hyperframes/docs/catalog/components/slit-scan-reveal.mdx

---
title: "Slit Scan Reveal"
description: "The frame's rows sample an authored subject at offset times: a canvas painter draws row slices of one pure position function evaluated at t minus offset(row), smearing arrival through time until the offsets collapse to zero and the mark holds coherent."
mode: "frame"
---

import { CatalogDetail, CatalogSlot } from "/snippets/catalog-detail.jsx";
import { InstallCommand } from "/snippets/install-command.jsx";

<CatalogDetail
  previewSrc="/public/catalog/components/slit-scan-reveal.json"
  compositionId="slit-scan-reveal"
  compositionSrc="compositions/components/slit-scan-reveal.html"
  title="Slit Scan Reveal"
  description="The frame's rows sample an authored subject at offset times: a canvas painter draws row slices of one pure position function evaluated at t minus offset(row), smearing arrival through time until the offsets collapse to zero and the mark holds coherent."
  variables={[{"id":"axis","type":"enum","role":"style","label":"Axis","description":"rows smears arrival across horizontal slices; cols across vertical slices.","default":"rows","options":[{"value":"rows","label":"Rows"},{"value":"cols","label":"Columns"}]},{"id":"spread","type":"number","role":"timing","label":"Spread","description":"Maximum sampling offset in seconds across the frame; larger smears further through time.","default":0.45},{"id":"resolve_at","type":"number","role":"timing","label":"Resolve at","description":"Seconds from mount start when the offsets start collapsing to zero. Clamped so the collapse and any exit stay inside the clip.","default":2.2},{"id":"accent","type":"enum","role":"style","label":"Accent","description":"Subject ring and orbit color: green rides --brand, blue rides --accent, violet rides --accent-2.","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 resolved mark holds until the frame cuts.","default":"none","options":[{"value":"none","label":"None"},{"value":"fade","label":"Fade"},{"value":"up","label":"Up"}]}]}
  meta={{"category":"Motion Scenes","badge":"Stable","codeLines":332}}
  attribution={{"path":"registry/components/slit-scan-reveal","tags":["motion-primitive","time","slit-scan","canvas","deterministic","experiment"]}}
  hasCode
  rawUrl="https://raw.githubusercontent.com/heygen-com/hyperframes/main/registry/components/slit-scan-reveal/slit-scan-reveal.html"
>

