Add THREE.CompressedCubeTexture

[donmccurdy]

Related:

• Creating a CubeTexture from 6 CompressedTextures doesn't work after r136 #24065
• KTX2Loader: Return LODs through DataTexture's mipmaps field. #25871
• KTX2Loader: Support compressed cubemaps #25909

Adds a THREE.CompressedCubeTexture class, and updates THREE.KTX2Loader to use it where appropriate. This resolves issues discussed in #25909, where the renderer failed to recognize 'synthetic' compressed cube textures in some cases.

I've kept the constructor signature simple, at least for the time being:

constructor( images, format, type ) { ... }

Tested against the texture below:

pisa.ktx2.zip

The texture was generated from our Pisa PNG cubemap, with the KTX-Software v4.3 alpha release. I ran into an issue with the alpha release, tracked in KhronosGroup/KTX-Software#728, but in future stable releases the command below should work as-is:

ktx create --cubemap --format R8G8B8_SRGB --encode uastc --assign-oetf srgb \
  px.png nx.png py.png ny.png pz.png nz.png pisa.ktx2

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

Filesize dev	Filesize PR	Diff
643.1 kB (159.5 kB)	643.3 kB (159.5 kB)	+179 B

🌳 Bundle size after tree-shaking

Minimal build including a renderer, camera, empty scene, and dependencies.

Filesize dev	Filesize PR	Diff
436.4 kB (105.6 kB)	436.4 kB (105.6 kB)	+0 B

[Methuselah96]

@donmccurdy Would it work to pass in [] for mipmaps instead of undefined? I'm working on the types for this. If taken strictly, Texture.mipmaps and CompressedTexture.mipmaps would now need to be ImageData[] | undefined instead of ImageData[], which is more disruptive of a change for the users of the types.

[donmccurdy]

I believe it's correct that the .mipmaps property is a non-nullable array, but not safe to pass an empty array up to the constructor here... I would just assume that mipmaps gets populated correctly during texture initialization, and not make the property nullable in the TS definitions.

[Methuselah96]

Okay, thanks, good to know. For my own education, where do the mipmaps end up getting set for the CompressedCubeTexture in KTX2Loader?

[Methuselah96]

I see mipmaps getting set for other textures in createRawTexture, but don't do something similar in _createTextureFrom where CompressedCubeTexture is used.

[donmccurdy]

You can see where it would be set in #26642, but I can't promise that KTX2Loader sets up all texture types correctly today. Constructing compressed array, cube, and 3D textures is not a fully-documented API, and we don't have many test cases for it, so I'm kind of trial-and-erroring my through this part. Maybe once #26642 is working we'll have a better idea how to construct textures for each of these cases...