mdx-m3-viewer/src/common/bitstream.ts

A browser WebGL model viewer. Mainly focused on models of the games Warcraft 3 and Starcraft 2.

/**
 * A bit stream.
 */
export default class BitStream {
  buffer: ArrayBuffer;
  uint8array: Uint8Array;
  index: number = 0;
  byteLength: number;
  bitBuffer: number = 0;
  bits: number = 0;

  constructor(buffer: ArrayBuffer | TypedArray, byteOffset?: number, byteLength?: number) {
    // If given a view, use its properties.
    if (ArrayBuffer.isView(buffer)) {
      byteOffset = buffer.byteOffset;
      byteLength = buffer.byteLength;
      buffer = buffer.buffer;
    }

    if (!(buffer instanceof ArrayBuffer)) {
      throw new TypeError(`BitStream: expected ArrayBuffer or TypedArray, got ${buffer}`);
    }

    // For browsers not supporting the spec.
    // Once upon a time I reported this issue on the Firefox tracker.
    // Seems like Safari needs an issue report too.
    byteOffset = byteOffset || 0;
    byteLength = byteLength || buffer.byteLength;

    this.buffer = buffer;
    this.uint8array = new Uint8Array(buffer, byteOffset, byteLength);
    this.byteLength = buffer.byteLength;
  }

  /**
   * Peek a number of bits.
   */
  peekBits(bits: number) {
    this.loadBits(bits);

    return this.bitBuffer & ((1 << bits) - 1);
  }

  /**
   * Read a number of bits.
   */
  readBits(bits: number) {
    let data = this.peekBits(bits);

    this.bitBuffer >>>= bits;
    this.bits -= bits;

    return data;
  }

  /**
   * Skip a number of bits.
   */
  skipBits(bits: number) {
    this.loadBits(bits);

    this.bitBuffer >>>= bits;
    this.bits -= bits;
  }

  /**
   * Load more bits into the buffer.
   */
  loadBits(bits: number) {
    while (this.bits < bits) {
      this.bitBuffer += this.uint8array[this.index] << this.bits;
      this.bits += 8;
      this.index += 1;
    }
  }
}