Skills

create-composition

Installation
SKILL.md

Create Composition Workflow

A Helios composition is a web page (HTML/JS) that uses the @helios-project/core library to drive animations. This page can be viewed in the Browser, embedded in the Player, or rendered to video by the Renderer.

1. Basic Structure

Create a composition.html file. This is the entry point.

<!DOCTYPE html>
<html>
<head>
    <title>My Composition</title>
    <style>
        body { margin: 0; overflow: hidden; background: black; }
        canvas { display: block; width: 100vw; height: 100vh; }
    </style>
</head>
<body>
    <canvas id="canvas"></canvas>
    <script type="module" src="./src/main.ts"></script>
</body>
</html>

2. Initialize Helios

In your script (main.ts or inline), initialize Helios and set up the render loop.

import { Helios } from '@helios-project/core';

// 1. Config
const width = 1920;
const height = 1080;
const fps = 30;
const duration = 10; // seconds

// 2. Define Input Schema (Optional but recommended)
const schema = {
  type: 'object',
  properties: {
    title: { type: 'string', default: "Hello World" },
    color: { type: 'string', default: "#ff0000" }
  }
};

// 3. Setup Canvas
const canvas = document.getElementById('canvas') as HTMLCanvasElement;
canvas.width = width;
canvas.height = height;
const ctx = canvas.getContext('2d');

// 4. Initialize Engine
const helios = new Helios({
    duration,
    fps,
    width,
    height,
    schema, // Pass schema
    inputProps: { title: "Hello World", color: "#ff0000" }, // Initial props
    autoSyncAnimations: true // Optional: Sync CSS/WAAPI
});

// 5. Bind to Document Timeline (CRITICAL for Renderer/Player)
helios.bindToDocumentTimeline();

// 6. Expose to Window (CRITICAL for detection)
// @ts-ignore
window.helios = helios;

// 7. Define Render Function
function draw(frame: number, props: any) {
    // Clear
    ctx.fillStyle = 'black';
    ctx.fillRect(0, 0, width, height);

    // Calculate time/progress
    const time = frame / fps;
    const progress = time / duration;

    // Draw something using props
    const x = progress * width;

    ctx.fillStyle = props.color;
    ctx.font = '100px sans-serif';
    ctx.fillText(props.title, x, height/2);
}

// 8. Subscribe to State Changes
helios.subscribe((state) => {
    draw(state.currentFrame, state.inputProps);
});

// 9. Initial Draw
const state = helios.getState();
draw(state.currentFrame, state.inputProps);

Checklist

  • Instance Created: new Helios(...) called with duration/fps/props.
  • Timeline Bound: helios.bindToDocumentTimeline() called.
  • Window Exposed: window.helios = helios set.
  • State Subscribed: helios.subscribe(...) used to trigger renders.
  • Canvas/DOM Ready: Elements are sized correctly (usually 100vw/100vh or fixed resolution).

Auto-Sync Animations

If you are using CSS animations or Web Animations API (WAAPI), set autoSyncAnimations: true in the constructor. Helios will automatically hijack the document timeline and sync these animations to the current frame when scrubbing.

Frameworks

For React, Vue, or Svelte, wrap this logic in a component or hook. See examples/react/SKILL.md, examples/vue/SKILL.md, or examples/svelte/SKILL.md.

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