Implement note spawner.

rhythm_game/note/view/note_view.gd

@@ -8,12 +8,41 @@ class_name NoteView extends View
 func get_data() -> NoteArray:
 	return notes
 
-func update_current_beat(beat: float) -> void:
-	_current_beat = beat
-	_update_view_relative_to_notes(notes)
+func update(beat: float) -> void:
+	_update_view_relative_to_notes(notes, beat)
+	_previous_beat = beat
+
+func reset_view() -> void:
+	super.reset_view()
+	_previous_beat = -999.0
 
 # ======= IMPLEMENTATION ======= #
+var _previous_beat: float = -999.0
 
 func _set_notes(p_notes: NoteArray) -> void:
 	notes = p_notes
-	_reset_view()
+	reset_view()
+
+## Update the view to match _current_beat.
+func _update_view_relative_to_notes(p_notes: NoteArray, new_beat: float) -> void:
+	var new_begin = _begin
+	var new_end = _end
+	if new_beat > _previous_beat:
+		# Update forward.
+		while(new_begin < p_notes.size()) and (p_notes.beat_at(new_begin) < new_beat + offset_begin):
+			new_begin += 1
+		while(new_end < p_notes.size()) and (p_notes.beat_at(new_end) <= new_beat + offset_end):
+			new_end += 1
+	elif new_beat < _previous_beat:
+		# Update backward.
+		while(new_begin >= 0) and (p_notes.beat_at(new_begin) >= new_beat + offset_begin):
+			_begin -= 1
+		while(new_end >= 0) and (p_notes.beat_at(new_end) > new_beat + offset_end):
+			new_end -= 1
+		if(new_begin != _begin):
+			new_begin += 1
+		if(new_end != _end):
+			new_end += 1
+	
+	_begin = new_begin
+	_end = new_end