circle · chain · relay · step 062 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="color-scheme" content="light dark">
  <title>Animated Circle - Interactive Demo</title>
  <meta name="description" content="A responsive, accessible circle that changes color when clicked">
  <meta name="theme-color" content="#ffffff" media="(prefers-color-scheme: light)">
  <meta name="theme-color" content="#111111" media="(prefers-color-scheme: dark)">
  <link rel="icon" href="data:,">
  <style>
    *,
    *::before,
    *::after {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
    }
    :root {
      color-scheme: light dark;
      --bg: #fff;
      --text: #374151;
      --fg: #2563eb;
      --shadow: rgba(0, 0, 0, 0.1);
      --kbd-bg: rgba(0, 0, 0, 0.1);
      --drop: drop-shadow(0 4px 12px var(--shadow));
    }
    [data-color="red"] { --fg: #dc2626; }
    /* Dark enough to keep 3:1 against --bg at the resting 0.85 opacity */
    [data-color="green"] { --fg: #15803d; }
    [data-color="amber"] { --fg: #b45309; }
    [data-color="violet"] { --fg: #7c3aed; }
    [data-color="cyan"] { --fg: #0e7490; }
    @media (prefers-color-scheme: dark) {
      :root {
        --bg: #111;
        --text: #d1d5db;
        --fg: #93c5fd;
        --shadow: rgba(0, 0, 0, 0.6);
        --kbd-bg: rgba(255, 255, 255, 0.15);
      }
      [data-color="red"] { --fg: #fca5a5; }
      [data-color="green"] { --fg: #86efac; }
      [data-color="amber"] { --fg: #fcd34d; }
      [data-color="violet"] { --fg: #c4b5fd; }
      [data-color="cyan"] { --fg: #67e8f9; }
    }
    @media (prefers-contrast: more) {
      :root {
        --shadow: rgba(0, 0, 0, 0.9);
        --drop: drop-shadow(0 2px 8px var(--shadow));
      }
      .circle svg {
        opacity: 1;
      }
    }
    @media (forced-colors: active) {
      /* The color is the content here, so keep it; the stroke guarantees the shape */
      .circle svg {
        forced-color-adjust: none;
        color: var(--fg);
      }
      svg circle {
        stroke: CanvasText;
        stroke-width: 2;
      }
    }
    body {
      min-height: 100vh;
      min-height: 100dvh;
      display: grid;
      place-items: center;
      padding: 1rem;
      background: var(--bg);
      color: var(--text);
      font-family: system-ui, -apple-system, sans-serif;
    }
    main {
      width: 100%;
      display: flex;
      flex-direction: column;
      align-items: center;
      text-align: center;
    }
    .circle {
      display: block;
      width: min(360px, 100%, 60vh);
      width: min(360px, 100%, 60dvh);
      aspect-ratio: 1;
      border: 0;
      border-radius: 50%;
      background: none;
      color: var(--fg);
      cursor: pointer;
      touch-action: manipulation;
      -webkit-tap-highlight-color: transparent;
      -webkit-user-select: none;
      user-select: none;
      -webkit-touch-callout: none;
      transition: color 0.4s;
      min-height: 48px;
      min-width: 48px;
    }
    .no-transition,
    .no-transition svg {
      transition: none !important;
    }
    .circle:focus-visible {
      outline: 3px solid currentColor;
      outline-offset: 12px;
    }
    svg {
      display: block;
      width: 100%;
      height: 100%;
      overflow: visible;
      /* Leave hit testing to the button's rounded box, not the svg's square one */
      pointer-events: none;
      opacity: 0.85;
      filter: var(--drop);
      transition: opacity 0.3s;
    }
    .circle:active svg,
    .circle:focus-visible svg {
      opacity: 1;
    }
    @keyframes pulse {
      0% {
        filter: var(--drop) drop-shadow(0 0 16px currentColor);
      }
      100% {
        filter: var(--drop) drop-shadow(0 0 0 transparent);
      }
    }
    @media (hover: hover) {
      .circle:hover svg {
        opacity: 1;
      }
    }
    @media (prefers-reduced-motion: no-preference) {
      svg {
        transition: transform 0.3s cubic-bezier(0.34, 1.56, 0.64, 1), opacity 0.3s;
      }
      .circle:focus-visible svg {
        transform: scale(1.05);
      }
      .circle:active svg {
        transform: scale(0.97);
      }
      .circle.color-changed svg {
        animation: pulse 0.5s ease-out;
      }
    }
    @media (hover: hover) and (prefers-reduced-motion: no-preference) {
      .circle:hover:not(:active) svg {
        transform: scale(1.05);
      }
    }
    .visually-hidden {
      position: absolute;
      width: 1px;
      height: 1px;
      overflow: hidden;
      clip-path: inset(50%);
      white-space: nowrap;
    }
    .status {
      margin-top: 2rem;
      font-weight: 600;
    }
    .hint {
      margin-top: 0.25rem;
      font-size: 0.875rem;
      line-height: 1.75;
      text-wrap: balance;
    }
    .help-button {
      margin-left: 0.5rem;
      display: inline-block;
      width: 1.5rem;
      height: 1.5rem;
      border-radius: 50%;
      background: var(--kbd-bg);
      border: 1px solid var(--text);
      color: var(--text);
      cursor: pointer;
      font: inherit;
      font-size: 0.75rem;
      font-weight: bold;
      line-height: 1;
      text-align: center;
      vertical-align: middle;
      touch-action: manipulation;
      transition: background-color 0.2s, color 0.2s;
    }
    .help-button:focus-visible {
      outline: 2px solid currentColor;
      outline-offset: 2px;
    }
    @media (hover: hover) {
      .help-button:hover {
        background: var(--text);
        color: var(--bg);
      }
    }
    .keys {
      display: none;
    }
    .keys.visible {
      display: inline;
    }
    @media (hover: none) and (pointer: coarse) {
      .hint .keys {
        display: none !important;
      }
      .help-button {
        display: none;
      }
    }
    kbd {
      display: inline-block;
      padding: 0.125rem 0.375rem;
      background: var(--kbd-bg);
      border: 1px solid transparent;
      border-radius: 0.25rem;
      font-family: monospace;
      font-size: 0.75em;
      line-height: 1.2;
    }
  </style>
</head>
<body>
  <main>
    <h1 class="visually-hidden">Animated Circle</h1>
    <button type="button" class="circle no-transition" aria-label="Change circle color" aria-describedby="status hint">
      <svg viewBox="0 0 100 100" aria-hidden="true" focusable="false" xmlns="http://www.w3.org/2000/svg">
        <circle cx="50" cy="50" r="50" fill="currentColor" stroke="none"/>
      </svg>
    </button>
    <p class="status" id="status" role="status" aria-live="polite">Blue</p>
    <p class="hint"><span id="hint"><span class="verb">Click</span> to cycle • <span class="double-verb">Double-click</span> or hold to reset<span class="keys" id="keys"> • <kbd>Shift</kbd>+click reverse • <kbd>↑↓←→</kbd> navigate • <kbd>Home</kbd>/<kbd>End</kbd> jump</span></span> <button type="button" class="help-button" aria-label="Keyboard shortcuts" aria-expanded="false" aria-controls="keys"><span aria-hidden="true">?</span></button></p>
    <noscript><p class="hint">JavaScript is required to change the color.</p></noscript>
  </main>
  <script>
    const config = {
      colors: ['blue', 'red', 'green', 'amber', 'violet', 'cyan'],
      storageKey: 'circle-color',
      hapticDuration: 50,
      longPressDuration: 500,
      longPressTolerance: 10,
      keySteps: { ArrowRight: 1, ArrowDown: 1, ArrowLeft: -1, ArrowUp: -1 },
    };

