03Flow field line art

<main class="stage">
<div class="ff is-demo" id="root">
  <svg class="ff__art" id="art" viewBox="0 0 240 150" role="img" data-label="A picture drawn with lines flowing along a field of angles, seed {n}"></svg>
  <div class="ff__bar">
    <p class="ff__seed">
      <svg xmlns="http://www.w3.org/2000/svg" class="ff__ic" viewBox="0 0 256 256" aria-hidden="true"><g fill="currentColor"><path d="M216 64v128a24 24 0 0 1-24 24H64a24 24 0 0 1-24-24V64a24 24 0 0 1 24-24h128a24 24 0 0 1 24 24" opacity=".2"/><path d="M192 32H64a32 32 0 0 0-32 32v128a32 32 0 0 0 32 32h128a32 32 0 0 0 32-32V64a32 32 0 0 0-32-32m16 160a16 16 0 0 1-16 16H64a16 16 0 0 1-16-16V64a16 16 0 0 1 16-16h128a16 16 0 0 1 16 16ZM104 92a12 12 0 1 1-12-12a12 12 0 0 1 12 12m72 0a12 12 0 1 1-12-12a12 12 0 0 1 12 12m-72 72a12 12 0 1 1-12-12a12 12 0 0 1 12 12m36-36a12 12 0 1 1-12-12a12 12 0 0 1 12 12m36 36a12 12 0 1 1-12-12a12 12 0 0 1 12 12"/></g></svg>
      Seed <b id="num">7</b>
    </p>
    <button class="ff__btn" type="button" id="again">
      <svg xmlns="http://www.w3.org/2000/svg" class="ff__ic" viewBox="0 0 256 256" aria-hidden="true"><g fill="currentColor"><path d="M107.14 98.8L128 128l-20.86 29.2A64 64 0 0 1 55.06 184H32V72h23.06a64 64 0 0 1 52.08 26.8m93.8-26.8a64 64 0 0 0-52.08 26.8L128 128l20.86 29.2a64 64 0 0 0 52.08 26.8H232V72Z" opacity=".2"/><path d="M237.66 178.34a8 8 0 0 1 0 11.32l-24 24a8 8 0 0 1-11.32-11.32L212.69 192h-11.75a72.12 72.12 0 0 1-58.59-30.15l-41.72-58.4A56.1 56.1 0 0 0 55.06 80H32a8 8 0 0 1 0-16h23.06a72.12 72.12 0 0 1 58.59 30.15l41.72 58.4A56.1 56.1 0 0 0 200.94 176h11.75l-10.35-10.34a8 8 0 0 1 11.32-11.32ZM143 107a8 8 0 0 0 11.16-1.86l1.2-1.67A56.1 56.1 0 0 1 200.94 80h11.75l-10.35 10.34a8 8 0 0 0 11.32 11.32l24-24a8 8 0 0 0 0-11.32l-24-24a8 8 0 0 0-11.32 11.32L212.69 64h-11.75a72.12 72.12 0 0 0-58.59 30.15l-1.2 1.67A8 8 0 0 0 143 107m-30 42a8 8 0 0 0-11.16 1.86l-1.2 1.67A56.1 56.1 0 0 1 55.06 176H32a8 8 0 0 0 0 16h23.06a72.12 72.12 0 0 0 58.59-30.15l1.2-1.67A8 8 0 0 0 113 149"/></g></svg>
      <span class="ff__label">Regenerate</span>
    </button>
    <button class="ff__btn" type="button" id="copy" data-done="Copied">
      <svg xmlns="http://www.w3.org/2000/svg" class="ff__ic" viewBox="0 0 256 256" aria-hidden="true"><g fill="currentColor"><path d="M216 40v128h-48V88H88V40Z" opacity=".2"/><path d="M216 32H88a8 8 0 0 0-8 8v40H40a8 8 0 0 0-8 8v128a8 8 0 0 0 8 8h128a8 8 0 0 0 8-8v-40h40a8 8 0 0 0 8-8V40a8 8 0 0 0-8-8m-56 176H48V96h112Zm48-48h-32V88a8 8 0 0 0-8-8H96V48h112Z"/></g></svg>
      <span class="ff__label">Copy SVG</span>
    </button>
  </div>
</div>
</main>

@use "../../../../site/static/demo-tokens" as *;

// 플로우 필드 선 그림 — 자리마다 각도를 하나씩 정해 둔 방향장 위를 짧은 걸음으로 걸어 곡선을 만든다.
// 경로 계산은 JS, 그리는 연출은 CSS: pathLength="1" 로 길이를 1 로 정규화하고
// stroke-dashoffset 을 1 → 0 → -1 로 돌린다. 1 과 -1 은 둘 다 "감춰짐" 이라 한 바퀴 끝에서 안 튄다.

