04Gradient stroke ring

<main class="stage">
  <div class="gd is-demo">
    <div class="gd__dial">
      <svg class="gd__svg" viewBox="0 0 128 128" width="128" height="128" aria-hidden="true">
        <defs>
          <linearGradient id="gdStroke" gradientUnits="userSpaceOnUse" x1="12" y1="12" x2="116" y2="116">
            <stop class="gd__stop-a" offset="0"/>
            <stop class="gd__stop-b" offset="1"/>
          </linearGradient>
        </defs>
        <circle class="gd__track" cx="64" cy="64" r="52"/>
        <circle class="gd__ring" cx="64" cy="64" r="52"/>
      </svg>
      <div class="gd__center">
        <span class="gd__num" role="status" aria-label="Current value"></span>
        <span class="gd__cap">Conversion</span>
      </div>
    </div>
    <label class="gd__slider">
      <span class="gd__slider-label">Adjust value</span>
      <input class="gd__range" type="range" min="0" max="100" value="74">
    </label>
  </div>
</main>

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

$duration: $dur-loop;
$easing: $ease-spring;
$color: $subject-sky;

@include stage($stage-paper);

@property --num {
  syntax: "<integer>";
  inherits: true;
  initial-value: 0;
}

.gd {
  --num: 74;
  box-sizing: border-box;
  display: grid;
  justify-items: center;
  gap: $sp-4;
  color: $stage-ink;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
}

.gd__dial { position: relative; display: grid; place-items: center; }
.gd__svg {
  width: clamp(108px, 32vw, 128px);
  height: clamp(108px, 32vw, 128px);
  transform: rotate(-90deg);
}

// 그라디언트 두 끝은 CSS 에서 준다 — 토큰 밖의 색을 SVG 안에 다시 쓰지 않으려고
.gd__stop-a { stop-color: $color; }
.gd__stop-b { stop-color: $subject-pink; }

.gd__track {
  fill: none;
  stroke: rgba(23, 20, 26, .1);
  stroke-width: 14;
}
.gd__ring {
  fill: none;
  stroke: url(#gdStroke);
  stroke-width: 14;
  // 둥근 끝은 반지름만큼 삐져나온다 — 0% 에서도 점이 남는 이유
  stroke-linecap: round;
  stroke-dasharray: 326.726;
  stroke-dashoffset: calc(326.726 * (1 - var(--num) / 100));
}

.gd__center { position: absolute; display: grid; justify-items: center; gap: $sp-1; pointer-events: none; }
.gd__num {
  font-size: clamp(22px, 7vw, 26px);
  font-weight: 800;
  font-variant-numeric: tabular-nums;
  line-height: 1.1;
}
.gd__num::after {
  counter-reset: n var(--num);
  content: counter(n) "%";
}
.gd__cap { font-size: 10px; font-weight: 700; color: rgba(23, 20, 26, .5); }

.gd__slider { display: grid; justify-items: center; gap: $sp-2; }
.gd__slider-label { font-size: 10px; font-weight: 700; color: rgba(23, 20, 26, .72); }
.gd__range {
  width: clamp(152px, 56vw, 188px);
  accent-color: $color;
  cursor: pointer;
}

// ── 자동 루프: 0 → 74 → 0. 감고 푸는 한 바퀴라 끝에서 처음으로 튀지 않는다 ──
.gd.is-demo { animation: gd-fill $duration $easing infinite; }
@keyframes gd-fill {
  0%       { --num: 0; }
  45%, 55% { --num: 74; }
  100%     { --num: 0; }
}

@media (max-width: 340px) {
  .gd { gap: $sp-3; }
}

@media (prefers-reduced-motion: reduce) {
  .gd.is-demo { animation: none !important; --num: 74; }
}

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

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

@property --num {
  syntax: "<integer>";
  inherits: true;
  initial-value: 0;
}
.gd {
  --num: 74;
  box-sizing: border-box;
  display: grid;
  justify-items: center;
  gap: 16px;
  color: #17141a;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
}

.gd__dial {
  position: relative;
  display: grid;
  place-items: center;
}

.gd__svg {
  width: clamp(108px, 32vw, 128px);
  height: clamp(108px, 32vw, 128px);
  transform: rotate(-90deg);
}

