progress method
void
progress()
Progress through the list of messages.
If the focus moves past the end of the list, then onDone is called.
Implementation
void progress() {
if (position >= messages.length) {
onDone();
} else {
_sound = game.outputMessage(
messages.elementAt(position),
oldSound: _sound,
soundChannel: soundChannel,
);
position++;
}
}