prepare method
Prepare the object to be written to the stream
Implementation
@override
void prepare() {
buf.putBytes(data!);
super.prepare();
params['/FunctionType'] = const PdfNum(0);
params['/BitsPerSample'] = PdfNum(bitsPerSample);
params['/Order'] = PdfNum(order);
params['/Domain'] = PdfArray.fromNum(domain);
params['/Range'] = PdfArray.fromNum(range);
params['/Size'] = PdfArray.fromNum(<int>[data!.length ~/ order]);
}