Method readNextRow

lib/GfxRenderer/Bitmap.cpp:181–283

packed 2bpp output, 0 = black, 1 = dark gray, 2 = light gray, 3 = white

// packed 2bpp output, 0 = black, 1 = dark gray, 2 = light gray, 3 = white
BmpReaderError Bitmap::readNextRow(uint8_t* data, uint8_t* rowBuffer) const {
  // Note: rowBuffer should be pre-allocated by the caller to size 'rowBytes'
  if (file.read(rowBuffer, rowBytes) != rowBytes) return BmpReaderError::ShortReadRow;

  prevRowY += 1;

  uint8_t* outPtr = data;
  uint8_t currentOutByte = 0;
  int bitShift = 6;
  int currentX = 0;

  // Helper lambda to pack 2bpp color into the output stream
  auto packPixel = [&](const uint8_t lum) {
    uint8_t color;
    if (atkinsonDitherer) {
      color = atkinsonDitherer->processPixel(adjustPixel(lum), currentX);
    } else if (fsDitherer) {
      color = fsDitherer->processPixel(adjustPixel(lum), currentX);
    } else {
      if (nativePalette) {
        // Palette matches native gray levels: direct mapping (still apply brightness/contrast/gamma)
        color = static_cast<uint8_t>(adjustPixel(lum) >> 6);
      } else {
        // Non-native palette with dithering disabled: simple quantization
        color = quantize(adjustPixel(lum), currentX, prevRowY);
      }
    }
    currentOutByte |= (color << bitShift);
    if (bitShift == 0) {
      *outPtr++ = currentOutByte;
      currentOutByte = 0;
      bitShift = 6;
    } else {
      bitShift -= 2;
    }
    currentX++;
  };

  uint8_t lum;

  switch (bpp) {
    case 32: {
      const uint8_t* p = rowBuffer;
      for (int x = 0; x < width; x++) {
        lum = (77u * p[2] + 150u * p[1] + 29u * p[0]) >> 8;
        packPixel(lum);
        p += 4;
      }
      break;
    }
    case 24: {
      const uint8_t* p = rowBuffer;
      for (int x = 0; x < width; x++) {
        lum = (77u * p[2] + 150u * p[1] + 29u * p[0]) >> 8;
        packPixel(lum);
        p += 3;
      }
      break;