glTF KHR_texture_basisu extension feasibility

[andreasplesch]

Complex. Requires parsing of ktx2 files, and transcoding of 3 formats to GPU compressed formats depending on availability.

Collecting resources:

https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_texture_basisu

https://github.com/BabylonJS/Babylon.js/pull/13284/files (for example)
https://github.com/mrdoob/three.js/blob/b02c13bdeefddcf48cb9f012dd7695a24fc00ff1/examples/jsm/loaders/KTX2Loader.js
mrdoob/three.js#21984
mrdoob/three.js#21984 (comment)
https://github.com/donmccurdy/three.js/blob/dev/examples/jsm/libs/basis/basis_transcoder.wasm (480KB!)
https://github.com/donmccurdy/KTX-Parse

[andreasplesch]

KhronosGroup/KTX-Software#754

[andreasplesch]

The ktx2 basis formats are:

• ETC1S with BasisLZ (used for color-perceptual content)
• UASTC with optional Zstandard compression (used for data content)

They need to a transcoded to GPU supported format:

            s3tc: !!gl.getExtension('WEBGL_compressed_texture_s3tc'),
            etc1: !!gl.getExtension('WEBGL_compressed_texture_etc1'),
            etc2: !!gl.getExtension('WEBGL_compressed_texture_etc'),
            pvrtc: !!gl.getExtension('WEBGL_compressed_texture_pvrtc'),
            astc: !!gl.getExtension('WEBGL_compressed_texture_astc'),
            bptc: !!gl.getExtension('EXT_texture_compression_bptc')

https://caniuse.com/mdn-api_webgl_compressed_texture_s3tc
https://caniuse.com/mdn-api_webgl_compressed_texture_etc1
https://caniuse.com/mdn-api_webgl_compressed_texture_etc
https://caniuse.com/mdn-api_webgl_compressed_texture_pvrtc
https://caniuse.com/mdn-api_webgl_compressed_texture_astc
https://caniuse.com/?search=bptc

Filtering for IOS, Android and Firefox leaves only:
astc !