Cesium中的QuadtreeTile.js类

/**
 * A single tile in a {@link QuadtreePrimitive}.
 *
 * @alias QuadtreeTile
 * @constructor
 * @private
 *
 * @param {Number} options.level The level of the tile in the quadtree.
 * @param {Number} options.x The X coordinate of the tile in the quadtree.  0 is the westernmost tile.
 * @param {Number} options.y The Y coordinate of the tile in the quadtree.  0 is the northernmost tile.
 * @param {TilingScheme} options.tilingScheme The tiling scheme in which this tile exists.
 * @param {QuadtreeTile} [options.parent] This tile's parent, or undefined if this is a root tile.
 */

function QuadtreeTile(options) {
  //>>includeStart('debug', pragmas.debug);
  if (!defined(options)) {
    throw new DeveloperError("options is required.");
  }
  if (!defined(options.x)) {
    throw new DeveloperError("options.x is required.");
  } else if (!defined(options.y)) {
    throw new DeveloperError("options.y is required.");
  } else if (options.x < 0 || options.y < 0) {
    throw new DeveloperError(
      "options.x and options.y must be greater than or equal to zero."
    );
  }
  if (!defined(options.level)) {
    throw new DeveloperError(
      "options.level is required and must be greater than or equal to zero."
    );
  }
  if (!defined(options.tilingScheme)) {
    throw new DeveloperError("options.tilingScheme is required.");
  }
  //>>includeEnd('debug');

  this._tilingScheme = options.tilingScheme;
  this._x = options.x;
  this._y = options.y;
  this._level = options.level;
  this._parent = options.parent;
  this._rectangle = this._tilingScheme.tileXYToRectangle(
    this._x,
    this._y,
    this._level
  );

  this._southwestChild = undefined;
  this._southeastChild = undefined;
  this._northwestChild = undefined;
  this._northeastChild = undefined;

  // TileReplacementQueue gets/sets these private properties.
  this.replacementPrevious = undefined;
  this.replacementNext = undefined;

  // The distance from the camera to this tile, updated when the tile is selected
  // for rendering.  We can get rid of this if we have a better way to sort by
  // distance - for example, by using the natural ordering of a quadtree.
  // QuadtreePrimitive gets/sets this private property.
  this._distance = 0.0;
  this._loadPriority = 0.0;

  this._customData = [];
  this._frameUpdated = undefined;
  this._lastSelectionResult = TileSelectionResult.NONE;
  this._lastSelectionResultFrame = undefined;
  this._loadedCallbacks = {};

  /**
   * Gets or sets the current state of the tile in the tile load pipeline.
   * @type {QuadtreeTileLoadState}
   * @default {@link QuadtreeTileLoadState.START}
   */
  this.state = QuadtreeTileLoadState.START;

  /**
   * Gets or sets a value indicating whether or not the tile is currently renderable.
   * @type {Boolean}
   * @default false
   */
  this.renderable = false;

  /**
   * Gets or set a value indicating whether or not the tile was entirely upsampled from its
   * parent tile.  If all four children of a parent tile were upsampled from the parent,
   * we will render the parent instead of the children even if the LOD indicates that
   * the children would be preferable.
   * @type {Boolean}
   * @default false
   */
  this.upsampledFromParent = false;

  /**
   * Gets or sets the additional data associated with this tile.  The exact content is specific to the
   * {@link QuadtreeTileProvider}.
   * @type {Object}
   * @default undefined
   */
  this.data = undefined;
}