decode static method

Implementation

static Jpeg12BitImage decode(Uint8List input) {
  Pointer<jpeg12_decompress_struct> cinfo = nullptr;
  Pointer<jpeg12_error_mgr> jerr = nullptr;
  Pointer<JSAMPROW> row_pointer = nullptr;
  JSAMPROW rowptr = nullptr;
  Pointer<UnsignedChar> inbuffer = nullptr;

  try {
    cinfo = calloc();
    jerr = calloc();

    _lib.jpeg12_CreateDecompress(
        cinfo, JPEG12_LIB_VERSION, sizeOf<jpeg12_decompress_struct>());
    cinfo.ref.err = _lib.jpeg12_std_error(jerr);

    row_pointer = calloc.allocate(_NUM_DECODE_ROWS * sizeOf<JSAMPROW>());
    inbuffer = calloc.allocate(input.length);
    inbuffer.cast<Uint8>().asTypedList(input.length).setAll(0, input);

    // TODO: Error function

    _lib.jpeg12_mem_src(cinfo, inbuffer, input.length);
    if (_lib.jpeg12_read_header(cinfo, 1) != JPEG12_HEADER_OK) {
      throw Exception("Error reading JPEG header");
    }

    if (cinfo.ref.data_precision != _NUM_BITS) {
      throw Exception("JPEG not using 12 bit precision!");
    }

    if (cinfo.ref.num_components != 1) {
      throw Exception("Not a grayscale jpeg picture!");
    }

    _lib.jpeg12_start_decompress(cinfo);

    int numPixels = cinfo.ref.output_width * cinfo.ref.output_height;
    final res = Uint16List(numPixels);
    final rowsize = cinfo.ref.output_width * sizeOf<JSAMPLE>();
    rowptr = calloc.allocate(rowsize * _NUM_DECODE_ROWS);
    for (int i = 0; i < _NUM_DECODE_ROWS; i++) {
      row_pointer[i] = Pointer.fromAddress(rowptr.address + (i * rowsize));
    }
    int minVal = 4095;
    int maxVal = 0;
    while (cinfo.ref.output_scanline < cinfo.ref.image_height) {
      int currentRow = cinfo.ref.output_scanline;
      int read =
          _lib.jpeg12_read_scanlines(cinfo, row_pointer, _NUM_DECODE_ROWS);
      if (read == 0) {
        throw Exception("Error decoding JPEG");
      }
      for (int i = 0; i < read; i++) {
        for (int j = 0; j < cinfo.ref.output_width; j++) {
          int p = (currentRow + i) * cinfo.ref.output_width + j;
          int x = row_pointer[i][j];
          minVal = min(minVal, x);
          maxVal = max(maxVal, x);
          res[p] = x;
        }
      }
    }

    _lib.jpeg12_finish_decompress(cinfo);
    return Jpeg12BitImage._(
      height: cinfo.ref.image_height,
      width: cinfo.ref.image_width,
      data: res,
      minVal: minVal,
      maxVal: maxVal,
    );
  } finally {
    _lib.jpeg12_destroy_decompress(cinfo);
    calloc.free(cinfo);
    calloc.free(jerr);
    calloc.free(row_pointer);
    calloc.free(inbuffer);
    calloc.free(rowptr);
  }
}