text: /*global define*/
  define([
          '../Core/BoundingRectangle',
          '../Core/Cartesian2',
          '../Core/Cartesian3',
          '../Core/Color',
          '../Core/defaultValue',
          '../Core/defined',
          '../Core/defineProperties',
          '../Core/DeveloperError',
          '../Core/DistanceDisplayCondition',
          '../Core/NearFarScalar',
          './Billboard',
          './HeightReference',
          './HorizontalOrigin',
          './LabelStyle',
          './VerticalOrigin'
      ], function(
          BoundingRectangle,
          Cartesian2,
          Cartesian3,
          Color,
          defaultValue,
          defined,
          defineProperties,
          DeveloperError,
          DistanceDisplayCondition,
          NearFarScalar,
          Billboard,
          HeightReference,
          HorizontalOrigin,
          LabelStyle,
          VerticalOrigin) {
      'use strict';
  
      function rebindAllGlyphs(label) {
          if (!label._rebindAllGlyphs && !label._repositionAllGlyphs) {
              // only push label if it's not already been marked dirty
              label._labelCollection._labelsToUpdate.push(label);
          }
          label._rebindAllGlyphs = true;
      }
  
      function repositionAllGlyphs(label) {
          if (!label._rebindAllGlyphs && !label._repositionAllGlyphs) {
              // only push label if it's not already been marked dirty
              label._labelCollection._labelsToUpdate.push(label);
          }
          label._repositionAllGlyphs = true;
      }
  
      /**
       * A Label draws viewport-aligned text positioned in the 3D scene.  This constructor
       * should not be used directly, instead create labels by calling {@link LabelCollection#add}.
       *
       * @alias Label
       * @internalConstructor
       *
       * @exception {DeveloperError} translucencyByDistance.far must be greater than translucencyByDistance.near
       * @exception {DeveloperError} pixelOffsetScaleByDistance.far must be greater than pixelOffsetScaleByDistance.near
       * @exception {DeveloperError} distanceDisplayCondition.far must be greater than distanceDisplayCondition.near
       *
       * @see LabelCollection
       * @see LabelCollection#add
       *
       * @demo {@link http://cesiumjs.org/Cesium/Apps/Sandcastle/index.html?src=Labels.html|Cesium Sandcastle Labels Demo}
       */
      function Label(options, labelCollection) {
          options = defaultValue(options, defaultValue.EMPTY_OBJECT);
  
          //>>includeStart('debug', pragmas.debug);
          if (defined(options.translucencyByDistance) && options.translucencyByDistance.far <= options.translucencyByDistance.near) {
              throw new DeveloperError('translucencyByDistance.far must be greater than translucencyByDistance.near.');
          }
          if (defined(options.pixelOffsetScaleByDistance) && options.pixelOffsetScaleByDistance.far <= options.pixelOffsetScaleByDistance.near) {
              throw new DeveloperError('pixelOffsetScaleByDistance.far must be greater than pixelOffsetScaleByDistance.near.');
          }
          if (defined(options.distanceDisplayCondition) && options.distanceDisplayCondition.far <= options.distanceDisplayCondition.near) {
              throw new DeveloperError('distanceDisplayCondition.far must be greater than distanceDisplayCondition.near');
          }
          //>>includeEnd('debug');
  
          this._text = defaultValue(options.text, '');
          this._show = defaultValue(options.show, true);
          this._font = defaultValue(options.font, '30px sans-serif');
          this._fillColor = Color.clone(defaultValue(options.fillColor, Color.WHITE));
          this._outlineColor = Color.clone(defaultValue(options.outlineColor, Color.BLACK));
          this._outlineWidth = defaultValue(options.outlineWidth, 1.0);
          this._style = defaultValue(options.style, LabelStyle.FILL);
          this._verticalOrigin = defaultValue(options.verticalOrigin, VerticalOrigin.BOTTOM);
          this._horizontalOrigin = defaultValue(options.horizontalOrigin, HorizontalOrigin.LEFT);
          this._pixelOffset = Cartesian2.clone(defaultValue(options.pixelOffset, Cartesian2.ZERO));
          this._eyeOffset = Cartesian3.clone(defaultValue(options.eyeOffset, Cartesian3.ZERO));
          this._position = Cartesian3.clone(defaultValue(options.position, Cartesian3.ZERO));
          this._scale = defaultValue(options.scale, 1.0);
          this._id = options.id;
          this._translucencyByDistance = options.translucencyByDistance;
          this._pixelOffsetScaleByDistance = options.pixelOffsetScaleByDistance;
          this._heightReference = defaultValue(options.heightReference, HeightReference.NONE);
          this._distanceDisplayCondition = options.distanceDisplayCondition;
  
          this._labelCollection = labelCollection;
          this._glyphs = [];
  
          this._rebindAllGlyphs = true;
          this._repositionAllGlyphs = true;
  
          this._actualClampedPosition = undefined;
          this._removeCallbackFunc = undefined;
          this._mode = undefined;
  
          this._clusterShow = true;
  
          this._updateClamping();
      }
  
      defineProperties(Label.prototype, {
          /**
           * Determines if this label will be shown.  Use this to hide or show a label, instead
           * of removing it and re-adding it to the collection.
           * @memberof Label.prototype
           * @type {Boolean}
           */
          show : {
              get : function() {
                  return this._show;
              },
              set : function(value) {
                  //>>includeStart('debug', pragmas.debug);
                  if (!defined(value)) {
                      throw new DeveloperError('value is required.');
                  }
                  //>>includeEnd('debug');
  
                  if (this._show !== value) {
                      this._show = value;
  
                      var glyphs = this._glyphs;
                      for (var i = 0, len = glyphs.length; i < len; i++) {
                          var billboard = glyphs[i].billboard;
                          if (defined(billboard)) {
                              billboard.show = value;
                          }
                      }
                  }
              }
          },
  
