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hyperframes/docs/catalog/components/echo-trail.mdx
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Miguel ÁngelandMiguel Angel Simon Sierra 1ae2067b8d feat(catalog): put the variables panel back, on payloads (#3199) 
* feat(catalog): put the variables panel back, on payloads

The panel drove its preview by loading an .html from docs/public, a type the
host does not publish, so it showed an empty frame in production and was
parked when the catalog was re-landed.

It now mounts the same JSON payload the plain player uses and re-mounts it as
values change, injecting them as window.__hfVariables into the composition head
before any of its scripts run, which is where the runtime reads overrides from.
Doing it in the markup rather than after load is what stops the composition
initialising with the wrong values first.

172 items with variables get the panel back; the playhead carries across a
change so a tweak mid-shot does not jump back to frame zero.

* fix(docs): drop the unused url form and the needless escapes

* fix(docs): the panel cannot reference a binding beside the export

* feat(catalog): make importing an SVG the obvious move

A reader arrives at this control with a shape, not with path data, and the
panel asked for the coordinates first. Import is now the primary action in a
drop target you can see is a drop target, and the raw path sits behind a
disclosure for anyone who wants it.

* feat(cli): let a fruitless catalog search report the gap

An agent that searches by meaning and finds nothing worth installing knows
something we do not: the name of a move the catalog is missing. There was no
way to tell us, so that knowledge was lost at the end of every run.

hyperframes feedback --search-miss "<query>" --wanted "<the move>" records it.
It carries no rating, so it never lands in the rating metric, and it is a
separate deliberate command rather than something catalog --query does on its
own: plain search still sends nothing, which is what the CLI promises.

--rating stops being required at the arg level, since a miss has no rating to
give. The check moved into the run body, where an absent one is now handled
rather than crashing on undefined.

* feat(cli): carry tuned variable values into the install snippet

Someone who tunes a block on its catalog page had no way to keep those values:
the install command was the same one everybody gets, and the tuning stayed on
the page.

hyperframes add <item> --vars '<json>' now prints a mount element carrying
data-variable-values, so the values land where the block is used.

They ride on the host rather than being written into the installed file. That
keeps the composition on disk byte-identical to the registry's, so a later
reinstall can still tell an edit from an update, and it lets two mounts of the
same block carry different values.

* fix(catalog): serve the item's own directory so runtime paths resolve

Some compositions assemble their asset URLs at run time —
"compositions/components/" + texture + ".png" for the texture masks, a font the
compiler pulled into _remote_media — and no scan of the markup can see a string
that does not exist until a script concatenates it. Those items either rendered
black or were dropped to a video that had never been uploaded.

Each item that needs it now has its prepared directory published, and its
payload carries a <base> pointing at it, so any relative path the composition
invents resolves. caption-texture renders its masks again, and
variable-font-flex has a preview at all for the first time: its MP4 and poster
are both 403.

Both layouts are published, because which one a composition asks for differs
per item, and a directory only earns that if it is under 2 MB. The 12 MB
texture sheet keeps the recorded video it already had.

* fix(catalog): let the variables panel actually drive the composition

Every control on the panel was inert. The values reached the composition and
nothing repainted, because the payload had already been compiled: compiling
inlines a mounted component and resolves its variables into the markup and CSS,
so by the time a reader turns a knob there is nothing left to change.

An item that declares variables now ships uncompiled, keeping the mount the
runtime loads at run time, which is the only state where data-variable-values
still means anything. The component travels inline as a data URI rather than a
sibling file, because .html is the one type the docs host will not publish. The
demo's own pinned values come off, so the reader's choices reach the mount
instead of losing to the values the demo picked to show itself off.

Measured on the rendered frame rather than the DOM: green rgb(98,207,144),
blue rgb(6,6,199), violet rgb(177,147,230), and back to green.

docs/public/catalog drops from 48 MB to 35 MB along the way, since an
uncompiled payload carries far less than an inlined one.

