04사인 두 겹을 더해 만든 파도 섹션 경계

<main class="stage">
<div class="dv is-demo" id="dvRoot">
  <svg class="dv__svg" id="dvSvg" viewBox="0 0 320 110" aria-hidden="true" focusable="false">
    <rect class="dv__under" x="0" y="0" width="320" height="110"></rect>
    <path class="dv__over" id="dvPath" d="M0 0H320V55H0Z"></path>
  </svg>
  <div class="dv__bar">
  <button class="dv__btn" id="dvBtn" type="button">파도 겹 수 바꾸기</button>
  <p class="dv__meta"><span class="dv__tag">WAVE_LAYERS</span> <b id="dvLayers">2</b></p>
  </div>
</div>
</main>

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

// 핵심: 경계선 높이를 주기가 다른 사인 WAVE_LAYERS 개의 합으로 계산해 SVG path 로 그린다.

$over-color: $subject-pink;
$under-color: $subject-sky;

@include stage($stage-ink);

.dv {
  width: min(100%, 360px);
  display: grid;
  gap: $sp-2;
  justify-items: center;
}

.dv__svg {
  display: block;
  width: 100%;
  height: auto;
  border-radius: $r-card;
  overflow: hidden;
}
.dv__under { fill: $under-color; }
.dv__over { fill: $over-color; }

.dv__btn {
  box-sizing: border-box;
  height: 40px;
  padding: 0 $sp-5;
  border: 0;
  border-radius: $r-control;
  background: $subject-lilac;
  color: $subject-ink;
  font-family: inherit;
  font-size: 14px;
  font-weight: 700;
  line-height: 20px;
  cursor: pointer;
}
.dv__btn:focus-visible { outline: 3px solid $stage-paper; outline-offset: 3px; }

.dv__meta {
  margin: 0;
  display: flex;
  align-items: baseline;
  gap: $sp-2;
  font-size: 12px;
  line-height: 16px;
  color: rgba($stage-paper, .78);
}
.dv__tag { font-weight: 700; letter-spacing: .08em; }
.dv__meta b { min-width: 2ch; text-align: right; font-variant-numeric: tabular-nums; color: $stage-paper; }

@media (prefers-reduced-motion: reduce) {
  .dv__btn { transition: none; }
}

.dv__bar { box-sizing: border-box; width: 100%; display: flex; flex-wrap: wrap; align-items: center; justify-content: space-between; gap: $sp-2 $sp-3; }

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);
}

.dv {
  width: min(100%, 360px);
  display: grid;
  gap: 8px;
  justify-items: center;
}

.dv__svg {
  display: block;
  width: 100%;
  height: auto;
  border-radius: 16px;
  overflow: hidden;
}

.dv__under {
  fill: #6ec8ff;
}

.dv__over {
  fill: #ff9ebb;
}

.dv__btn {
  box-sizing: border-box;
  height: 40px;
  padding: 0 20px;
  border: 0;
  border-radius: 12px;
  background: #b9a0ff;
  color: #17141a;
  font-family: inherit;
  font-size: 14px;
  font-weight: 700;
  line-height: 20px;
  cursor: pointer;
}

.dv__btn:focus-visible {
  outline: 3px solid #ffffff;
  outline-offset: 3px;
}

.dv__meta {
  margin: 0;
  display: flex;
  align-items: baseline;
  gap: 8px;
  font-size: 12px;
  line-height: 16px;
  color: rgba(255, 255, 255, 0.78);
}

.dv__tag {
  font-weight: 700;
  letter-spacing: 0.08em;
}

.dv__meta b {
  min-width: 2ch;
  text-align: right;
  font-variant-numeric: tabular-nums;
  color: #ffffff;
}

@media (prefers-reduced-motion: reduce) {
  .dv__btn {
    transition: none;
  }
}
.dv__bar {
  box-sizing: border-box;
  width: 100%;
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 8px 12px;
}

(function () {
  // 기법: 경계 높이 y(x) = BASE_Y + 각 겹(진폭 * sin(2π x / 주기 + 위상 * 속도배수))의 합. 두 주기를 일부러 서로 약분되지 않게 잡아 반복이 덜 보인다.
  // 점을 STEP_PX 간격으로 찍어 SVG path 의 d 를 직접 만든다.
  var WAVE_LAYERS = 2;
  var WAVE_AMP = [16, 9, 5];
  var WAVE_PERIOD = [190, 83, 47];
  var WAVE_SPEED = [1, 1.7, 2.3];
  var BASE_Y = 62;
  var VIEW_W = 320;
  var STEP_PX = 4;
  var RATE_RAD_PER_S = 2.4;

  var root = document.getElementById('dvRoot');
  var pathEl = document.getElementById('dvPath');
  var btn = document.getElementById('dvBtn');
  var layersEl = document.getElementById('dvLayers');
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  var phase = 0;

