pack method

@override Uint8List pack()

Corresponding parser should be called from frame_app.lua data_handler()

Implementation

@override
Uint8List pack() {
  int widthMsb = _width >> 8;
  int widthLsb = _width & 0xFF;
  int heightMsb = _height >> 8;
  int heightLsb = _height & 0xFF;
  int bpp = 0;
  Uint8List packed;
  switch (_numColors) {
    case <= 2:
      bpp = 1;
      packed = pack1Bit(_pixelData);
      break;
    case <= 4:
      bpp = 2;
      packed = pack2Bit(_pixelData);
      break;
    case <= 16:
      bpp = 4;
      packed = pack4Bit(_pixelData);
      break;
    default:
      throw Exception(
          'Image must have 16 or fewer colors. Actual: $_numColors');
  }

  // preallocate the list of bytes to send - sprite header, palette, pixel data
  // (packed.length already adds the extra byte if WxH is not divisible by 8)
  Uint8List payload =
      Uint8List.fromList(List.filled(6 + _numColors * 3 + packed.length, 0));

  // NB: palette data could be numColors=12 x 3 (RGB) bytes even if bpp is 4 (max 16 colors)
  // hence we provide both numColors and bpp here.
  // sendMessage will prepend the data byte, msgCode to each packet
  // and the Uint16 payload length to the first packet
  payload
      .setAll(0, [widthMsb, widthLsb, heightMsb, heightLsb, bpp, _numColors]);
  payload.setAll(6, _paletteData);
  payload.setAll(6 + _numColors * 3, packed);

  return payload;
}