glTF extension support?

[bertt]

Hi,

I'm trying to validate a glTF with EXT_structural_metadata/EXT_mesh_gpu_instancing/EXT_instance_features but the validation tool says those extensions are not supported.

$ git clone https://github.com/CesiumGS/3d-tiles-validator
$ cd 3d-tiles-validator
$ npm run build
$ npx ts-node src/main.ts --tileContentFile specs/data/gltfExtensions/instanceFeatures/ValidInstanceFeatures.gltf

Result:

 "issues": [
    {
      "type": "CONTENT_VALIDATION_INFO",
      "path": "ValidInstanceFeatures.gltf",
      "message": "Content ValidInstanceFeatures.gltf caused validation infos",
      "severity": "INFO",
      "causes": [
        {
          "type": "CONTENT_VALIDATION_INFO",
          "path": "/extensionsUsed/0",
          "message": "Cannot validate an extension as it is not supported by the validator: 'EXT_structural_metadata'.",
          "severity": "INFO"
        },
        {
          "type": "CONTENT_VALIDATION_INFO",
          "path": "/extensionsUsed/1",
          "message": "Cannot validate an extension as it is not supported by the validator: 'EXT_mesh_gpu_instancing'.",
          "severity": "INFO"
        },
        {
          "type": "CONTENT_VALIDATION_INFO",
          "path": "/extensionsUsed/2",
          "message": "Cannot validate an extension as it is not supported by the validator: 'EXT_instance_features'.",
          "severity": "INFO"
        },

How can I validate glTF with those extensions?

[javagl]

These messages are part of the output of the glTF-Validator.

Internally, the glTF-Validator is called on each tile content. The messages that are generated by the glTF-Validator are (translated into the structure for the 3d-tiles-validator and) listed as possible 'causes' of a single validation issue for the content.

So these are really just INFO messages from the glTF-Validator. If there was any issue with the extensions themself, they should be caught by the actual validation functionality of the 3d-tiles-validator, and listed as ERROR or WARNING explicitly.

We could/should, however, consider to filter out the messages that you showed. Although the extensions are not (yet?) supported by the glTF-Validator, every aspect of their validity should be covered by the validation that is done by the 3d-tiles-validator.

(Eventually, we might add support for these extensions in the glTF-Validator, but there is no timeline for that yet)

[bertt]

ah ok I thought/hoped validation of the extensions was added to the 3d-tiles-validator, but apparently not yet

[javagl]

The validation has been added.

When one of the GLB files uses the extension, then it will be sent to the glTF-Validator for the "baseline" validation. This will cause the "info" messages that say that the extensions are not supported by the glTF-Validator (!).

If the baseline glTF validation passes without errors, then the 3d-tiles-validator will perform the validation of the glTF extensions. Spec/Unit-test level examples for glTF assets with these extensions are in https://github.com/CesiumGS/3d-tiles-validator/tree/main/specs/data/gltfExtensions

If you encounter a glTF with one of these extensions that passes validation, but of which you think that it should not be considered valid, then feel free to open an issue (or add a comment here). There may always be cases that are not properly validated, despite our best efforts.

[javagl]

I assume that this can be closed. Specific questions can be (and are) tracked more easily in dedicated issues.