Expose functionality to compress individual textures

[krispya]

When creating an asset pipeline there are often situations where I need to transform data, such as compressing individual textures, without it being embedded in a gltf or glb. Instead of cherry picking these functions out of gltf-transform, it would be great if were exported. For example, being able to compress any texture to KTX2 via a node call.

[donmccurdy]

For other formats (PNG, JPG, WEBP, AVIF) you can use the compressTexture function. But yes, exposing a nice API for KTX2 compression has been more of a challenge, because it requires shell sessions. This is also why it hasn't become part of the @gltf-transform/functions package.

Also see:

• Support compressing KTX2 textures without CLI #675

This would be easier if an suitable npm library existed for KTX2 compression, as it is, I need logic to create temporary scratch directories and so on, which would also need to be handled per-texture here.

I probably will not spend time on this myself unless/until #675 gets unblocked, but I'd be happy to review a PR if someone would like to try splitting toktx() into separate functions, perhaps textureCompressKTX2 for the transform and compressTextureKTX2 for the single-texture function.

[krispya]

I see, thanks for pointing that out. I am exploring this area now. I'll report back if I discover anything useful

[Makio64]

@krispya If it can help the technique I currently use is to save the image data to a file of the texture i want to save, call the ktx cli tools to convert and then push it back to gltftransform.

[jo-chemla]

I've doing something similar (using a temporary file on disk and processing it via the ktx CLI) for ktx2 decompression (from image texture file embedded within the glb).

For ktx2 compression would it be possible to enclose these 2 toktx CLI calls within a wrapper function, something like compressKtx2? So the function call would be more like the simple draco or other texture compress transforms?

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

Lines 411 to 435 in 0bf0ecb

	if (opts.textureCompress === 'ktx2') {
	const { default: encoder } = await import('sharp');
	const slotsUASTC = micromatch.makeRe(
	'{normalTexture,occlusionTexture,metallicRoughnessTexture}',
	MICROMATCH_OPTIONS,
	);
	transforms.push(
	toktx({
	encoder,
	resize: [opts.textureSize, opts.textureSize],
	mode: Mode.UASTC,
	slots: slotsUASTC,
	level: 4,
	rdo: true,
	rdoLambda: 4,
	limitInputPixels: options.limitInputPixels as boolean,
	}),
	toktx({
	encoder,
	resize: [opts.textureSize, opts.textureSize],
	mode: Mode.ETC1S,
	quality: 255,
	limitInputPixels: options.limitInputPixels as boolean,
	}),
	);

[donmccurdy]

@jo-chemla I'm not sure I want to maintain those two calls wrapped as a scripting API for upstream applications. It's common that you'd want to make different choices about which texture slots are UASTC vs. ETC1S, or the settings for each, there's nothing magic about my choices here.

I'd be happy to review a PR making the changes described by #1162 (comment), though. Or maybe two separate functions are needed, like compressTextureUASTC(texture, options) and compressTextureETC1S(texture, options).