Editable Children = on breaks paths to instanced SubViewports & manual fixes are not retained

paulmiller commented 8 months ago

Tested versions

reproduced in 4.0.4.stable & 4.2.1.stable

System information

Godot v4.2.1.stable unknown - Arch Linux #1 SMP PREEMPT_DYNAMIC Fri, 05 Jan 2024 16:20:41 +0000 - Tty - Vulkan (Forward+) - dedicated NVIDIA GeForce GTX 1070 (nvidia; 545.29.06) - Intel(R) Core(TM) i7-6700 CPU @ 3.40GHz (8 Threads)

Issue description

If a scene instances another scene with "Editable Children" enabled, and the child scene contains a SubViewport, and a material rendering that SubViewport, the material's "Viewport Path" will be wrong. It'll render a magenta texture instead of the SubViewport. You can fix the path manually, but the editor revert to the wrong path after reloading.

Steps to reproduce

The attached subviewport_instance_tests.zip has 2 Godot projects, standard_project & shader_project. They demonstrate the same problem, using a StandardMaterial3D and a ShaderMaterial. I tried both projects under Godot 4.0.4 & 4.2.1 and got the same results all 4 times.

Consider standard_project. Scene A has:

A
├ Camera3D
├ MeshInstance3D
└ SubViewport
  ├ Camera3D
  └ Label3D (text = "A")

The MeshInstance3D displays the SubViewport. Running scene A (open a.tscn in the editor > right click the "a" tab > "Play This Scene") works as expected - "A" appears on the MeshInstance3D.

Scene B instances A:

B
├ Camera3D
└ A

Running scene B also works as expected.

Scene C is exactly like B, except C's A instance has "Editable Children" enabled. In C, the MeshInstance3D shows a solid magenta texture, and there's an error, "ViewportTexture: Path to node is invalid".

It seems that "Editable Children" causes the ViewportTexture's viewport_path to be interpreted as an absolute path from the root (the C node).

I tested this with scene D. D is like C, except I added a SubViewport at that absolute path:

D
├ Camera3D
├ A
└ SubViewport
  ├ Camera3D
  └ Label3D (text = "D")

Playing scene D, A's MeshInstance3D shows "D", not "A".

We can fix scenes C and D manually:

Select the MeshInstance3D.
In the inspector, go to "Geometry" > "Material Override" > "Albedo" > "Texture"
change "Viewport Path" from "SubViewport" to "A/SubViewport".
Run the scene.

Now C and D work as expected. But this only helps temporarily - certain combinations of opening, saving, & closing cause the viewport_path to revert. It's a bit hard to repro, but this sequence seems to trigger it pretty reliably:

Do the manual fix on scene C.
Save & close the whole project.
Reopen the project.
Close scene A.
Reopen scene A.
Save the whole project again.
Return to scene C. The texture is magenta again, and "Viewport Path" has reverted to just "SubViewport".

You can try the same steps in shader_project and get the same result. The ViewportTexture is a uniform named tex. You can fix tex in the material inspector, but it also gets reverted.