* feat(catalog): keep variable changes in the url

A reader who tuned a piece lost it on reload, and had nothing to send anyone.
The values now live in the query string, scoped by composition id so two links
never read each other,and only the ones that differ from the defaults are
written, so changing one knob gives a short URL rather than every variable
spelled out.

replaceState rather than pushState: dragging a slider should not leave a trail
of history entries. An unreadable value is ignored rather than thrown, so a
truncated or hand-edited link opens the piece at its defaults.

* fix(catalog): only rewrite the url when a value actually changed

* refactor(catalog): memoise the declared defaults on their content

* feat(catalog): offer an install command carrying the tuned values

The Install block is generated before anyone touches a knob, so it can only
ever print the plain command. Someone who spent a minute tuning a piece copied
it and got the defaults back.

The panel now carries its own command in the Snippet tab, with --vars holding
exactly the values that differ. An untouched piece still offers the same short
command, so nothing gets noisier for the common case.

* fix(catalog): a piece with nothing to render is a skip, not a failure

caption-blend-difference is a stylesheet and a paragraph of prose — a class you
add to your own captions, with no standalone scene to show. The generator
treated that as a build failure, so every run ended by reporting something
broken when nothing was.

It now reports the shape it is and keeps its recorded video, which is the only
honest preview such an item has. A genuine render failure still throws.

* fix(catalog): restore variables from the url on a cold load

A shared link opened at the defaults. The first render happens on the server,
where there is no window to read the query string from, and React then hydrates
against that markup and never revisits it — so the values only appeared once you
touched a control.

The URL is read again after mount, which is the first moment it exists. The
value is also escaped once now rather than twice: URLSearchParams already
decodes on the way out, and decoding a second time turned an SVG path full of
percent-escapes into something that no longer parsed, besides doubling the
length of every link.

* fix(catalog): mount the preview with the values a link carried

The frame was built from the declared defaults and the shared values were
posted to it afterwards, which is too late for anything the composition reads
once at init: a path arrived after the mark had already been drawn from the
default one, so a link looked right in the panel and wrong on screen.

* feat(catalog): the install command follows the values you tuned

Copying the Install line gave the plain command back, because that block is
generated before anyone touches a knob and had no way to know what changed. The
tuned command only existed in the panel Snippet tab, which is not where anyone
looks for it.

The line now reads the same query string the panel writes, so the two agree
without either component knowing the other exists, and a shared link carries the
right command too. replaceState fires no event, so the panel announces its own
writes.

* fix(catalog): send a text variable to the preview once it is finished

Every other control in the explorer reports a whole value on every event: a
slider at any position is a position, a swatch is a colour. A text field is
not. Typing v3 into a badge posted v first, so the preview remounted and
rendered a composition built from half a word.

The post now waits while a text field has focus and goes out when the edit is
committed, with Enter or by clicking away. The field itself is unchanged and
still tracks every keystroke.

---------

Co-authored-by: Miguel Angel Simon Sierra <miguelangelsi07@gmail.com>
2026-08-10 22:40:01 -04:00