$duration: $dur-loop;
$easing: cubic-bezier(.7, 0, .85, .4);
$color: $subject-cream;

@include stage($stage-ink);

.ff { display: grid; justify-items: center; gap: $sp-3; width: 100%; }

.ff__art { display: block; width: clamp(176px, 60vw, 320px); height: auto; }

.ff__line {
  fill: none;
  stroke-width: 1.5;
  stroke-linecap: round;
  stroke-linejoin: round;
  stroke-dasharray: 1;          // pathLength="1" 이라 1 = 경로 전체 길이
  stroke-dashoffset: 0;         // 정적 상태는 선이 다 그려진 그림
}
.ff__line--a { stroke: $color; opacity: .82; }
.ff__line--b { stroke: $subject-blue; }

.ff__bar { display: flex; flex-wrap: wrap; align-items: center; justify-content: center; gap: $sp-2; }

.ff__seed {
  margin: 0;
  display: inline-flex; align-items: center; gap: $sp-1;
  color: rgba(255, 247, 230, .8);
  font-weight: 700; font-size: clamp(9px, 2.4vw, 11px);
}

.ff__btn {
  display: inline-flex; align-items: center; gap: $sp-1;
  border: 0; border-radius: $r-pill;
  padding: $sp-1 $sp-3;
  background: $subject-cream; color: $subject-ink;
  font-family: inherit; font-weight: 700; font-size: clamp(9px, 2.4vw, 11px);
  cursor: pointer;
}
.ff__btn:focus-visible { outline: 3px solid $subject-blue; outline-offset: 2px; }

.ff__ic { width: 12px; height: 12px; flex: none; }

// ── 미리보기 루프: 「다시 생성」을 눌렀을 때 실제로 도는 것과 같은 그리기 연출을 무한 반복한다.
//    그리기는 느리게 시작해 끝에서 빨라지고 지우기는 그 반대라, 프레임당 변화가 가장 큰 순간이
//    「선이 거의 다 있는」 장면에 온다 — poster 가 빈 화면으로 뽑히지 않는다.
.ff.is-demo .ff__line {
  animation-name: ffFlow;
  animation-duration: $duration;
  animation-timing-function: $easing;
  animation-iteration-count: infinite;
  animation-fill-mode: backwards;
  animation-delay: calc(var(--i) * 62ms);
}

.ff.is-draw .ff__line {
  animation-name: ffDraw;
  animation-duration: $dur-enter;
  animation-timing-function: $ease-out;
  animation-iteration-count: 1;
  animation-fill-mode: backwards;
  animation-delay: calc(var(--i) * 30ms);
}

@keyframes ffFlow {
  0%   { stroke-dashoffset: 1; animation-timing-function: $easing; }
  40%  { stroke-dashoffset: 0; animation-timing-function: linear; }
  52%  { stroke-dashoffset: 0; animation-timing-function: $ease-out; }
  86%  { stroke-dashoffset: -1; }
  100% { stroke-dashoffset: -1; }
}

@keyframes ffDraw {
  from { stroke-dashoffset: 1; }
  to   { stroke-dashoffset: 0; }
}

@media (max-width: 340px) {
  .ff { gap: $sp-2; }
  .ff__ic { width: 10px; height: 10px; }
}

@media (prefers-reduced-motion: reduce) {
  .ff.is-demo .ff__line,
  .ff.is-draw .ff__line { animation: none !important; stroke-dashoffset: 0 !important; }
}

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);
}

.ff {
  display: grid;
  justify-items: center;
  gap: 12px;
  width: 100%;
}

.ff__art {
  display: block;
  width: clamp(176px, 60vw, 320px);
  height: auto;
}

.ff__line {
  fill: none;
  stroke-width: 1.5;
  stroke-linecap: round;
  stroke-linejoin: round;
  stroke-dasharray: 1;
  stroke-dashoffset: 0;
}

.ff__line--a {
  stroke: #fff7e6;
  opacity: 0.82;
}

.ff__line--b {
  stroke: #2f6df6;
}

.ff__bar {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: center;
  gap: 8px;
}