<CatalogSlot slot="code">

```html slit-scan-reveal.html
<!doctype html>
<!--
  slit-scan-reveal: HyperFrames video primitive (time)

  The frame's rows sample the subject at offset times. The subject is an
  authored token mark (an accent-ringed disc with an orbit dot) whose
  motion is one pure position function pos(t): it sweeps in from the wing
  on a decaying sine bob and rests dead-center. A canvas painter draws the
  frame as row (or column) slices, slice i showing the subject's state at
  t - offset(i): arrival smears through time, near bands leading, far
  bands trailing. On the resolve cue the offsets collapse to zero with one
  eased pass, the smear zips shut, and the subject holds coherent.

  Variables (declared in data-composition-variables below):
    - axis ("rows" | "cols"): horizontal row slices or vertical column
      slices.
    - spread (seconds): the maximum sampling offset across the frame.
    - resolve_at (seconds): when the offsets start collapsing to zero
      (0.6s eased collapse). Clamped so the collapse and any exit stay
      inside the clip.
    - accent ("green" | "blue" | "violet"): green rides --brand, blue
      rides --accent, violet rides --accent-2.
    - exit ("none" | "fade" | "up", default none): frame roots own
      transitions; the default holds the resolved mark to the last pixel.

  Envelope, fixed IN and OUT with elastic HOLD only (never timeScale):
    the subject's travel and the collapse are authored against the cues;
    HOLD = D - (resolve end) - OUT, truly still (after the collapse every
    slice samples the same resting state, so repaints are identical).
    OUT_BASE = 0.45s only when exit != none.

  Determinism (canvas 2D law): per-slice offset jitter comes from one
  table computed once during synchronous timeline construction from fixed
  LCG seed 0x51175c4e. Every painted frame is a pure
  function of (that table, the timeline's current time): the timeline's
  onUpdate clears the canvas and, for every slice, clips to the slice band
  and redraws the whole subject at its sampled time from scratch. pos(t)
  is closed-form (cubic ease + integer sine cycles that end at zero), so
  any sampled time is exact. No Math.random, no wall clock, no
  incremental state: eventful seeks repaint identically in any order and
  either direction.

  Mount contract: the runtime clones only this template. #root fills the
  host box (no data-width/data-height, container-type: size, cqmin units),
  is styled via #root only, and registers one paused timeline under the
  LITERAL "slit-scan-reveal" key. All DOM state is set with explicit
  endpoints (gsap.set + fromTo) so any seek order lands identical frames.
-->
<html
  lang="en"
  data-composition-id="slit-scan-reveal"
  data-composition-duration="4"
  data-composition-variables='[
    { "id": "axis", "type": "enum", "role": "style", "label": "Axis", "description": "rows smears arrival across horizontal slices; cols across vertical slices.", "default": "rows", "options": [{ "value": "rows", "label": "Rows" }, { "value": "cols", "label": "Columns" }] },
    { "id": "spread", "type": "number", "role": "timing", "label": "Spread", "description": "Maximum sampling offset in seconds across the frame; larger smears further through time.", "default": 0.45 },
    { "id": "resolve_at", "type": "number", "role": "timing", "label": "Resolve at", "description": "Seconds from mount start when the offsets start collapsing to zero. Clamped so the collapse and any exit stay inside the clip.", "default": 2.2 },
    { "id": "accent", "type": "enum", "role": "style", "label": "Accent", "description": "Subject ring and orbit color: green rides --brand, blue rides --accent, violet rides --accent-2.", "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 resolved mark 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>Slit Scan Reveal</title>
  </head>
  <body>
    <template>
      <div id="root" data-composition-id="slit-scan-reveal" data-duration="4" data-fps="30">
        <style>
          *,
          *::before,
          *::after {
            box-sizing: border-box;
          }

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

          .ssr-clip {
            position: absolute;
            inset: 0;
            overflow: hidden;
            background: var(--bg, transparent);
          }

          .ssr-stage {
            position: absolute;
            inset: 0;
            will-change: transform, opacity;
          }

          .ssr-canvas {
            position: absolute;
            inset: 0;
            width: 100%;
            height: 100%;
          }
        </style>

        <div
          id="slit-scan-reveal-clip"
          class="ssr-clip clip"
          data-start="0"
          data-duration="4"
          data-track-index="0"
        >
          <div class="ssr-stage">
            <canvas class="ssr-canvas" aria-hidden="true"></canvas>
          </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");
            var stage = root.querySelector(".ssr-stage");
            var canvas = root.querySelector(".ssr-canvas");
            var vars =
              window.__hyperframes && window.__hyperframes.getVariables
                ? window.__hyperframes.getVariables()
                : {};

            var axis = vars.axis === "cols" ? "cols" : "rows";
            var spreadRaw = parseFloat(vars.spread);
            var spread = isFinite(spreadRaw) ? Math.min(Math.max(0.1, spreadRaw), 1.2) : 0.45;
            var resolveRaw = parseFloat(vars.resolve_at);
            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";

            // Envelope. The collapse is 0.6s; resolve_at is clamped so the
            // collapse and any exit always fit inside the clip.
            var duration = Math.max(0.001, parseFloat(root.dataset.duration || "4"));
            var OUT = exit === "none" ? 0 : 0.45;
            var COLLAPSE = 0.6;
            var resolveAt = isFinite(resolveRaw) ? resolveRaw : 2.2;
            resolveAt = Math.min(
              Math.max(0.4, resolveAt),
              Math.max(0.4, duration - COLLAPSE - OUT - 0.1),
            );
            // The subject's travel ends just before the collapse begins so
            // the zip-shut lands on a resting subject.
            var MOVE_START = 0.25;
            var MOVE_END = Math.max(MOVE_START + 0.6, resolveAt - 0.1);
            var OUT_START = duration - OUT;

            // Canvas raster basis, fixed once at mount (elastic root).
            var dpr = Math.min(2, Math.max(1, Number(window.devicePixelRatio) || 1));
            var box = root.getBoundingClientRect();
            var cssW = Math.max(1, Math.round(box.width) || 640);
            var cssH = Math.max(1, Math.round(box.height) || 360);
            canvas.width = Math.round(cssW * dpr);
            canvas.height = Math.round(cssH * dpr);
            var ctx = canvas.getContext("2d");
