Method layoutAndExtractLines

lib/Epub/Epub/ParsedText.cpp:466–534

Consumes data to minimize memory usage

}
// Consumes data to minimize memory usage
void ParsedText::layoutAndExtractLines(const GfxRenderer& renderer, const int fontId, const uint16_t viewportWidth,
                                       const std::function<void(std::shared_ptr<TextBlock>)>& processLine,
                                       const bool includeLastLine) {
  if (words.empty()) {
    return;
  }

  // Per-paragraph RTL auto-detection: only when CSS/HTML didn't explicitly set direction.
  // Explicit dir="ltr" must be respected and not overridden by content heuristic.
  if (!blockStyle.directionDefined && hasRtlWord) {
    // Check the first few words for RTL letter codepoints (no heap allocation).
    const size_t wordsToScan = std::min(words.size(), RTL_PARAGRAPH_PROBE_WORDS);
    for (size_t i = 0; i < wordsToScan; ++i) {
      if (BidiUtils::startsWithRtl(words[i].c_str(), BidiUtils::RTL_PARAGRAPH_PROBE_DEPTH)) {
        blockStyle.isRtl = true;
        break;
      }
    }
  }

  isNaturalAlign =
      blockStyle.alignment == CssTextAlign::Justify ||
      (blockStyle.isRtl ? blockStyle.alignment == CssTextAlign::Right : blockStyle.alignment == CssTextAlign::Left);

  // Ensure SD card font glyph metrics are loaded before measuring word widths.
  // For flash-based fonts isSdCardFont() returns false and this block is skipped
  // entirely — no heap allocation. For SD card fonts this reads glyph metadata
  // (advanceX only, no bitmaps) for all unique codepoints in this paragraph so
  // that calculateWordWidths() can measure text without on-demand SD I/O.
  if (renderer.isSdCardFont(fontId)) {
    // Style mask: only ask the SD font to load advances for styles actually
    // used in this paragraph. Style index is the low two bits (regular/bold/
    // italic/bold-italic); the underline bit is irrelevant to advance metrics.
    uint8_t styleMask = 0;
    for (auto s : wordStyles) {
      styleMask |= static_cast<uint8_t>(1u << (static_cast<uint8_t>(s) & 0x03));
    }
    if (styleMask == 0) styleMask = 0x01;  // defensive: regular only
    renderer.ensureSdCardFontReady(fontId, words, hyphenationEnabled, styleMask);
  }

  const int pageWidth = viewportWidth;
  auto wordWidths = calculateWordWidths(renderer, fontId);

  std::vector<size_t> lineBreakIndices;
  if (hyphenationEnabled) {
    // Use greedy layout that can split words mid-loop when a hyphenated prefix fits.
    lineBreakIndices =
        computeHyphenatedLineBreaks(renderer, fontId, pageWidth, wordWidths, wordContinues, wordNoSpaceBefore);
  } else {
    lineBreakIndices = computeLineBreaks(renderer, fontId, pageWidth, wordWidths, wordContinues, wordNoSpaceBefore);
  }
  const size_t lineCount = includeLastLine ? lineBreakIndices.size() : lineBreakIndices.size() - 1;

  for (size_t i = 0; i < lineCount; ++i) {
    extractLine(i, pageWidth, wordWidths, wordContinues, wordNoSpaceBefore, lineBreakIndices, processLine, renderer,
                fontId);
  }