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docs: add comprehensive panel detection documentation

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Document the new panel detection feature with detailed explanations
of functionality, requirements, and usage.

New documentation sections:
- How It Works: Explains three-tier fallback system
  * Tier 1: OpenCV edge detection (fast, accurate)
  * Tier 2: COCO-SSD ML detection (handles irregular layouts)
  * Tier 3: Grid-based detection (lightweight, always works)

- Content Security Policy (CSP) Requirements:
  * Documents 'unsafe-eval' requirement for OpenCV.js
  * Explains why it's safe for ebook reading context
  * Provides example CSP configuration

- Usage: Complete API examples showing:
  * How to enable panel mode
  * Navigation methods (nextPanel, prevPanel)
  * Panel information properties (panelCount, currentPanelIndex)

- Keyboard Shortcuts: Available shortcuts for demo reader
  * P: Toggle panel mode
  * Arrow keys/h/l: Navigate panels
  * Escape: Exit panel mode

- Technical Details:
  * Vendored library sizes and sources
  * Dynamic loading strategy
  * UMD/global build approach for browser compatibility

- Browser Compatibility:
  * Minimum versions (Chromium 90+, Firefox 88+, Safari 15+)
  * Graceful degradation on older browsers

Updated Features section to reflect:
- Panel detection now included with vendored libraries
- Total vendor size: ~25MB (was 13MB, added 12.5MB)
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john-okeefe
2026-04-13 19:15:06 -04:00
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README.md
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@@ -4,7 +4,7 @@ Library for rendering e-books in the browser.
Features: Features:
- Supports EPUB, MOBI, KF8 (AZW3), FB2, CBZ, PDF (experimental; requires PDF.js) - Supports EPUB, MOBI, KF8 (AZW3), FB2, CBZ, PDF (experimental; requires PDF.js)
- Optional panel detection for manga and comics (requires optional dependencies) - Panel detection for manga and comics (ML/CV libraries vendored, ~25MB total)
- Add support for other formats yourself by implementing the book interface - Add support for other formats yourself by implementing the book interface
- Pure JavaScript - Pure JavaScript
- Small and modular - Small and modular
@@ -144,50 +144,85 @@ CBZs are similarly handled like fixed-layout EPUBs.
### Panel Detection ### Panel Detection
The fixed-layout renderer includes an optional panel detection feature for manga, comics, and other fixed-layout content. When enabled, it automatically detects panel boundaries and allows for panel-by-panel navigation. The fixed-layout renderer includes an optional panel detection feature for manga, comics, and other fixed-layout content. When enabled, it automatically detects panel boundaries and allows for panel-by-panel navigation, making it easier to read complex page layouts on smaller screens.
This feature requires optional dependencies that are not installed by default: #### How It Works
```bash Panel detection uses a multi-tier fallback system that automatically selects the best detection method:
# Install with panel detection (includes ~4.5MB of ML/CV libraries)
npm install foliate-js
# Install without panel detection (lightweight, uses grid-based fallback) 1. **OpenCV Edge Detection** (Tier 1): Fast, accurate detection using computer vision algorithms. Works best for manga/comics with clear panel borders and high contrast.
npm install foliate-js --omit=optional 2. **COCO-SSD ML Detection** (Tier 2): Machine learning-based detection that handles irregular layouts, speech bubbles, and scenes without clear panel boundaries.
3. **Grid-Based Detection** (Tier 3): Lightweight fallback that divides pages into a configurable grid. Always works regardless of image content.
The system automatically falls back through the tiers if a higher tier fails to detect panels or if required libraries aren't available.
#### Content Security Policy (CSP) Requirements
The ML-based detection methods (Tiers 1 and 2) require the `'unsafe-eval'` CSP directive because OpenCV.js uses `eval()` and `new Function()` internally for performance optimization.
If your CSP doesn't allow `'unsafe-eval'`, the system will automatically fall back to grid-based detection. To enable full ML detection, configure your CSP like this:
```http
Content-Security-Policy: default-src 'self'; script-src 'self' 'unsafe-eval'
``` ```
When panel detection is available, it uses a multi-tier fallback system: This is safe for ebook reading because:
1. OpenCV edge detection (fast, accurate for clear panel borders) - The ML/CV libraries are vendored from trusted sources (OpenCV, TensorFlow)
2. ML-based detection with COCO-SSD (handles irregular layouts) - No user-provided scripts are executed
3. Grid-based detection (lightweight, always works) - The libraries only run on page content, not external code
To use panel detection: #### Usage
Basic usage:
```js ```js
const view = document.createElement('foliate-view') const view = document.createElement('foliate-view')
await view.open('manga.epub') await view.open('manga.epub')
// Check if renderer supports panel detection // Enable panel mode
if (view.renderer.togglePanelMode) { await view.renderer.togglePanelMode()
// Enable panel mode
view.renderer.togglePanelMode()
// Navigate between panels // Navigate between panels
await view.renderer.nextPanel() await view.renderer.nextPanel() // go to next panel
await view.renderer.prevPanel() await view.renderer.prevPanel() // go to previous panel
// Get panel information // Get panel information
console.log(view.renderer.panelCount) // number of panels console.log(view.renderer.panelCount) // total number of panels
console.log(view.renderer.currentPanelIndex) // current panel console.log(view.renderer.currentPanelIndex) // current panel (0-indexed)
}
``` ```
Panel mode can also be toggled via keyboard shortcuts: The renderer exposes these panel-related methods and properties:
- `P` to toggle panel mode on/off - `togglePanelMode()`: Enable or disable panel mode
- Arrow keys or `h`/`l` to navigate panels when in panel mode - `nextPanel()`: Navigate to the next panel
- `Escape` to exit panel mode - `prevPanel()`: Navigate to the previous panel
- `panelCount`: Number of detected panels on current page
- `currentPanelIndex`: Index of current panel (0 to panelCount - 1)
The renderer will gracefully fall back to grid-based detection if the optional dependencies are not available, so panel navigation will work regardless of whether the ML/CV libraries are installed. #### Keyboard Shortcuts
When using the library with the demo reader (`reader.html`), these keyboard shortcuts are available:
- `P`: Toggle panel mode on/off
- Arrow keys (←/→) or `h`/`l`: Navigate between panels when in panel mode
- `Escape`: Exit panel mode and return to normal page view
#### Technical Details
The panel detection system uses vendored ML/CV libraries (approximately 12.5MB):
- **OpenCV.js** (~11MB): Computer vision library for edge detection
- **TensorFlow.js** (~1.5MB): ML runtime for COCO-SSD model
- **COCO-SSD** (~9KB): Pre-trained object detection model
These libraries are loaded dynamically the first time panel detection is used, minimizing initial load time. The libraries are vendored in the `vendor/` directory and loaded as UMD/global builds to ensure browser compatibility without requiring ES module imports.
#### Browser Compatibility
Panel detection requires modern JavaScript features and works on:
- Chromium 90+
- Firefox 88+
- Safari 15+
The feature gracefully degrades on older browsers by falling back to grid-based detection.
### The Renderers ### The Renderers