Clamp 2d not working in Main scene

Question

in Godot3.2,clamp2d(Player) works in standalone scene but doesn't work when instanced in Main scene(both as Child node through Scene ui and as a Packed Scene through Script).
While trying to clamp a kinematic body2d sprite,it is clamped only along positive X&Yaxis and at the right and bottom borders the sprite goes off screen.What's missing?

Main setup-
Player scene
Game Background (Sprite)

Player setup -
KinematicBody2d
ColllisionShape2d-
Sprite

extends KinematicBody2D
var speed = 40
var screen_size 
var sprite_x
var sprite_y 

func _ready():
    screen_size = get_viewport_rect().size
    sprite_x = $Sprite.texture.get_width()/ 2.0 
    sprite_y = $Sprite.texture.get_height() / 2.0  

    print("screen_size.x - sprite_x = ",screen_size.x - sprite_x)
    print("screen_size.y- sprite_y = ",screen_size.y - sprite_y)




func _process(_delta):
    var velocity = Vector2()  # player movement 
    if Input.is_action_pressed("ui_right"):
        velocity.x += 1.0
    if Input.is_action_pressed("ui_left"):
        velocity.x -= 1.0
    if Input.is_action_pressed("ui_down"):
        velocity.y += 1.0
    if Input.is_action_pressed("ui_up"):
        velocity.y -= 1.0
    if velocity.length() > 0:
        velocity = velocity.normalized() * speed 

    position += velocity * _delta

    position.x = clamp(position.x, 0, screen_size.x - sprite_x) 
    position.y = clamp(position.y, 0, screen_size.y - sprite_y)     

    position = move_and_slide(position)

Answer 1

position = move_and_slide(position) is wrong

corrected code :

func _process(_delta):
  var velocity = Vector2()  # player movement 
  if Input.is_action_pressed("ui_right"):
      velocity.x += 1.0
  if Input.is_action_pressed("ui_left"):
      velocity.x -= 1.0
  if Input.is_action_pressed("ui_down"):
      velocity.y += 1.0
  if Input.is_action_pressed("ui_up"):
      velocity.y -= 1.0

  velocity = velocity.normalized() * speed 
  move_and_slide(velocity)

  position.x = clamp(position.x, 0, screen_size.x - sprite_x) 
  position.y = clamp(position.y, 0, screen_size.y - sprite_y)     

Comments

This doesn't change anything.Move and slide() returns a positon vector ,which If not stored in var position makes the debugger to "complain".Infact it is better to store moveandslide() in position to stop unnecessary debug complains.