circle · chain · Sonnet 5 · step 044 of 64

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="description" content="An accessible, animated pulsing circle with adjustable speed and pause controls.">
  <meta name="color-scheme" content="dark">
  <meta name="theme-color" content="#0d0d17">
  <title>Pulsing Circle</title>
  <link rel="icon" href="data:,">

  <style>
    :root {
      --circle-hue: #8ec5ff;
      --circle-core: #4a7dd9;
      --circle-shadow: #1f3a75;
      --cycle: 2.5s;
    }
    * {
      margin: 0;
      padding: 0;
      box-sizing: border-box;
    }
    body {
      width: 100vw;
      height: 100vh;
      height: 100dvh;
      display: flex;
      flex-direction: column;
      justify-content: center;
      align-items: center;
      gap: 24px;
      background: radial-gradient(circle at center, #1a1a2e 0%, #0d0d17 100%);
      overflow: hidden;
    }
    svg {
      width: min(400px, 80vmin);
      height: min(400px, 80vmin);
      overflow: visible;
      cursor: pointer;
      user-select: none;
      -webkit-tap-highlight-color: transparent;
      transition: filter 0.3s ease;
    }
    .circle-btn:hover svg {
      filter: brightness(1.08);
    }
    .ambient {
      fill: var(--circle-hue);
      opacity: 0.12;
      filter: blur(30px);
      animation: breathe var(--cycle) cubic-bezier(0.4, 0, 0.2, 1) infinite;
      transform-origin: 200px 200px;
      will-change: transform, opacity;
    }
    .core {
      animation: pulse var(--cycle) cubic-bezier(0.4, 0, 0.2, 1) infinite;
      transform-origin: 200px 200px;
      filter: url(#glow);
      will-change: transform, opacity;
    }
    .highlight {
      fill: url(#highlightGradient);
      transform-origin: 200px 200px;
      animation: pulse var(--cycle) cubic-bezier(0.4, 0, 0.2, 1) infinite;
      pointer-events: none;
      will-change: transform, opacity;
    }
    .ring {
      fill: none;
      stroke: var(--circle-hue);
      stroke-width: 2.5;
      transform-origin: 200px 200px;
      animation: ripple var(--cycle) cubic-bezier(0.2, 0.6, 0.4, 1) infinite;
      will-change: transform, opacity, stroke-width;
    }
    .ring--delay-1 {
      animation-delay: calc(var(--cycle) / 3);
    }
    .ring--delay-2 {
      animation-delay: calc(var(--cycle) / 3 * 2);
    }
    @keyframes pulse {
      0%, 100% {
        transform: scale(1);
        opacity: 0.9;
      }
      50% {
        transform: scale(1.05);
        opacity: 1;
      }
    }
    @keyframes breathe {
      0%, 100% {
        transform: scale(0.95);
        opacity: 0.1;
      }
      50% {
        transform: scale(1.1);
        opacity: 0.18;
      }
    }
    @keyframes ripple {
      0% {
        transform: scale(1);
        opacity: 0.6;
        stroke-width: var(--ring-width, 2.5);
      }
      100% {
        transform: scale(1.35);
        opacity: 0;
        stroke-width: calc(var(--ring-width, 2.5) / 5);
      }
    }
    body.paused .core,
    body.paused .ring,
    body.paused .ambient,
    body.paused .highlight {
      animation-play-state: paused;
    }
    /* Force-paused until JS takes over (below), avoiding a flash of motion;
       once JS is ready, control defers entirely to body.paused so the user
       can still explicitly resume even with reduced motion preferred. */
    @media (prefers-reduced-motion: reduce) {
      body:not(.js-ready) .core,
      body:not(.js-ready) .ring,
      body:not(.js-ready) .ambient,
      body:not(.js-ready) .highlight {
        animation-play-state: paused;
      }
    }
    .speed-label {
      color: var(--circle-hue);
      font-family: system-ui, sans-serif;
      font-size: 0.85rem;
      letter-spacing: 0.05em;
      opacity: 0.85;
      user-select: none;
      text-align: center;
    }
    .hint {
      display: block;
      margin-top: 4px;
      font-size: 0.7rem;
      opacity: 1;
    }
    .controls {
      display: flex;
      align-items: center;
      gap: 12px;
      max-width: min(320px, 90vw);
    }
    .pause-btn {
      display: inline-flex;
      align-items: center;
      justify-content: center;
      width: 44px;
      height: 44px;
      padding: 0;
      border-radius: 50%;
      border: 1px solid var(--circle-hue);
      background: transparent;
      color: var(--circle-hue);
      cursor: pointer;
      touch-action: manipulation;
      transition: background 0.2s ease;
    }
    .pause-btn:hover {
      background: rgba(142, 197, 255, 0.15);
    }
    .pause-btn:focus-visible {
      outline: 2px solid var(--circle-hue);