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---
title: "Echo Trail"
description: "A moving element renders with N ghosted copies of itself at t minus i times delta, opacity stepped down per ghost; one traversal, echoes collapsing into the settled element at rest."
---
import { InstallCommand } from "/snippets/install-command.jsx";
import { VariablesExplorer } from "/snippets/variables-explorer.jsx";
<VariablesExplorer
previewSrc="/public/catalog/components/echo-trail.json"
compositionId="echo-trail"
compositionSrc="compositions/components/echo-trail.html"
variables={[{"id":"echoes","type":"number","role":"style","label":"Echoes","description":"Ghost copy count, clamped 2 to 6.","default":4},{"id":"delta","type":"number","role":"timing","label":"Delta","description":"Lag between successive ghosts in seconds, clamped 0.03 to 0.3.","default":0.09},{"id":"path","type":"enum","role":"timing","label":"Path","description":"Authored traversal preset.","default":"sweep","options":[{"value":"sweep","label":"Sweep"},{"value":"rise","label":"Rise"},{"value":"arc","label":"Arc"}]},{"id":"accent","type":"enum","role":"style","label":"Accent","description":"Subject accent 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 settled element holds until the frame cuts.","default":"none","options":[{"value":"none","label":"None"},{"value":"fade","label":"Fade"},{"value":"up","label":"Up"}]}]}
>
```html echo-trail.html
<!doctype html>
<!--
echo-trail: HyperFrames video primitive (trails)
The generalized onion skin: a moving element renders with N ghosted
copies of itself, each ghost showing the element where it was at
t minus i * delta, opacity stepped down per ghost. One traversal along
an authored path; as the element decelerates into rest the echoes
collapse into it and vanish, leaving a clean settled hold.
The subject is a SLOT. Callers supply content by placing an inert
template anywhere in the HOST page (templates never render, and the
runtime wipes the host clip's own children on mount, so the slot lives
at document level):
<template data-slot="echo-trail-subject"> ... </template>
Ghosts are deep clones of the subject content. With no slot, the
primitive renders a token card (surface, hairline border, accent dot,
two skeleton lines, contract tokens only).
Variables (declared in data-composition-variables below):
- echoes (number 2 to 6, default 4): ghost copy count.
- delta (number seconds, default 0.09, clamped 0.03 to 0.3): the lag
between successive ghosts.
- path ("sweep" | "rise" | "arc", default "sweep"): the authored
traversal preset.
- accent ("green" | "blue" | "violet", default "green"): green rides
--brand, blue rides --accent, violet rides --accent-2.
- exit ("none" | "fade" | "up", default "none"): frame roots own
transitions; the default holds the final frame to the last pixel.
Envelope, fixed IN and OUT with elastic HOLD only (never timeScale):
IN_BASE = TRAVEL (2.1s) + echoes * delta + 0.2s settle; the lead
rests at TRAVEL and the last ghost has converged (and is
exactly invisible) by IN
HOLD = max(0, D - IN - OUT)
OUT_BASE = 0.45s only when exit != none
If D < IN_BASE + OUT_BASE, the whole envelope compresses together.
Determinism: ghost i's position at time t is path(ease(clamp01((t -
i * delta) / TRAVEL))) and its opacity is its stepped base times a pure
function of its distance to the lead; both are recomputed from
tl.time() on every update. No Math.random, no wall clock, no
incremental state, no requestAnimationFrame. Eventful seeks
(suppressEvents=false, the engine's render path) land identical frames
in any order and either direction; at rest every ghost is coincident
with the lead at opacity exactly zero, so the HOLD is truly still.
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 "echo-trail" key.
-->
<html
lang="en"
data-composition-id="echo-trail"
data-composition-duration="3.5"