    const DOM = {
      button: document.querySelector('.circle'),
      status: document.querySelector('.status'),
      helpButton: document.querySelector('.help-button'),
      keyHint: document.querySelector('.keys'),
      verbSpan: document.querySelector('.verb'),
      doubleVerbSpan: document.querySelector('.double-verb'),
    };

    const state = {
      index: 0,
      shiftHeld: false,
      hoverCapable: true,
      reducedMotion: matchMedia('(prefers-reduced-motion: reduce)'),
      hoverQuery: matchMedia('(hover: none)'),
      longPressTimer: null,
      longPressed: false,
      pressX: 0,
      pressY: 0,
      pointerType: '',
    };

    function loadColor() {
      try {
        return localStorage.getItem(config.storageKey);
      } catch {
        return null;
      }
    }

    function saveColor(color) {
      try {
        localStorage.setItem(config.storageKey, color);
      } catch {}
    }

    function applyColor() {
      const color = config.colors[state.index];
      // The first color is the :root default, so it needs no attribute
      if (state.index === 0) delete DOM.button.dataset.color;
      else DOM.button.dataset.color = color;
      DOM.status.textContent = color[0].toUpperCase() + color.slice(1);
    }

    function syncFromStorage(color = loadColor()) {
      const index = config.colors.indexOf(color);
      state.index = index === -1 ? 0 : index;
      applyColor();
    }

    // acknowledge: give feedback even when the color is already the requested one
    function setIndex(next, { haptic = false, acknowledge = false } = {}) {
      const changed = next !== state.index;
      if (!changed && !acknowledge) return;
      if (changed) {
        state.index = next;
        applyColor();
        saveColor(config.colors[state.index]);
      }

      if (haptic && navigator.vibrate) navigator.vibrate(config.hapticDuration);

      if (state.reducedMotion.matches) return;
      DOM.button.classList.remove('color-changed');
      void DOM.button.offsetWidth;
      DOM.button.classList.add('color-changed');
    }

    function changeColor(step) {
      setIndex((state.index + step + config.colors.length) % config.colors.length, { haptic: true });
    }

    function updateDeviceVerbs() {
      state.hoverCapable = !state.hoverQuery.matches;
      DOM.verbSpan.textContent = state.hoverCapable ? 'Click' : 'Tap';
      DOM.doubleVerbSpan.textContent = state.hoverCapable ? 'Double-click' : 'Double-tap';
    }

