Avatar Group Hover

<!--
  Avatar Group Hover - transitions.dev-inspired primitive for HyperFrames.

  Paste the markup and CSS into a composition. Use the timeline integration
  note at the bottom as the starting point for deterministic GSAP animation.

  Variables. The script reads each one, falls back to the declared default on
  anything missing or unrecognised, and writes the result as a custom property
  the CSS consumes. The timeline recipe below is untouched by them: it still
  drives one lift offset, and these decide what it lifts.

    - size (small | standard | large, default standard): avatar diameter,
      42px, 54px or 70px. The initials scale with it.
    - overlap (tight | standard | loose, default standard): how far each
      avatar tucks under the one before it, as a share of its own diameter:
      half, a third, or barely an eighth.
    - accent (blue | violet | green, default blue): the colour the avatar
      gradient resolves into out of the shared near-black.

  On every default the result is identical to the original: 54px avatars
  overlapping by 18px in the blue gradient.
-->

<div
  class="hf-transition-avatar-group-hover"
  data-composition-variables='[
    { "id": "size", "type": "enum", "role": "style", "label": "Size", "description": "Avatar diameter, with the initials scaling alongside it.", "default": "standard", "options": [{ "value": "small", "label": "Small" }, { "value": "standard", "label": "Standard" }, { "value": "large", "label": "Large" }] },
    { "id": "overlap", "type": "enum", "role": "style", "label": "Overlap", "description": "How far each avatar tucks under the one before it, as a share of its own diameter.", "default": "standard", "options": [{ "value": "tight", "label": "Tight" }, { "value": "standard", "label": "Standard" }, { "value": "loose", "label": "Loose" }] },
    { "id": "accent", "type": "enum", "role": "style", "label": "Accent", "description": "Colour the avatar gradient resolves into.", "default": "blue", "options": [{ "value": "blue", "label": "Blue" }, { "value": "violet", "label": "Violet" }, { "value": "green", "label": "Green" }] }
  ]'
>
  <span>A</span><span>B</span><span>C</span><span>D</span>
</div>

<style>
  .hf-transition-avatar-group-hover {
    display: inline-flex;
    align-items: center;
    padding-left: var(--hf-avatar-overlap, 18px);
    font-family: Inter, system-ui, sans-serif;
  }
  .hf-transition-avatar-group-hover span {
    display: grid;
    place-items: center;
    width: var(--hf-avatar-size, 54px);
    height: var(--hf-avatar-size, 54px);
    margin-left: calc(-1 * var(--hf-avatar-overlap, 18px));
    border: 3px solid #fff;
    border-radius: 999px;
    background: linear-gradient(135deg, #111827, var(--hf-avatar-accent, #0ea5e9));
    color: #fff;
    font-size: var(--hf-avatar-font, 1em);
    font-weight: 900;
    box-shadow: 0 12px 30px rgba(24, 24, 27, 0.18);
    transform: translateY(var(--hf-avatar-y, 0px));
  }
</style>

<script>
  (function () {
    "use strict";

    var vars =
      window.__hyperframes && window.__hyperframes.getVariables
        ? window.__hyperframes.getVariables()
        : {};

    // Unrecognised overrides return to their declared defaults.
    var sizes = { small: 42, standard: 54, large: 70 };
    var fonts = { small: "0.8em", standard: "1em", large: "1.3em" };
    // Overlap is a share of the diameter, so the two knobs stay independent.
    var overlaps = { tight: 0.5, standard: 1 / 3, loose: 0.12 };
    var accents = { blue: "#0ea5e9", violet: "#a78bfa", green: "#34d399" };

    function pick(table, value, fallback) {
      return Object.prototype.hasOwnProperty.call(table, value) ? value : fallback;
    }

    var sizeName = pick(sizes, vars.size, "standard");
    var overlapName = pick(overlaps, vars.overlap, "standard");
    var accent = accents[pick(accents, vars.accent, "blue")];
    var diameter = sizes[sizeName];
    var overlap = Math.round(diameter * overlaps[overlapName]);

    var roots = document.querySelectorAll(".hf-transition-avatar-group-hover");
    for (var i = 0; i < roots.length; i += 1) {
      var style = roots[i].style;
      style.setProperty("--hf-avatar-size", diameter + "px");
      style.setProperty("--hf-avatar-font", fonts[sizeName]);
      style.setProperty("--hf-avatar-overlap", overlap + "px");
      style.setProperty("--hf-avatar-accent", accent);
    }
  })();
</script>

<!--
  Timeline integration:
  tl.to('.hf-transition-avatar-group-hover span', { '--hf-avatar-y': '-18px', duration: 0.28, stagger: { each: 0.035, from: 'center' }, ease: 'back.out(1.8)' }, startTime); tl.to('.hf-transition-avatar-group-hover span', { '--hf-avatar-y': '0px', duration: 0.42, stagger: { each: 0.035, from: 'center' }, ease: 'bounce.out' }, startTime + 0.36);
-->