Wylan SwetsandClaude Sonnet 4.6
bf894fd343
## Summary **Goal:** Fix bidirectional KOSync position matching between CrossPoint and KOReader so that syncing in either direction lands on the correct page with character-level accuracy. **Changes included:** **Download — `toCrossPoint` (server XPath → CrossPoint page)** - **XPath ancestry mode for structured elements**: The previous `ParagraphStreamer` only tracked `<p>` elements. Replaced with a full ancestor-walking mode that correctly resolves XPaths pointing into `<li>`, `<ul>`, and other structured elements. Char offset within the target element is bounded to the matched element's content only. - **Slash-in-attribute-value corrupts depth tracking**: `processByteInTag()` treated every `/` byte as a self-closing tag marker, including `/` inside quoted attribute values (e.g. `xmlns="http://..."`, `src="Links/image.jpg"`). This drove `htmlDepth` to 0 prematurely, causing the ancestry search to exit far short of the target paragraph. Fixed with `inAttrQuote` tracking. - **Off-by-one in page formula**: `intra * totalPages` rounds up incorrectly for last-page positions. Changed to `intra * (totalPages - 1)` to map the `[0, 1]` intra fraction correctly onto the `[0, totalPages-1]` page range. Example: page 14 of 17 was returned as 15. **Upload — `toKOReader` (CrossPoint page → server XPath)** - **Off-by-one in page-to-intra formula**: Symmetric fix — `pageNumber / totalPages` changed to `pageNumber / (totalPages - 1)`, with the guard updated from `> 0` to `> 1` to avoid division by zero. - **`<li>`-based XPath generation**: When the current page starts on a list item, `findXPathForProgress` now generates `ul[N]/li[M]` XPaths rather than falling back to the preceding `<p>`. Requires the new `listItemIndex` field in `PageLutEntry` (section cache version bumped to 23). - **Text-node precision with correct `text()[N].M` format**: KOReader expects `text()[N].M` where `N` is the 1-based index of the specific text node within the element. The previous attempt generated `text().M` (no brackets), which caused KOReader to jump to the front of the book. Implements a per-element text-node index stack in `XPathProgressResolver` — parallel to the existing element path stack — that correctly tracks text node indices relative to each element. Empty text nodes from bare anchor elements (`<a id="anchor"/>`) are intentionally skipped, matching KOReader's own text node counting behavior. **Reviewer-caught bugs** - **Double `onCloseTag()` on malformed `</br/>`**: Both the `tagIsClose` path and the self-closing `/` check were firing, double-decrementing `htmlDepth`. Fixed with a `!tagIsClose` guard. - **Dangling pointer in `LOG_DBG`**: `std::to_string(*nextParagraphPage).c_str()` passed a pointer to a temporary destroyed before the variadic call. Fixed with `snprintf` into a stack `char[8]` buffer. ## Additional Context - Section cache version bumped from 22 → 23 due to the new `listItemIndex` field in `PageLutEntry`. Users upgrading will see a one-time re-render of all cached sections on first load — no data loss. - The `textNodeIndexStack` in `XPathProgressResolver` is a `std::vector<int>` that mirrors the existing `path` and `parentStates` stacks — same depth, same lifetime. No additional heap pressure beyond what was already present. - All fixes verified on device with *Gentle and Lowly* by Dane C. Ortlund (spine 21, 17 pages). Download syncs land on the correct page; upload syncs land at the correct paragraph with character-level offset. ## Test plan - [ ] Download: sync from KOReader → CrossPoint lands on correct page for `text()[N].M` XPaths - [ ] Download: ancestry correctly resolves `<li>` positions inbound from KOReader - [ ] Upload: sync from CrossPoint → KOReader lands within one page for mid-paragraph positions - [ ] Upload: sync from CrossPoint → KOReader correctly targets `<li>` elements when page starts on a list item - [ ] Upload: `text()[N].M` format XPaths do not cause KOReader to jump to front of book - [ ] Section cache version 23: delete `.crosspoint/` and verify clean re-parse with no crashes --- ### AI Usage Did you use AI tools to help write this code? **YES** — developed with Claude Code (Anthropic). --------- Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
CrossPoint Reader
Firmware for the Xteink X4 e-paper display reader (unaffiliated with Xteink). Built using PlatformIO and targeting the ESP32-C3 microcontroller.
CrossPoint Reader is a purpose-built firmware designed to be a drop-in, fully open-source replacement for the official Xteink firmware. It aims to match or improve upon the standard EPUB reading experience.
Motivation
E-paper devices are fantastic for reading, but most commercially available readers are closed systems with limited customisation. The Xteink X4 is an affordable, e-paper device, however the official firmware remains closed. CrossPoint exists partly as a fun side-project and partly to open up the ecosystem and truly unlock the device's potential.
CrossPoint Reader aims to:
- Provide a fully open-source alternative to the official firmware.
- Offer a document reader capable of handling EPUB content on constrained hardware.
- Support customisable font, layout, and display options.
- Run purely on the Xteink X4 hardware.
This project is not affiliated with Xteink; it's built as a community project.
