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feat: <sup> and <sub> support (#2131)

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## Summary

* **What is the goal of this PR?** Support for `<sup>` and `<sub>` tags.

## Additional Context

This isn't my work, but @jpirnay 's (missing you here, man!). I migrated
his work from
https://github.com/jpirnay/crosspoint-reader/commit/bcd8c32cf26447ccc792cfedd2fdbfce4fee5210
with some micro-optimizations.

Screenshots: 

[Subscript-and-Superscript-Tests_ch2_p1_10pct_55632.bmp](https://github.com/user-attachments/files/28196936/Subscript-and-Superscript-Tests_ch2_p1_10pct_55632.bmp)

[Subscript-and-Superscript-Tests_ch3_p1_21pct_77473.bmp](https://github.com/user-attachments/files/28196937/Subscript-and-Superscript-Tests_ch3_p1_21pct_77473.bmp)


---

### 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? _**< YES >**_

---------

Co-authored-by: jpirnay <jens@pirnay.com>
Co-authored-by: Julia <julia@uxj.io>
This commit is contained in:
Uri Tauber
2026-05-26 12:38:40 -04:00
committed by GitHub
co-authored by jpirnay Julia
parent 34e923d722
commit c5e861d71c
11 changed files with 443 additions and 18 deletions
Download Patch File Download Diff File Expand all files Collapse all files
lib/Epub/Epub/blocks/TextBlock.cpp
+16 -4
View File
@@ -18,11 +18,23 @@ void TextBlock::render(const GfxRenderer& renderer, const int fontId, const int
return;
}
const int ascender = renderer.getFontAscenderSize(fontId);
for (size_t i = 0; i < words.size(); i++) {
const int wordX = wordXpos[i] + x;
const EpdFontFamily::Style currentStyle = wordStyles[i];
const uint8_t boundary = hasFocus ? wordFocusBoundary[i] : 0;
// SUP/SUB shift the baseline passed to drawText; the glyph is also scaled 50% inside
// drawText, so these offsets are chosen relative to the full-size ascender:
// SUP: raise by 40% of ascender — sits clearly above the cap-height
// SUB: lower by 25% of ascender — descends below baseline without clashing with ascenders below
int wordY = y;
if ((currentStyle & EpdFontFamily::SUP) != 0) {
wordY -= ascender * 2 / 5;
} else if ((currentStyle & EpdFontFamily::SUB) != 0) {
wordY += ascender / 4;
}
if (boundary > 0) {
// Focus split: draw bold prefix, then the regular suffix at a pre-computed x offset.
// The bold prefix is bounded to 9 codepoints by the clamp on targetBoldChars in
@@ -36,18 +48,18 @@ void TextBlock::render(const GfxRenderer& renderer, const int fontId, const int
const size_t boldLen = std::min<size_t>({static_cast<size_t>(boundary), words[i].size(), sizeof(boldBuf) - 1});
memcpy(boldBuf, words[i].c_str(), boldLen);
boldBuf[boldLen] = '\0';
renderer.drawText(fontId, wordX, y, boldBuf, true, boldStyle);
renderer.drawText(fontId, wordX, wordY, boldBuf, true, boldStyle);
const int suffixX = wordX + wordFocusSuffixX[i];
renderer.drawText(fontId, suffixX, y, words[i].c_str() + boldLen, true, currentStyle);
renderer.drawText(fontId, suffixX, wordY, words[i].c_str() + boldLen, true, currentStyle);
} else {
renderer.drawText(fontId, wordX, y, words[i].c_str(), true, currentStyle);
renderer.drawText(fontId, wordX, wordY, words[i].c_str(), true, currentStyle);
}
if ((currentStyle & EpdFontFamily::UNDERLINE) != 0) {
const std::string& w = words[i];
const int fullWordWidth = renderer.getTextWidth(fontId, w.c_str(), currentStyle);
// y is the top of the text line; add ascender to reach baseline, then offset 2px below
const int underlineY = y + renderer.getFontAscenderSize(fontId) + 2;
const int underlineY = wordY + ascender + 2;
int startX = wordX;
int underlineWidth = fullWordWidth;