Prevent obj importer from printing misleading error

[briansemrau]

When importing .obj files with local paths to their .mtl files, a misleading error is printed.

Couldn't open MTL file 'some_file.mtl', it may not exist or not be readable.

The mtl file loads just fine anyway.

May be relevant to #28203, #36173
Cherrypickable for 3.3, 3.4, 3.x

[fire]

The new code is more clear. I'm in the middle of something so can you try doing some test cases importing objs for me and report back the results. It should do as you expect.

The code is shorter and easier to review.

[briansemrau]

I've tested with https://www.kenney.nl/assets/retro-medieval-kit (OBJ format) and this error is no longer printed. This pack doesn't have absolute paths, so I added the absolute path to the mtl into an obj file and it still outputs as expected.

[fracteed]

Would really appreciate if you could also backport this to 3.4. I get many crashes when re-importing an obj with mtl in 3.3 and 3.4. I think it is related to this error spam, as I only get the crash when Godot is open and I replace an obj.

If I shut down Godot and replace the mesh, I still get this error in the console upon the auto re-import, but at least Godot doesn't crash. It is frustrating to have to shut down Godot every time I replace a mesh. Btw, it never crashes if I replace an obj without an mtl.

[briansemrau]

@fracteed If your issue is the engine crashing (losing unsaved work and requiring the engine to be restarted), then this change will not fix that. It's possible you're encountering a separate issue. Regardless, if this bug exists* in 3.3/3.4 then this might be able to be cherrypicked.

*Edit: confirmed, this is present in 3.x

[fracteed]

@briansemrau I don't lose any work when the engine crashes, as the file re-imports correctly when I then restart Godot. But the error warning about the mtl is still there in the console. For some reason having Godot open when I replace the mesh and the auto re-import happens is what causes the crash. Either way I still get that error message in the console about the mtl that you refer to in this commit.

This doesn't happen with any other reimported mesh formats, such as a plain obj, gltf or collada. It is something to do with the mtl. Even though the mtl does import correctly, so I am guessing it is something to do with this error message being triggered. The only way to really know, is if the error message is not spawned. If you can backport this to 3.4 then at the very least there is not a misleading error message in the console any more. Cheers!

[fire]

Looks good to me. We discussed some validations tests done in one of the comments.

[akien-mga]

Thanks!

[akien-mga]

Cherry-picked for 3.5.

[akien-mga]

Cherry-picked for 3.4.1.