data-composition-variables='[
{ "id": "echoes", "type": "number", "role": "style", "label": "Echoes", "description": "Ghost copy count, clamped 2 to 6.", "default": 4 },
{ "id": "delta", "type": "number", "role": "timing", "label": "Delta", "description": "Lag between successive ghosts in seconds, clamped 0.03 to 0.3.", "default": 0.09 },
{ "id": "path", "type": "enum", "role": "timing", "label": "Path", "description": "Authored traversal preset.", "default": "sweep", "options": [{ "value": "sweep", "label": "Sweep" }, { "value": "rise", "label": "Rise" }, { "value": "arc", "label": "Arc" }] },
{ "id": "accent", "type": "enum", "role": "style", "label": "Accent", "description": "Subject accent 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 settled element 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>Echo Trail</title>
</head>
<body>
<template>
<div id="root" data-composition-id="echo-trail" 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;
color: var(--fg, #f8fafc);
font-family: var(--font-display, "Inter", system-ui, sans-serif);
pointer-events: none;
}
.et-clip {
position: absolute;
inset: 0;
overflow: hidden;
background: var(--bg, transparent);
}
.et-stage {
position: absolute;
inset: 0;
will-change: transform, opacity;
}
.et-ghost,
.et-lead {
position: absolute;
left: 0;
top: 0;
will-change: opacity;
}
.et-ghost {
opacity: 0;
}
.et-lead {
opacity: 0;
}
.et-card {
width: 30cqmin;
padding: var(--space-3, 3cqmin);
display: grid;
gap: var(--space-2, 2cqmin);
border: 0.18cqmin solid var(--border, #475569);
border-radius: var(--radius, 2.4cqmin);
background: var(--surface, #14171c);
box-shadow: 0 1.6cqmin 5cqmin color-mix(in srgb, var(--bg, #000000) 30%, transparent);
}
.et-card-dot {
width: 3.2cqmin;
height: 3.2cqmin;
border-radius: 50%;
background: var(--et-accent);
}
.et-card-line {
height: 1.6cqmin;
border-radius: 0.8cqmin;
background: color-mix(in srgb, var(--fg, #f8fafc) 16%, transparent);
}
.et-card-line.short {
width: 62%;
}
</style>
<div
id="echo-trail-clip"
class="et-clip clip"
data-start="0"
data-duration="3.5"
data-track-index="0"
>
<div class="et-stage">
<div class="et-lead">
<div class="et-card">
<div class="et-card-dot"></div>
<div class="et-card-line"></div>
<div class="et-card-line short"></div>
</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");
var stage = root.querySelector(".et-stage");
var lead = root.querySelector(".et-lead");
var vars =
window.__hyperframes && window.__hyperframes.getVariables
? window.__hyperframes.getVariables()
: {};
var echoesRaw = parseFloat(vars.echoes);
var echoes = isFinite(echoesRaw) ? Math.min(6, Math.max(2, Math.round(echoesRaw))) : 4;
var deltaRaw = parseFloat(vars.delta);
var deltaVar = isFinite(deltaRaw) ? Math.min(0.3, Math.max(0.03, deltaRaw)) : 0.09;
var pathName = vars.path === "rise" || vars.path === "arc" ? vars.path : "sweep";
// Each enum choice routes to a DIFFERENT contract token so the
// variable stays meaningful under a theme.
var accentColors = {
green: "var(--brand, #52525b)",
blue: "var(--accent, #52525b)",
violet: "var(--accent-2, #52525b)",
};
var accent = Object.prototype.hasOwnProperty.call(accentColors, vars.accent)
? vars.accent
: "green";
var exit = vars.exit === "fade" || vars.exit === "up" ? vars.exit : "none";
root.style.setProperty("--et-accent", accentColors[accent]);
// SLOT. Caller templates live at HOST DOCUMENT level (the mount
// wipes host-clip children, and templates never render).
var hostDoc = root.ownerDocument;
var slotTemplate = null;
try {
slotTemplate = hostDoc.querySelector('template[data-slot="echo-trail-subject"]');
} catch (error) {
slotTemplate = null;
}
if (slotTemplate) {
lead.querySelector(".et-card").remove();
lead.appendChild(hostDoc.importNode(slotTemplate.content, true));
}
// Ghosts: deep clones of the subject, inserted BEFORE the lead
// so the lead always renders on top. ghosts[0] is the nearest
