edouard.paris / crosspoint-reader
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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

---

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authored by

Eunchurn Park and committed by
GitHub 12940cc5 21277e03

+3 -3
+3 -3
lib/Xtc/Xtc.cpp
··· 203 203 coverBmp.write(reinterpret_cast<const uint8_t*>(&colorsImportant), 4); 204 204 205 205 // Color palette (2 colors for 1-bit) 206 - // XTC uses inverted polarity: 0 = black, 1 = white 206 + // XTC 1-bit polarity: 0 = black, 1 = white (standard BMP palette order) 207 207 // Color 0: Black (text/foreground in XTC) 208 208 uint8_t black[4] = {0x00, 0x00, 0x00, 0x00}; 209 209 coverBmp.write(black, 4); ··· 506 506 // Bounds check for buffer access 507 507 if (byteIdx < bitmapSize) { 508 508 const uint8_t pixelBit = (pageBuffer[byteIdx] >> bitIdx) & 1; 509 - // XTC polarity: 1=black, 0=white 510 - grayValue = pixelBit ? 0 : 255; 509 + // XTC 1-bit polarity: 0=black, 1=white (same as BMP palette) 510 + grayValue = pixelBit ? 255 : 0; 511 511 } 512 512 } 513 513