Method parseHeaders

lib/GfxRenderer/Bitmap.cpp:85–178

}

BmpReaderError Bitmap::parseHeaders() {
  if (!file) return BmpReaderError::FileInvalid;
  if (!file.seek(0)) return BmpReaderError::SeekStartFailed;

  // --- BMP FILE HEADER ---
  const uint16_t bfType = readLE16(file);
  if (bfType != 0x4D42) return BmpReaderError::NotBMP;

  file.seekCur(8);
  bfOffBits = readLE32(file);

  // --- DIB HEADER ---
  const uint32_t biSize = readLE32(file);
  if (biSize < 40) return BmpReaderError::DIBTooSmall;

  width = static_cast<int32_t>(readLE32(file));
  const auto rawHeight = static_cast<int32_t>(readLE32(file));
  topDown = rawHeight < 0;
  height = topDown ? -rawHeight : rawHeight;

  const uint16_t planes = readLE16(file);
  bpp = readLE16(file);
  const uint32_t comp = readLE32(file);
  const bool validBpp = bpp == 1 || bpp == 2 || bpp == 4 || bpp == 8 || bpp == 24 || bpp == 32;

  if (planes != 1) return BmpReaderError::BadPlanes;
  if (!validBpp) return BmpReaderError::UnsupportedBpp;
  // Allow BI_RGB (0) for all, and BI_BITFIELDS (3) for 32bpp which is common for BGRA masks.
  if (!(comp == 0 || (bpp == 32 && comp == 3))) return BmpReaderError::UnsupportedCompression;

  file.seekCur(12);  // biSizeImage, biXPelsPerMeter, biYPelsPerMeter
  colorsUsed = readLE32(file);
  // BMP spec: colorsUsed==0 means default (2^bpp for paletted formats)
  if (colorsUsed == 0 && bpp <= 8) colorsUsed = 1u << bpp;
  if (colorsUsed > 256u) return BmpReaderError::PaletteTooLarge;
  file.seekCur(4);  // biClrImportant

  if (width <= 0 || height <= 0) return BmpReaderError::BadDimensions;

  // Safety limits to prevent memory issues on ESP32
  constexpr int MAX_IMAGE_WIDTH = 2048;
  constexpr int MAX_IMAGE_HEIGHT = 3072;
  if (width > MAX_IMAGE_WIDTH || height > MAX_IMAGE_HEIGHT) {
    return BmpReaderError::ImageTooLarge;
  }

  // Pre-calculate Row Bytes to avoid doing this every row
  rowBytes = (width * bpp + 31) / 32 * 4;

  for (int i = 0; i < 256; i++) paletteLum[i] = static_cast<uint8_t>(i);
  if (colorsUsed > 0) {
    for (uint32_t i = 0; i < colorsUsed; i++) {
      uint8_t rgb[4];
      file.read(rgb, 4);  // Read B, G, R, Reserved in one go
      paletteLum[i] = (77u * rgb[2] + 150u * rgb[1] + 29u * rgb[0]) >> 8;
    }
  }