## Summary
* **What is the goal of this PR?**
Add Vietnamese glyphs support for the reader's built-in fonts, enabling
proper rendering of Vietnamese text in EPUB content.
* **What changes are included?**
- Added 3 new Unicode intervals to `fontconvert.py` covering Vietnamese
characters:
- **Latin Extended-B** (Vietnamese subset only): `U+01A0–U+01B0` — Ơ/ơ,
Ư/ư
- **Vietnamese Extended**: `U+1EA0–U+1EF9` — All precomposed Vietnamese
characters with tone marks (Ả, Ấ, Ầ, Ẩ, Ẫ, Ậ, Ắ, …, Ỹ)
- Re-generated all 54 built-in font header files (Bookerly, Noto Sans,
OpenDyslexic, Ubuntu across all sizes and styles) to include the new
Vietnamese glyphs.
## Additional Context
* **Scope**: This PR only covers the **reader** fonts. The outer UI
still uses the Ubuntu font which does not fully support Vietnamese — UI
and i18n will be addressed in a follow-up PR (per discussion in PR
#1124).
* **Memory impact**:
| Metric | Before | After | Delta |
|---|---|---|---|
| Flash Data (`.rodata`) | 2,971,028 B | 3,290,748 B | **+319,720 B
(+10.8%)** |
| Total image size | 4,663,235 B | 4,982,955 B | **+319,720 B (+6.9%)**
|
| Flash usage | 69.1% | 74.0% | **+4.9 pp** |
| RAM usage | 29.0% | 29.0% | **No change** |
* **Risk**: Low — this is a data-only change (font glyph tables in
`.rodata`). No logic changes, no RAM impact. Flash headroom remains
comfortable at 74%.
---
### AI Usage
Did you use AI tools to help write this code? _**PARTIALLY**_
AI was used to identify the minimal set of Unicode ranges needed for
Vietnamese support and to assist with the PR description.
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Co-authored-by: danoooob <danoooob@example.com>
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