tfxParser.ts

export interface TfxFileHeader {
  // Specifies TressFX version number
  version: number; // float version;

  // Number of hair strands in this file. All strands in this file are guide strands.
  // Follow hair strands are generated procedurally.
  numHairStrands: number; // unsigned int numHairStrands;

  // From 4 to 64 inclusive (POW2 only). This should be a fixed value within tfx value.
  // The total vertices from the tfx file is numHairStrands * numVerticesPerStrand.
  numVerticesPerStrand: number; // unsigned int numVerticesPerStrand;

  // Offsets to array data starts here. Offset values are in bytes, aligned on 8 bytes boundaries,
  // and relative to beginning of the .tfx file
  // ALL ARE UNSIGNED INTS!
  offsetVertexPosition: number;   // Array size: FLOAT4[numHairStrands]
  offsetStrandUV: number;         // Array size: FLOAT2[numHairStrands], if 0 no texture coordinates
  offsetVertexUV: number;         // Array size: FLOAT2[numHairStrands * numVerticesPerStrand], if 0, no per vertex texture coordinates
  offsetStrandThickness: number;  // Array size: float[numHairStrands]
  offsetVertexColor: number;      // Array size: FLOAT4[numHairStrands * numVerticesPerStrand], if 0, no vertex colors

  // unsigned int reserved[32];           // Reserved for future versions
}

export interface TfxFileData {
  header: TfxFileHeader;
  totalVertices: number;
  vertexPositionsBuffer: Float32Array;
}


const requestBinaryFile = async (path: string) => {
  const resp = await fetch(path);
  if (!resp.ok) {
    throw `Could not download tfx file '${path}'`;
  }
  return await resp.arrayBuffer();
};

const parseHeader = (rawData: ArrayBuffer): TfxFileHeader => {
  const version = new Float32Array(rawData, 0, 1)[0]; // offset 0bytes, read single float
  const uints = new Uint32Array(rawData, 4, 7); // offset 4bytes cause version is float, read 7 uint-values

  return {
    version,
    numHairStrands: uints[0],
    numVerticesPerStrand: uints[1],
    offsetVertexPosition: uints[2],
    offsetStrandUV: uints[3],
    offsetVertexUV: uints[4],
    offsetStrandThickness: uints[5],
    offsetVertexColor: uints[6],
  };
};


export const loadTfxFile = async (path: string): Promise<TfxFileData> => {
  const fileData = await requestBinaryFile(path);

  const header = parseHeader(fileData);
  console.log('Loaded Tfx file with header', header);

  const totalVertices = header.numHairStrands * header.numVerticesPerStrand;
  const positionsBuf = new Float32Array(fileData, header.offsetVertexPosition, totalVertices * 4);

  return {
    header,
    totalVertices,
    vertexPositionsBuffer: positionsBuf,
  };
};