# **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**.

---

## **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`).

---

## **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
```

---

## **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)

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

Copy into the extension directory:

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

Ensure executable bit:

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

---

## **Running**

### Launch normally (clean page)

```sh
./simplenotes
```

### Launch with a PBM document restored

```sh
./simplenotes page.pbm
```

---

## **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               |

---

## **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/`

---

## **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:

  ```c
  system("eips -r");
  ```

---

## **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.

---

## **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

---

## **License**

MIT License (recommended, adjust if needed).

---

## **Credits**

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