Import of gltf with blendshapes without tangents fails

[lyuma]

Tested versions

• Not reproducible in 4.2beta5
• Reproducible in 4.2beta6 through 4.2.1

System information

Godot v4.2.beta6 - Windows 10.0.19045 - Vulkan (Forward+) - dedicated NVIDIA GeForce RTX 3090 (NVIDIA; 31.0.15.3713) - Intel(R) Core(TM) i9-9900K CPU @ 3.60GHz (16 Threads)

Issue description

Importing a gltf file without tangents in the editor with Ensure Tangents unchecked will fail for all meshes containing blend shapes with the following error log:

  Blend shape format must match the main array format for Vertex, Normal and Tangent arrays.
  scene/resources/mesh.cpp:1802 - Condition "err != OK" is true.
  scene/resources/mesh.cpp:1923 - Index p_idx = -1 is out of bounds (surfaces.size() = 0).
  scene/resources/mesh.cpp:1943 - Index p_idx = -1 is out of bounds (surfaces.size() = 0).
  servers/rendering/renderer_rd/storage_rd/mesh_storage.cpp:891 - Index p_shape = 0 is out of bounds ((int)mi->blend_weights.size() = 0).

The same thing happens at runtime. Since there is no option to enable Ensure Tangents for runtime that I can find, this is not possible to workaround for runtime import.

The issue affects the https://github.com/V-Sekai/godot-vrm/ project, however it happens with these models in the builtin gltf importer.

issues may be related:

• Obscure warning "Attempting to use a shader that requires tangents with a mesh that doesn't contain tangents." is spammed. #84875
• 4.2 imported models have broken normals #85406
  I filed this issue since it is easy to reproduce and leads to a missing mesh during import, but maybe solving those issues will also address this one.

Steps to reproduce

1. Open the attached project.
2. Clear the console and reimport Godette_vrm_v4.glb - this will produce errors.
3. Open sample_scene.tscn and notice the models are all missing faces.
4. Click play to run the project. This will run load_at_runtime_scene.tscn which loads a gltf at runtime. this is also missing the face and produces errors in the Debugger -> Errors tab.
5. Optional: enable "Ensure Tangents" in the import dock and notice that the glb files now contain a face in the editor. This does not solve the runtime case.

Minimal reproduction project (MRP)

MeshTangents.zip

Adding an additional MRP from a companion issue #85960: https://github.com/godotengine/godot/files/13623984/resource_loader_test.zip

[lyuma]

for runtime import, we found that using gltf_document.append_from_file(path, gltf_state, 8) works around the issue:

8 is the constant for EditorSceneFormatImporter.IMPORT_GENERATE_TANGENT_ARRAYS

Even though there is a workaround, I still think this is a bug: it only affects models with blend shapes.

[Calandiel]

I think this is related to another issue I raised in #86698
Perhaps we could close the one I opened and add the MRP from it to this issue?

[clayjohn]

I think this is related to another issue I raised in #86698 Perhaps we could close the one I opened and add the MRP from it to this issue?

#86698 is a different issue unfortunately, so we should leave it open