02Smoke That Curls Sideways Along a Wind Flow Field

<main class="stage">
<div class="smk is-demo" id="smkRoot">
  <canvas class="smk__canvas" id="smkCanvas" width="480" height="300"></canvas>
  <p class="smk__caption">As the flow-field value increases, the smoke column bends further sideways the higher it rises.</p>
</div>
</main>

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

.smk {
  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: $stage-yellow;
}

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

.smk__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, 255, 255, .82);
  color: $subject-ink;
  font-weight: 500;
  font-size: 12px;
  line-height: 1.4;
  pointer-events: none;
}

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

@media (prefers-reduced-motion: reduce) {
  .smk { cursor: default; }
}

html, body {
  margin: 0;
  overflow: hidden;
}

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ffd23f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.smk {
  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: #ffd23f;
}

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

.smk__caption {
  position: absolute;
  left: 12px;
  bottom: 12px;
  max-width: 78%;
  margin: 0;
  padding: 4px 12px;
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.82);
  color: #17141a;
  font-weight: 500;
  font-size: 12px;
  line-height: 1.4;
  pointer-events: none;
}

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

(function () {
  // 기법: 값 노이즈로 만든 방향장(flow field)의 각도를 입자 위치·시간에서 샘플링해 수평
  // 속도로 쓴다. 흐름장 세기(WIND_FLOW_STRENGTH)에 바람이 부는 세기가 시간에 따라 오르내리는
  // 게인(gustEnvelope)을 곱해, 같은 상수라도 순간마다 휘는 정도가 달라지는 걸 보여준다.
  // 높이 비율(f)을 곱해 위로 갈수록 휘어짐이 커지도록 전파한다.
  var root = document.getElementById('smkRoot');
  var canvas = document.getElementById('smkCanvas');
  var ctx = canvas.getContext('2d');
  var wrap = canvas.parentElement;

  var CALC_W = 160, CALC_H = 100;
  var SMOKE_RISE_SPEED_PX = 26;
  var WIND_FLOW_STRENGTH = 60;
  var PLUME_SPAWN_PER_S = 40;
  var PLUME_LIFE_MS = 2400;

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

  var NOISE_DIM = 40;
  var noiseRand = seedRand(423021);
  var noiseTable = new Float32Array(NOISE_DIM * NOISE_DIM);
  for (var ni = 0; ni < noiseTable.length; ni += 1) noiseTable[ni] = noiseRand();
  function noiseAt(xi, yi) {
    var wx = ((xi % NOISE_DIM) + NOISE_DIM) % NOISE_DIM;
    var wy = ((yi % NOISE_DIM) + NOISE_DIM) % NOISE_DIM;
    return noiseTable[wy * NOISE_DIM + wx];
  }
  function smoothstep(t) { return t * t * (3 - 2 * t); }
  function valueNoise2D(x, y) {
    var x0 = Math.floor(x), y0 = Math.floor(y);
    var tx = smoothstep(x - x0), ty = smoothstep(y - y0);
    var v00 = noiseAt(x0, y0), v10 = noiseAt(x0 + 1, y0);
    var v01 = noiseAt(x0, y0 + 1), v11 = noiseAt(x0 + 1, y0 + 1);
    var a = v00 + (v10 - v00) * tx;
    var b = v01 + (v11 - v01) * tx;
    return a + (b - a) * ty;
  }
  function flowAngle(x, y, t) {
    return (valueNoise2D(x * 0.06, y * 0.06 + t * 0.0004) - 0.5) * Math.PI * 2.2;
  }
  function gustEnvelope(t) {
    return 0.5 + 0.5 * Math.sin(t * 0.0009);
  }

  var pRand = seedRand(423022);
  var particles = [];
  var spawnAcc = 0;

  function spawn(bornMs) {
    particles.push({
      x: CALC_W * 0.5 + (pRand() - 0.5) * 8,
      y: CALC_H - 6,
      born: bornMs
    });
  }

  function stepSim(dtMs, nowMs) {
    var dtS = dtMs / 1000;
    spawnAcc += dtMs * PLUME_SPAWN_PER_S / 1000;
    while (spawnAcc >= 1) { spawn(nowMs); spawnAcc -= 1; }
    var gust = gustEnvelope(nowMs);
    var alive = [];
    for (var i = 0; i < particles.length; i += 1) {
      var p = particles[i];
      var f = Math.max(0, Math.min(1, (nowMs - p.born) / PLUME_LIFE_MS));
      var ang = flowAngle(p.x, p.y, nowMs);
      p.x += Math.sin(ang) * WIND_FLOW_STRENGTH * gust * f * dtS;
      p.y -= SMOKE_RISE_SPEED_PX * dtS;
      if (nowMs - p.born < PLUME_LIFE_MS) alive.push(p);
    }
    particles = alive;
  }

  function drawSmoke(nowMs) {
    var sx = cw / CALC_W, sy = ch / CALC_H;
    ctx.clearRect(0, 0, cw, ch);
    for (var i = 0; i < particles.length; i += 1) {
      var p = particles[i];
      var f = Math.max(0, Math.min(1, (nowMs - p.born) / PLUME_LIFE_MS));
      var r = 6 + f * 26;
      var alpha = Math.sin(f * Math.PI) * 0.6;
      if (alpha <= 0.01) continue;
      var dx = p.x * sx, dy = p.y * sy, dr = r * ((sx + sy) / 2);
      var g = ctx.createRadialGradient(dx, dy, 0, dx, dy, dr);
      g.addColorStop(0, 'rgba(40,34,26,' + alpha + ')');
      g.addColorStop(1, 'rgba(40,34,26,0)');
      ctx.fillStyle = g;
      ctx.beginPath();
      ctx.arc(dx, dy, dr, 0, Math.PI * 2);
      ctx.fill();
    }
  }

