Godot: Draw trail with Line2D

Player.gd

extends KinematicBody2D

var speed = 500
var velocity := Vector2.ZERO
var input_vector := Vector2.ZERO
var current_line: Line2D

func _process(delta):
	update_move(delta)
	update_line(delta)

func update_move(delta):
	input_vector.x = -int(Input.is_action_pressed("ui_left")) + int(Input.is_action_pressed("ui_right"))
	input_vector.y = -int(Input.is_action_pressed("ui_up")) + int(Input.is_action_pressed("ui_down"))
	input_vector = input_vector.normalized()
	velocity = lerp(velocity, input_vector * speed, 0.15)
	position += (velocity * delta)
	
func update_line(delta):
	var should_start_line = Input.is_action_just_pressed("ui_select")
	var should_end_line = Input.is_action_just_released("ui_select")
	
	if (should_start_line):
		start_line()
	elif (should_end_line):
		current_line = null
	
	if (is_instance_valid(current_line)):
		current_line.add_point(position)

func start_line():
	current_line = Line2D.new()
	get_tree().get_root().add_child(current_line)
	current_line.add_point(position)