Parallax Zoom

<!--
  Parallax Zoom — center card scales up while siblings parallax outward.

  Inspired by the eBay Playbook hero transition: a grid of cards collapses
  as the focal card grows to fill the frame.

  Usage:
  1. Wrap your card grid with class="parallax-zoom-grid".
  2. Mark each card with class="parallax-zoom-card".
  3. Add data-pz-row="0|1|2|..." and data-pz-col="0|1|2|..." per card
     so the snippet knows each card's grid offset.
  4. Mark the focal card with data-pz-focus="true" — this is the one
     that scales up to fill the frame.
  5. Drive --pz-progress 0 → 1 on the .parallax-zoom-grid from your
     composition's paused GSAP timeline (see example at bottom).

  Tunable CSS variables on .parallax-zoom-grid:
  - --pz-focus-scale  (default 6)      maximum scale of the focused card
  - --pz-sibling-push (default 900px)  outward translation strength
  - --pz-sibling-fade (default 1)      sibling opacity falloff (0–1)
-->

<style>
  .parallax-zoom-grid {
    --pz-progress: 0;
    --pz-focus-scale: 6;
    --pz-sibling-push: 900px;
    --pz-sibling-fade: 1;
    position: relative;
  }

  .parallax-zoom-card {
    transform-origin: center center;
    will-change: transform, opacity;
    transform: translate3d(
        calc(var(--pz-dx, 0px) * var(--pz-progress)),
        calc(var(--pz-dy, 0px) * var(--pz-progress)),
        0
      )
      scale(calc(1 - var(--pz-progress) * 0.4));
    opacity: calc(1 - var(--pz-progress) * var(--pz-sibling-fade));
  }

  .parallax-zoom-card[data-pz-focus="true"] {
    z-index: 10;
    transform: translate3d(0, 0, 0)
      scale(calc(1 + var(--pz-progress) * (var(--pz-focus-scale) - 1)));
    opacity: 1;
  }
</style>

<script>
  (function () {
    const grids = document.querySelectorAll(".parallax-zoom-grid");

    grids.forEach((grid) => {
      const cards = Array.from(grid.querySelectorAll(".parallax-zoom-card"));
      if (cards.length === 0) return;

      let focal = cards.find((c) => c.dataset.pzFocus === "true");
      if (!focal) {
        focal = cards[Math.floor(cards.length / 2)];
        focal.dataset.pzFocus = "true";
      }

      const focusRow = Number(focal.dataset.pzRow ?? 0);
      const focusCol = Number(focal.dataset.pzCol ?? 0);
      const push = parseFloat(getComputedStyle(grid).getPropertyValue("--pz-sibling-push")) || 900;

      cards.forEach((card) => {
        if (card === focal) return;
        const row = Number(card.dataset.pzRow ?? 0);
        const col = Number(card.dataset.pzCol ?? 0);
        const dCol = col - focusCol;
        const dRow = row - focusRow;
        const mag = Math.hypot(dCol, dRow) || 1;
        const nx = (dCol / mag) * push * mag;
        const ny = (dRow / mag) * push * mag;
        card.style.setProperty("--pz-dx", `${nx}px`);
        card.style.setProperty("--pz-dy", `${ny}px`);
      });
    });
  })();
</script>

<!--
  Timeline integration example (paste into your composition's GSAP timeline):

  tl.fromTo(
    ".parallax-zoom-grid",
    { "--pz-progress": 0 },
    {
      "--pz-progress": 1,
      duration: 2.4,
      ease: "power2.inOut",
    },
    1.0, // start time in seconds
  );
-->