Icon Swap

<!--
  Icon Swap - transitions.dev-inspired primitive for HyperFrames.

  Paste the markup, CSS and script 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 above
  consumes. The timeline recipe below is untouched by them.

    - tone (dark | light | accent, default dark): button fill and glyph colour. dark is the
      matte chip, light inverts it for bright frames, accent rides --brand.
    - size (small | standard | large, default standard): the button box and the glyph inside
      it, 44px, 58px or 76px.
    - shape (rounded | circle | square, default rounded): corner radius of the box.
    - blur (soft | standard | heavy, default standard): scales the blur radius the timeline
      drives through the swap, from a light haze to a full smear.

  On every default the result is identical to the original: a 58px near-black chip with
  16px corners and an 8px swap blur.
-->

<button
  class="hf-transition-icon-swap"
  type="button"
  data-composition-variables='[
    { "id": "tone", "type": "enum", "role": "style", "label": "Tone", "description": "Button fill and glyph colour. Accent rides --brand.", "default": "dark", "options": [{ "value": "dark", "label": "Dark" }, { "value": "light", "label": "Light" }, { "value": "accent", "label": "Accent" }] },
    { "id": "size", "type": "enum", "role": "layout", "label": "Size", "description": "Button box and glyph size, from a toolbar chip to a hero action.", "default": "standard", "options": [{ "value": "small", "label": "Small" }, { "value": "standard", "label": "Standard" }, { "value": "large", "label": "Large" }] },
    { "id": "shape", "type": "enum", "role": "style", "label": "Shape", "description": "Corner treatment of the button box.", "default": "rounded", "options": [{ "value": "rounded", "label": "Rounded" }, { "value": "circle", "label": "Circle" }, { "value": "square", "label": "Square" }] },
    { "id": "blur", "type": "enum", "role": "motion", "label": "Blur", "description": "Scales the blur radius the timeline drives through the swap, from a light haze to a full smear.", "default": "standard", "options": [{ "value": "soft", "label": "Soft" }, { "value": "standard", "label": "Standard" }, { "value": "heavy", "label": "Heavy" }] }
  ]'
>
  <span class="from">+</span><span class="to">OK</span>
</button>

<style>
  .hf-transition-icon-swap {
    position: relative;
    display: grid;
    place-items: center;
    width: var(--hf-icon-size, 58px);
    height: var(--hf-icon-size, 58px);
    border: 0;
    border-radius: var(--hf-icon-radius, 16px);
    background: var(--hf-icon-bg, #18181b);
    color: var(--hf-icon-fg, #fff);
    font:
      900 28px/1 Inter,
      system-ui,
      sans-serif;
    font-size: var(--hf-icon-font-size, 28px);
    box-shadow: 0 18px 44px rgba(24, 24, 27, 0.22);
  }
  .hf-transition-icon-swap span {
    position: absolute;
    filter: blur(calc(var(--hf-icon-blur, 0px) * var(--hf-icon-blur-scale, 1)));
    transform: scale(var(--hf-icon-scale, 1)) rotate(var(--hf-icon-rotate, 0deg));
    will-change: transform, filter, opacity;
  }
  .hf-transition-icon-swap .to {
    opacity: 0;
  }
</style>

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

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

    // Unrecognised overrides return to their declared defaults.
    function pick(table, value, fallback) {
      return Object.prototype.hasOwnProperty.call(table, value) ? value : fallback;
    }

    var tones = {
      dark: { bg: "#18181b", fg: "#ffffff" },
      light: { bg: "#fafafa", fg: "#18181b" },
      accent: { bg: "var(--brand, #34d399)", fg: "#052e21" },
    };
    var sizes = {
      small: { box: "44px", font: "22px" },
      standard: { box: "58px", font: "28px" },
      large: { box: "76px", font: "38px" },
    };
    var shapes = { rounded: "16px", circle: "50%", square: "6px" };
    var blurScales = { soft: 0.45, standard: 1, heavy: 2.2 };

    var tone = tones[pick(tones, vars.tone, "dark")];
    var size = sizes[pick(sizes, vars.size, "standard")];
    var shape = shapes[pick(shapes, vars.shape, "rounded")];
    var blurScale = blurScales[pick(blurScales, vars.blur, "standard")];

    var roots = document.querySelectorAll(".hf-transition-icon-swap");
    for (var i = 0; i < roots.length; i += 1) {
      roots[i].style.setProperty("--hf-icon-bg", tone.bg);
      roots[i].style.setProperty("--hf-icon-fg", tone.fg);
      roots[i].style.setProperty("--hf-icon-size", size.box);
      roots[i].style.setProperty("--hf-icon-font-size", size.font);
      roots[i].style.setProperty("--hf-icon-radius", shape);
      roots[i].style.setProperty("--hf-icon-blur-scale", String(blurScale));
    }
  })();
</script>

<!--
  Timeline integration:
  tl.to('.hf-transition-icon-swap .from', { opacity: 0, '--hf-icon-scale': 0.55, '--hf-icon-blur': '8px', '--hf-icon-rotate': '-18deg', duration: 0.18, ease: 'power2.in' }, startTime); tl.fromTo('.hf-transition-icon-swap .to', { opacity: 0, '--hf-icon-scale': 1.35, '--hf-icon-blur': '8px', '--hf-icon-rotate': '18deg' }, { opacity: 1, '--hf-icon-scale': 1, '--hf-icon-blur': '0px', '--hf-icon-rotate': '0deg', duration: 0.26, ease: 'back.out(1.7)' }, startTime + 0.12);
-->