2D in 3D demo is unclear

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1

Godot Version

3.5.2

Question

Yo, yo, internet!

I’m trying to get a mesh instance to show a 2D health bar. This section is a bit confusing, I was looking at 2D in 3D demo in the Asset Lib to grasp how to do it, but I don’t see the sprites for the Pong game in the 2D view… so IDK how they set things up?

This is the code in the Pong game that’s supposed to make this work.

extends Spatial


func _ready():
	# Clear the viewport.
	var viewport = $Viewport
	$Viewport.set_clear_mode(Viewport.CLEAR_MODE_ONLY_NEXT_FRAME)

	# Let two frames pass to make sure the vieport is captured.
	yield(get_tree(), "idle_frame")
	yield(get_tree(), "idle_frame")

	# Retrieve the texture and set it to the viewport quad.
	$ViewportQuad.material_override.albedo_texture = viewport.get_texture()

If I do this, I get an error saying that idle_frame is a null instance of a null instance…
Is there something I am completely missing here? Where is the pong game screen the viewport is looking at?