07Background Wind Leaning Toward the Pointer Position

<main class="stage">
<div class="rn is-demo" id="rnRoot" tabindex="0" role="img" aria-label="A scene where moving the pointer left or right, or pressing the arrow keys, lays the rain over toward that side">
  <canvas class="rn__canvas" id="rnCanvas" width="480" height="300"></canvas>
  <p class="rn__caption">The wind vector's direction is recalculated by how far the pointer sits from the center, so every streak leans and falls in that same direction while the pointer moves.</p>
  <p class="rn__hint">Move the pointer or press ← →</p>
</div>
</main>

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

.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: #241812;
  cursor: pointer;

  &:focus-visible {
    outline: 3px solid $subject-orange-deep;
    outline-offset: 2px;
  }
}

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

.rn__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;
}

.rn__hint {
  position: absolute;
  right: $sp-3;
  top: $sp-3;
  margin: 0;
  padding: $sp-1 $sp-2;
  border-radius: $r-pill;
  background: rgba(23, 20, 26, .55);
  color: $subject-cream;
  font-size: 11px;
  line-height: 1.4;
  pointer-events: none;
}

@media (max-width: 340px) {
  .rn__caption { font-size: 10px; padding: $sp-1 $sp-2; }
  .rn__hint { display: none; }
}

@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: #ff4d1f;
  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: #241812;
  cursor: pointer;
}
.rn:focus-visible {
  outline: 3px solid #c93000;
  outline-offset: 2px;
}

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

.rn__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;
}

.rn__hint {
  position: absolute;
  right: 12px;
  top: 12px;
  margin: 0;
  padding: 4px 8px;
  border-radius: 999px;
  background: rgba(23, 20, 26, 0.55);
  color: #fff7e6;
  font-size: 11px;
  line-height: 1.4;
  pointer-events: none;
}

@media (max-width: 340px) {
  .rn__caption {
    font-size: 10px;
    padding: 4px 8px;
  }
  .rn__hint {
    display: none;
  }
}
@media (prefers-reduced-motion: reduce) {
  .rn {
    cursor: default;
  }
}

(function () {
  // 기법: windLeanTarget() 이 포인터(또는 가상 포인터) x 위치를 -1~1 로 정규화해 기울기 목표각을 정하고,
  // 실제 기울기는 POINTER_WIND_LERP 비율로 목표각을 매 프레임 뒤쫓는다(즉시 꺾이지 않고 관성처럼 따라감).
  // virtualPointerSweep() 은 실제 입력이 없을 때 같은 함수를 그대로 호출하는 자동 시연 경로.
  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 POINTER_WIND_LERP = 0.06;
  var WIND_LEAN_MAX_DEG = 22;
  var RAIN_STREAK_COUNT = 90;
  var SWEEP_PERIOD_MS = 3400;

  function seedRand(seed) {
    var s = seed >>> 0;
    return function () { s = (s * 1664525 + 1013904223) >>> 0; return s / 4294967296; };
  }
  var rRand = seedRand(431071);

  var streaks = [];
  for (var i = 0; i < RAIN_STREAK_COUNT; i += 1) {
    streaks.push({ x: rRand() * CALC_W, y: rRand() * CALC_H, speed: 100 + rRand() * 80, thick: 0.6 + rRand() * 1.1 });
  }

  var manual = false;
  var pointerNormX = 0;
  var manualReleaseTimer = null;

  function windLeanTarget(normX) {
    return normX * WIND_LEAN_MAX_DEG;
  }

  function virtualPointerSweep(nowMs) {
    return Math.sin((nowMs / SWEEP_PERIOD_MS) * Math.PI * 2);
  }

  var leanDeg = 0;
  function stepSim(dtS, nowMs) {
    var normX = manual ? pointerNormX : virtualPointerSweep(nowMs);
    var target = windLeanTarget(normX);
    leanDeg += (target - leanDeg) * Math.min(1, POINTER_WIND_LERP * (dtS * 60));
    var leanRad = (leanDeg * Math.PI) / 180;
    for (var i = 0; i < streaks.length; i += 1) {
      var s = streaks[i];
      s.y += s.speed * dtS;
      s.x += Math.sin(leanRad) * s.speed * 0.7 * dtS;
      if (s.y > CALC_H + 4) { s.y = -4 - rRand() * 6; s.x = rRand() * CALC_W; }
      if (s.x < -6) s.x = CALC_W + 6;
      if (s.x > CALC_W + 6) s.x = -6;
    }
  }

  var cw = 480, ch = 300;
  function draw() {
    var sx = cw / CALC_W, sy = ch / CALC_H;
    ctx.clearRect(0, 0, cw, ch);
    ctx.fillStyle = 'rgba(38,20,10,0.06)';
    ctx.fillRect(0, 0, cw, ch);
    var leanRad = (leanDeg * Math.PI) / 180;
    var dx = Math.sin(leanRad) * 6, dy = Math.cos(leanRad) * 6;
    ctx.strokeStyle = 'rgba(255,236,214,0.55)';
    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 - dx * s.thick * (sx / 6), y - dy * s.thick * (sy / 6));
      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();
  }

  function setManualFromClientX(clientX) {
    var r = canvas.getBoundingClientRect();
    var normX = ((clientX - r.left) / Math.max(1, r.width)) * 2 - 1;
    pointerNormX = Math.max(-1, Math.min(1, normX));
    manual = true;
    root.classList.remove('is-demo');
    if (manualReleaseTimer) clearTimeout(manualReleaseTimer);
  }

  function scheduleRelease() {
    if (manualReleaseTimer) clearTimeout(manualReleaseTimer);
    manualReleaseTimer = setTimeout(function () { manual = false; }, 2600);
  }

  canvas.addEventListener('pointermove', function (e) {
    setManualFromClientX(e.clientX);
    scheduleRelease();
  });
  canvas.addEventListener('pointerdown', function (e) {
    setManualFromClientX(e.clientX);
    scheduleRelease();
  });
  canvas.addEventListener('pointerleave', function () {
    scheduleRelease();
  });

  root.addEventListener('keydown', function (e) {
    if (e.key === 'ArrowLeft' || e.key === 'ArrowRight') {
      e.preventDefault();
      manual = true;
      root.classList.remove('is-demo');
      var step = e.key === 'ArrowLeft' ? -0.18 : 0.18;
      pointerNormX = Math.max(-1, Math.min(1, pointerNormX + step));
      scheduleRelease();
    }
  });

  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  var elapsed = 0;
  if (reduce) root.classList.remove('is-demo');
  var warmSteps = reduce ? 30 : 40;
  for (var w = 0; w < warmSteps; w += 1) { elapsed += 20; stepSim(0.02, 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;
      stepSim(dt / 1000, elapsed);
      draw();
    }
    requestAnimationFrame(tick);
  }
  fit();
  window.addEventListener('resize', fit);
  draw();
  requestAnimationFrame(tick);
})();

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

type Streak = { x: number; y: number; speed: number; thick: number };

export default function RainEffectCanvasPointerWindLean() {
  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 POINTER_WIND_LERP = 0.06;
    const WIND_LEAN_MAX_DEG = 22;
    const RAIN_STREAK_COUNT = 90;
    const SWEEP_PERIOD_MS = 3400;

    function seedRand(seed: number) {
      let s = seed >>> 0;
      return function () { s = (s * 1664525 + 1013904223) >>> 0; return s / 4294967296; };
    }
    const rRand = seedRand(431072);

    const streaks: Streak[] = [];
    for (let i = 0; i < RAIN_STREAK_COUNT; i += 1) {
      streaks.push({ x: rRand() * CALC_W, y: rRand() * CALC_H, speed: 100 + rRand() * 80, thick: 0.6 + rRand() * 1.1 });
    }

    let manual = false;
    let pointerNormX = 0;
    let manualReleaseTimer: number | undefined;

    function windLeanTarget(normX: number) {
      return normX * WIND_LEAN_MAX_DEG;
    }

    function virtualPointerSweep(nowMs: number) {
      return Math.sin((nowMs / SWEEP_PERIOD_MS) * Math.PI * 2);
    }

    let leanDeg = 0;
    function stepSim(dtS: number, nowMs: number) {
      const normX = manual ? pointerNormX : virtualPointerSweep(nowMs);
      const target = windLeanTarget(normX);
      leanDeg += (target - leanDeg) * Math.min(1, POINTER_WIND_LERP * (dtS * 60));
      const leanRad = (leanDeg * Math.PI) / 180;
      for (let i = 0; i < streaks.length; i += 1) {
        const s = streaks[i];
        s.y += s.speed * dtS;
        s.x += Math.sin(leanRad) * s.speed * 0.7 * dtS;
        if (s.y > CALC_H + 4) { s.y = -4 - rRand() * 6; s.x = rRand() * CALC_W; }
        if (s.x < -6) s.x = CALC_W + 6;
        if (s.x > CALC_W + 6) s.x = -6;
      }
    }