// past copy (highest stepped opacity).
var ghosts = [];
for (var g = 0; g < echoes; g += 1) {
var ghost = hostDoc.createElement("div");
ghost.className = "et-ghost";
ghost.setAttribute("aria-hidden", "true");
for (var c = 0; c < lead.children.length; c += 1) {
ghost.appendChild(lead.children[c].cloneNode(true));
}
stage.insertBefore(ghost, lead);
ghosts.push(ghost);
}
// Envelope: fixed IN/OUT, elastic HOLD, never time-scaled.
var TRAVEL_BASE = 2.1;
var IN_BASE = TRAVEL_BASE + echoes * deltaVar + 0.2;
var OUT_BASE = exit === "none" ? 0 : 0.45;
var duration = Math.max(0.001, parseFloat(root.dataset.duration || "3.5"));
var totalBase = Math.max(0.001, IN_BASE + OUT_BASE);
var scale = duration < totalBase ? duration / totalBase : 1;
var TRAVEL = TRAVEL_BASE * scale;
var delta = deltaVar * scale;
var IN = IN_BASE * scale;
var OUT = OUT_BASE * scale;
var HOLD = Math.max(0, duration - (IN + OUT));
var OUT_START = IN + HOLD;
// Path presets in percent-of-stage coordinates; the subject is
// centered on the point via a one-time -50%/-50% translate.
function pathPoint(u) {
if (pathName === "rise") {
return { x: 50 + 6 * Math.sin(Math.PI * u), y: 76 - 44 * u };
}
if (pathName === "arc") {
return { x: 16 + 68 * u, y: 64 - 34 * Math.sin(Math.PI * u) };
}
// sweep: a shallow S from left to right through center.
return { x: 18 + 64 * u, y: 50 + 10 * Math.cos(Math.PI * u) };
}
function easeInOut(t) {
return t < 0.5 ? 2 * t * t : 1 - 2 * (1 - t) * (1 - t);
}
function clamp01(v) {
return v < 0 ? 0 : v > 1 ? 1 : v;
}
function posAt(timeSeconds) {
var u = easeInOut(clamp01(TRAVEL > 0 ? timeSeconds / TRAVEL : 1));
return pathPoint(u);
}
// One-time static transforms: center anchor plus a slight
// per-ghost scale step for depth. GSAP owns the transform, the
// per-update writes touch only left/top/opacity.
gsap.set(lead, { xPercent: -50, yPercent: -50 });
for (var i = 0; i < ghosts.length; i += 1) {
gsap.set(ghosts[i], {
xPercent: -50,
yPercent: -50,
scale: 1 - 0.015 * (i + 1),
});
}
// Stepped ghost bases: nearest past copy strongest.
var bases = [];
for (var b = 0; b < echoes; b += 1) {
bases.push(0.55 * (1 - b / echoes));
}
// Pure per-update apply: every position and every ghost alpha
// is a function of tl.time() alone. Ghost alpha is its stepped
// base times a separation ramp, so echoes are invisible before
// motion starts and collapse to exactly zero at rest. Writes
// are idempotent, so the HOLD repaints identically.
function applyTime(timeSeconds) {
var leadPos = posAt(timeSeconds);
gsap.set(lead, {
left: leadPos.x.toFixed(4) + "%",
top: leadPos.y.toFixed(4) + "%",
});
for (var n = 0; n < ghosts.length; n += 1) {
var p = posAt(timeSeconds - (n + 1) * delta);
var dist = Math.hypot(p.x - leadPos.x, p.y - leadPos.y);
var alpha = bases[n] * clamp01(dist / 2.2);
gsap.set(ghosts[n], {
left: p.x.toFixed(4) + "%",
top: p.y.toFixed(4) + "%",
opacity: alpha < 0.002 ? 0 : alpha,
});
}
}
gsap.set(stage, { opacity: 1, y: "0cqh" });
var tl = gsap.timeline({
paused: true,
onUpdate: function () {
applyTime(tl.time());
},
});
// Anchor tween: an inert plain-object tween spanning the full
// authored duration so the timeline covers [0, D], onUpdate
// fires for every eventful seek, and holds never clamp short.
tl.to({ p: 0 }, { p: 1, duration: duration, ease: "none" }, 0);
// Lead entrance: both endpoints authored. Ghosts need no
// entrance; the separation ramp keeps them at zero until the
// traversal opens a gap.
tl.fromTo(
lead,
{ opacity: 0 },
{ opacity: 1, duration: 0.22 * scale, ease: "power2.out" },
0,
);
// HOLD: truly still. The lead rests at path(1) and every ghost
// is coincident at opacity exactly zero.
// 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);
applyTime(0);
window.__timelines = window.__timelines || {};
window.__timelines["echo-trail"] = tl;
})();
</script>
</div>
</template>
</body>
</html>
```