  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;
    drawSmoke(elapsed);
  }

  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  var elapsed = 0;
  if (reduce) root.classList.remove('is-demo');
  var warmSteps = reduce ? 160 : 120;
  for (var w = 0; w < warmSteps; w += 1) { elapsed += 20; stepSim(20, 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, elapsed);
      drawSmoke(elapsed);
    }
    requestAnimationFrame(tick);
  }
  fit();
  window.addEventListener('resize', fit);
  drawSmoke(elapsed);
  requestAnimationFrame(tick);
})();

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

type Particle = { x: number; y: number; born: number; wSeed: number };

export default function SmokeEffectWindDriftFlowfield() {
  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 WIND_FLOW_STRENGTH = 60;
    const SMOKE_RISE_SPEED_PX = 26;
    const PLUME_SPAWN_PER_S = 40;
    const PLUME_LIFE_MS = 2400;

    function seedRand(seed: number) {
      let s = seed >>> 0;
      return function () { s = (s * 1664525 + 1013904223) >>> 0; return s / 4294967296; };
    }
    const NOISE_DIM = 40;
    const noiseRand = seedRand(423020);
    const noiseTable = new Float32Array(NOISE_DIM * NOISE_DIM);
    for (let ni = 0; ni < noiseTable.length; ni += 1) noiseTable[ni] = noiseRand();
    function noiseAt(xi: number, yi: number) {
      const wx = ((xi % NOISE_DIM) + NOISE_DIM) % NOISE_DIM;
      const wy = ((yi % NOISE_DIM) + NOISE_DIM) % NOISE_DIM;
      return noiseTable[wy * NOISE_DIM + wx];
    }
    function smoothstep(t: number) { return t * t * (3 - 2 * t); }
    function valueNoise2D(x: number, y: number) {
      const x0 = Math.floor(x), y0 = Math.floor(y);
      const tx = smoothstep(x - x0), ty = smoothstep(y - y0);
      const v00 = noiseAt(x0, y0), v10 = noiseAt(x0 + 1, y0);
      const v01 = noiseAt(x0, y0 + 1), v11 = noiseAt(x0 + 1, y0 + 1);
      const a = v00 + (v10 - v00) * tx;
      const b = v01 + (v11 - v01) * tx;
      return a + (b - a) * ty;
    }
    function flowAngle(x: number, y: number, t: number) {
      return (valueNoise2D(x * 0.05 + t, y * 0.05) - 0.5) * Math.PI * 1.6;
    }
    function gustEnvelope(t: number) { return 0.5 + 0.5 * Math.sin(t * 0.0009); }

    const pRand = seedRand(423021);
    let particles: Particle[] = [];
    let spawnAcc = 0;

    function spawn(bornMs: number) {
      particles.push({
        x: CALC_W * 0.5 + (pRand() - 0.5) * 10,
        y: CALC_H - 6,
        born: bornMs,
        wSeed: pRand() * 1000
      });
    }

    function stepSim(dtMs: number, nowMs: number) {
      const dtS = dtMs / 1000;
      spawnAcc += dtMs * PLUME_SPAWN_PER_S / 1000;
      while (spawnAcc >= 1) { spawn(nowMs); spawnAcc -= 1; }
      const gust = gustEnvelope(nowMs);
      const alive: Particle[] = [];
      for (let i = 0; i < particles.length; i += 1) {
        const p = particles[i];
        const ang = flowAngle(p.wSeed, p.y, nowMs * 0.0007);
        p.x += Math.sin(ang) * WIND_FLOW_STRENGTH * gust * dtS;
        p.y -= SMOKE_RISE_SPEED_PX * dtS;
        if (nowMs - p.born < PLUME_LIFE_MS) alive.push(p);
      }
      particles = alive;
    }

    let cw = 480, ch = 300;
    function drawSmoke(nowMs: number) {
      const sx = cw / CALC_W, sy = ch / CALC_H;
      ctx!.clearRect(0, 0, cw, ch);
      for (let i = 0; i < particles.length; i += 1) {
        const p = particles[i];
        const f = Math.max(0, Math.min(1, (nowMs - p.born) / PLUME_LIFE_MS));
        const r = 6 + f * 26;
        const alpha = Math.sin(f * Math.PI) * 0.6;
        if (alpha <= 0.01) continue;
        const dx = p.x * sx, dy = p.y * sy, dr = r * ((sx + sy) / 2);
        const g = ctx!.createRadialGradient(dx, dy, 0, dx, dy, dr);
        g.addColorStop(0, "rgba(40,34,26," + alpha + ")");
        g.addColorStop(1, "rgba(40,34,26,0)");
        ctx!.fillStyle = g;
        ctx!.beginPath();
        ctx!.arc(dx, dy, dr, 0, Math.PI * 2);
        ctx!.fill();
      }
    }

    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;
      drawSmoke(elapsed);
    }

    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    let elapsed = 0;
    if (reduce) root.classList.remove("is-demo");
    const warmSteps = reduce ? 160 : 130;
    for (let w = 0; w < warmSteps; w += 1) { elapsed += 20; stepSim(20, 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, elapsed);
        drawSmoke(elapsed);
      }
      raf = requestAnimationFrame(tick);
    }
    fit();
    window.addEventListener("resize", fit);
    drawSmoke(elapsed);
    raf = requestAnimationFrame(tick);

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

  return (
    <main className={styles.stage}>
      <div className={`${styles.smk} is-demo`} ref={rootRef}>
        <canvas className={styles.smk__canvas} ref={canvasRef} width={480} height={300} />
        <p className={styles.smk__caption}>흐름장 값이 커질수록 연기 기둥이 위로 갈수록 더 크게 옆으로 휘어진다</p>
      </div>
    </main>
  );
}