example-react

name	example-react
description	Patterns for using Helios with React. Use when building compositions in a React environment.

React Composition Patterns

Integrate Helios into React components using hooks for state management and Refs for canvas access.

Quick Start

1. Create useVideoFrame Hook

This hook subscribes to Helios and returns the current frame, triggering re-renders.

// hooks/useVideoFrame.js
import { useState, useEffect } from 'react';

export function useVideoFrame(helios) {
  const [frame, setFrame] = useState(helios.currentFrame.peek());

  useEffect(() => {
    // Subscribe to updates
    const unsubscribe = helios.subscribe((state) => {
      setFrame(state.currentFrame);
    });
    return unsubscribe;
  }, [helios]);

  return frame;
}

2. Create Composition Component

// App.jsx
import React, { useRef, useEffect } from 'react';
import { Helios } from '@helios-project/core';
import { useVideoFrame } from './hooks/useVideoFrame';

// Initialize Singleton (outside component to persist across re-renders)
const helios = new Helios({
  duration: 10,
  fps: 30
});
helios.bindToDocumentTimeline();

// Expose for Renderer/Player
if (typeof window !== 'undefined') window.helios = helios;

export default function App() {
  const canvasRef = useRef(null);
  const frame = useVideoFrame(helios);

  useEffect(() => {
    const ctx = canvasRef.current?.getContext('2d');
    if (!ctx) return;

    const { width, height } = canvasRef.current;

    // Clear
    ctx.clearRect(0, 0, width, height);

    // Draw based on frame
    const progress = frame / (helios.duration * helios.fps);
    ctx.fillStyle = '#61dafb';
    ctx.fillRect(progress * width, height / 2 - 50, 100, 100);

  }, [frame]); // Re-run draw when frame changes

  return <canvas ref={canvasRef} width={1920} height={1080} />;
}

Optimization

For complex scenes, avoid React state updates for every frame (which triggers full component re-render). Instead, use a useRef to hold the frame and an animation loop, or update the canvas imperatively inside subscribe.

Imperative Pattern (High Performance)

useEffect(() => {
  const ctx = canvasRef.current.getContext('2d');

  const unsubscribe = helios.subscribe((state) => {
    // Draw directly without triggering React render
    drawScene(ctx, state.currentFrame);
  });

  return unsubscribe;
}, []);

Source Files

• Example: examples/react-canvas-animation/