</VariablesExplorer>
## Install
<InstallCommand command="npx hyperframes add echo-trail" item="echo-trail" />
That writes one file: `compositions/components/echo-trail.html`.
## Paste it into your composition
Open `compositions/components/echo-trail.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 |
| --- | --- | --- | --- |
| `echoes` | `4` | number | Ghost copy count, clamped 2 to 6. |
| `delta` | `0.09` | number | Lag between successive ghosts in seconds, clamped 0.03 to 0.3. |
| `path` | `sweep` | `sweep`, `rise`, `arc` | Authored traversal preset. |
| `accent` | `green` | `green`, `blue`, `violet` | Subject accent color: green rides --brand, blue rides --accent, violet rides --accent-2. |
| `exit` | `none` | `none`, `fade`, `up` | Optional departure. Default none: the settled element 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="echo-trail"
data-composition-src="compositions/components/echo-trail.html"
data-variable-values='{"echoes":4,"delta":0.09,"path":"sweep","accent":"green","exit":"none"}'
></div>
```
## Source
<Accordion title={`echo-trail.html`}>
```html
<!doctype html>
<!--
echo-trail: HyperFrames video primitive (trails)
The generalized onion skin: a moving element renders with N ghosted
copies of itself, each ghost showing the element where it was at
t minus i * delta, opacity stepped down per ghost. One traversal along
an authored path; as the element decelerates into rest the echoes
collapse into it and vanish, leaving a clean settled hold.
The subject is a SLOT. Callers supply content by placing an inert
template anywhere in the HOST page (templates never render, and the
runtime wipes the host clip's own children on mount, so the slot lives
at document level):
<template data-slot="echo-trail-subject"> ... </template>
Ghosts are deep clones of the subject content. With no slot, the
primitive renders a token card (surface, hairline border, accent dot,
two skeleton lines, contract tokens only).
Variables (declared in data-composition-variables below):
- echoes (number 2 to 6, default 4): ghost copy count.
- delta (number seconds, default 0.09, clamped 0.03 to 0.3): the lag
between successive ghosts.
- path ("sweep" | "rise" | "arc", default "sweep"): the authored
traversal preset.
- accent ("green" | "blue" | "violet", default "green"): green rides
--brand, blue rides --accent, violet rides --accent-2.
- exit ("none" | "fade" | "up", default "none"): frame roots own
transitions; the default holds the final frame to the last pixel.
Envelope, fixed IN and OUT with elastic HOLD only (never timeScale):
IN_BASE = TRAVEL (2.1s) + echoes * delta + 0.2s settle; the lead
rests at TRAVEL and the last ghost has converged (and is
exactly invisible) by IN
HOLD = max(0, D - IN - OUT)
OUT_BASE = 0.45s only when exit != none
If D < IN_BASE + OUT_BASE, the whole envelope compresses together.
Determinism: ghost i's position at time t is path(ease(clamp01((t -
i * delta) / TRAVEL))) and its opacity is its stepped base times a pure
function of its distance to the lead; both are recomputed from
tl.time() on every update. No Math.random, no wall clock, no
incremental state, no requestAnimationFrame. Eventful seeks
(suppressEvents=false, the engine's render path) land identical frames
in any order and either direction; at rest every ghost is coincident
with the lead at opacity exactly zero, so the HOLD is truly still.
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 "echo-trail" key.
-->
<html
lang="en"
data-composition-id="echo-trail"
data-composition-duration="3.5"
data-composition-variables='[
{ "id": "echoes", "type": "number", "role": "style", "label": "Echoes", "description": "Ghost copy count, clamped 2 to 6.", "default": 4 },
{ "id": "delta", "type": "number", "role": "timing", "label": "Delta", "description": "Lag between successive ghosts in seconds, clamped 0.03 to 0.3.", "default": 0.09 },