.ff__seed {
  margin: 0;
  display: inline-flex;
  align-items: center;
  gap: 4px;
  color: rgba(255, 247, 230, 0.8);
  font-weight: 700;
  font-size: clamp(9px, 2.4vw, 11px);
}

.ff__btn {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  border: 0;
  border-radius: 999px;
  padding: 4px 12px;
  background: #fff7e6;
  color: #17141a;
  font-family: inherit;
  font-weight: 700;
  font-size: clamp(9px, 2.4vw, 11px);
  cursor: pointer;
}

.ff__btn:focus-visible {
  outline: 3px solid #2f6df6;
  outline-offset: 2px;
}

.ff__ic {
  width: 12px;
  height: 12px;
  flex: none;
}

.ff.is-demo .ff__line {
  animation-name: ffFlow;
  animation-duration: 2s;
  animation-timing-function: cubic-bezier(0.7, 0, 0.85, 0.4);
  animation-iteration-count: infinite;
  animation-fill-mode: backwards;
  animation-delay: calc(var(--i) * 62ms);
}

.ff.is-draw .ff__line {
  animation-name: ffDraw;
  animation-duration: 600ms;
  animation-timing-function: ease-out;
  animation-iteration-count: 1;
  animation-fill-mode: backwards;
  animation-delay: calc(var(--i) * 30ms);
}

@keyframes ffFlow {
  0% {
    stroke-dashoffset: 1;
    animation-timing-function: cubic-bezier(0.7, 0, 0.85, 0.4);
  }
  40% {
    stroke-dashoffset: 0;
    animation-timing-function: linear;
  }
  52% {
    stroke-dashoffset: 0;
    animation-timing-function: ease-out;
  }
  86% {
    stroke-dashoffset: -1;
  }
  100% {
    stroke-dashoffset: -1;
  }
}
@keyframes ffDraw {
  from {
    stroke-dashoffset: 1;
  }
  to {
    stroke-dashoffset: 0;
  }
}
@media (max-width: 340px) {
  .ff {
    gap: 8px;
  }
  .ff__ic {
    width: 10px;
    height: 10px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .ff.is-demo .ff__line,
  .ff.is-draw .ff__line {
    animation: none !important;
    stroke-dashoffset: 0 !important;
  }
}

var root = document.getElementById('root');
var art = document.getElementById('art');
var num = document.getElementById('num');
var W = 240, H = 150, COLS = 5, ROWS = 3, GX = 9, GY = 6, STEPS = 30, STEP = 4.4;
var seed = 7;

// mulberry32 — 32비트 정수 Seed 하나로 언제나 같은 난수열을 돌려준다. 재현 가능한 생성의 뿌리
function mulberry32(a) {
  return function () {
    a = a + 0x6D2B79F5 | 0;
    var t = Math.imul(a ^ a >>> 15, 1 | a);
    t = t + Math.imul(t ^ t >>> 7, 61 | t) ^ t;
    return ((t ^ t >>> 14) >>> 0) / 4294967296;
  };
}

// 성긴 격자에 난수를 놓고 사이를 smoothstep 으로 이어 자리마다 하나의 각도를 준다 = 방향장
function makeAngles(s) {
  var rand = mulberry32(s), lat = [], r, c;
  for (r = 0; r <= ROWS; r++) { lat.push([]); for (c = 0; c <= COLS; c++) { lat[r].push(rand()); } }
  return function (x, y) {
    var gx = Math.max(0, Math.min(COLS - 0.001, x / W * COLS));
    var gy = Math.max(0, Math.min(ROWS - 0.001, y / H * ROWS));
    var ix = Math.floor(gx), iy = Math.floor(gy), fx = gx - ix, fy = gy - iy;
    var sx = fx * fx * (3 - 2 * fx), sy = fy * fy * (3 - 2 * fy);
    var top = lat[iy][ix] + (lat[iy][ix + 1] - lat[iy][ix]) * sx;
    var bot = lat[iy + 1][ix] + (lat[iy + 1][ix + 1] - lat[iy + 1][ix]) * sx;
    return (top + (bot - top) * sy) * Math.PI * 3;
  };
}