    function toggleKeyHintVisibility() {
      const expanded = DOM.keyHint.classList.toggle('visible');
      DOM.helpButton.setAttribute('aria-expanded', expanded);
    }

    function syncKeyHint() {
      DOM.keyHint.classList.toggle('visible', state.hoverCapable);
      DOM.helpButton.setAttribute('aria-expanded', state.hoverCapable);
    }

    function handleKeyDown(event) {
      if (event.key === 'Enter' || event.key === ' ') {
        if (!event.repeat) state.shiftHeld = event.shiftKey;
        if (event.key === 'Enter' && event.repeat) event.preventDefault();
        return;
      }

      if (event.altKey || event.ctrlKey || event.metaKey) return;

      if (event.key in config.keySteps) {
        event.preventDefault();
        changeColor(config.keySteps[event.key]);
      } else if (event.key === 'Home') {
        event.preventDefault();
        setIndex(0, { haptic: true });
      } else if (event.key === 'End') {
        event.preventDefault();
        setIndex(config.colors.length - 1, { haptic: true });
      }
    }

    function handleEscape(event) {
      if (event.key !== 'Escape' || event.defaultPrevented) return;
      if (DOM.keyHint.classList.contains('visible')) toggleKeyHintVisibility();
    }

    // Initialize
    syncFromStorage();

    // Wait two frames to ensure layout is complete before enabling transitions
    requestAnimationFrame(() => requestAnimationFrame(() => {
      DOM.button.classList.remove('no-transition');
    }));

    updateDeviceVerbs();
    syncKeyHint();
    // e.g. a tablet gaining or losing a trackpad/keyboard
    state.hoverQuery.addEventListener('change', () => {
      updateDeviceVerbs();
      syncKeyHint();
    });

    // Event listeners
    function clearLongPressTimer() {
      if (state.longPressTimer) clearTimeout(state.longPressTimer);
      state.longPressTimer = null;
    }

    function attachEventListeners() {
      DOM.button.addEventListener('keydown', handleKeyDown);
      DOM.button.addEventListener('keyup', (event) => {
        if (event.key === ' ') state.shiftHeld = event.shiftKey;
      });
      DOM.button.addEventListener('blur', () => {
        state.shiftHeld = false;
        clearLongPressTimer();
      });
      DOM.button.addEventListener('pointerdown', (event) => {
        clearLongPressTimer();
        state.longPressed = false;
        state.pointerType = event.pointerType;
        if (!event.isPrimary || event.button !== 0) return;
        state.pressX = event.clientX;
        state.pressY = event.clientY;
        state.longPressTimer = setTimeout(() => {
          state.longPressTimer = null;
          state.longPressed = true;
          setIndex(0, { haptic: true, acknowledge: true });
        }, config.longPressDuration);
      }, { passive: true });
      // Touch pointers are captured, so a finger sliding away never fires pointerleave
      DOM.button.addEventListener('pointermove', (event) => {
        if (!state.longPressTimer) return;
        const distance = Math.hypot(event.clientX - state.pressX, event.clientY - state.pressY);
        if (distance > config.longPressTolerance) clearLongPressTimer();
      }, { passive: true });
      DOM.button.addEventListener('contextmenu', (event) => {
        if (state.pointerType === 'mouse') {
          clearLongPressTimer();
        } else if (state.longPressTimer || state.longPressed) {
          event.preventDefault();
        }
      });
      DOM.button.addEventListener('pointerup', clearLongPressTimer, { passive: true });
      DOM.button.addEventListener('pointercancel', clearLongPressTimer, { passive: true });
      DOM.button.addEventListener('pointerleave', clearLongPressTimer, { passive: true });
      DOM.button.addEventListener('click', (event) => {
        clearLongPressTimer();
        const afterLongPress = state.longPressed && event.detail !== 0;
        state.longPressed = false;
        const reverse = event.shiftKey || state.shiftHeld;
        state.shiftHeld = false;
        // Only the second click of a run belongs to dblclick; later ones cycle again
        if (afterLongPress || event.detail === 2) return;
        changeColor(reverse ? -1 : 1);
      });
      DOM.button.addEventListener('dblclick', (event) => {
        // Some engines fire dblclick again on every even click of a run
        if (event.detail > 2) return;
        setIndex(0, { haptic: true, acknowledge: true });
      });
      DOM.button.addEventListener('animationend', () => {
        DOM.button.classList.remove('color-changed');
      });

      DOM.helpButton.addEventListener('click', toggleKeyHintVisibility);
      addEventListener('keydown', handleEscape);
    }

    attachEventListeners();

    addEventListener('storage', (event) => {
      // Sync if changed key matches or if entire storage was cleared (key === null)
      if (event.key !== config.storageKey && event.key !== null) return;
      syncFromStorage(event.newValue);
    });
    // Storage events are not delivered while the page sits in the bfcache
    addEventListener('pageshow', (event) => {
      if (event.persisted) syncFromStorage();
    });
  </script>
</body>
</html>