riot games tex file converter

tex_to_dds.js

/**
 * @param {Buffer} data
 * @returns {Buffer}
 */
const tex_to_dds = (data) => {
  if (data.byteLength < 12 || data.subarray(0, 4).toString() !== "TEX\0") {
    throw new Error("invalid TEX file");
  }

  const width = data.readUInt16LE(4);
  const height = data.readUInt16LE(6);
  const format = data.readUInt8(9);
  const hasMipmaps = data.readUint8(11);

  const ddspf = Buffer.alloc(32);
  ddspf.writeUInt32LE(32, 0);
  switch (format) {
    case 10: // DXT1
      ddspf.writeUInt32LE(0x4, 4);
      ddspf.write("DXT1", 8);
      break;

    case 12: // DXT5
      ddspf.writeUInt32LE(0x4, 4);
      ddspf.write("DXT5", 8);
      break;

    case 20: // RGBA8
      ddspf.writeUInt32LE(0x41, 4);
      ddspf.writeUInt32LE(32, 8);
      ddspf.writeUInt32LE(0x000000ff, 12);
      ddspf.writeUInt32LE(0x0000ff00, 16);
      ddspf.writeUInt32LE(0x00ff0000, 20);
      ddspf.writeUInt32LE(0xff000000, 24);
      break;

    default:
      throw new Error(`unsupported TEX format: ${format}`);
  }

  let pixels;
  if (hasMipmaps) {
    // Note: only convert the largest mipmap

    let blockSize = 0;
    let bytesPerBlock = 0;
    switch (format) {
      case 10: // DXT1
        blockSize = 4;
        bytesPerBlock = 8;
        break;

      case 12: // DXT5
        blockSize = 4;
        bytesPerBlock = 16;
        break;

      case 20: // RGBA8
        blockSize = 4;
        bytesPerBlock = 4;
        break;
    }

    // Find mipmap count
    // let mipmapCount = 0;
    // for (let i = Math.max(width, height); i > 0; i >>= 1) {
    //   ++mipmapCount;
    // }

    const blockWidth = Math.floor((width + blockSize - 1) / blockSize);
    const blockheight = Math.floor((height + blockSize - 1) / blockSize);
    const mipmapSize = bytesPerBlock * blockWidth * blockheight;
    pixels = data.subarray(-mipmapSize);
  } else {
    pixels = data.subarray(12);
  }

  const ddsHeader = Buffer.alloc(128);
  ddsHeader.write("DDS ", 0);
  ddsHeader.writeUInt32LE(124, 4);
  ddsHeader.writeUInt32LE(0x1007, 8);
  ddsHeader.writeUInt32LE(height, 12);
  ddsHeader.writeUInt32LE(width, 16);
  ddspf.copy(ddsHeader, 76);
  ddsHeader.writeUInt32LE(0x1000, 108);

  return Buffer.concat([ddsHeader, pixels]);
};