Support `KHR_texture_basisu` in bevy_gltf

[jf908]

What problem does this solve or what need does it fill?

When a gltf file is loaded that uses the KHR_texture_basisu extension, bevy fails to load the asset with a KHR_texture_basisu is not supported error.

What solution would you like?

Bevy should load the file.

What alternative(s) have you considered?

None

Additional context

This error was surprising to me because there is a sample gltf file that uses ktx2 texture files but it turns out this file has been altered so that it can be loaded in bevy.

By default, gltf files only support jpg and png images but there are official extensions for ktx2, webp, and dds. Bevy supports loading image of those types but they are specified in gltf files in a different way, explained here, to allow for jpg/png fallbacks.

As far I could tell, gltf-rs does not support those custom image extensions and will error if they are required of the gltf file but if gltf is compiled with the allow_empty_texture feature, it would be somewhat simple for bevy to just read the json and load the correct path.

[jf908]

I would be willing to make a PR for this myself

[janhohenheim]

FYI, what works as a workaround right now is to just stubbornly replace all mentions of some_texture.png with some_texture.ktx2 in the glTF, which Bevy will load correctly.
See klafsa

[mockersf]

I would be willing to make a PR for this myself

Could you PR it to the gltf-rs repo? I would prefer to avoid adding more workaround in Bevy's gltf loader

[jf908]

Could you PR it to the gltf-rs repo? I would prefer to avoid adding more workaround in Bevy's gltf loader

There actually already is a PR for it but it's been open for a years - gltf-rs/gltf#392.

[mockersf]

Last message by the maintainer was left without response... you can maybe try to reply or adopt the PR