GLTFLoader: Add KHR_materials_volume and KHR_materials_ior extensions support

[takahirox]

Description

This PR adds KHR_materials_volume and KHR_materials_ior extensions support and updates the webgl_loader_gltf_transmission example.

The video of this PR with #22116.

transmission.mp4

I replaced the TransmissionTest model in webgl_loader_gltf_transmission example with IridescentDishWithOlives.

[mrdoob]

Thanks!

[mrdoob]

Hmm, seems like the shader has some overblown colors?

Screen.Recording.2021-07-13.at.11.44.57.mov

I think it's the same issue as number 3 in @WestLangley list? #22009 (comment)

[WestLangley]

I think it's the same issue as number 3 in @WestLangley list? #22009 (comment)

It is issue number 7 in @WestLangley list. #22009 (comment)

[mrdoob]

@WestLangley Sure is! #22125

[takahirox]

@donmccurdy

Regarding the glb file you shared. Did you cut off specular color texture? According to the repository it seems to have specular color texture. I need it for testing KHR_materials_specular.

[donmccurdy]

That turned out to be the issue in donmccurdy/glTF-Transform#286 yes, had implemented a pre-release version of the spec. I'll regenerate the file later today, or this should work on the most recent gltf-transform release:

gltf-transform cp input.gltf output.glb

[donmccurdy]

Two versions here:

IridescentDishWithOlives.glb.zip
IridescentDishWithOlivesDraco.glb.zip

[takahirox]

Thanks! Do you mind if compressing the textures? The file size is a bit too huge 7.5MB and I'm wondering if we can reduce the size more.

[donmccurdy]

Sure, got this down to about 4MB with squoosh.app/ -

IridescentDishWithOlivesCompressed.glb.zip

[takahirox]

Thanks so much!

[takahirox]

The textures in the glb file don't seem to be compressed because no KHR_texture_basisu extension in extensionsUsed.

[donmccurdy]

Ah, I just used OxiPNG and MozJPEG compression in this case, not Basis. Would take a bit more time to get KTX2/Basis fine-tuned for these textures I think, and may or may not reduce the file size as much. Can give that a try if we want it but it will be a couple days.

[takahirox]

I just used OxiPNG and MozJPEG compression in this case, not Basis.

OK OK, that's fine if it's intentional. Thanks!

[ManishJu]

which software currently supports the export of volumetric GLTF models like this : https://github.com/wallabyway/gltf-presskit-transparency/blob/main/docs/MosquitoInAmber_withRefraction.glb ? Afaik Blender is not ready yet ....

[donmccurdy]

These extensions were just announced as ratified/complete this week, it'll take a bit longer for implementations to arrive in DCC products. Gestaltor (https://ux3d.io/gestaltor) is the only one I'm sure of at the moment. Perhaps Adobe Dimension, but I don't have access to a copy to check. PRs to https://github.com/KhronosGroup/glTF-Blender-IO are always welcome too, IOR and Specular are in progress (KhronosGroup/glTF-Blender-IO#1158) but I don't think anyone has started a PR for volume yet.

A more roundabout option would be to export the extra volumetric textures from Blender separately, then use a script to attach them to the glTF file.

[gonnavis]

Hello @takahirox, Thanks for the PR! I found that current example has gaps if look from side view or back view:

But front view is OK.
I tried with a simple box, seems all refracted pixel are pushed to +Z axis a little?

[takahirox]

@gonnavis Thanks for the report. Would you mind reporting it in #22009, too, because this PR has been already closed and that thread may be the best place to discuss the transmission issues.

[gonnavis]

OK, I re-commented there.