Line Swap

Install

That writes one file: compositions/components/line-swap.html.

Paste it into your composition

Open compositions/components/line-swap.html and copy what is inside into your own composition. A component has no size or duration of its own. It takes both from the composition you paste it into.

Variables

Every one of these has a default, so the piece works untouched. Set the ones you want to change on the element:

Variable	Default	Accepts	What it does
`line_a`	`Everyone promised you AI.`	string	First line; holds center inside the mask, then exits up on the swap beat.
`line_b`	`Almost nobody promised you control.`	string	Replacement line; enters bottom-up on the swap beat and holds.
`swap_at`	`1.5`	number	Second (from mount start) of the beat replacement. Clamped so the swap and underline complete before any exit.
`underline_word`	`control`	string	First case-insensitive substring match in line B gets the accent underline after landing. Empty disables it.
`accent`	`green`	`green`, `blue`, `violet`	Underline color from the contract token map.
`exit`	`none`	`none`, `fade`, `up`	Optional departure. Default none: the landed line holds until the frame cuts.

Set them with data-variable-values on the element that mounts it. These are the defaults, so this behaves exactly like the preview above until you change one:

<div
  data-composition-id="line-swap"
  data-composition-src="compositions/components/line-swap.html"
  data-variable-values='{"line_a":"Everyone promised you AI.","line_b":"Almost nobody promised you control.","swap_at":1.5,"underline_word":"control","accent":"green","exit":"none"}'
></div>

Source

line-swap.html

<!doctype html>
<!--
  line-swap: HyperFrames video primitive (text effects / beat replacement)

  A masked full-line beat replacement, generalizing flagship frame 01: line_a
  rises into an overflow-hidden mask and holds center, then on the swap beat
  it exits up through the mask as line_b enters bottom-up on the same beat.
  One restrained slam, smooth ease, no overshoot. Optionally an accent
  underline draws left to right beneath underline_word of line_b after it
  lands (scaleX from a left origin, the flagship bar draw).

  Variables:
    line_a (string): the first line, replaced on the beat.
    line_b (string): the line that lands and holds.
    swap_at (seconds): the beat, relative to mount start. Clamped so line_a
      finishes entering first and line_b plus the underline complete before
      any exit begins.
    underline_word (string): first case-insensitive substring match inside
      line_b gets the underline. Empty or unmatched disables it.
    accent (green | blue | violet): underline color via the contract token map.
    exit (none | fade | up, default none): frame roots own transitions;
      holds end films.

  Envelope, fixed IN and OUT with elastic HOLD only (never time-scaled):
    IN_A_BASE  = 0.50s  line_a enters bottom-up through the mask
    SWAP span  = 0.72s  line_a up-and-out (0.35s) overlapping line_b in
                        (starts 0.22s after the beat, lands 0.50s later)
    UL span    = 0.60s  0.15s beat after the land, then a 0.45s draw
                        (0 when underline_word is empty or unmatched)
    HOLD       = max(0, D - phases), completely still
    OUT_BASE   = 0s for exit none, otherwise 0.45s
    If D is shorter than the fixed phases, they compress together.

  Mount contract: the runtime clones only this template. #root fills the host
  box, establishes the container query basis, has no data-width or
  data-height, and registers one paused timeline under the literal
  line-swap key.
-->
<html
  lang="en"
  data-composition-id="line-swap"
  data-composition-duration="3.5"
  data-composition-variables='[
    { "id": "line_a", "type": "string", "role": "content", "label": "Line A", "description": "First line; holds center inside the mask, then exits up on the swap beat.", "default": "Everyone promised you AI." },
    { "id": "line_b", "type": "string", "role": "content", "label": "Line B", "description": "Replacement line; enters bottom-up on the swap beat and holds.", "default": "Almost nobody promised you control." },
    { "id": "swap_at", "type": "number", "role": "timing", "label": "Swap at", "description": "Second (from mount start) of the beat replacement. Clamped so the swap and underline complete before any exit.", "default": 1.5, "min": 0, "step": 0.1, "unit": "s" },
    { "id": "underline_word", "type": "string", "role": "content", "label": "Underline word", "description": "First case-insensitive substring match in line B gets the accent underline after landing. Empty disables it.", "default": "control" },
    { "id": "accent", "type": "enum", "role": "style", "label": "Accent", "description": "Underline color from the contract token map.", "default": "green", "options": [{ "value": "green", "label": "Green" }, { "value": "blue", "label": "Blue" }, { "value": "violet", "label": "Violet" }] },
    { "id": "exit", "type": "enum", "role": "timing", "label": "Exit", "description": "Optional departure. Default none: the landed line holds until the frame cuts.", "default": "none", "options": [{ "value": "none", "label": "None" }, { "value": "fade", "label": "Fade" }, { "value": "up", "label": "Up" }] }
  ]'
>
  <head>
    <meta charset="UTF-8" />
    <title>Line Swap</title>
  </head>
  <body>
    <template>
      <div id="root" data-composition-id="line-swap" data-duration="3.5" data-fps="30">
        <style>
          *,
          *::before,
          *::after {
            box-sizing: border-box;
          }

