02Ring follows cursor

<main class="stage">
  <p class="hint">Portfolio</p>
  <div class="dot is-demo" aria-hidden="true"></div>
  <div class="ring is-demo" aria-hidden="true"></div>
</main>

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

$duration: $dur-loop;                                // 점이 경로를 한 바퀴 도는 시간
$easing: $ease-spring;
$color: $subject-ink;                                 // 링 색

@include stage($stage-yellow);

.stage { position: relative; overflow: hidden; cursor: none; }

.hint {
  margin: 0;
  font-weight: 700; font-size: clamp(16px, 5vw, 22px); line-height: 1.3; font-family: inherit;
  color: rgba($stage-ink, .72);                       // AA: 옐로 면 위 6.06:1
}

.dot,
.ring {
  position: absolute;
  top: 0;
  left: 0;
  border-radius: 50%;
  pointer-events: none;
}

.dot {
  width: 8px;
  height: 8px;
  background: $color;
}

.ring {
  width: 34px;
  height: 34px;
  margin: -13px 0 0 -13px;                            // 점과 중심을 맞춘다
  border: 2px solid $color;
  transition: transform 180ms $easing;                 // 실제 조작에서 링이 뒤늦게 쫓아오는 이유
}

.dot.is-demo { animation: cursor-path $duration $easing infinite; }
.ring.is-demo { animation: cursor-path $duration $easing infinite; animation-delay: -140ms; }

@keyframes cursor-path {
  0%   { transform: translate(50px, 40px); }
  35%  { transform: translate(230px, 70px); }
  70%  { transform: translate(150px, 150px); }
  100% { transform: translate(50px, 40px); }
}

@media (pointer: coarse) {
  .dot, .ring { display: none; }
  .stage { cursor: auto; }
}

@media (prefers-reduced-motion: reduce) {
  .dot.is-demo, .ring.is-demo { animation: none; transform: translate(50px, 40px); }
  .ring { transition: none; }
}

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);
}

.stage {
  position: relative;
  overflow: hidden;
  cursor: none;
}

.hint {
  margin: 0;
  font-weight: 700;
  font-size: clamp(16px, 5vw, 22px);
  line-height: 1.3;
  font-family: inherit;
  color: rgba(23, 20, 26, 0.72);
}

.dot,
.ring {
  position: absolute;
  top: 0;
  left: 0;
  border-radius: 50%;
  pointer-events: none;
}

.dot {
  width: 8px;
  height: 8px;
  background: #17141a;
}

.ring {
  width: 34px;
  height: 34px;
  margin: -13px 0 0 -13px;
  border: 2px solid #17141a;
  transition: transform 180ms cubic-bezier(0.2, 0.8, 0.2, 1);
}

.dot.is-demo {
  animation: cursor-path 2s cubic-bezier(0.2, 0.8, 0.2, 1) infinite;
}

.ring.is-demo {
  animation: cursor-path 2s cubic-bezier(0.2, 0.8, 0.2, 1) infinite;
  animation-delay: -140ms;
}

@keyframes cursor-path {
  0% {
    transform: translate(50px, 40px);
  }
  35% {
    transform: translate(230px, 70px);
  }
  70% {
    transform: translate(150px, 150px);
  }
  100% {
    transform: translate(50px, 40px);
  }
}
@media (pointer: coarse) {
  .dot, .ring {
    display: none;
  }
  .stage {
    cursor: auto;
  }
}
@media (prefers-reduced-motion: reduce) {
  .dot.is-demo, .ring.is-demo {
    animation: none;
    transform: translate(50px, 40px);
  }
  .ring {
    transition: none;
  }
}

// 실제 포인터가 움직이면 점과 링이 같은 좌표를 따라가되 링에는 transition 지연이 있어 뒤처져 보인다.
if (matchMedia('(pointer: fine)').matches) {
  var stage = document.querySelector('.stage');
  var dot = document.querySelector('.dot');
  var ring = document.querySelector('.ring');
  stage.addEventListener('pointermove', function (e) {
    var r = stage.getBoundingClientRect();
    dot.classList.remove('is-demo'); ring.classList.remove('is-demo');
    var v = 'translate(' + (e.clientX - r.left) + 'px,' + (e.clientY - r.top) + 'px)';
    dot.style.transform = v; ring.style.transform = v;
  });
}

import { useState } from "react";
import type { CSSProperties, PointerEvent } from "react";
import styles from "./CursorRingFollow.module.scss";

export type CursorRingFollowProps = {
  hint?: string;
  duration?: number;
  easing?: string;
  color?: string;
};

type Vars = CSSProperties & { "--duration"?: string; "--easing"?: string; "--color"?: string };

export default function CursorRingFollow({
  hint = "포트폴리오",
  duration = 2000,
  easing = "cubic-bezier(.2,.8,.2,1)",
  color = "#17141a",
}: CursorRingFollowProps) {
  const [demo, setDemo] = useState(true);
  const [pos, setPos] = useState({ x: 50, y: 40 });

  const move = (e: PointerEvent<HTMLDivElement>) => {
    const r = e.currentTarget.getBoundingClientRect();
    setDemo(false);
    setPos({ x: e.clientX - r.left, y: e.clientY - r.top });
  };

  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };
  const t = `translate(${pos.x}px,${pos.y}px)`;

  return (
    <div className={styles.stage} style={vars} onPointerMove={move}>
      <p className={styles.hint}>{hint}</p>
      <div className={demo ? `${styles.dot} ${styles.isDemo}` : styles.dot} style={demo ? undefined : { transform: t }} />
      <div className={demo ? `${styles.ring} ${styles.isDemo}` : styles.ring} style={demo ? undefined : { transform: t }} />
    </div>
  );
}