{ "id": "path", "type": "enum", "role": "timing", "label": "Path", "description": "Authored traversal preset.", "default": "sweep", "options": [{ "value": "sweep", "label": "Sweep" }, { "value": "rise", "label": "Rise" }, { "value": "arc", "label": "Arc" }] },
{ "id": "accent", "type": "enum", "role": "style", "label": "Accent", "description": "Subject accent 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 settled element 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>Echo Trail</title>
</head>
<body>
<template>
<div id="root" data-composition-id="echo-trail" 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;
color: var(--fg, #f8fafc);
font-family: var(--font-display, "Inter", system-ui, sans-serif);
pointer-events: none;
}
.et-clip {
position: absolute;
inset: 0;
overflow: hidden;
background: var(--bg, transparent);
}
.et-stage {
position: absolute;
inset: 0;
will-change: transform, opacity;
}
.et-ghost,
.et-lead {
position: absolute;
left: 0;
top: 0;
will-change: opacity;
}
.et-ghost {
opacity: 0;
}
.et-lead {
opacity: 0;
}
.et-card {
width: 30cqmin;
padding: var(--space-3, 3cqmin);
display: grid;
gap: var(--space-2, 2cqmin);
border: 0.18cqmin solid var(--border, #475569);
border-radius: var(--radius, 2.4cqmin);
background: var(--surface, #14171c);
box-shadow: 0 1.6cqmin 5cqmin color-mix(in srgb, var(--bg, #000000) 30%, transparent);
}
.et-card-dot {
width: 3.2cqmin;
height: 3.2cqmin;
border-radius: 50%;
background: var(--et-accent);
}
.et-card-line {
height: 1.6cqmin;
border-radius: 0.8cqmin;
background: color-mix(in srgb, var(--fg, #f8fafc) 16%, transparent);
}
.et-card-line.short {
width: 62%;
}
</style>
<div
id="echo-trail-clip"
class="et-clip clip"
data-start="0"
data-duration="3.5"
data-track-index="0"
>
<div class="et-stage">
<div class="et-lead">
<div class="et-card">
<div class="et-card-dot"></div>
<div class="et-card-line"></div>
<div class="et-card-line short"></div>
</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");
var stage = root.querySelector(".et-stage");
var lead = root.querySelector(".et-lead");
var vars =
window.__hyperframes && window.__hyperframes.getVariables
? window.__hyperframes.getVariables()
: {};
var echoesRaw = parseFloat(vars.echoes);
var echoes = isFinite(echoesRaw) ? Math.min(6, Math.max(2, Math.round(echoesRaw))) : 4;
var deltaRaw = parseFloat(vars.delta);
var deltaVar = isFinite(deltaRaw) ? Math.min(0.3, Math.max(0.03, deltaRaw)) : 0.09;
var pathName = vars.path === "rise" || vars.path === "arc" ? vars.path : "sweep";
// Each enum choice routes to a DIFFERENT contract token so the
// variable stays meaningful under a theme.
var accentColors = {
green: "var(--brand, #52525b)",
blue: "var(--accent, #52525b)",
violet: "var(--accent-2, #52525b)",
};
var accent = Object.prototype.hasOwnProperty.call(accentColors, vars.accent)
? vars.accent
: "green";
var exit = vars.exit === "fade" || vars.exit === "up" ? vars.exit : "none";
root.style.setProperty("--et-accent", accentColors[accent]);
// SLOT. Caller templates live at HOST DOCUMENT level (the mount
// wipes host-clip children, and templates never render).
var hostDoc = root.ownerDocument;
var slotTemplate = null;
try {
slotTemplate = hostDoc.querySelector('template[data-slot="echo-trail-subject"]');
} catch (error) {
slotTemplate = null;
}
if (slotTemplate) {
lead.querySelector(".et-card").remove();
lead.appendChild(hostDoc.importNode(slotTemplate.content, true));
}
// Ghosts: deep clones of the subject, inserted BEFORE the lead
// so the lead always renders on top. ghosts[0] is the nearest
// past copy (highest stepped opacity).
var ghosts = [];
for (var g = 0; g < echoes; g += 1) {
var ghost = hostDoc.createElement("div");
ghost.className = "et-ghost";
ghost.setAttribute("aria-hidden", "true");
for (var c = 0; c < lead.children.length; c += 1) {
ghost.appendChild(lead.children[c].cloneNode(true));
}
stage.insertBefore(ghost, lead);