.gd__stop-a {
  stop-color: #6ec8ff;
}

.gd__stop-b {
  stop-color: #ff9ebb;
}

.gd__track {
  fill: none;
  stroke: rgba(23, 20, 26, 0.1);
  stroke-width: 14;
}

.gd__ring {
  fill: none;
  stroke: url(#gdStroke);
  stroke-width: 14;
  stroke-linecap: round;
  stroke-dasharray: 326.726;
  stroke-dashoffset: calc(326.726 * (1 - var(--num) / 100));
}

.gd__center {
  position: absolute;
  display: grid;
  justify-items: center;
  gap: 4px;
  pointer-events: none;
}

.gd__num {
  font-size: clamp(22px, 7vw, 26px);
  font-weight: 800;
  font-variant-numeric: tabular-nums;
  line-height: 1.1;
}

.gd__num::after {
  counter-reset: n var(--num);
  content: counter(n) "%";
}

.gd__cap {
  font-size: 10px;
  font-weight: 700;
  color: rgba(23, 20, 26, 0.5);
}

.gd__slider {
  display: grid;
  justify-items: center;
  gap: 8px;
}

.gd__slider-label {
  font-size: 10px;
  font-weight: 700;
  color: rgba(23, 20, 26, 0.72);
}

.gd__range {
  width: clamp(152px, 56vw, 188px);
  accent-color: #6ec8ff;
  cursor: pointer;
}

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

@keyframes gd-fill {
  0% {
    --num: 0;
  }
  45%, 55% {
    --num: 74;
  }
  100% {
    --num: 0;
  }
}
@media (max-width: 340px) {
  .gd {
    gap: 12px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .gd.is-demo {
    animation: none !important;
    --num: 74;
  }
}

// 실제 동작: 슬라이더가 --num 하나를 바꾸고, 링의 dashoffset 과 가운데 숫자가 둘 다 그 값을 읽는다.
var gd = document.querySelector('.gd');
var range = gd.querySelector('.gd__range');
range.addEventListener('input', function () {
  gd.classList.remove('is-demo');
  gd.style.setProperty('--num', range.value);
});

import { useState } from "react";
import type { CSSProperties } from "react";
import styles from "./GradientStrokeRing.module.scss";

let gradSeq = 0;

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

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

export default function GradientStrokeRing({
  duration = 220,
  easing = "cubic-bezier(.2, .8, .2, 1)",
  color = "#6ec8ff",
}: GradientStrokeRingProps) {
  const [num, setNum] = useState(74);
  // 한 페이지에 여러 개를 놔도 gradient id 가 부딪히지 않게 한다 (콜론은 url() 에서 못 쓴다)
  // 한 페이지에 여러 개를 놔도 그라디언트 id 가 안 부딪히게 인스턴스마다 새 번호를 받는다
  const [gradientId] = useState(() => `gdStroke-${++gradSeq}`);
  const vars: Vars = {
    "--duration": `${duration}ms`,
    "--easing": easing,
    "--color": color,
    "--num": String(num),
  };

  return (
    <div className={styles.gd} style={vars}>
      <div className={styles.dial}>
        <svg className={styles.svg} viewBox="0 0 128 128" width="128" height="128" aria-hidden="true">
          <defs>
            <linearGradient id={gradientId} gradientUnits="userSpaceOnUse" x1="12" y1="12" x2="116" y2="116">
              <stop className={styles.stopA} offset="0" />
              <stop className={styles.stopB} offset="1" />
            </linearGradient>
          </defs>
          <circle className={styles.track} cx="64" cy="64" r="52" />
          <circle className={styles.ring} cx="64" cy="64" r="52" style={{ stroke: `url(#${gradientId})` }} />
        </svg>
        <div className={styles.center}>
          <span className={styles.num} role="status" aria-label="Current value" />
          <span className={styles.cap}>Conversion</span>
        </div>
      </div>
      <label className={styles.slider}>
        <span className={styles.sliderLabel}>Adjust value</span>
        <input
          className={styles.range}
          type="range"
          min={0}
          max={100}
          value={num}
          onChange={(e: any) => setNum(Number(e.currentTarget.value))}
        />
      </label>
    </div>
  );
}