      outline-offset: 2px;
    }
    @media (prefers-contrast: more) {
      .pause-btn {
        border-width: 2px;
      }
      .ring {
        --ring-width: 3.5;
      }
    }
    .pause-btn svg {
      width: 14px;
      height: 14px;
    }
    .circle-btn {
      display: inline-flex;
      padding: 0;
      border: none;
      background: none;
      cursor: pointer;
      touch-action: manipulation;
      -webkit-tap-highlight-color: transparent;
      border-radius: 50%;
    }
    .circle-btn:focus-visible {
      outline: none;
    }
    .circle-btn:focus-visible svg {
      outline: 2px solid var(--circle-hue);
      outline-offset: 8px;
      border-radius: 50%;
    }
    .no-js .controls {
      display: none;
    }
    .no-js .circle-btn {
      cursor: default;
    }
    .visually-hidden {
      position: absolute;
      width: 1px;
      height: 1px;
      padding: 0;
      margin: -1px;
      overflow: hidden;
      clip: rect(0, 0, 0, 0);
      white-space: nowrap;
      border: 0;
    }
    .noscript-note {
      color: var(--circle-hue);
      font-family: system-ui, sans-serif;
      font-size: 0.8rem;
      opacity: 0.75;
      text-align: center;
      max-width: min(320px, 90vw);
    }
  </style>
</head>
<body class="no-js">
  <h1 class="visually-hidden">Pulsing Circle</h1>
  <button type="button" class="circle-btn" id="circleBtn" aria-label="Pulsing blue circle animation" aria-describedby="speedText" title="Pulsing blue circle animation">
  <svg viewBox="0 0 400 400" focusable="false" aria-hidden="true">
    <defs>
      <radialGradient id="circleGradient" cx="35%" cy="35%" r="65%">
        <stop offset="0%" style="stop-color: var(--circle-hue)"/>
        <stop offset="55%" style="stop-color: var(--circle-core)"/>
        <stop offset="100%" style="stop-color: var(--circle-shadow)"/>
      </radialGradient>
      <radialGradient id="highlightGradient" cx="32%" cy="28%" r="22%">
        <stop offset="0%" stop-color="#ffffff" stop-opacity="0.55"/>
        <stop offset="100%" stop-color="#ffffff" stop-opacity="0"/>
      </radialGradient>
      <filter id="glow" x="-80%" y="-80%" width="260%" height="260%">
        <feGaussianBlur in="SourceGraphic" stdDeviation="10" result="blur"/>
        <feColorMatrix in="blur" type="matrix"
          values="0 0 0 0 0.55  0 0 0 0 0.77  0 0 0 0 1  0 0 0 0.9 0" result="tintedBlur"/>
        <feMerge>
          <feMergeNode in="tintedBlur"/>
          <feMergeNode in="SourceGraphic"/>
        </feMerge>
      </filter>
    </defs>
    <circle class="ambient" cx="200" cy="200" r="160"/>
    <circle class="ring" cx="200" cy="200" r="140"/>
    <circle class="ring ring--delay-1" cx="200" cy="200" r="140"/>
    <circle class="ring ring--delay-2" cx="200" cy="200" r="140"/>
    <circle class="core" cx="200" cy="200" r="140" fill="url(#circleGradient)"/>
    <circle class="highlight" cx="200" cy="200" r="140"/>
  </svg>
  </button>
  <div class="controls">
    <button type="button" class="pause-btn" id="pauseBtn" aria-pressed="false" aria-label="Pause animation" title="Pause animation">
      <svg id="pauseIcon" viewBox="0 0 24 24" fill="currentColor" aria-hidden="true">
        <path d="M6 4h4v16H6zM14 4h4v16h-4z"/>
      </svg>
    </button>
    <p class="speed-label" id="speedLabel">
      <span id="speedText" aria-live="polite">Normal speed</span>
      <span class="hint" aria-hidden="true">Activate circle to change speed</span>
    </p>
  </div>
  <noscript>
    <p class="noscript-note">Enable JavaScript to change the animation speed or pause it.</p>
  </noscript>
  <script>
    const circleBtn = document.getElementById('circleBtn');
    const speedText = document.getElementById('speedText');
    const pauseBtn = document.getElementById('pauseBtn');
    const pauseIcon = document.getElementById('pauseIcon');
    const animatedEls = document.querySelectorAll('.core, .ring, .ambient, .highlight');
    const PLAY_ICON = '<path d="M8 5l11 7-11 7z"/>';
    const PAUSE_ICON = pauseIcon.innerHTML;
    const speeds = [
      { value: '2.5s', name: 'Normal speed' },
      { value: '1.2s', name: 'Fast speed' },
      { value: '4.5s', name: 'Slow speed' },
    ];
    const reducedMotionQuery = window.matchMedia('(prefers-reduced-motion: reduce)');
    let speedIndex = 0;
    let manuallyPaused = reducedMotionQuery.matches;
    // Once the user has explicitly toggled pause/play, respect that choice
    // instead of letting a later OS-level reduced-motion change override it.
    let userHasChosen = false;

