posSetUnderline static method
设置下划线 @param line @return
Implementation
static Uint8List? posSetUnderline(int line) {
if ((line < 0 || line > 2)) return null;
Command.escMinus[2] = line;
Command.fsMinus[2] = line;
return Uint8List.fromList(Command.escMinus + Command.fsMinus);
}