Tracking In

<!--
  Tracking In - letter-spacing reveal.

  Add class="hf-tracking-in" to text elements, then animate the CSS variable
  from wide tracking to the final value in your composition timeline.

  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
  on the document root, which every element carrying the class inherits. The
  timeline recipe below is untouched by them: it keeps driving one tracking
  value and one opacity, and these decide how wide that tracking reads, where
  the text starts, and what colour it settles in.

    - tracking (tight | standard | wide, default standard): multiplies the
      letter-spacing the timeline drives. It scales the whole curve, so the
      reveal starts proportionally wider or tighter and settles the same way.
      tight is 0.6 of the shipped spacing, wide is 1.8 of it.
    - rise (subtle | standard | bold, default standard): the vertical offset
      the text starts from, which the timeline reads as the start of its
      travel and eases to zero. subtle is 4px, standard the shipped 8px, bold
      18px.
    - tone (inherit | ink | paper | accent, default inherit): text colour.
      inherit leaves the surrounding page colour alone, ink is near-black for
      light frames, paper near-white for dark ones, accent rides --brand.
      The class starts at opacity 0, so the colour only becomes visible once
      the timeline reveals the text.

  On every default the result is identical to the original: text at the page
  colour rising 8px into place out of 0.28em tracking.
-->

<style
  data-composition-variables='[
    { "id": "tracking", "type": "enum", "role": "style", "label": "Tracking", "description": "Multiplies the letter-spacing the timeline drives, so the reveal starts and settles proportionally wider or tighter.", "default": "standard", "options": [{ "value": "tight", "label": "Tight" }, { "value": "standard", "label": "Standard" }, { "value": "wide", "label": "Wide" }] },
    { "id": "rise", "type": "enum", "role": "motion", "label": "Rise", "description": "Vertical offset the text starts from, which the timeline reads as the start of its travel and eases to zero.", "default": "standard", "options": [{ "value": "subtle", "label": "Subtle" }, { "value": "standard", "label": "Standard" }, { "value": "bold", "label": "Bold" }] },
    { "id": "tone", "type": "enum", "role": "style", "label": "Tone", "description": "Text colour: inherit keeps the surrounding page colour, ink suits light frames, paper dark ones, accent rides --brand.", "default": "inherit", "options": [{ "value": "inherit", "label": "Inherit" }, { "value": "ink", "label": "Ink" }, { "value": "paper", "label": "Paper" }, { "value": "accent", "label": "Accent" }] }
  ]'
>
  .hf-tracking-in {
    opacity: 0;
    color: var(--hf-tracking-color, inherit);
    letter-spacing: calc(var(--hf-tracking-value, 0.28em) * var(--hf-tracking-reach, 1));
    transform: translateY(var(--hf-tracking-y, 8px));
    will-change: opacity, letter-spacing, transform;
  }
</style>

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

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

    // Unrecognised overrides return to their declared defaults.
    var reaches = { tight: 0.6, standard: 1, wide: 1.8 };
    var rises = { subtle: "4px", standard: "8px", bold: "18px" };
    var tones = {
      inherit: "inherit",
      ink: "#18181b",
      paper: "#fafafa",
      accent: "var(--brand, #34d399)",
    };

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

    var reach = reaches[pick(reaches, vars.tracking, "standard")];
    var rise = rises[pick(rises, vars.rise, "standard")];
    var tone = tones[pick(tones, vars.tone, "inherit")];

    // The class is applied to arbitrary host elements, so the resolved values
    // ride the document root and inherit down to every one of them.
    var host = document.documentElement;
    host.style.setProperty("--hf-tracking-reach", String(reach));
    host.style.setProperty("--hf-tracking-y", rise);
    host.style.setProperty("--hf-tracking-color", tone);
  })();
</script>

<!--
  Timeline integration:

  tl.to(".hf-tracking-in", {
    opacity: 1,
    "--hf-tracking-value": "0.02em",
    y: 0,
    duration: 0.9,
    ease: "power3.out",
    stagger: 0.1,
  }, startTime);
-->