Features & Usage
- EPUB parsing and rendering (EPUB 2 and EPUB 3)
- Image support within EPUB
- Saved reading position
- File explorer with file picker
- Basic EPUB picker from root directory
- Support nested folders
- EPUB picker with cover art
- Custom sleep screen
- Cover sleep screen
- Wifi book upload
- Wifi OTA updates
- KOReader Sync integration for cross-device reading progress
- Configurable font, layout, and display options
- User provided fonts
- Full UTF support
- Screen rotation
Multi-language support: Read EPUBs in various languages, including English, Spanish, French, German, Italian, Portuguese, Russian, Ukrainian, Polish, Swedish, Norwegian, and more.
See the user guide for instructions on operating CrossPoint, including the KOReader Sync quick setup.
For more details about the scope of the project, see the SCOPE.md document.
Installing
Web (latest firmware)
- Connect your Xteink X4 to your computer via USB-C and wake/unlock the device
- Go to https://xteink.dve.al/ and click "Flash CrossPoint firmware"
To revert back to the official firmware, you can flash the latest official firmware from https://xteink.dve.al/, or swap back to the other partition using the "Swap boot partition" button here https://xteink.dve.al/debug.
Web (specific firmware version)
- Connect your Xteink X4 to your computer via USB-C
- Download the
firmware.binfile from the release of your choice via the releases page - Go to https://xteink.dve.al/ and flash the firmware file using the "OTA fast flash controls" section
To revert back to the official firmware, you can flash the latest official firmware from https://xteink.dve.al/, or swap back to the other partition using the "Swap boot partition" button here https://xteink.dve.al/debug.
Command line (specific firmware version)
- Install
esptool:
pip install esptool
- Download the
firmware.binfile from the release of your choice via the releases page - Connect your Xteink X4 to your computer via USB-C.
- Note the device location. On Linux, run
dmesgafter connecting. On MacOS, run :
log stream --predicate 'subsystem == "com.apple.iokit"' --info
- Flash the firmware :
esptool.py --chip esp32c3 --port /dev/ttyACM0 --baud 921600 write_flash 0x10000 /path/to/firmware.bin
Change /dev/ttyACM0 to the device for your system.
Manual
See Development below.
Development
Prerequisites
- PlatformIO Core (
pio) or VS Code + PlatformIO IDE - Python 3.8+
- USB-C cable for flashing the ESP32-C3
- Xteink X4
Checking out the code
CrossPoint uses PlatformIO for building and flashing the firmware. To get started, clone the repository:
git clone --recursive https://github.com/crosspoint-reader/crosspoint-reader
# Or, if you've already cloned without --recursive:
git submodule update --init --recursive
Flashing your device
Connect your Xteink X4 to your computer via USB-C and run the following command.
pio run --target upload
Debugging
After flashing the new features, it’s recommended to capture detailed logs from the serial port.
First, make sure all required Python packages are installed:
python3 -m pip install pyserial colorama matplotlib
after that run the script:
# For Linux
# This was tested on Debian and should work on most Linux systems.
python3 scripts/debugging_monitor.py
# For macOS
python3 scripts/debugging_monitor.py /dev/cu.usbmodem2101
Minor adjustments may be required for Windows.
Internals
CrossPoint Reader is pretty aggressive about caching data down to the SD card to minimise RAM usage. The ESP32-C3 only has ~380KB of usable RAM, so we have to be careful. A lot of the decisions made in the design of the firmware were based on this constraint.
Data caching
The first time chapters of a book are loaded, they are cached to the SD card. Subsequent loads are served from the
cache. This cache directory exists at .crosspoint on the SD card. The structure is as follows:
.crosspoint/
├── epub_12471232/ # Each EPUB is cached to a subdirectory named `epub_<hash>`
│ ├── progress.bin # Stores reading progress (chapter, page, etc.)
│ ├── cover.bmp # Book cover image (once generated)
│ ├── book.bin # Book metadata (title, author, spine, table of contents, etc.)
│ └── sections/ # All chapter data is stored in the sections subdirectory
│ ├── 0.bin # Chapter data (screen count, all text layout info, etc.)
│ ├── 1.bin # files are named by their index in the spine
│ └── ...
│
└── epub_189013891/
Deleting the .crosspoint directory will clear the entire cache.
Due the way it's currently implemented, the cache is not automatically cleared when a book is deleted and moving a book file will use a new cache directory, resetting the reading progress.
For more details on the internal file structures, see the file formats document.
Contributing
Contributions are very welcome!
If you are new to the codebase, start with the contributing docs.
If you're looking for a way to help out, take a look at the ideas discussion board. If there's something there you'd like to work on, leave a comment so that we can avoid duplicated effort.
Everyone here is a volunteer, so please be respectful and patient. For more details on our governance and community principles, please see GOVERNANCE.md.
To submit a contribution:
- Fork the repo
- Create a branch (
feature/dithering-improvement) - Make changes
- Submit a PR
CrossPoint Reader is not affiliated with Xteink or any manufacturer of the X4 hardware.
Huge shoutout to diy-esp32-epub-reader by atomic14, which was a project I took a lot of inspiration from as I was making CrossPoint.