            var minDim = Math.min(canvas.width, canvas.height);

            // Resolve tokens to concrete colors once at mount so canvas
            // fills never depend on style recalc during seeks.
            var hostDoc = root.ownerDocument;
            function resolveColor(cssColor, fallback) {
              var probe = hostDoc.createElement("span");
              probe.style.color = cssColor;
              root.appendChild(probe);
              var value = getComputedStyle(probe).color || fallback;
              probe.remove();
              return value;
            }
            var accentColor = resolveColor(accentColors[accent], "#71f5a7");
            var surfaceColor = resolveColor("var(--surface, #14171c)", "#14171c");
            var fgColor = resolveColor("var(--fg, #f8fafc)", "#f8fafc");

            // Seeded per-slice offset jitter: a stable table, computed once.
            var SLICES = 96;
            var jitter = (function () {
              var state = 0x51175c4e;
              function next() {
                state = (Math.imul(1664525, state) + 1013904223) >>> 0;
                return state / 4294967296;
              }
              var rows = [];
              for (var i = 0; i < SLICES; i += 1) {
                rows.push(0.96 + 0.08 * next());
              }
              return rows;
            })();

            function clamp01(v) {
              return v < 0 ? 0 : v > 1 ? 1 : v;
            }

            // The subject's authored motion: ONE pure position function.
            // Cubic-eased sweep from the wing to dead center with a
            // decaying two-cycle sine bob (integer cycles, exactly zero at
            // u = 1) and a settling scale. The sweep runs ACROSS the slice
            // axis (rows: left wing in, cols: top wing down) so every band
            // cuts the travel and the offsets read as a staircase smear,
            // not a local skew. Defined for every t; clamped flat outside
            // [MOVE_START, MOVE_END], so sampled times before mount or
            // into the hold are exact and still.
            function subjectState(t) {
              var u = clamp01((t - MOVE_START) / (MOVE_END - MOVE_START));
              var e = 1 - Math.pow(1 - u, 3);
              var decay = (1 - u) * (1 - u);
              var travel = -0.16 + 0.66 * e;
              var bob = 0.5 + 0.15 * Math.sin(Math.PI * 2 * 2 * u) * decay;
              return {
                x: (axis === "rows" ? travel : bob) * canvas.width,
                y: (axis === "rows" ? bob : travel) * canvas.height,
                rot: 0.5 * Math.sin(Math.PI * 2 * u) * decay,
                scale: 0.82 + 0.18 * e,
                appear: clamp01(u / 0.12),
              };
            }

            // Draw the whole subject (token disc + accent ring + orbit dot)
            // at one sampled state. Callers clip to a slice band first.
            function drawSubject(s) {
              if (s.appear <= 0) return;
              var r = 0.15 * minDim * s.scale;
              ctx.save();
              ctx.translate(s.x, s.y);
              ctx.rotate(s.rot);
              ctx.globalAlpha = s.appear;
              // Disc body.
              ctx.fillStyle = surfaceColor;
              ctx.beginPath();
              ctx.arc(0, 0, r, 0, Math.PI * 2);
              ctx.fill();
              // Accent ring.
              ctx.strokeStyle = accentColor;
              ctx.lineWidth = Math.max(1, 0.016 * minDim);
              ctx.beginPath();
              ctx.arc(0, 0, r, 0, Math.PI * 2);
              ctx.stroke();
              // Inner core.
              ctx.fillStyle = fgColor;
              ctx.globalAlpha = s.appear * 0.92;
              ctx.beginPath();
              ctx.arc(0, 0, r * 0.3, 0, Math.PI * 2);
              ctx.fill();
              // Orbit dot: the asymmetry that makes the smear legible.
              ctx.fillStyle = accentColor;
              ctx.globalAlpha = s.appear;
              ctx.beginPath();
              ctx.arc(r * 0.72, 0, r * 0.13, 0, Math.PI * 2);
              ctx.fill();
              ctx.restore();
            }

            // Pure repaint: for every slice, clip to its band and draw the
            // subject at t - offset(slice) * collapse(t).
            function paint(t) {
              ctx.clearRect(0, 0, canvas.width, canvas.height);
              var collapse = 1 - clamp01((t - resolveAt) / COLLAPSE);
              // Eased collapse: smooth both ends (power2.inOut shape).
              collapse =
                collapse < 0.5 ? 2 * collapse * collapse : 1 - Math.pow(-2 * collapse + 2, 2) / 2;
              if (collapse <= 0) {
                // Resolved: one coherent draw, no per-slice clipping.
                drawSubject(subjectState(t));
                return;
              }
              var along = axis === "rows" ? canvas.height : canvas.width;
              var band = along / SLICES;
              for (var i = 0; i < SLICES; i += 1) {
                var frac = i / (SLICES - 1);
                var offset = spread * frac * jitter[i] * collapse;
                var s = subjectState(t - offset);
                if (s.appear <= 0) continue;
                ctx.save();
                ctx.beginPath();
                if (axis === "rows") {
                  ctx.rect(0, i * band, canvas.width, band + 1);
                } else {
                  ctx.rect(i * band, 0, band + 1, canvas.height);
                }
                ctx.clip();
                drawSubject(s);
                ctx.restore();
              }
            }

            gsap.set(stage, { opacity: 1, y: "0cqh" });

            var tl = gsap.timeline({
              paused: true,
              onUpdate: function () {
                paint(tl.time());
              },
            });

            // Anchor tween: an inert plain-object tween spanning the full
            // authored duration so tl.time() covers [0, D] and onUpdate
            // repaints the canvas on every eventful seek.
            tl.to({ p: 0 }, { p: 1, duration: duration, ease: "none" }, 0);

            // HOLD: truly still. After the collapse every slice samples the
            // same resting state, so the canvas repaints one coherent mark.

            // OUT: optional departure; exit none holds until the frame cuts.
            if (exit === "up") {
              tl.to(stage, { y: "-4cqh", duration: OUT, ease: "power2.in" }, OUT_START);
              tl.to(stage, { opacity: 0, duration: OUT, ease: "power2.in" }, OUT_START);
            } else if (exit === "fade") {
              tl.to(stage, { opacity: 0, duration: OUT, ease: "power2.in" }, OUT_START);
            }

            tl.seek(0);
            paint(0);
            window.__timelines = window.__timelines || {};
            window.__timelines["slit-scan-reveal"] = tl;
          })();
        </script>
      </div>
    </template>
  </body>
</html>
```