          #root {
            position: absolute;
            inset: 0;
            overflow: hidden;
            container-type: size;
            isolation: isolate;
            background: var(--bg, #0b0c0e);
            color: var(--fg, #f8fafc);
            font-family: var(--font-display, Inter, system-ui, sans-serif);
            pointer-events: none;
          }

          .ls-clip {
            position: absolute;
            inset: 0;
            display: grid;
            place-items: center;
            overflow: hidden;
          }

          .ls-stage {
            width: 94cqw;
            will-change: transform, opacity;
          }

          /* Beat mask: both lines live inside; the swap slides through it. */
          .ls-mask {
            position: relative;
            width: 100%;
            height: calc(var(--ls-font-size, min(7cqw, 16cqh)) * 1.42);
            overflow: hidden;
          }

          .ls-line {
            position: absolute;
            inset: 0;
            display: flex;
            align-items: center;
            justify-content: center;
            font-size: var(--ls-font-size, min(7cqw, 16cqh));
            font-weight: 600;
            line-height: 1;
            letter-spacing: -0.02em;
            white-space: nowrap;
            will-change: transform;
          }

          /* One inline wrapper per line: a bare text node next to the
             underline span would become separate flex items and the boundary
             space would collapse ("youcontrol."). */
          .ls-line-inner {
            display: inline;
          }

          .ls-ul-wrap {
            position: relative;
            display: inline-block;
            white-space: nowrap;
          }

          .ls-underline {
            position: absolute;
            left: 0.02em;
            right: 0.02em;
            bottom: -0.14em;
            height: 0.055em;
            border-radius: 0.03em;
            transform-origin: left center;
          }
        </style>

        <div
          id="line-swap-clip"
          class="ls-clip clip"
          data-start="0"
          data-duration="3.5"
          data-track-index="0"
        >
          <div class="ls-stage" role="img">
            <div class="ls-mask">
              <div class="ls-line ls-line-a"><span class="ls-line-inner"></span></div>
              <div class="ls-line ls-line-b"><span class="ls-line-inner"></span></div>
            </div>
          </div>
        </div>

        <script src="https://cdn.jsdelivr.net/npm/gsap@3.14.2/dist/gsap.min.js"></script>
        <script>
          (function () {
            "use strict";

            var root = document.getElementById("root");
            // Literal key: the flattening step strips data-composition-id off
            // the mounted root, so reading it back would register "null".
            var compositionId = "line-swap";
            var stage = root.querySelector(".ls-stage");
            var lineAEl = root.querySelector(".ls-line-a");
            var lineBEl = root.querySelector(".ls-line-b");
            var lineAInner = lineAEl.querySelector(".ls-line-inner");
            var lineBInner = lineBEl.querySelector(".ls-line-inner");
            var vars =
              window.__hyperframes && window.__hyperframes.getVariables
                ? window.__hyperframes.getVariables()
                : {};

            function asLine(value, fallback) {
              return value == null ? fallback : String(value).trim().replace(/\s+/g, " ");
            }
            var lineA = asLine(vars.line_a, "Everyone promised you AI.");
            var lineB = asLine(vars.line_b, "Almost nobody promised you control.");
            var underlineWord = asLine(vars.underline_word, "control");
            var accentColors = {
              green: "var(--brand, #71f5a7)",
              blue: "var(--accent, #61a8ff)",
              violet: "var(--accent-2, #c5a3ff)",
            };
            var accent = Object.prototype.hasOwnProperty.call(accentColors, vars.accent)
              ? vars.accent
              : "green";
            var exit = vars.exit === "fade" || vars.exit === "up" ? vars.exit : "none";

            lineAInner.textContent = lineA;

            // Split line_b around the first case-insensitive underline match.
            // textContent nodes only, never innerHTML.
            var matchIndex =
              underlineWord.length > 0
                ? lineB.toLowerCase().indexOf(underlineWord.toLowerCase())
                : -1;
            var underlineEl = null;
            if (matchIndex >= 0) {
              var before = lineB.slice(0, matchIndex);
              var matched = lineB.slice(matchIndex, matchIndex + underlineWord.length);
              var after = lineB.slice(matchIndex + underlineWord.length);
              if (before) lineBInner.appendChild(document.createTextNode(before));

              var wrap = document.createElement("span");
              wrap.className = "ls-ul-wrap";
              wrap.appendChild(document.createTextNode(matched));
              underlineEl = document.createElement("span");
              underlineEl.className = "ls-underline";
              underlineEl.setAttribute("aria-hidden", "true");
              // style.background, not a class: var() resolves at point of use.
              underlineEl.style.background = accentColors[accent];
              wrap.appendChild(underlineEl);
              lineBInner.appendChild(wrap);
              if (after) lineBInner.appendChild(document.createTextNode(after));
            } else {
              lineBInner.textContent = lineB;
            }
            stage.setAttribute("aria-label", lineA + " " + lineB);