ghosts.push(ghost);
}
// Envelope: fixed IN/OUT, elastic HOLD, never time-scaled.
var TRAVEL_BASE = 2.1;
var IN_BASE = TRAVEL_BASE + echoes * deltaVar + 0.2;
var OUT_BASE = exit === "none" ? 0 : 0.45;
var duration = Math.max(0.001, parseFloat(root.dataset.duration || "3.5"));
var totalBase = Math.max(0.001, IN_BASE + OUT_BASE);
var scale = duration < totalBase ? duration / totalBase : 1;
var TRAVEL = TRAVEL_BASE * scale;
var delta = deltaVar * scale;
var IN = IN_BASE * scale;
var OUT = OUT_BASE * scale;
var HOLD = Math.max(0, duration - (IN + OUT));
var OUT_START = IN + HOLD;
// Path presets in percent-of-stage coordinates; the subject is
// centered on the point via a one-time -50%/-50% translate.
function pathPoint(u) {
if (pathName === "rise") {
return { x: 50 + 6 * Math.sin(Math.PI * u), y: 76 - 44 * u };
}
if (pathName === "arc") {
return { x: 16 + 68 * u, y: 64 - 34 * Math.sin(Math.PI * u) };
}
// sweep: a shallow S from left to right through center.
return { x: 18 + 64 * u, y: 50 + 10 * Math.cos(Math.PI * u) };
}
function easeInOut(t) {
return t < 0.5 ? 2 * t * t : 1 - 2 * (1 - t) * (1 - t);
}
function clamp01(v) {
return v < 0 ? 0 : v > 1 ? 1 : v;
}
function posAt(timeSeconds) {
var u = easeInOut(clamp01(TRAVEL > 0 ? timeSeconds / TRAVEL : 1));
return pathPoint(u);
}
// One-time static transforms: center anchor plus a slight
// per-ghost scale step for depth. GSAP owns the transform, the
// per-update writes touch only left/top/opacity.
gsap.set(lead, { xPercent: -50, yPercent: -50 });
for (var i = 0; i < ghosts.length; i += 1) {
gsap.set(ghosts[i], {
xPercent: -50,
yPercent: -50,
scale: 1 - 0.015 * (i + 1),
});
}
// Stepped ghost bases: nearest past copy strongest.
var bases = [];
for (var b = 0; b < echoes; b += 1) {
bases.push(0.55 * (1 - b / echoes));
}
// Pure per-update apply: every position and every ghost alpha
// is a function of tl.time() alone. Ghost alpha is its stepped
// base times a separation ramp, so echoes are invisible before
// motion starts and collapse to exactly zero at rest. Writes
// are idempotent, so the HOLD repaints identically.
function applyTime(timeSeconds) {
var leadPos = posAt(timeSeconds);
gsap.set(lead, {
left: leadPos.x.toFixed(4) + "%",
top: leadPos.y.toFixed(4) + "%",
});
for (var n = 0; n < ghosts.length; n += 1) {
var p = posAt(timeSeconds - (n + 1) * delta);
var dist = Math.hypot(p.x - leadPos.x, p.y - leadPos.y);
var alpha = bases[n] * clamp01(dist / 2.2);
gsap.set(ghosts[n], {
left: p.x.toFixed(4) + "%",
top: p.y.toFixed(4) + "%",
opacity: alpha < 0.002 ? 0 : alpha,
});
}
}
gsap.set(stage, { opacity: 1, y: "0cqh" });
var tl = gsap.timeline({
paused: true,
onUpdate: function () {
applyTime(tl.time());
},
});
// Anchor tween: an inert plain-object tween spanning the full
// authored duration so the timeline covers [0, D], onUpdate
// fires for every eventful seek, and holds never clamp short.
tl.to({ p: 0 }, { p: 1, duration: duration, ease: "none" }, 0);
// Lead entrance: both endpoints authored. Ghosts need no
// entrance; the separation ramp keeps them at zero until the
// traversal opens a gap.
tl.fromTo(
lead,
{ opacity: 0 },
{ opacity: 1, duration: 0.22 * scale, ease: "power2.out" },
0,
);
// HOLD: truly still. The lead rests at path(1) and every ghost
// is coincident at opacity exactly zero.
// 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);
applyTime(0);
window.__timelines = window.__timelines || {};
window.__timelines["echo-trail"] = tl;
})();
</script>
</div>
</template>
</body>
</html>
```
</Accordion>
{/* hf:generated-footer */}
Tagged `motion-primitive` `demonstrate` `trail` `onion-skin` `ghosts` `deterministic`.
## Related topics
- [Browse the complete Catalog](/catalog)
- [Add assets and Catalog items in Studio](/studio/assets-and-blocks)
- [Build a richer composition](/go-further)
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