Proper support of superscript/subscript

lib/Epub/Epub/BookMetadataCache.cpp

@@ -11,7 +11,7 @@
 #include "FsHelpers.h"
 
 namespace {
-constexpr uint8_t BOOK_CACHE_VERSION = 8;
+constexpr uint8_t BOOK_CACHE_VERSION = 9;
 constexpr char bookBinFile[] = "/book.bin";
 constexpr char tmpSpineBinFile[] = "/spine.bin.tmp";
 constexpr char tmpTocBinFile[] = "/toc.bin.tmp";

lib/Epub/Epub/blocks/TextBlock.cpp

@@ -12,10 +12,21 @@ 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];
-    renderer.drawText(fontId, wordX, y, words[i].c_str(), true, currentStyle);
+    // 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;
+    }
+    renderer.drawText(fontId, wordX, wordY, words[i].c_str(), true, currentStyle);
 
     const std::string& w = words[i];
     const bool hasEmSpacePrefix = w.size() >= 3 && static_cast<uint8_t>(w[0]) == 0xE2 &&

lib/Epub/Epub/parsers/ChapterHtmlSlimParser.cpp

@@ -205,6 +205,8 @@ void ChapterHtmlSlimParser::updateEffectiveInlineStyle() {
   effectiveStrikethrough =
       currentCssStyle.hasTextDecoration() && (static_cast<uint8_t>(currentCssStyle.textDecoration) &
                                               static_cast<uint8_t>(CssTextDecoration::LineThrough)) != 0;
+  effectiveSup = false;
+  effectiveSub = false;
 
   // Apply inline style stack in order
   for (const auto& entry : inlineStyleStack) {
@@ -220,6 +222,14 @@ void ChapterHtmlSlimParser::updateEffectiveInlineStyle() {
     if (entry.hasStrikethrough) {
       effectiveStrikethrough = entry.strikethrough;
     }
+    if (entry.hasSup) {
+      effectiveSup = entry.sup;
+      if (entry.sup) effectiveSub = false;
+    }
+    if (entry.hasSub) {
+      effectiveSub = entry.sub;
+      if (entry.sub) effectiveSup = false;
+    }
   }
 }
 
@@ -280,6 +290,11 @@ bool ChapterHtmlSlimParser::flushPartWordBuffer() {
   if (isStrikethrough) {
     fontStyle = static_cast<EpdFontFamily::Style>(fontStyle | EpdFontFamily::STRIKETHROUGH);
   }
+  if (effectiveSup) {
+    fontStyle = static_cast<EpdFontFamily::Style>(fontStyle | EpdFontFamily::SUP);
+  } else if (effectiveSub) {
+    fontStyle = static_cast<EpdFontFamily::Style>(fontStyle | EpdFontFamily::SUB);
+  }
 
   // flush the buffer — route to table cell text when inside a <td>/<th>
   partWordBuffer[partWordBufferIndex] = '\0';
@@ -1168,12 +1183,17 @@ void XMLCALL ChapterHtmlSlimParser::startElement(void* userData, const XML_Char*
       if (!self->flushPartWordBuffer()) return;
       self->nextWordContinues = true;
     }
-    const char* prefix = (strcmp(name, "sup") == 0) ? "^" : "_";
-    self->currentTextBlock->addWord(prefix, EpdFontFamily::REGULAR, false, true);
-    self->nextWordContinues = true;
     StyleStackEntry entry;
     entry.depth = self->depth;
+    if (strcmp(name, "sup") == 0) {
+      entry.hasSup = true;
+      entry.sup = true;
+    } else {
+      entry.hasSub = true;
+      entry.sub = true;
+    }
     self->inlineStyleStack.push_back(entry);
+    self->updateEffectiveInlineStyle();
   } else if (strcmp(name, "span") == 0 || !isHeaderOrBlock(name)) {
     // Handle span and other inline elements for CSS styling
     if (cssStyle.hasFontWeight() || cssStyle.hasFontStyle() || cssStyle.hasTextDecoration()) {

lib/Epub/Epub/parsers/ChapterHtmlSlimParser.h

@@ -66,6 +66,8 @@ class ChapterHtmlSlimParser final : public Print {
     bool hasItalic = false, italic = false;
     bool hasUnderline = false, underline = false;
     bool hasStrikethrough = false, strikethrough = false;
+    bool hasSup = false, sup = false;
+    bool hasSub = false, sub = false;
   };
   std::vector<StyleStackEntry> inlineStyleStack;
   CssStyle currentCssStyle;
@@ -73,6 +75,8 @@ class ChapterHtmlSlimParser final : public Print {
   bool effectiveItalic = false;
   bool effectiveUnderline = false;
   bool effectiveStrikethrough = false;
+  bool effectiveSup = false;
+  bool effectiveSub = false;
   // Buffered table model — populated while inside <table>, emitted on </table>
   struct BufferedTableCell {
     std::unique_ptr<ParsedText> text;