Implement note visuals update method.

rhythm_game/note/visual/hold/hold_note.gd

@@ -6,13 +6,36 @@ class_name HoldNote extends NoteVisual
 
 var start_id: int
 var end_id: int
+var start_beat: float
+var end_beat: float
 
 func reset() -> void:
 	start_id = -1
 	end_id = -1
+	start_beat = -999.0
+	end_beat = -999.0
 
 func in_use() -> bool:
 	return start_id >= 0 or end_id >= 0
 
 func update(beat: float) -> void:
-	pass
+	var start_scroll: float
+	if start_beat:
+		start_scroll = _calculate_scroll(start_beat, beat)
+	else:
+		start_scroll = 999.0 # Decently up. (TODO Replace with offset_begin).
+	_set_start_scroll(start_scroll)
+	
+	var end_scroll: float
+	if end_beat:
+		end_scroll = _calculate_scroll(end_beat, beat)
+	else:
+		end_scroll = -999.0 # Decently down. (TODO Replace with offset_end).
+	_set_end_scroll(end_scroll)
+
+# ======== IMPLEMENTATION ======== #
+func _set_start_scroll(scroll: float) -> void:
+	start.y = scroll
+
+func _set_end_scroll(scroll: float) -> void:
+	end.y = scroll