            // Deterministic character-count fit against the longer line; both
            // lines are nowrap, so the fit keeps them inside the stage.
            var characters = Math.max(1, Array.from(lineA).length, Array.from(lineB).length);
            var fitted = Math.max(3.4, Math.min(9, 168 / characters));
            root.style.setProperty("--ls-font-size", "min(" + fitted.toFixed(3) + "cqw, 16cqh)");

            // RETIME RANGE: fixed phases; HOLD is the only elastic span.
            var IN_A_BASE = 0.5;
            var EXIT_A_BASE = 0.35;
            var LAG_BASE = 0.22; // line_b starts this long after the beat
            var IN_B_BASE = 0.5;
            var UL_BEAT_BASE = 0.15;
            var UL_BASE = underlineEl ? 0.45 : 0;
            var OUT_BASE = exit === "none" ? 0 : 0.45;
            var duration = Math.max(0.001, parseFloat(root.dataset.duration || "3.5"));
            var swapSpanBase = LAG_BASE + IN_B_BASE;
            var ulSpanBase = underlineEl ? UL_BEAT_BASE + UL_BASE : 0;
            var totalBase = IN_A_BASE + swapSpanBase + ulSpanBase + OUT_BASE;
            var scale = duration < totalBase ? duration / totalBase : 1;
            var IN_A = IN_A_BASE * scale;
            var EXIT_A = EXIT_A_BASE * scale;
            var LAG = LAG_BASE * scale;
            var IN_B = IN_B_BASE * scale;
            var UL_BEAT = UL_BEAT_BASE * scale;
            var UL = UL_BASE * scale;
            var OUT = OUT_BASE * scale;
            var OUT_START = duration - OUT;

            var swapAtRaw = Number(vars.swap_at);
            var swapAt = Number.isFinite(swapAtRaw) ? Math.max(0, swapAtRaw) : 1.5;
            // line_a fully arrives before the beat; the swap and the
            // underline always complete before the exit begins.
            swapAt = Math.min(swapAt, Math.max(IN_A, OUT_START - (LAG + IN_B + UL_BEAT + UL)));
            swapAt = Math.max(swapAt, IN_A);
            var landB = swapAt + LAG + IN_B;

            gsap.set(lineBEl, { yPercent: 115 });
            if (underlineEl) gsap.set(underlineEl, { scaleX: 0 });

            var tl = gsap.timeline({ paused: true });

            // IN: line_a enters bottom-up through the mask. One move.
            tl.fromTo(
              lineAEl,
              { yPercent: 115 },
              { yPercent: 0, duration: IN_A, ease: "power4.out" },
              0,
            );

            // SWAP: the beat replacement. line_a exits up through the mask as
            // line_b slides in bottom-up. Single restrained slam, smooth ease.
            tl.fromTo(
              lineAEl,
              { yPercent: 0 },
              { yPercent: -115, duration: EXIT_A, ease: "power2.in", immediateRender: false },
              swapAt,
            );
            tl.fromTo(
              lineBEl,
              { yPercent: 115 },
              { yPercent: 0, duration: IN_B, ease: "power4.out" },
              swapAt + LAG,
            );

            // UNDERLINE: accent bar draws left to right after line_b lands.
            if (underlineEl) {
              tl.fromTo(
                underlineEl,
                { scaleX: 0 },
                { scaleX: 1, duration: UL, ease: "power2.out" },
                landB + UL_BEAT,
              );
            }

            // HOLD: completely still.

            // OUT: optional departure; exit none holds until the frame cuts.
            if (exit === "fade") {
              tl.to(stage, { opacity: 0, duration: OUT, ease: "power2.in" }, OUT_START);
            } else if (exit === "up") {
              tl.to(stage, { opacity: 0, y: "-7cqh", duration: OUT, ease: "power2.in" }, OUT_START);
            }

            tl.seek(0);
            window.__timelines = window.__timelines || {};
            window.__timelines[compositionId] = tl;
          })();
        </script>
      </div>
    </template>
  </body>
</html>

Tagged motion-primitive text-effects swap beat deterministic.

Overview

Text & captions

Code

Transitions

Data & charts

Scenes & demos

Motion & effects

Surfaces

Blocks

Install

Paste it into your composition

Variables

Source

​Install

​Paste it into your composition

​Variables

​Source

​Related topics

Install

Paste it into your composition

Variables

Source

Related topics