onRgba method
Implementation
@override
Future<bool> onRgba(
    int key, Uint8List data, int height, int width, int strideAlign) async {
  return await methodChannel.invokeMethod<bool>('onRgba', {
        "data": data,
        "height": height,
        "width": width,
        "key": key,
        "stride_align": strideAlign,
      }) ??
      false;
}