Kscribe (penpad) — Native Kindle Scribe Notepad

simplenotes is a fully native drawing and note-taking application for the Kindle Scribe, written in C and built directly on top of:

• /dev/input/stylus
• /dev/input/touch
• /dev/fb0 (8-bit grayscale framebuffer)
• direct eInk refresh via eips
• custom PBM + PNG export (LodePNG)

It runs without the Kindle framework interfering by exclusively grabbing stylus and touch events. The code is optimized for real-time drawing, fast refresh, and full-screen handwriting.

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Features

Drawing

• Smooth line drawing using Bresenham.
• Adjustable stroke thickness (STROKE_PX).
• Fast thick-point rasterization optimized for eInk.
• Top-bar protected region to prevent accidental strokes.

Input Mapping

• Fully calibrated raw stylus → pixel mapping.
• Reversed X and inverted Y axes (matching Scribe hardware).
• Touch and stylus suppressed from the framework using EVIOCGRAB.

Saving & Loading

• PBM Save: 1-bit P1 PBM file (latest.fb) stored at: /mnt/us/extensions/simplenotes/bin/latest.fb
• PNG Export: full-resolution PNG saved with timestamp to: /mnt/us/simplenotes/note-YYYYmmdd-HHMMSS.png
• Load on startup: pass a PBM file as argv[1] to restore a page on launch.

Gesture Controls

Gestures are based on double-tap with the stylus:

Region	Gesture	Action
Top-left	double-tap	Save PBM + PNG
Top-right	double-tap	Exit the program
Bottom-right	double-tap	Reset page (no save)

Gesture detection uses a 2-second timing window.

UI

• Title bar drawn using eips.
• PNG icons (exit.png, reset.png, save.png) shown via eips -g.
• Automatic refresh throttling (REFRESH_INTERVAL_MS).

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Directory Layout

/mnt/us/extensions/simplenotes/
│
├── bin/
│   ├── simplenotes (compiled binary)
│   └── latest.fb              # always overwritten on save
│
├── assets/
│   ├── exit.png
│   ├── reset.png
│   └── save.png
│
└── (other KUAL metadata)

User-visible notebooks (PNG exports):

/mnt/us/simplenotes/note-YYYYmmdd-HHMMSS.png

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Build Instructions

Requirements

• GCC for ARM (Kindle cross-compile) or KindleToolchain.

• LodePNG included in source tree.

• A jailbroken Kindle Scribe with:

  • KUAL
  • USBNet / SSH

Compile (on device or cross-compiled)

gcc -O2 -std=c99 penpad_fb2.c lodepng.c -o simplenotes

Copy into the extension directory:

scp simplenotes root@kindle:/mnt/us/extensions/simplenotes/bin/

Ensure executable bit:

chmod +x /mnt/us/extensions/simplenotes/bin/simplenotes

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Running

Launch normally (clean page)

./simplenotes

Launch with a PBM document restored

./simplenotes page.pbm

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Controls

Drawing

Just use the stylus. Drawing stops in:

• the top gesture bar (TOPBAR_H)
• the UI icon region

Gestures

All gestures require two quick pen-down events in the target zone.

Gesture	Behavior
Top-left double-tap	Save PBM + PNG, clear screen, redraw UI
Top-right double-tap	Exit program
Bottom-right double-tap	Reset page without saving

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File Formats

PBM Export

• 1-bit P1 format
• Always stored as /mnt/us/extensions/simplenotes/bin/latest.fb
• Useful for restoring a session exactly

PNG Export

• Real 8-bit grayscale → 32-bit RGBA PNG conversion via LodePNG
• Timestamped filename
• Stored in /mnt/us/simplenotes/

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Technical Overview

Framebuffer

• Reads framebuffer geometry via FBIOGET_FSCREENINFO + FBIOGET_VSCREENINFO

• Maps /dev/fb0 using mmap

• Writes raw grayscale values directly:

  • 0x00 = black
  • 0xFF = white

Internal Bitmap

• Maintains a full-screen 1-bit buffer g_bitmap
• Used for PBM and PNG export
• Updated simultaneously with framebuffer writes

Refresh Model

• Partial refresh every REFRESH_INTERVAL_MS

• Full refresh on demand:

  system("eips -r");
  

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Known Limitations

• No undo/redo (possible future enhancement).
• No multi-page notebook support.
• PNG rendering limited by Kindle CPU; PBM much faster.
• eips -g sometimes logs a harmless “barcode missing” warning.

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Future Extensions

These are explicitly listed in the project notes and remain possible next steps:

• Undo / Redo system
• Multi-page notebook (page stack)
• Layer support
• Pressure sensitivity
• PNG import
• fbink integration for faster partial refresh
• UI overlay mode
• Eraser tool

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License

MIT License (recommended, adjust if needed).

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Credits

Developed by maru21 Testing, calibration, and optimization performed directly on Kindle Scribe hardware.