带你读《2022技术人的百宝黑皮书》——内存优化: 纹理压缩技术（3）

// KhronosTextureContainer
constructor(arrayBuffer, facesExpected, baseOffset = 0) { this.arrayBuffer = arrayBuffer;
this.baseOffset = baseOffset;
// 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, this.baseOffset, 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) { return;
}
// load the reset of the header in native 32 bit uint
const dataSize = Uint32Array.BYTES_PER_ELEMENT;
const headerDataView = new DataView(this.arrayBuffer, this.baseOffset + 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_RG-
B,space after the header for meta-data
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
  ...
  }