Fix invalid 2D global position when read outside tree

[KoBeWi]

MRP for the bug:
repro.tscn.txt

When you get global_position of a CanvasItem outside tree, it will assign its position to global position (roughly speaking). When the node enters tree, its global transform is not invalidated, so global_position will still return its position. This also leads to some abnormalities, like sprite not displaying at its real position (as observed in the MRP).

Bugsquad edit: Fixes #75676. Fixes #76327.

[kleonc]

The global transform can still be not invalidated when changing top level for a CanvasItem outside the tree (it would need to be invalidated for the whole branch):

godot/scene/main/canvas_item.cpp

Lines 392 to 408 in 44d5394

	void CanvasItem::set_as_top_level(bool p_top_level) {
	if (top_level == p_top_level) {
	return;
	}
	if (!is_inside_tree()) {
	top_level = p_top_level;
	return;
	}
	_exit_canvas();
	top_level = p_top_level;
	_top_level_changed();
	_enter_canvas();
	_notify_transform();
	}

[KoBeWi]

@kleonc Does it lead to any issue? I tried bugging it, but it prints a correct global position.

[kleonc]

@kleonc Does it lead to any issue? I tried bugging it, but it prints a correct global position.

Here's an example:

func foo() -> void:
	var a := Node2D.new()
	a.position = Vector2(1, 1)

	var b := Node2D.new()
	b.position = Vector2(2, 2)

	a.add_child(b)

#	b.global_position
	b.top_level = true
	print(b.global_position)

With the b.global_position line commented out it correctly outputs (2, 2).
With the b.global_position line uncommented it incorrectly outputs (3, 3).

[KoBeWi]

Ok fixed.

[kleonc]

LGTM.
(haven't actually tested it after the changes though 🙃)

[lawnjelly]

Also looks fine to me.

[akien-mga]

Thanks!

[YuriSizov]

Cherry-picked for 4.0.3.