC_H;
    var umbX = umbBaseX + Math.sin((nowMs / UMBRELLA_SWAY_PERIOD_MS) * Math.PI * 2) * UMBRELLA_SWAY_PX;
    ctx.clearRect(0, 0, cw, ch);
    ctx.fillStyle = '#eef1ef';
    ctx.fillRect(0, 0, cw, ch);

    ctx.strokeStyle = 'rgba(90,110,140,0.5)';
    for (var i = 0; i < streaks.length; i += 1) {
      var s = streaks[i];
      var x = s.x * sx, y = s.y * sy;
      ctx.lineWidth = Math.max(0.6, s.thick * ((sx + sy) / 2));
      ctx.beginPath();
      ctx.moveTo(x, y);
      ctx.lineTo(x, y - s.thick * 4 * sy);
      ctx.stroke();
    }

    for (var b = 0; b < bounces.length; b += 1) {
      var p = bounces[b];
      var f = 1 - p.born / p.life;
      ctx.fillStyle = 'rgba(90,110,140,' + Math.max(0, f * 0.8).toFixed(3) + ')';
      ctx.beginPath();
      ctx.arc(p.x * sx, p.y * sy, Math.max(0.8, 1.6 * f * ((sx + sy) / 2)), 0, Math.PI * 2);
      ctx.fill();
    }

    var cx = umbX * sx, cy = umbY * sy, rx = UMBRELLA_RADIUS_PX * sx, ry = UMBRELLA_HEIGHT_PX * sy;
    ctx.fillStyle = '#2c2430';
    ctx.beginPath();
    ctx.ellipse(cx, cy, rx, ry, 0, Math.PI, Math.PI * 2);
    ctx.lineTo(cx + rx, cy);
    ctx.closePath();
    ctx.fill();

    ctx.strokeStyle = 'rgba(255,255,255,0.18)';
    ctx.lineWidth = 1;
    for (var k = -2; k <= 2; k += 1) {
      var t = k / 2.4;
      var ex = cx + t * rx;
      var ey = cy - Math.sqrt(Math.max(0, 1 - t * t)) * ry;
      ctx.beginPath();
      ctx.moveTo(cx, cy - ry * 0.2);
      ctx.lineTo(ex, ey);
      ctx.stroke();
    }

    ctx.strokeStyle = '#2c2430';
    ctx.lineWidth = Math.max(1.2, 1.4 * ((sx + sy) / 2));
    ctx.beginPath();
    ctx.moveTo(cx, cy);
    ctx.lineTo(cx, cy + ry * 3.2);
    ctx.quadraticCurveTo(cx, cy + ry * 4.2, cx + rx * 0.22, cy + ry * 4);
    ctx.stroke();
  }

  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(elapsedGlobal);
  }

  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  var elapsed = 0;
  if (reduce) root.classList.remove('is-demo');
  var warmSteps = reduce ? 30 : 45;
  for (var w = 0; w < warmSteps; w += 1) { elapsed += 20; stepSim(0.02, elapsed); }
  elapsedGlobal = elapsed;

  var lastTs = null;
  function tick(ts) {
    if (lastTs === null) lastTs = ts;
    var dt = Math.min(ts - lastTs, 48);
    lastTs = ts;
    if (!reduce) {
      elapsed += dt;
      elapsedGlobal = elapsed;
      stepSim(dt / 1000, elapsed);
      draw(elapsed);
    }
    requestAnimationFrame(tick);
  }
  fit();
  window.addEventListener('resize', fit);
  draw(elapsed);
  requestAnimationFrame(tick);
})();

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

type Streak = { x: number; y: number; speed: number; thick: number };
type Bounce = { x: number; y: number; vx: number; vy: number; born: number; life: number };

export default function RainEffectCanvasUmbrellaOcclusion() {
  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 CALC_W = 160, CALC_H = 100;
    const UMBRELLA_RADIUS_PX = 34;
    const UMBRELLA_HEIGHT_PX = 16;
    const UMBRELLA_BOUNCE_COUNT = 5;
    const UMBRELLA_SWAY_PX = 6;
    const UMBRELLA_SWAY_PERIOD_MS = 4200;
    const UMBRELLA_BOUNCE_GRAVITY = 240;
    const RAIN_STREAK_COUNT = 80;

    function seedRand(seed: number) {
      let s = seed >>> 0;
      return function () { s = (s * 1664525 + 1013904223) >>> 0; return s / 4294967296; };
    }
    const rRand = seedRand(431082);

    const umbY = 58, umbBaseX = CALC_W / 2;

    const streaks: Streak[] = [];
    for (let i = 0; i < RAIN_STREAK_COUNT; i += 1) {
      streaks.push({ x: rRand() * CALC_W, y: rRand() * CALC_H, speed: 110 + rRand() * 80, thick: 0.6 + rRand() * 1 });
    }
    const bounces: Bounce[] = [];

    function umbrellaOcclusion(x: number, y: number, umbX: number) {
      const dx = (x - umbX) / UMBRELLA_RADIUS_PX;
      if (Math.abs(dx) > 1) return false;
      const edgeY = umbY - UMBRELLA_HEIGHT_PX * Math.sqrt(Math.max(0, 1 - dx * dx));
      return y >= edgeY && y <= umbY;
    }

    function umbrellaBounce(x: number, y: number, umbX: number) {
      const dx = (x - umbX) / UMBRELLA_RADIUS_PX;
      const nx = dx;
      for (let i = 0; i < UMBRELLA_BOUNCE_COUNT; i += 1) {
        const spread = (rRand() - 0.5) * 40;
        bounces.push({
          x, y,
          vx: nx * (40 + rRand() * 30) + spread,
          vy: -(30 + rRand() * 40),
          born: 0,
          life: 380 + rRand() * 200,
        });
      }
    }

