Method fetchAdvancesForCodepoints

lib/EpdFont/SdCardFont.cpp:1095–1195

Given a sorted array of unique codepoints, resolve glyph indices per style, batch-read advanceX from SD, and merge into the persistent advance table. Caller owns the codepoints buffer.

// batch-read advanceX from SD, and merge into the persistent advance table.
// Caller owns the codepoints buffer.
int SdCardFont::fetchAdvancesForCodepoints(uint32_t* codepoints, uint32_t cpCount, uint8_t styleMask) {
  int totalMissed = 0;
  for (uint8_t si = 0; si < MAX_STYLES; si++) {
    if (!(styleMask & (1 << si)) || !styles_[si].present) continue;
    const auto& s = styles_[si];

    // Stop fetching once the cache is full — further inserts would be dropped
    // by the merge anyway. The renderer fast path tolerates missing entries
    // (returns 0); the slow path is still correct for those codepoints.
    if (advanceTableSize_[si] >= ADVANCE_CACHE_LIMIT) continue;

    // For each codepoint in `codepoints`, skip those already cached, then
    // resolve to a glyph index. Build a parallel array sorted by glyph index
    // for sequential SD reads.
    struct CpIdx {
      uint32_t codepoint;
      int32_t glyphIndex;
    };
    std::unique_ptr<CpIdx[]> mappings(new (std::nothrow) CpIdx[cpCount]);
    if (!mappings) {
      LOG_ERR("SDCF", "buildAdvanceTable: failed to allocate mappings for style %u", si);
      totalMissed += cpCount;
      continue;
    }

    uint32_t needCount = 0;
    uint32_t missedThisStyle = 0;
    const int32_t replacementIdx = findGlobalGlyphIndex(s, REPLACEMENT_GLYPH);
    for (uint32_t i = 0; i < cpCount; i++) {
      const uint32_t cp = codepoints[i];
      if (advanceTableLookup(si, cp, nullptr)) continue;  // already cached
      int32_t idx = findGlobalGlyphIndex(s, cp);
      if (idx < 0) {
        if (replacementIdx < 0) {
          missedThisStyle++;
          continue;
        }
        idx = replacementIdx;
      }
      mappings[needCount].codepoint = cp;
      mappings[needCount].glyphIndex = idx;
      needCount++;
    }
    totalMissed += static_cast<int>(missedThisStyle);

    if (needCount == 0) continue;

    // Sort by glyph index so SD reads are mostly sequential.
    std::sort(mappings.get(), mappings.get() + needCount,
              [](const CpIdx& a, const CpIdx& b) { return a.glyphIndex < b.glyphIndex; });

    // Open file once and read advanceX for each needed glyph.
    HalFile file;
    if (!Storage.openFileForRead("SDCF", filePath_, file)) {
      LOG_ERR("SDCF", "buildAdvanceTable: failed to open .cpfont for style %u", si);
      continue;
    }