// 한 점에서 시작해 그 자리의 각도로 한 걸음씩 옮기며 좌표를 이어 붙인다
function walk(angleAt, x, y) {
  var d = 'M' + x.toFixed(1) + ' ' + y.toFixed(1), i;
  for (i = 0; i < STEPS; i++) {
    var a = angleAt(x, y);
    x += Math.cos(a) * STEP;
    y += Math.sin(a) * STEP;
    if (x < -8 || x > W + 8 || y < -8 || y > H + 8) { break; }
    d += 'L' + x.toFixed(1) + ' ' + y.toFixed(1);
  }
  return d;
}

function build() {
  var angleAt = makeAngles(seed), rand = mulberry32(seed + 991), parts = [], gx, gy;
  // 시작점을 흔들린 격자에서 뽑아 화면 전체에 고르게 깔리게 한다 (순수 난수면 한쪽에 뭉친다)
  for (gy = 0; gy < GY; gy++) {
    for (gx = 0; gx < GX; gx++) {
      var x = (gx + 0.15 + rand() * 0.7) / GX * W, y = (gy + 0.15 + rand() * 0.7) / GY * H;
      var tone = rand() < 0.34 ? 'b' : 'a';
      parts.push('<path class="ff__line ff__line--' + tone + '" style="--i:' + ((gx + gy) % 11) + '" pathLength="1" d="' + walk(angleAt, x, y) + '"/>');
    }
  }
  art.innerHTML = parts.join('');
  art.setAttribute('aria-label', art.getAttribute('data-label').replace('{n}', seed));
  num.textContent = seed;
}

document.getElementById('again').addEventListener('click', function () {
  seed = (seed * 7 + 13) % 991 + 1;
  build();
  root.classList.remove('is-demo');
  root.classList.remove('is-draw');
  void art.getBoundingClientRect().width;   // 한 번 읽어 리플로를 일으켜야 같은 애니메이션이 처음부터 다시 돈다
  root.classList.add('is-draw');
});

var copyBtn = document.getElementById('copy');
copyBtn.addEventListener('click', function () {
  var label = copyBtn.querySelector('.ff__label');
  var before = label.textContent;
  if (navigator.clipboard && navigator.clipboard.writeText) {
    navigator.clipboard.writeText(art.outerHTML).catch(function () {});
  }
  label.textContent = copyBtn.getAttribute('data-done');
  setTimeout(function () { label.textContent = before; }, 1200);
});

build();

// FlowFieldLines — vanilla 판(run/293/demo/03-generative-flow-field-lines/index.html) 의 React 포트.
// 자리마다 각도를 하나씩 정해 둔 방향장 위를 짧은 걸음으로 걸어 곡선을 만든다. 경로는 JS, 그리는 연출은 CSS.
// 시드·격자 수·걸음 수·걸음 길이는 vanilla 와 같은 값이다.
import { useMemo, useRef, useState } from "react";
import type { CSSProperties } from "react";
import styles from "./FlowFieldLines.module.scss";

export type FlowFieldLinesProps = {
  duration?: number;
  easing?: string;
  color?: string;
  label?: string;
  seedText?: string;
  regenerateText?: string;
  copyText?: string;
  copiedText?: string;
};

type Vars = CSSProperties & { "--duration"?: string; "--easing"?: string; "--color"?: string };
// useRef 는 T | null 을 돌려준다. 처음부터 값이 있고 절대 비지 않는 상자는 이렇게 좁혀 쓴다
type Box<T> = { current: T };
type Line = { key: number; tone: string; i: number; d: string };

const W = 240;
const H = 150;
const COLS = 5;
const ROWS = 3;
const GX = 9;
const GY = 6;
const STEPS = 30;
const STEP = 4.4;

// mulberry32 — 32비트 정수 시드 하나로 언제나 같은 난수열을 돌려준다. 재현 가능한 생성의 뿌리
function mulberry32(a: number): () => number {
  return function (): number {
    a = a + 0x6D2B79F5 | 0;
    let t = Math.imul(a ^ a >>> 15, 1 | a);
    t = t + Math.imul(t ^ t >>> 7, 61 | t) ^ t;
    return ((t ^ t >>> 14) >>> 0) / 4294967296;
  };
}

