@arcmantle/image-viewer

A high-performance image viewer web component built with web workers and offscreen canvas for smooth image manipulation and display.

Features

• 🚀 High Performance: Uses web workers and OffscreenCanvas for non-blocking image operations
• 🎯 Interactive Navigation: Pan, zoom, and rotate images with mouse and touch support
• 📱 Touch Gestures: Multi-touch zoom and pan support for mobile devices
• ⚡ Hardware Accelerated: Leverages GPU acceleration through canvas rendering
• 🎨 Smooth Animations: Frame-rate limited interactions for optimal performance
• 🔧 Programmatic API: Full control through JavaScript API

Installation

npm install @arcmantle/image-viewer

pnpm add @arcmantle/image-viewer

yarn add @arcmantle/image-viewer

Usage

Basic HTML Usage

<iv-image-viewer
  image-src="/path/to/your/image.jpg"
  reset-on-new-image
  fit-on-new-image
></iv-image-viewer>

JavaScript/TypeScript Usage

import { ImageViewer } from '@arcmantle/image-viewer';

// Using the component
const viewer = document.createElement('iv-image-viewer');
viewer.imageSrc = '/path/to/image.jpg';
viewer.resetOnNewImage = true;
document.body.appendChild(viewer);

// Programmatic control
viewer.adapter.api.zoom(1.5);
viewer.adapter.api.rotate(90);
viewer.adapter.api.fitToView();
viewer.adapter.api.reset();

React/JSX Usage

import { ImageViewer } from '@arcmantle/image-viewer';

function App() {
  return (
    <ImageViewer
      image-src="/spiral.jpg"
      reset-on-new-image
      fit-on-new-image
    />
  );
}

Properties

Property	Type	Default	Description
imageSrc	string	''	URL or path to the image to display
resetOnNewImage	boolean	false	Whether to reset view transformations when a new image is loaded
fitOnNewImage	boolean	false	Whether to automatically fit the image to view when loaded

API Methods

The component exposes an API object with the following methods:

// Access the API
const api = imageViewer.adapter.api;

// Reset view to default state
api.reset();

// Fit image to viewport
api.fitToView();

// Zoom by factor (1.5 = 150%, 0.5 = 50%)
api.zoom(1.5);

// Rotate by degrees (positive = clockwise)
api.rotate(90);

Interaction Controls

Mouse Controls

• Left Click + Drag: Pan the image
• Mouse Wheel: Zoom in/out at cursor position

Touch Controls

• Single Touch + Drag: Pan the image
• Pinch Gesture: Zoom in/out at gesture center
• Two Finger Touch: Multi-touch zoom and pan

Keyboard Support

The component is focusable and can receive keyboard events when focused.

Architecture

The image viewer uses a sophisticated architecture for optimal performance:

Web Worker Architecture

• Main Thread: Handles UI interactions and event management
• Worker Thread: Performs all canvas operations and image transformations
• OffscreenCanvas: Enables GPU-accelerated rendering off the main thread

Performance Optimizations

• Frame Rate Limiting: Interactions are throttled to 100fps to prevent overwhelming the system
• Transferable Objects: Efficiently passes data between main thread and worker
• Smart Rendering: Only redraws when necessary
• Image Smoothing: Automatically adjusted based on zoom level

Canvas Management

The component uses a WorkerView class that provides:

• Viewport calculations and transformations
• Scale, rotation, and translation management
• Automatic image centering and fitting
• Boundary constraints and limits

Styling

The component can be styled with CSS:

iv-image-viewer {
  width: 800px;
  height: 600px;
  border: 1px solid #ccc;
  border-radius: 8px;
}

/* The component focuses cleanly */
iv-image-viewer:focus {
  outline: 2px solid #0066cc;
}

Advanced Usage

Custom Controls

// Create custom zoom controls
function createZoomControls(viewer) {
  const zoomIn = document.createElement('button');
  zoomIn.textContent = 'Zoom In';
  zoomIn.onclick = () => viewer.adapter.api.zoom(1.2);

  const zoomOut = document.createElement('button');
  zoomOut.textContent = 'Zoom Out';
  zoomOut.onclick = () => viewer.adapter.api.zoom(0.8);

  const reset = document.createElement('button');
  reset.textContent = 'Reset';
  reset.onclick = () => viewer.adapter.api.reset();

  return { zoomIn, zoomOut, reset };
}

Dynamic Image Loading

async function loadImage(viewer, imageUrl) {
  try {
    // Set the image source
    viewer.imageSrc = imageUrl;

    // Optionally fit to view after loading
    // The component will handle the loading automatically
    setTimeout(() => {
      viewer.adapter.api.fitToView();
    }, 100);
  } catch (error) {
    console.error('Failed to load image:', error);
  }
}

Browser Support

• Modern Browsers: Chrome 69+, Firefox 105+, Safari 15+
• Required Features:
  • OffscreenCanvas support
  • Web Workers
  • ImageBitmap API
  • ES2020+ JavaScript features

Development

Building

pnpm install
pnpm build

Development Server

pnpm dev

Running Demo

pnpm build-demo
pnpm preview-demo

Contributing

1. Fork the repository
2. Create a feature branch
3. Make your changes
4. Add tests if applicable
5. Submit a pull request

License

This project is licensed under the Apache 2.0 License - see the Apache License 2.0 for details.

Related Packages

This component is part of the @arcmantle ecosystem:

• @arcmantle/adapter-element - Base web component framework
• @arcmantle/library - Core utilities and canvas helpers
• @arcmantle/lit-jsx - JSX support for Lit-based components

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