    const STORAGE_KEY = 'pulsing-circle-prefs';
    try {
      const saved = JSON.parse(localStorage.getItem(STORAGE_KEY));
      if (saved && Number.isInteger(saved.speedIndex) && speeds[saved.speedIndex]) {
        speedIndex = saved.speedIndex;
        circleBtn.style.setProperty('--cycle', speeds[speedIndex].value);
      }
      if (saved && typeof saved.manuallyPaused === 'boolean') {
        manuallyPaused = saved.manuallyPaused;
        userHasChosen = true;
      }
    } catch {
      // Ignore malformed or inaccessible storage; fall back to defaults.
    }

    function savePrefs() {
      try {
        localStorage.setItem(STORAGE_KEY, JSON.stringify({ speedIndex, manuallyPaused }));
      } catch {
        // Storage may be unavailable (e.g. private browsing); ignore.
      }
    }

    function updateLabels() {
      const { name } = speeds[speedIndex];
      speedText.textContent = manuallyPaused ? `${name} (paused)` : name;
      circleBtn.title = `Activate to change pulse speed (currently ${name})`;
    }

    function cycleSpeed() {
      speedIndex = (speedIndex + 1) % speeds.length;
      const { value } = speeds[speedIndex];
      circleBtn.style.setProperty('--cycle', value);
      restartAnimations();
      updateLabels();
      savePrefs();
    }

    // Restart animations from the beginning so a new speed feels immediate
    // instead of jumping mid-cycle.
    function restartAnimations() {
      animatedEls.forEach((el) => {
        el.style.animation = 'none';
        void el.offsetWidth;
        el.style.animation = '';
      });
    }

    function applyPauseState() {
      document.body.classList.toggle('paused', document.hidden || manuallyPaused);
      pauseBtn.setAttribute('aria-pressed', String(manuallyPaused));
      pauseBtn.setAttribute('aria-label', manuallyPaused ? 'Resume animation' : 'Pause animation');
      pauseBtn.setAttribute('title', manuallyPaused ? 'Resume animation' : 'Pause animation');
      pauseIcon.innerHTML = manuallyPaused ? PLAY_ICON : PAUSE_ICON;
      updateLabels();
    }

    function togglePause() {
      manuallyPaused = !manuallyPaused;
      userHasChosen = true;
      applyPauseState();
      savePrefs();
    }

    circleBtn.addEventListener('click', cycleSpeed);
    pauseBtn.addEventListener('click', togglePause);

    document.addEventListener('visibilitychange', applyPauseState);

    const onReducedMotionChange = (e) => {
      if (userHasChosen) return;
      manuallyPaused = e.matches;
      applyPauseState();
    };
    if (reducedMotionQuery.addEventListener) {
      reducedMotionQuery.addEventListener('change', onReducedMotionChange);
    } else if (reducedMotionQuery.addListener) {
      // Safari < 14 fallback.
      reducedMotionQuery.addListener(onReducedMotionChange);
    }

    // Keep multiple open tabs/windows of this page in sync with each other.
    window.addEventListener('storage', (e) => {
      if (e.key !== STORAGE_KEY || !e.newValue) return;
      try {
        const saved = JSON.parse(e.newValue);
        if (Number.isInteger(saved.speedIndex) && speeds[saved.speedIndex] && saved.speedIndex !== speedIndex) {
          speedIndex = saved.speedIndex;
          circleBtn.style.setProperty('--cycle', speeds[speedIndex].value);
          restartAnimations();
        }
        if (typeof saved.manuallyPaused === 'boolean') {
          manuallyPaused = saved.manuallyPaused;
          userHasChosen = true;
        }
        applyPauseState();
        updateLabels();
      } catch {
        // Ignore malformed storage updates from other tabs.
      }
    });

    applyPauseState();
    updateLabels();
    circleBtn.setAttribute('aria-label', 'Pulsing blue circle animation. Activate to change pulse speed.');
    document.body.classList.add('js-ready');
    document.body.classList.remove('no-js');
  </script>
</body>
</html>