function BillboardTexture(billboardCollection) {
  //>>includeStart('debug', pragmas.debug);
  Check.defined("billboardCollection", billboardCollection);
  //>>includeEnd('debug');

  this._billboardCollection = billboardCollection;

  this._id = undefined;
  this._loadState = BillboardLoadState.NONE;
  this._loadError = undefined;

  this._index = -1;
  this._width = undefined;
  this._height = undefined;

  this._hasSubregion = false;

  /**
   * Used by billboardCollection to track whcih billboards to update.
   * @type {boolean}
   * @private
   */
  this.dirty = false;
}
Tracks a reference to an image and it's loading state, as used in a BillboardCollection and stored in a texture atlas.
@constructor
@private
@see BillboardCollection
@see Billboard#image
@alias BillboardTexture
@param {BillboardCollection} billboardCollection The associated billboard collecion.