Rnote Viewer for Android

Android viewer for .rnote files (from the open-source application Rnote).

⚠️ Disclaimer
This is a very basic and experimental project. It is unstable, incomplete, and was developed primarily for personal use.
It may not work correctly in many cases.

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📸 Screenshot

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Features

• Open .rnote files
  • From file manager
  • From toolbar
  • Via Android system intents
• Pan and pinch-to-zoom
  • Smooth navigation with double tap to reset to page width
• All drawing elements supported
  • Pen strokes
  • Geometric shapes
  • Keyboard text
  • Bitmap images
• Backgrounds
  • Grid
  • Ruled
  • Dots
  • Blank
• Highlighter
  • Rendered as a 40% opacity layer
• Multi-page documents
  • Optimized for documents with hundreds of pages
• Fast navigation
  • Vertical scrollbar
  • Page indicator
  • "Go to page" dialog
• Custom fonts
  • Install .ttf / .otf via system file picker

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Navigation

The vertical bar on the right side allows fast scrolling by dragging.

A page indicator appears for 1.5 seconds showing:
current page / total pages

The floating action button (FAB) opens a numeric dialog to jump directly to a specific page.

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Custom Fonts

The Manage fonts... option in the toolbar opens a dialog listing installed fonts.

• Tap + Add font to select a .ttf or .otf file
• The app reads font family and style from the OpenType Name Table
• Fonts are indexed by name (e.g. "Indie Flower")
• Stored in internal storage: filesDir/fonts/
• Persist across sessions

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Architecture and Optimizations

Streaming Parsing

.rnote files are gzip archives containing JSON.

The parser uses: - GZIPInputStream - JsonReader (Gson streaming API)

No full JSON string is ever loaded into memory.

Parsing produces a list of CanvasElement (sealed hierarchy), ordered using chrono_components.

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R-tree (Sort-Tile-Recursive)

All elements are indexed using an R-tree built with the STR algorithm.

• Query: rtree.query(minX, minY, maxX, maxY)
• Complexity: O(log n + k)
• Only visible elements are processed

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Tile Cache (Band Rendering)

The canvas is split into horizontal bands of 512 document units.

• Rendered off-screen via coroutines (Dispatchers.IO)
• Stored in an LruCache (48 MB limit)
• Rendering scale capped at 1536 px width to avoid oversized tiles

Only visible tiles are drawn; adjacent tiles are preloaded (±1 look-ahead).

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Anti-flickering

Tile cache invalidation happens only after pinch-to-zoom ends, with a 150 ms debounce.

During zoom: - The document is scaled via matrix - No re-rendering occurs

Tiles are regenerated only once after the gesture ends.

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Project Structure

app/src/main/java/com/example/rnoteviewer/
├── RnoteDocument.kt        — CanvasElement data models
├── RnoteParser.kt          — Streaming gzip + JSON parser
├── RTree.kt                — Spatial R-tree (STR bulk-load)
├── TileCache.kt            — LRU tile cache + rendering
├── RnoteView.kt            — Custom View (pan, zoom, rendering, navigation)
├── DocumentViewModel.kt    — Async loading (coroutines + ViewModel)
├── MainActivity.kt         — Activity, file picker, UI controls
├── FontManager.kt          — Font loading (TTF/OTF, OpenType parsing)
└── FontsDialogFragment.kt  — Font management dialog

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Supported Elements

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JSON Type Kotlin Class Notes

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brushstroke StrokeElement Pressure, color, thickness

textstroke TextElement Position via affine transform

bitmapimage BitmapElement Position / scale / rotation

shapestroke → line LineShape

shapestroke → arrow ArrowShape

shapestroke → rect RectShape

shapestroke → ellipse EllipseShape

shapestroke → quadbez QuadBezShape

shapestroke → cubbez CubBezShape

shapestroke → polygon PolygonShape

shapestroke → polyline PolylineShape

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.rnote Format --- Key Fields

JSON Field Meaning

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document.config.format Page size, DPI document.config.background Background style document.height Total canvas height stroke_components[].brushstroke.path Stroke points stroke_components[].textstroke.transform.affine Position matrix stroke_components[].textstroke.text_style Font info stroke_components[].bitmapimage.rectangle Transform stroke_components[].bitmapimage.image Raw pixel data stroke_components[].shapestroke.shape Geometry chrono_components[].t Drawing order

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Compatibility Notes

• Tested only with Rnote version 0.13.1
• Designed specifically for:
  • Vertical continuous layout
  • White or grid backgrounds

Other formats or versions may not work correctly.

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Limitations

• Very basic implementation
• Likely contains bugs and incomplete features
• Many things may not work as expected
• Built primarily for personal notes

This app was designed specifically for my own notes, so behavior with other files may vary.

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Maintenance

I do not have strong Android development expertise, and this project is:

• ❌ Not actively maintained\
• ❌ Not guaranteed to be updated

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Contributing / Forking

If you find this project useful:

• Feel free to fork it
• Improve it
• Adapt it to your needs

Contributions are welcome, but there is no guarantee of review or updates.

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Purpose

This is not a full-featured viewer.

It is simply a basic way to visualize .rnote files on Android when no official solution is available.