Node2D inside a SubViewport returning (0, 0) from get_mouse_position()

[rbarongr]

Godot version

v4.0.beta17.official [c400205]

System information

macOS 13.0.1

Issue description

When a Control node is over a SubViewportContainer (with a SubViewport as a child), both in Full Rect anchors, asking for the get_viewport().get_mouse_position() from a scene inside the SubViewport returns (0, 0) as the position of the mouse.

This wasn't happening in at least Beta 15. I was getting the mouse position without any problems before Beta 17. I didn't try Beta 16.

Steps to reproduce

1. Create a Control node
2. Add two children: A SubViewportContainer and a Control node
3. Put both in Full Rect anchors so the Control node (child) is covering the SubViewportContainer
4. Ask for the get_viewport().get_mouse_position() from inside a scene of the SubViewport

As you can see in this screenshot: asking for the mouse position from inside the Node2D script always returns (0, 0).

Only If the Control (child) mouse filtering is set to Ignore you can get the mouse position. But with that you are losing the mouse inputs from that Control node.

You can find the setup of these nodes in the MRP.

Minimal reproduction project

Run the main scene (control.tscn) and move the mouse around the screen. Look for the print in the Output tab.

SubViewportMousePositionIssue.zip

[Sauermann]

Sounds similar to #60390 which happened long before beta 15, so this isn't an exact duplicate.
Can confirm the bug on Linux since v4.0.beta16.official [518b9e5].