6. TextureProgress

We create a MarginContainer node (with margins left and right 20, and margins top and bottom 75). We have to set the anchors for bottom and right to 1 so it starts measuring from bottom-right for these two margins.

Then, as the MaginContainer's child, we create a TextureProgress. The under, progress, and over images are shown here:

Under: (Background).

Progress: (this will be clipped by Range.value).

Over: (every pixel is transparent except 4 corners are white - click to verify).

---

We attach this script to Node:

extends Node

const SPEED = 50
var mc = MarginContainer.new()
var tp

func _ready():
    VisualServer.set_default_clear_color(ColorN("white"))
    mc.anchor_bottom = 1
    mc.anchor_right = 1
    mc.margin_left = 20
    mc.margin_right = 20
    mc.margin_top = 75
    mc.margin_bottom = 75
    tp = TextureProgress.new()
    tp.texture_progress = load("res://progress.png")
    tp.texture_over = load("res://over.png")
    tp.texture_under = load("res://under.png")
    mc.add_child(tp)
    add_child(mc)
 
func _process(delta):
    tp.value = fmod(tp.value + SPEED * delta, 100)

The output, with window size of 200,200 and clear color of white, when the progress is about half: