Fix dragging in mesh preview will create a "drag and drop" action

[jsjtxietian]

MaterialEditor doesn't have this problem. Did some check and found they have different parent class that caused the behaviour difference. So I change MeshEditor's parent from SubViewportContainer to Control. Tested locally, it worked.

I would appreciate any feedback or alternative suggestions.

Fixes #83171

[akien-mga]

Why does changing the parent class specifically fix this issue?

The only functional difference I see is the added call to set_anchors_and_offsets_preset(PRESET_FULL_RECT);, which could be done while keeping the SubViewportContainer as the parent class.

It makes sense IMO to unify similar editors but I think in the past we've actually gone the other direction of trying to remove unnecessary intermediate nodes (CC @YeldhamDev).

[jsjtxietian]

First, thank you for your suggestions!

Why does changing the parent class specifically fix this issue?

I tested locally and find that set_anchors_and_offsets_preset(PRESET_FULL_RECT); won't fix this bug, it just affects some ui location.

To be honest I do not know how the drag and drop works but I suspect it may have something to do with subviewportcontainer's event propagation. And the material editor works well when inheriting Control, I tried and it worked. We definitely should investiagte more, someone know drag and drop well can help here.

Also, unify similar editors is one concern, another one is that it reduces the inheritance chain which could be beneficial.

[akien-mga]

CC @Sauermann who might know why drag and drop behaves differently on Control and SubViewportContainer.

[Sauermann]

For me this part of the editor is difficult to digest.
I found out, that the Control, node, that gets dragged, is a EditorPropertyResource.
This class inherits from EditorProperty, which has dragging enabled:

godot/editor/editor_inspector.cpp

Lines 802 to 817 in fd33c7b

	Variant EditorProperty::get_drag_data(const Point2 &p_point) {
	if (property == StringName()) {
	return Variant();
	}
	Dictionary dp;
	dp["type"] = "obj_property";
	dp["object"] = object;
	dp["property"] = property;
	dp["value"] = object->get(property);
	Label *drag_label = memnew(Label);
	drag_label->set_text(property);
	set_drag_preview(drag_label);
	return dp;
	}

I have the feeling, that it is intentional, that dragging a EditorPropertyResource leads to a drag & drop operation. Although in this case it looks like it is not what is expected, because this EditorPropertyResource contains a SubViewport, where dragging should result in rotating the object.

Perhaps the EditorPropertyResource requires a way to tell it, if drag and drop should be used for dragging the resource or not.

Without knowing this part of the code-base, I have the feeling, that replacing the Node inheritance (SubViewportContainer -> Control) just hides the underlying problem. But please note that this is just a guess.

I have also tested, that #67531 (rebased on fd33c7b) also shows the same drag and drop behavior.

[KoBeWi]

Looks like the issue is no longer reproducible.

[KoBeWi]

Ok confirmed fixed by some another PR.
Thanks for the contribution nonetheless.