    function stepSim(dtS: number, nowMs: number) {
      const umbX = umbBaseX + Math.sin((nowMs / UMBRELLA_SWAY_PERIOD_MS) * Math.PI * 2) * UMBRELLA_SWAY_PX;
      for (let i = 0; i < streaks.length; i += 1) {
        const s = streaks[i];
        const prevY = s.y;
        s.y += s.speed * dtS;
        if (!(prevY >= umbY) && umbrellaOcclusion(s.x, s.y, umbX)) {
          umbrellaBounce(s.x, umbY - 1, umbX);
          s.y = -4 - rRand() * 10;
          s.x = rRand() * CALC_W;
        }
        if (s.y > CALC_H + 4) { s.y = -4 - rRand() * 6; s.x = rRand() * CALC_W; }
      }
      for (let b = bounces.length - 1; b >= 0; b -= 1) {
        const p = bounces[b];
        p.born += dtS * 1000;
        p.vy += UMBRELLA_BOUNCE_GRAVITY * dtS;
        p.x += p.vx * dtS;
        p.y += p.vy * dtS;
        if (p.born > p.life) bounces.splice(b, 1);
      }
    }

    let cw = 480, ch = 300, elapsedGlobal = 0;
    function draw(nowMs: number) {
      const sx = cw / CALC_W, sy = ch / CALC_H;
      const umbX = umbBaseX + Math.sin((nowMs / UMBRELLA_SWAY_PERIOD_MS) * Math.PI * 2) * UMBRELLA_SWAY_PX;
      ctx!.clearRect(0, 0, cw, ch);
      ctx!.fillStyle = "#eef1ef";
      ctx!.fillRect(0, 0, cw, ch);

      ctx!.strokeStyle = "rgba(90,110,140,0.5)";
      for (let i = 0; i < streaks.length; i += 1) {
        const s = streaks[i];
        const x = s.x * sx, y = s.y * sy;
        ctx!.lineWidth = Math.max(0.6, s.thick * ((sx + sy) / 2));
        ctx!.beginPath();
        ctx!.moveTo(x, y);
        ctx!.lineTo(x, y - s.thick * 4 * sy);
        ctx!.stroke();
      }

      for (let b = 0; b < bounces.length; b += 1) {
        const p = bounces[b];
        const f = 1 - p.born / p.life;
        ctx!.fillStyle = "rgba(90,110,140," + Math.max(0, f * 0.8).toFixed(3) + ")";
        ctx!.beginPath();
        ctx!.arc(p.x * sx, p.y * sy, Math.max(0.8, 1.6 * f * ((sx + sy) / 2)), 0, Math.PI * 2);
        ctx!.fill();
      }

      const cx = umbX * sx, cy = umbY * sy, rx = UMBRELLA_RADIUS_PX * sx, ry = UMBRELLA_HEIGHT_PX * sy;
      ctx!.fillStyle = "#2c2430";
      ctx!.beginPath();
      ctx!.ellipse(cx, cy, rx, ry, 0, Math.PI, Math.PI * 2);
      ctx!.lineTo(cx + rx, cy);
      ctx!.closePath();
      ctx!.fill();

      ctx!.strokeStyle = "rgba(255,255,255,0.18)";
      ctx!.lineWidth = 1;
      for (let k = -2; k <= 2; k += 1) {
        const t = k / 2.4;
        const ex = cx + t * rx;
        const ey = cy - Math.sqrt(Math.max(0, 1 - t * t)) * ry;
        ctx!.beginPath();
        ctx!.moveTo(cx, cy - ry * 0.2);
        ctx!.lineTo(ex, ey);
        ctx!.stroke();
      }

      ctx!.strokeStyle = "#2c2430";
      ctx!.lineWidth = Math.max(1.2, 1.4 * ((sx + sy) / 2));
      ctx!.beginPath();
      ctx!.moveTo(cx, cy);
      ctx!.lineTo(cx, cy + ry * 3.2);
      ctx!.quadraticCurveTo(cx, cy + ry * 4.2, cx + rx * 0.22, cy + ry * 4);
      ctx!.stroke();
      elapsedGlobal = nowMs;
    }

    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(elapsedGlobal);
    }

    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    let elapsed = 0;
    if (reduce) root.classList.remove("is-demo");
    const warmSteps = reduce ? 30 : 45;
    for (let w = 0; w < warmSteps; w += 1) { elapsed += 20; stepSim(0.02, elapsed); }
    elapsedGlobal = elapsed;

    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) {
        elapsed += dt;
        elapsedGlobal = elapsed;
        stepSim(dt / 1000, elapsed);
        draw(elapsed);
      }
      raf = requestAnimationFrame(tick);
    }
    fit();
    window.addEventListener("resize", fit);
    draw(elapsed);
    raf = requestAnimationFrame(tick);

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

  return (
    <main className={styles.stage}>
      <div className={`${styles.rn} is-demo`} ref={rootRef}>
        <canvas className={styles.rn__canvas} ref={canvasRef} width={480} height={300} />
        <p className={styles.rn__caption}>우산 모양의 경계 안에 빗줄기 좌표가 들어오는지 매 프레임 판정해, 경계 안쪽에 들어온 부분만 그리지 않아 우산이 실제로 비를 막는 것처럼 보인다</p>
      </div>
    </main>
  );
}