    let cw = 480, ch = 300;
    function draw() {
      const sx = cw / CALC_W, sy = ch / CALC_H;
      ctx!.clearRect(0, 0, cw, ch);
      ctx!.fillStyle = "rgba(38,20,10,0.06)";
      ctx!.fillRect(0, 0, cw, ch);
      const leanRad = (leanDeg * Math.PI) / 180;
      const ddx = Math.sin(leanRad) * 6, ddy = Math.cos(leanRad) * 6;
      ctx!.strokeStyle = "rgba(255,236,214,0.55)";
      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 - ddx * s.thick * (sx / 6), y - ddy * s.thick * (sy / 6));
        ctx!.stroke();
      }
    }

    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();
    }

    function setManualFromClientX(clientX: number) {
      const r = canvas!.getBoundingClientRect();
      const normX = ((clientX - r.left) / Math.max(1, r.width)) * 2 - 1;
      pointerNormX = Math.max(-1, Math.min(1, normX));
      manual = true;
      root!.classList.remove("is-demo");
      if (manualReleaseTimer) window.clearTimeout(manualReleaseTimer);
    }

    function scheduleRelease() {
      if (manualReleaseTimer) window.clearTimeout(manualReleaseTimer);
      manualReleaseTimer = window.setTimeout(function () { manual = false; }, 2600);
    }

    function onPointerMove(e: PointerEvent) { setManualFromClientX(e.clientX); scheduleRelease(); }
    function onPointerDown(e: PointerEvent) { setManualFromClientX(e.clientX); scheduleRelease(); }
    function onPointerLeave() { scheduleRelease(); }
    function onKeyDown(e: KeyboardEvent) {
      if (e.key === "ArrowLeft" || e.key === "ArrowRight") {
        e.preventDefault();
        manual = true;
        root!.classList.remove("is-demo");
        const step = e.key === "ArrowLeft" ? -0.18 : 0.18;
        pointerNormX = Math.max(-1, Math.min(1, pointerNormX + step));
        scheduleRelease();
      }
    }

    canvas.addEventListener("pointermove", onPointerMove);
    canvas.addEventListener("pointerdown", onPointerDown);
    canvas.addEventListener("pointerleave", onPointerLeave);
    root.addEventListener("keydown", onKeyDown);

    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    let elapsed = 0;
    if (reduce) root.classList.remove("is-demo");
    const warmSteps = reduce ? 30 : 40;
    for (let w = 0; w < warmSteps; w += 1) { elapsed += 20; stepSim(0.02, 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;
        stepSim(dt / 1000, elapsed);
        draw();
      }
      raf = requestAnimationFrame(tick);
    }
    fit();
    window.addEventListener("resize", fit);
    draw();
    raf = requestAnimationFrame(tick);

    return () => {
      cancelAnimationFrame(raf);
      if (manualReleaseTimer) window.clearTimeout(manualReleaseTimer);
      window.removeEventListener("resize", fit);
      canvas.removeEventListener("pointermove", onPointerMove);
      canvas.removeEventListener("pointerdown", onPointerDown);
      canvas.removeEventListener("pointerleave", onPointerLeave);
      root.removeEventListener("keydown", onKeyDown);
    };
  }, []);

  return (
    <main className={styles.stage}>
      <div
        className={`${styles.rn} is-demo`}
        ref={rootRef}
        tabIndex={0}
        role="img"
        aria-label="포인터를 좌우로 움직이거나 화살표 키를 누르면 비가 그쪽으로 눕는 장면"
      >
        <canvas className={styles.rn__canvas} ref={canvasRef} width={480} height={300} />
        <p className={styles.rn__caption}>포인터가 화면 중심에서 벗어난 만큼 바람 벡터의 방향을 다시 계산해, 포인터를 움직이는 동안 빗줄기 전체가 그 방향으로 같이 기울어 떨어진다</p>
        <p className={styles.rn__hint}>포인터를 움직이거나 ← → 키</p>
      </div>
    </main>
  );
}