Godot Prevent Player From Going Out of Screen (2D)

extends KinematicBody2Dconst GRAVITY = 200.0const WALK_SPEED = 200const JUMP_SPEED = 100var screen_sizevar velocity = Vector2()# Called when the node enters the scene tree for the first time.func _ready():    screen_size = get_viewport_rect().sizefunc _physics_process(delta):       # gravity    velocity.y += delta * GRAVITY        # left and right movement    if Input.is_action_pressed("ui_left"):        velocity.x = -WALK_SPEED    elif Input.is_action_pressed("ui_right"):        velocity.x =  WALK_SPEED    else:        velocity.x = 0            # jump    if Input.is_action_pressed("ui_up"):        velocity.y -= JUMP_SPEED            # move current node    move_and_slide(velocity, Vector2(0, -1))         # prevent movement exceed screen    position.x = clamp(position.x, 0, screen_size.x)    position.y = clamp(position.y, 0, screen_size.y)