GLTFLoader: Texture alpha should be ignored on opaque materials

[0b5vr]

In GLTFLoader we can load standard materials using StandardMaterial .
However, the alpha channel of its texture doesn't be handled properly, when renderer's alpha is activated.

In OPAQUE or MASK material, alpha channels of texture should be negated:
https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#alpha-coverage

Change the material's blend mode to ZERO-ONE (in GLTFLoader) might solve this problem?

This is how it should be (rendered in Unity):

Here's how it looks like in Three.js GLTFLoader:

This is the source code:
https://github.com/FMS-Cat/cube-gradient-alpha

Environment:

• Three.js version: r99
• Browser: Confirmed in Chrome, Firefox, Edge
• OSes: Windows. Has not tested in other env
• Hardware: Probably no requirements

[donmccurdy]

Have you checked that modifying the material's blend mode fixes the problem? You can do that after the model is returned from the loader:

gltf.scene.traverse((o) => {
  if (o.isMesh) {
    o.material.blending = THREE.CustomBlending;
    // ...
  }
});

If this is a setting that GLTFLoader should be applying only when the renderer's alpha property is enabled, a loader can't really know when to do that. :/

[0b5vr]

Wait uh I thought alpha is going to always be 1 regardless of map's alpha value under the ZERO-ONE blending settings... ._.
I just noticed the problem is harder one...
Priority is kinda low but we probably need to tweak our standard shader (or entire Three.js shaderchunks) to make it enable to negate all the alpha value

[donmccurdy]

I'm afraid I don't understand the issue — why do the texture's alpha values need to be negated? The link you gave to the Alpha Coverage section of the spec doesn't mention this.

In your sample source repository, which of the two models are you talking about?

[0b5vr]

Bleh I might have picked wrong words, negated -> ignored (I have a disability to my English)

[0b5vr]

You mean, we should treat the alpha as a "fourth component of the output" even if it's fully "OPAQUE"? That sounds pretty weird for me...
I thought "rendered output is fully opaque" means output alpha is always 1.0 .

In your sample source repository, which of the two models are you talking about?

cube-gradient-alpha.glb , has an alpha channel on its material.pbrMetallicRoughness.baseColorTexture but its material.alphaMode is OPAQUE . (Yes I'm talking about weird case)

[mrdoob]

Better late than never™ #22424