example code for ktx2 compression

[tom-deadline]

Hello,
I was reading docs of TextureBasisu extension and couldn't understand this part:

Compression is not done automatically when adding the extension as shown above — you must compress the image data first, then pass the .ktx2 payload to Texture.setImage. The glTF-Transform CLI has functions to help with this, or any similar KTX2-capable utility will work.

could you provide some example code of how it should be done?

[donmccurdy]

Several tools for converting textures to .ktx2 are discussed here:

https://github.com/KhronosGroup/3D-Formats-Guidelines/blob/main/KTXArtistGuide.md

The glTF-Transform CLI is one of them, and you can find my KTX conversion code in the repo as part of the CLI. Note that it relies on having KTX-Software installed to the machine, providing the toktx CLI program, and isn't a plain JavaScript solution.

If you need plain JavaScript and/or WASM, the basis_universal repository recently added a WASM KTX2 encoder, but I haven't worked with it yet: https://github.com/BinomialLLC/basis_universal/blob/master/webgl/ktx2_encode_test/index.html

[tom-deadline]

@donmccurdy Thanks, a lot. Right now I can convert png to ktx2 and add textures to gltf with your TextureBasisu extension(but old ones stay there too), but how can I replace old ones with new ones. manually I would just change URI, but if I change URI with setURI(), I get an error from the viewer:

So, how can I properly replace old textures with ktx2 files?

[donmccurdy]

Once you have a KTX2 image, the code here is all that I am doing, other than attaching the extension to the document:

glTF-Transform/packages/cli/src/transforms/toktx.ts

Lines 171 to 177 in 23ba620

	texture
	.setImage(BufferUtils.trim(fs.readFileSync(outPath)))
	.setMimeType('image/ktx2');
	if (texture.getURI()) {
	texture.setURI(FileUtils.basename(texture.getURI()) + '.ktx2');
	}

The version of the "glTF Validator" included in my viewer predates the KHR_texture_basisu extension, so I wouldn't worry too much about those validation errors. Just use gltf-transform inspect model.glb and confirm that the textures are all in the correct format.