KTX2Loader: Fix .minFilter default for untranscoded compressed textures

[donmccurdy]

KTX2Loader implements three 'paths' for textures:

1. Uncompressed DataTexture (F16, F32, Uint8, ...)
2. Raw CompressedTexture (ETC1/2, ASTC, BCn, ...)
3. Universal/transcoded CompressedTexture (BasisLZ/ETC1S, UASTC)

Basis UASTC HDR textures may take path (2) or (3) depending on device support for ASTC HDR formats, since the pre-transcode data is also valid ASTC data. In case (2), we weren't correctly setting .minFilter defaults for textures without mipmaps.

• Fixes Exr conversion to ktx2 added to background Mac system render exception #29884

[Mugen87]

Uncompressed DataTexture (F16, F32, Uint8, ...)

WebGLRenderer makes sure the use case of #29884 works by having two separate code paths (compressed vs uncompressed) for uploading data of CompressedTexturess, see:

three.js/src/renderers/webgl/WebGLTextures.js

Lines 957 to 997 in 5b51d6f

	if ( texture.format !== RGBAFormat ) {
	if ( glFormat !== null ) {
	if ( useTexStorage ) {
	if ( dataReady ) {
	state.compressedTexSubImage2D( _gl.TEXTURE_2D, i, 0, 0, mipmap.width, mipmap.height, glFormat, mipmap.data );
	}
	} else {
	state.compressedTexImage2D( _gl.TEXTURE_2D, i, glInternalFormat, mipmap.width, mipmap.height, 0, mipmap.data );
	}
	} else {
	console.warn( 'THREE.WebGLRenderer: Attempt to load unsupported compressed texture format in .uploadTexture()' );
	}
	} else {
	if ( useTexStorage ) {
	if ( dataReady ) {
	state.texSubImage2D( _gl.TEXTURE_2D, i, 0, 0, mipmap.width, mipmap.height, glFormat, glType, mipmap.data );
	}
	} else {
	state.texImage2D( _gl.TEXTURE_2D, i, glInternalFormat, mipmap.width, mipmap.height, 0, glFormat, glType, mipmap.data );
	}
	}

TBH, I was never happy with the exception handling of RGBAFormat since I think it's more clear when instances of CompressedTextures actually hold compressed data (and thus use a compressed format).

I wish we could avoid CompressedTexture with RGBAFormat since that would allow us a more clean implementation on the renderer side. In WebGPURenderer there is currently no separate RGBAFormat handling so the use case of #29884 does not work yet (neither in the WebGPU and WebGL backend, see https://jsfiddle.net/20j6an3x/). We could fix this on the renderer side but imo it would be more clear if compressed texture loaders return uncompressed data as instances of DataTexture.

[donmccurdy]

I think we could change KTX2Loader to return THREE.DataTexture instead of THREE.CompressedTexture conditionally, depending on the selected transcoding format. The only obstacle I see is that we'd need a new THREE.DataCubeTexture class, to handle all three cases here:

three.js/examples/jsm/loaders/KTX2Loader.js

Lines 299 to 311 in 19123ff

	if ( container.faceCount === 6 ) {
	texture = new CompressedCubeTexture( faces, format, type );
	} else {
	const mipmaps = faces[ 0 ].mipmaps;
	texture = container.layerCount > 1
	? new CompressedArrayTexture( mipmaps, width, height, container.layerCount, format, type )
	: new CompressedTexture( mipmaps, width, height, format, type );
	}