godot paint image on the fly

setup

onready var sprite = $BackgroundSceneRoot/Sprite

func _ready():

    img = Image.new()

    img.create(Globals.WIDTH, Globals.HEIGHT, false, Image.FORMAT_RGB8)

    tex = ImageTexture.new()

    tex.create_from_image(img, 0)

    sprite.texture = tex

update

    img.lock()

    img.set_pixel(x, y, Color(r, g, b))

    img.unlock()

    sprite.texture.set_data(img)