// 성긴 격자에 난수를 놓고 사이를 smoothstep 으로 이어 자리마다 하나의 각도를 준다 = 방향장
function makeAngles(s: number): (x: number, y: number) => number {
  const rand = mulberry32(s);
  const lat: number[][] = [];
  for (let r = 0; r <= ROWS; r++) {
    const row: number[] = [];
    for (let c = 0; c <= COLS; c++) { row.push(rand()); }
    lat.push(row);
  }
  return function (x: number, y: number): number {
    const gx = Math.max(0, Math.min(COLS - 0.001, x / W * COLS));
    const gy = Math.max(0, Math.min(ROWS - 0.001, y / H * ROWS));
    const ix = Math.floor(gx);
    const iy = Math.floor(gy);
    const fx = gx - ix;
    const fy = gy - iy;
    const sx = fx * fx * (3 - 2 * fx);
    const sy = fy * fy * (3 - 2 * fy);
    const top = lat[iy][ix] + (lat[iy][ix + 1] - lat[iy][ix]) * sx;
    const bot = lat[iy + 1][ix] + (lat[iy + 1][ix + 1] - lat[iy + 1][ix]) * sx;
    return (top + (bot - top) * sy) * Math.PI * 3;
  };
}

// 한 점에서 시작해 그 자리의 각도로 한 걸음씩 옮기며 좌표를 이어 붙인다
function walk(angleAt: (x: number, y: number) => number, x: number, y: number): string {
  let d = "M" + x.toFixed(1) + " " + y.toFixed(1);
  for (let i = 0; i < STEPS; i++) {
    const a = angleAt(x, y);
    x += Math.cos(a) * STEP;
    y += Math.sin(a) * STEP;
    if (x < -8 || x > W + 8 || y < -8 || y > H + 8) { break; }
    d += "L" + x.toFixed(1) + " " + y.toFixed(1);
  }
  return d;
}

export default function FlowFieldLines({
  duration = 2000,
  easing = "cubic-bezier(.7, 0, .85, .4)",
  color = "#fff7e6",
  label = "A picture drawn with lines flowing along a field of angles, seed {n}",
  seedText = "Seed",
  regenerateText = "Regenerate",
  copyText = "Copy SVG",
  copiedText = "Copied",
}: FlowFieldLinesProps) {
  const artRef = useRef<SVGSVGElement | null>(null);
  const timerRef = useRef<number>(0) as Box<number>;
  const [seed, setSeed] = useState(7);
  const [mode, setMode] = useState("demo");
  const [copyLabel, setCopyLabel] = useState(copyText);
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };

  // 시드가 바뀔 때만 다시 계산한다 — 같은 시드면 언제나 같은 경로 문자열이 나온다.
  // 시작점은 흔들린 격자에서 뽑아 화면 전체에 고르게 깔리게 한다 (순수 난수면 한쪽에 뭉친다)
  const lines = useMemo(() => {
    const angleAt = makeAngles(seed);
    const rand = mulberry32(seed + 991);
    const out: Line[] = [];
    for (let gy = 0; gy < GY; gy++) {
      for (let gx = 0; gx < GX; gx++) {
        const x = (gx + 0.15 + rand() * 0.7) / GX * W;
        const y = (gy + 0.15 + rand() * 0.7) / GY * H;
        const tone = rand() < 0.34 ? "lineB" : "lineA";
        out.push({ key: gy * GX + gx, tone, i: (gx + gy) % 11, d: walk(angleAt, x, y) });
      }
    }
    return out;
  }, [seed]);

  function regenerate(): void {
    setSeed((prev: number) => (prev * 7 + 13) % 991 + 1);
    setMode("draw");
  }

  function copySvg(): void {
    const art = artRef.current;
    if (!art) { return; }
    if (navigator.clipboard && navigator.clipboard.writeText) {
      navigator.clipboard.writeText(art.outerHTML).catch(function () {});
    }
    setCopyLabel(copiedText);
    clearTimeout(timerRef.current);
    timerRef.current = window.setTimeout(() => setCopyLabel(copyText), 1200);
  }

  const rootClass = `${styles.ff} ${mode === "demo" ? styles.isDemo : styles.isDraw}`;

  return (
    <div className={rootClass} style={vars}>
      <svg
        ref={artRef}
        className={styles.art}
        viewBox={`0 0 ${W} ${H}`}
        role="img"
        aria-label={label.replace("{n}", String(seed))}
      >
        {lines.map((l: Line) => (
          <path
            key={l.key}
            className={`${styles.line} ${styles[l.tone]}`}
            style={{ "--i": l.i } as CSSProperties}
            pathLength={1}
            d={l.d}
          />
        ))}
      </svg>
      <div className={styles.bar}>
        <p className={styles.seed}>{seedText} <b>{seed}</b></p>
        <button className={styles.btn} type="button" onClick={regenerate}>{regenerateText}</button>
        <button className={styles.btn} type="button" onClick={copySvg}>{copyLabel}</button>
      </div>
    </div>
  );
}