</CatalogSlot>

<CatalogSlot slot="install">

<InstallCommand command="npx hyperframes add slit-scan-reveal" item="slit-scan-reveal" />

That writes one file: `compositions/components/slit-scan-reveal.html`.

</CatalogSlot>

<CatalogSlot slot="docs">

## Paste it into your composition

Open `compositions/components/slit-scan-reveal.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 |
| --- | --- | --- | --- |
| `axis` | `rows` | `rows`, `cols` | rows smears arrival across horizontal slices; cols across vertical slices. |
| `spread` | `0.45` | number | Maximum sampling offset in seconds across the frame; larger smears further through time. |
| `resolve_at` | `2.2` | number | Seconds from mount start when the offsets start collapsing to zero. Clamped so the collapse and any exit stay inside the clip. |
| `accent` | `green` | `green`, `blue`, `violet` | Subject ring and orbit color: green rides --brand, blue rides --accent, violet rides --accent-2. |
| `exit` | `none` | `none`, `fade`, `up` | Optional departure. Default none: the resolved mark 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:

```html wrap
<div
  data-composition-id="slit-scan-reveal"
  data-composition-src="compositions/components/slit-scan-reveal.html"
  data-variable-values='{"axis":"rows","spread":0.45,"resolve_at":2.2,"accent":"green","exit":"none"}'
></div>
```

{/* hf:generated-footer */}

Tagged `motion-primitive` `time` `slit-scan` `canvas` `deterministic` `experiment`.

## Related topics

- [Browse the complete Catalog](/catalog)
- [Add assets and Catalog items in Studio](/studio/assets-and-blocks)
- [Build a richer composition](/go-further)

</CatalogSlot>

</CatalogDetail>