  function edgeY(x) {
    var y = BASE_Y;
    for (var i = 0; i < WAVE_LAYERS; i += 1) {
      y += WAVE_AMP[i] * Math.sin(2 * Math.PI * x / WAVE_PERIOD[i] + phase * WAVE_SPEED[i]);
    }
    return y;
  }
  function draw() {
    var d = 'M0 0H' + VIEW_W + 'V' + edgeY(VIEW_W).toFixed(1);
    for (var x = VIEW_W - STEP_PX; x >= 0; x -= STEP_PX) d += 'L' + x + ' ' + edgeY(x).toFixed(1);
    d += 'L0 ' + edgeY(0).toFixed(1) + 'Z';
    pathEl.setAttribute('d', d);
    layersEl.textContent = String(WAVE_LAYERS);
  }
  function stopDemo() { root.classList.remove('is-demo'); }

  btn.addEventListener('click', function () {
    WAVE_LAYERS = WAVE_LAYERS % 3 + 1;
    draw();
  });

  var lastTs = null;
  function tick(ts) {
    var dt = lastTs === null ? 0.016 : Math.min(0.05, (ts - lastTs) / 1000);
    lastTs = ts;
    if (root.classList.contains('is-demo')) {
      phase += RATE_RAD_PER_S * dt;
      draw();
    }
    requestAnimationFrame(tick);
  }

  draw();
  if (reduce) {
    stopDemo();
  } else {
    requestAnimationFrame(tick);
  }
})();

// WaveEdge — vanilla 판(04-divl-sine-wave-section-edge) 의 React 포트.
// 경계 높이를 주기가 다른 사인 WAVE_LAYERS 개의 합으로 계산해 SVG path 의 d 를 직접 만든다.
import { useEffect, useRef } from "react";
import styles from "./WaveEdge.module.scss";

type Box<T> = { current: T };

const WAVE_AMP: number[] = [16, 9, 5];
const WAVE_PERIOD: number[] = [190, 83, 47];
const WAVE_SPEED: number[] = [1, 1.7, 2.3];
const BASE_Y = 62;
const VIEW_W = 320;
const STEP_PX = 4;
const RATE_RAD_PER_S = 2.4;

export default function WaveEdge() {
  const pathRef = useRef<SVGPathElement | null>(null) as Box<SVGPathElement | null>;
  const btnRef = useRef<HTMLButtonElement | null>(null) as Box<HTMLButtonElement | null>;
  const layersRef = useRef<HTMLElement | null>(null) as Box<HTMLElement | null>;

  useEffect(() => {
    const pathEl = pathRef.current;
    const btn = btnRef.current;
    const layersEl = layersRef.current;
    if (!pathEl || !btn || !layersEl) return;
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    let demo = !reduce;
    let layers = 2;
    let phase = 0;
    let lastTs: number | null = null;
    let raf = 0;

    const edgeY = (x: number): number => {
      let y = BASE_Y;
      for (let i = 0; i < layers; i += 1) {
        y += WAVE_AMP[i] * Math.sin((2 * Math.PI * x) / WAVE_PERIOD[i] + phase * WAVE_SPEED[i]);
      }
      return y;
    };
    const draw = (): void => {
      let d = "M0 0H" + VIEW_W + "V" + edgeY(VIEW_W).toFixed(1);
      for (let x = VIEW_W - STEP_PX; x >= 0; x -= STEP_PX) d += "L" + x + " " + edgeY(x).toFixed(1);
      d += "L0 " + edgeY(0).toFixed(1) + "Z";
      pathEl.setAttribute("d", d);
      layersEl.textContent = String(layers);
    };
    const onClick = (): void => {
      layers = (layers % 3) + 1;
      draw();
    };
    btn.addEventListener("click", onClick);

    function tick(ts: number): void {
      const dt = lastTs === null ? 0.016 : Math.min(0.05, (ts - lastTs) / 1000);
      lastTs = ts;
      if (demo) {
        phase += RATE_RAD_PER_S * dt;
        draw();
      }
      raf = requestAnimationFrame(tick);
    }

    draw();
    if (!reduce) raf = requestAnimationFrame(tick);
    return () => {
      demo = false;
      cancelAnimationFrame(raf);
      btn.removeEventListener("click", onClick);
    };
  }, []);

  return (
    <div className={styles.dv}>
      <svg className={styles.svg} viewBox="0 0 320 110" aria-hidden="true" focusable="false">
        <rect className={styles.under} x="0" y="0" width="320" height="110" />
        <path className={styles.over} ref={pathRef} d="M0 0H320V55H0Z" />
      </svg>
      <div className={styles.bar}>
      <button className={styles.btn} ref={btnRef} type="button">파도 겹 수 바꾸기</button>
      <p className={styles.meta}>
        <span className={styles.tag}>WAVE_LAYERS</span> <b ref={layersRef}>2</b>
      </p>
      </div>
    </div>
  );
}