crosspoint-reader

Files

Eunchurn Park 12940cc546 fix: XTC 1-bit thumb BMP polarity inversion (#373 )

## Summary

* **What is the goal of this PR?** (e.g., Implements the new feature for
file uploading.)
* **What changes are included?**

- Fix inverted colors in Continue Reading cover image for 1-bit XTC
files

## Additional Context

* Add any other information that might be helpful for the reviewer
(e.g., performance implications, potential risks,
  specific areas to focus on).

- Fix `grayValue = pixelBit ? 0 : 255` → `grayValue = pixelBit ? 255 :
0` in `lib/Xtc/Xtc.cpp`
- The thumb BMP generation had inverted polarity compared to cover BMP
generation
- bit=0 should be black, bit=1 should be white (matching the BMP palette
order)
- Update misleading comment about XTC polarity

---

### AI Usage

While CrossPoint doesn't have restrictions on AI tools in contributing,
please be transparent about their usage as it
helps set the right context for reviewers.

Did you use AI tools to help write this code? _**PARTIALLY**_

2026-01-19 22:41:48 +11:00

Xtc

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README

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Xtc.cpp

fix: XTC 1-bit thumb BMP polarity inversion (#373 )

2026-01-19 22:41:48 +11:00

Xtc.h

Add cover image display in *Continue Reading* card with framebuffer caching (#200 )

2026-01-14 21:24:02 +11:00

README

# XTC/XTCH Library

XTC ebook format support for CrossPoint Reader.

## Supported Formats

| Format | Extension | Description                                  |
|--------|-----------|----------------------------------------------|
| XTC    | `.xtc`    | Container with XTG pages (1-bit monochrome)  |
| XTCH   | `.xtch`   | Container with XTH pages (2-bit grayscale)   |

## Format Overview

XTC/XTCH are container formats designed for ESP32 e-paper displays. They store pre-rendered bitmap pages optimized for the XTeink X4 e-reader (480x800 resolution).

### Container Structure (XTC/XTCH)

- 56-byte header with metadata offsets
- Optional metadata (title, author, etc.)
- Page index table (16 bytes per page)
- Page data (XTG or XTH format)

### Page Formats

#### XTG (1-bit monochrome)

- Row-major storage, 8 pixels per byte
- MSB first (bit 7 = leftmost pixel)
- 0 = Black, 1 = White

#### XTH (2-bit grayscale)

- Two bit planes stored sequentially
- Column-major order (right to left)
- 8 vertical pixels per byte
- Grayscale: 0=White, 1=Dark Grey, 2=Light Grey, 3=Black

## Reference

Original format info: <https://gist.github.com/CrazyCoder/b125f26d6987c0620058249f59f1327d>