WebIO gltf-transform problem(missing model parts)

[Oleksandr-Fedorov]

Hi,I've written to Three forum some time before about this problem,and i decided to write in a question section directly,because it concerns gltf-transform.

So i'll just copy all the text from my previous question:

I’m using gltf-transform by @donmccurdy to display KHR_materials_pbrSpecularGlossiness of materials correctly, I did everything like the example through WebIO, the model is displayed, but the problem is that some parts of it are lost
exmpl. from my canvas

, I went to gltf.report, where this library is used and there the situation is the same

, then I tried to do the same in 3dViewer and it displayed everything correctly,

it is definitely related to gltf-transform, because I tried to load the model without this functionality, it loaded correctly but without textures.

The initial model
skeleton_ratchet_rc_all_4_one.glb (3.7 MB)

Maybe this is not a problem with the library itself, I just want to know what this could be connected with, such a lack of model components, thanks for understanding.
Would you mind sharing your thoughts on this?

[donmccurdy]

Hi @Oleksandr-Fedorov! The result you're seeing is because the materials named "blitzer_ratchet" and "jetpack" have alpha values of 0.0. In general that would result in hiding the object, if perhaps still writing to the depth buffer depending on the viewer, but when the KHR_materials_pbrSpecularGlossiness extension is used in a viewer that doesn't recognize those materials, the alpha isn't applied and the parts still appear.

In Blender you'll see:

This could be a mistake in the model's authoring – alpha should be non-zero if you want to see the parts, and opaque if no transparency is intended — but you can correct it either in https://gltf.report or in your script with:

for (const material of document.getRoot().listMaterials()) {
  if (material.getAlpha() === 0.0) {
    console.warn('hidden: ', material);
    material.setAlphaMode('OPAQUE').setAlpha(1.0);
  }
}

[Oleksandr-Fedorov]

I can't express how grateful I am for your answer, that is, it is mostly due to the specificity of the user's configuration of materials in the model itself, and the user should first of all configure the model before displaying it on the 3D canvas. But, as you said, I have the opportunity to display this material in one way or another, just by checking its property directly, when I check each mesh of the resulting object.

What do you think, should I write a warning to the user in this case that he has such materials, for example, in the information panel of the model during its loading?

[donmccurdy]

In my own viewers I usually report validation issues identified by https://github.com/KhronosGroup/glTF-Validator, though alpha=0 isn't a case that the official validator currently checks. Whether to do so would depend on the goals of your users and application, I think — If this scene were loaded into a game engine, it might be plausible that the invisible meshes are intended for later use as physics colliders or some other non-rendering purpose. If this scene were loaded into a showcase platform like https://sketchfab.com/, it's more likely the user has made a mistake and would want to be warned.