wiki/node_modules/three/examples/jsm/loaders/PVRLoader.js

import {
	CompressedTextureLoader,
	RGBA_PVRTC_2BPPV1_Format,
	RGBA_PVRTC_4BPPV1_Format,
	RGB_PVRTC_2BPPV1_Format,
	RGB_PVRTC_4BPPV1_Format
} from 'three';

/**
 * A loader for the PVRTC texture compression format.
 *
 * ```js
 * const loader = new PVRLoader();
 *
 * const map = loader.load( 'textures/compressed/disturb_4bpp_rgb.pvr' );
 * map.colorSpace = THREE.SRGBColorSpace; // only for color textures
 * ```
 *
 * @augments CompressedTextureLoader
 * @three_import import { PVRLoader } from 'three/addons/loaders/PVRLoader.js';
 */
class PVRLoader extends CompressedTextureLoader {

	/**
	 * Constructs a new PVR loader.
	 *
	 * @param {LoadingManager} [manager] - The loading manager.
	 */
	constructor( manager ) {

		super( manager );

	}

	/**
	 * Parses the given PVRTC texture data.
	 *
	 * @param {ArrayBuffer} buffer - The raw texture data.
	 * @param {boolean} loadMipmaps - Whether to load mipmaps or not. This option is not yet supported by the loader.
	 * @return {CompressedTextureLoader~TexData} An object representing the parsed texture data.
	 */
	parse( buffer, loadMipmaps ) {

		const headerLengthInt = 13;
		const header = new Uint32Array( buffer, 0, headerLengthInt );

		const pvrDatas = {
			buffer: buffer,
			header: header,
			loadMipmaps: loadMipmaps
		};

		if ( header[ 0 ] === 0x03525650 ) {

			// PVR v3

			return _parseV3( pvrDatas );

		} else if ( header[ 11 ] === 0x21525650 ) {

			// PVR v2

			return _parseV2( pvrDatas );

		} else {

			console.error( 'THREE.PVRLoader: Unknown PVR format.' );

		}

	}

}

function _parseV3( pvrDatas ) {

	const header = pvrDatas.header;
	let bpp, format;


	const metaLen = header[ 12 ],
		pixelFormat = header[ 2 ],
		height = header[ 6 ],
		width = header[ 7 ],
		// numSurfs = header[ 9 ],
		numFaces = header[ 10 ],
		numMipmaps = header[ 11 ];

	switch ( pixelFormat ) {

		case 0 : // PVRTC 2bpp RGB
			bpp = 2;
			format = RGB_PVRTC_2BPPV1_Format;
			break;

		case 1 : // PVRTC 2bpp RGBA
			bpp = 2;
			format = RGBA_PVRTC_2BPPV1_Format;
			break;

		case 2 : // PVRTC 4bpp RGB
			bpp = 4;
			format = RGB_PVRTC_4BPPV1_Format;
			break;

		case 3 : // PVRTC 4bpp RGBA
			bpp = 4;
			format = RGBA_PVRTC_4BPPV1_Format;
			break;

		default :
			console.error( 'THREE.PVRLoader: Unsupported PVR format:', pixelFormat );

	}

	pvrDatas.dataPtr = 52 + metaLen;
	pvrDatas.bpp = bpp;
	pvrDatas.format = format;
	pvrDatas.width = width;
	pvrDatas.height = height;
	pvrDatas.numSurfaces = numFaces;
	pvrDatas.numMipmaps = numMipmaps;
	pvrDatas.isCubemap 	= ( numFaces === 6 );

	return _extract( pvrDatas );

}

function _parseV2( pvrDatas ) {

	const header = pvrDatas.header;

	const headerLength = header[ 0 ],
		height = header[ 1 ],
		width = header[ 2 ],
		numMipmaps = header[ 3 ],
		flags = header[ 4 ],
		// dataLength = header[ 5 ],
		// bpp =  header[ 6 ],
		// bitmaskRed = header[ 7 ],
		// bitmaskGreen = header[ 8 ],
		// bitmaskBlue = header[ 9 ],
		bitmaskAlpha = header[ 10 ],
		// pvrTag = header[ 11 ],
		numSurfs = header[ 12 ];


	const TYPE_MASK = 0xff;
	const PVRTC_2 = 24,
		PVRTC_4 = 25;

	const formatFlags = flags & TYPE_MASK;

	let bpp, format;
	const _hasAlpha = bitmaskAlpha > 0;

	if ( formatFlags === PVRTC_4 ) {

		format = _hasAlpha ? RGBA_PVRTC_4BPPV1_Format : RGB_PVRTC_4BPPV1_Format;
		bpp = 4;

	} else if ( formatFlags === PVRTC_2 ) {

		format = _hasAlpha ? RGBA_PVRTC_2BPPV1_Format : RGB_PVRTC_2BPPV1_Format;
		bpp = 2;

	} else {

		console.error( 'THREE.PVRLoader: Unknown PVR format:', formatFlags );

	}

	pvrDatas.dataPtr = headerLength;
	pvrDatas.bpp = bpp;
	pvrDatas.format = format;
	pvrDatas.width = width;
	pvrDatas.height = height;
	pvrDatas.numSurfaces = numSurfs;
	pvrDatas.numMipmaps = numMipmaps + 1;

	// guess cubemap type seems tricky in v2
	// it's just a pvr containing 6 surface (no explicit cubemap type)
	pvrDatas.isCubemap 	= ( numSurfs === 6 );

	return _extract( pvrDatas );

}


function _extract( pvrDatas ) {

	const pvr = {
		mipmaps: [],
		width: pvrDatas.width,
		height: pvrDatas.height,
		format: pvrDatas.format,
		mipmapCount: pvrDatas.numMipmaps,
		isCubemap: pvrDatas.isCubemap
	};

	const buffer = pvrDatas.buffer;

	let dataOffset = pvrDatas.dataPtr,
		dataSize = 0,
		blockSize = 0,
		blockWidth = 0,
		blockHeight = 0,
		widthBlocks = 0,
		heightBlocks = 0;

	const bpp = pvrDatas.bpp,
		numSurfs = pvrDatas.numSurfaces;

	if ( bpp === 2 ) {

		blockWidth = 8;
		blockHeight = 4;

	} else {

		blockWidth = 4;
		blockHeight = 4;

	}

	blockSize = ( blockWidth * blockHeight ) * bpp / 8;

	pvr.mipmaps.length = pvrDatas.numMipmaps * numSurfs;

	let mipLevel = 0;

	while ( mipLevel < pvrDatas.numMipmaps ) {

		const sWidth = pvrDatas.width >> mipLevel,
			sHeight = pvrDatas.height >> mipLevel;

		widthBlocks = sWidth / blockWidth;
		heightBlocks = sHeight / blockHeight;

		// Clamp to minimum number of blocks
		if ( widthBlocks < 2 ) widthBlocks = 2;
		if ( heightBlocks < 2 ) heightBlocks = 2;

		dataSize = widthBlocks * heightBlocks * blockSize;

		for ( let surfIndex = 0; surfIndex < numSurfs; surfIndex ++ ) {

			const byteArray = new Uint8Array( buffer, dataOffset, dataSize );

			const mipmap = {
				data: byteArray,
				width: sWidth,
				height: sHeight
			};

			pvr.mipmaps[ surfIndex * pvrDatas.numMipmaps + mipLevel ] = mipmap;

			dataOffset += dataSize;

		}

		mipLevel ++;

	}

	return pvr;

}

export { PVRLoader };