three.js/examples/jsm/loaders/KTXLoader.js

import {
	CompressedTextureLoader
} from 'three';

/**
 * for description see https://www.khronos.org/opengles/sdk/tools/KTX/
 * for file layout see https://www.khronos.org/opengles/sdk/tools/KTX/file_format_spec/
 *
 * ported from https://github.com/BabylonJS/Babylon.js/blob/master/src/Misc/khronosTextureContainer.ts
 */


class KTXLoader extends CompressedTextureLoader {

	constructor( manager ) {

		super( manager );

	}

	parse( buffer, loadMipmaps ) {

		const ktx = new KhronosTextureContainer( buffer, 1 );

		return {
			mipmaps: ktx.mipmaps( loadMipmaps ),
			width: ktx.pixelWidth,
			height: ktx.pixelHeight,
			format: ktx.glInternalFormat,
			isCubemap: ktx.numberOfFaces === 6,
			mipmapCount: ktx.numberOfMipmapLevels
		};

	}

}


const HEADER_LEN = 12 + ( 13 * 4 ); // identifier + header elements (not including key value meta-data pairs)
// load types
const COMPRESSED_2D = 0; // uses a gl.compressedTexImage2D()
//const COMPRESSED_3D = 1; // uses a gl.compressedTexImage3D()
//const TEX_2D = 2; // uses a gl.texImage2D()
//const TEX_3D = 3; // uses a gl.texImage3D()

class KhronosTextureContainer {

	/**
	 * @param {ArrayBuffer} arrayBuffer- contents of the KTX container file
	 * @param {number} facesExpected- should be either 1 or 6, based whether a cube texture or or
	 * @param {boolean} threeDExpected- provision for indicating that data should be a 3D texture, not implemented
	 * @param {boolean} textureArrayExpected- provision for indicating that data should be a texture array, not implemented
	 */
	constructor( arrayBuffer, facesExpected /*, threeDExpected, textureArrayExpected */ ) {

		this.arrayBuffer = arrayBuffer;

		// Test that it is a ktx formatted file, based on the first 12 bytes, character representation is:
		// '´', 'K', 'T', 'X', ' ', '1', '1', 'ª', '\r', '\n', '\x1A', '\n'
		// 0xAB, 0x4B, 0x54, 0x58, 0x20, 0x31, 0x31, 0xBB, 0x0D, 0x0A, 0x1A, 0x0A
		const identifier = new Uint8Array( this.arrayBuffer, 0, 12 );
		if ( identifier[ 0 ] !== 0xAB ||
			identifier[ 1 ] !== 0x4B ||
			identifier[ 2 ] !== 0x54 ||
			identifier[ 3 ] !== 0x58 ||
			identifier[ 4 ] !== 0x20 ||
			identifier[ 5 ] !== 0x31 ||
			identifier[ 6 ] !== 0x31 ||
			identifier[ 7 ] !== 0xBB ||
			identifier[ 8 ] !== 0x0D ||
			identifier[ 9 ] !== 0x0A ||
			identifier[ 10 ] !== 0x1A ||
			identifier[ 11 ] !== 0x0A ) {

			console.error( 'texture missing KTX identifier' );
			return;

		}

		// load the reset of the header in native 32 bit uint
		const dataSize = Uint32Array.BYTES_PER_ELEMENT;
		const headerDataView = new DataView( this.arrayBuffer, 12, 13 * dataSize );
		const endianness = headerDataView.getUint32( 0, true );
		const littleEndian = endianness === 0x04030201;

		this.glType = headerDataView.getUint32( 1 * dataSize, littleEndian ); // must be 0 for compressed textures
		this.glTypeSize = headerDataView.getUint32( 2 * dataSize, littleEndian ); // must be 1 for compressed textures
		this.glFormat = headerDataView.getUint32( 3 * dataSize, littleEndian ); // must be 0 for compressed textures
		this.glInternalFormat = headerDataView.getUint32( 4 * dataSize, littleEndian ); // the value of arg passed to gl.compressedTexImage2D(,,x,,,,)
		this.glBaseInternalFormat = headerDataView.getUint32( 5 * dataSize, littleEndian ); // specify GL_RGB, GL_RGBA, GL_ALPHA, etc (un-compressed only)
		this.pixelWidth = headerDataView.getUint32( 6 * dataSize, littleEndian ); // level 0 value of arg passed to gl.compressedTexImage2D(,,,x,,,)
		this.pixelHeight = headerDataView.getUint32( 7 * dataSize, littleEndian ); // level 0 value of arg passed to gl.compressedTexImage2D(,,,,x,,)
		this.pixelDepth = headerDataView.getUint32( 8 * dataSize, littleEndian ); // level 0 value of arg passed to gl.compressedTexImage3D(,,,,,x,,)
		this.numberOfArrayElements = headerDataView.getUint32( 9 * dataSize, littleEndian ); // used for texture arrays
		this.numberOfFaces = headerDataView.getUint32( 10 * dataSize, littleEndian ); // used for cubemap textures, should either be 1 or 6
		this.numberOfMipmapLevels = headerDataView.getUint32( 11 * dataSize, littleEndian ); // number of levels; disregard possibility of 0 for compressed textures
		this.bytesOfKeyValueData = headerDataView.getUint32( 12 * dataSize, littleEndian ); // the amount of space after the header for meta-data

		// Make sure we have a compressed type.  Not only reduces work, but probably better to let dev know they are not compressing.
		if ( this.glType !== 0 ) {

			console.warn( 'only compressed formats currently supported' );
			return;

		} else {

			// value of zero is an indication to generate mipmaps @ runtime.  Not usually allowed for compressed, so disregard.
			this.numberOfMipmapLevels = Math.max( 1, this.numberOfMipmapLevels );

		}

		if ( this.pixelHeight === 0 || this.pixelDepth !== 0 ) {

			console.warn( 'only 2D textures currently supported' );
			return;

		}

		if ( this.numberOfArrayElements !== 0 ) {

			console.warn( 'texture arrays not currently supported' );
			return;

		}

		if ( this.numberOfFaces !== facesExpected ) {

			console.warn( 'number of faces expected' + facesExpected + ', but found ' + this.numberOfFaces );
			return;

		}

		// we now have a completely validated file, so could use existence of loadType as success
		// would need to make this more elaborate & adjust checks above to support more than one load type
		this.loadType = COMPRESSED_2D;

	}

	mipmaps( loadMipmaps ) {

		const mipmaps = [];

		// initialize width & height for level 1
		let dataOffset = HEADER_LEN + this.bytesOfKeyValueData;
		let width = this.pixelWidth;
		let height = this.pixelHeight;
		const mipmapCount = loadMipmaps ? this.numberOfMipmapLevels : 1;

		for ( let level = 0; level < mipmapCount; level ++ ) {

			const imageSize = new Int32Array( this.arrayBuffer, dataOffset, 1 )[ 0 ]; // size per face, since not supporting array cubemaps
			dataOffset += 4; // size of the image + 4 for the imageSize field

			for ( let face = 0; face < this.numberOfFaces; face ++ ) {

				const byteArray = new Uint8Array( this.arrayBuffer, dataOffset, imageSize );

				mipmaps.push( { 'data': byteArray, 'width': width, 'height': height } );

				dataOffset += imageSize;
				dataOffset += 3 - ( ( imageSize + 3 ) % 4 ); // add padding for odd sized image

			}

			width = Math.max( 1.0, width * 0.5 );
			height = Math.max( 1.0, height * 0.5 );

		}

		return mipmaps;

	}

}

export { KTXLoader };