          /**
           * Gets or sets the Cartesian position of this label.
           * @memberof Label.prototype
           * @type {Cartesian3}
           */
          position : {
              get : function() {
                  return this._position;
              },
              set : function(value) {
                  //>>includeStart('debug', pragmas.debug);
                  if (!defined(value)) {
                      throw new DeveloperError('value is required.');
                  }
                  //>>includeEnd('debug');
  
                  var position = this._position;
                  if (!Cartesian3.equals(position, value)) {
                      Cartesian3.clone(value, position);
  
                      var glyphs = this._glyphs;
                      for (var i = 0, len = glyphs.length; i < len; i++) {
                          var billboard = glyphs[i].billboard;
                          if (defined(billboard)) {
                              billboard.position = value;
                          }
                      }
  
                      if (this._heightReference !== HeightReference.NONE) {
                          this._updateClamping();
                      }
                  }
              }
          },
  
          /**
           * Gets or sets the height reference of this billboard.
           * @memberof Label.prototype
           * @type {HeightReference}
           */
          heightReference : {
              get : function() {
                  return this._heightReference;
              },
              set : function(value) {
                  //>>includeStart('debug', pragmas.debug);
                  if (!defined(value)) {
                      throw new DeveloperError('value is required.');
                  }
                  //>>includeEnd('debug');
  
                  if (value !== this._heightReference) {
                      this._heightReference = value;
  
                      var glyphs = this._glyphs;
                      for (var i = 0, len = glyphs.length; i < len; i++) {
                          var billboard = glyphs[i].billboard;
                          if (defined(billboard)) {
                              billboard.heightReference = value;
                          }
                      }
  
                      repositionAllGlyphs(this);
  
                      this._updateClamping();
                  }
              }
          },
  
          /**
           * Gets or sets the text of this label.
           * @memberof Label.prototype
           * @type {String}
           */
          text : {
              get : function() {
                  return this._text;
              },
              set : function(value) {
                  //>>includeStart('debug', pragmas.debug);
                  if (!defined(value)) {
                      throw new DeveloperError('value is required.');
                  }
                  //>>includeEnd('debug');
  
                  if (this._text !== value) {
                      this._text = value;
                      rebindAllGlyphs(this);
                  }
              }
          },
  
          /**
           * Gets or sets the font used to draw this label. Fonts are specified using the same syntax as the CSS 'font' property.
           * @memberof Label.prototype
           * @type {String}
           * @see {@link http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#text-styles|HTML canvas 2D context text styles}
           */
          font : {
              get : function() {
                  return this._font;
              },
              set : function(value) {
                  //>>includeStart('debug', pragmas.debug);
                  if (!defined(value)) {
                      throw new DeveloperError('value is required.');
                  }
                  //>>includeEnd('debug');
  
                  if (this._font !== value) {
                      this._font = value;
                      rebindAllGlyphs(this);
                  }
              }
          },
  
          /**
           * Gets or sets the fill color of this label.
           * @memberof Label.prototype
           * @type {Color}
           * @see {@link http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#fill-and-stroke-styles|HTML canvas 2D context fill and stroke styles}
           */
          fillColor : {
              get : function() {
                  return this._fillColor;
              },
              set : function(value) {
                  //>>includeStart('debug', pragmas.debug);
                  if (!defined(value)) {
                      throw new DeveloperError('value is required.');
                  }
                  //>>includeEnd('debug');
  
                  var fillColor = this._fillColor;
                  if (!Color.equals(fillColor, value)) {
                      Color.clone(value, fillColor);
                      rebindAllGlyphs(this);
                  }
              }
          },
  
          /**
           * Gets or sets the outline color of this label.
           * @memberof Label.prototype
           * @type {Color}
           * @see {@link http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#fill-and-stroke-styles|HTML canvas 2D context fill and stroke styles}
           */
          outlineColor : {
              get : function() {
                  return this._outlineColor;
              },
              set : function(value) {
                  //>>includeStart('debug', pragmas.debug);
                  if (!defined(value)) {
                      throw new DeveloperError('value is required.');
                  }
                  //>>includeEnd('debug');
  
                  var outlineColor = this._outlineColor;
                  if (!Color.equals(outlineColor, value)) {
                      Color.clone(value, outlineColor);
                      rebindAllGlyphs(this);
                  }
              }
          },
  
          /**
           * Gets or sets the outline width of this label.
           * @memberof Label.prototype
           * @type {Number}
           * @see {@link http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#fill-and-stroke-styles|HTML canvas 2D context fill and stroke styles}
           */
          outlineWidth : {
              get : function() {
                  return this._outlineWidth;
              },
              set : function(value) {
                  //>>includeStart('debug', pragmas.debug);
                  if (!defined(value)) {
                      throw new DeveloperError('value is required.');
                  }
                  //>>includeEnd('debug');
  
                  if (this._outlineWidth !== value) {
                      this._outlineWidth = value;
                      rebindAllGlyphs(this);
                  }
              }
          },
  
          /**
           * Gets or sets the style of this label.
           * @memberof Label.prototype
           * @type {LabelStyle}
           */
          style : {
              get : function() {
                  return this._style;
              },
              set : function(value) {
                  //>>includeStart('debug', pragmas.debug);
                  if (!defined(value)) {
                      throw new DeveloperError('value is required.');
                  }
                  //>>includeEnd('debug');
  
                  if (this._style !== value) {
                      this._style = value;
                      rebindAllGlyphs(this);
                  }
              }
          },
  
          /**
           * Gets or sets the pixel offset in screen space from the origin of this label.  This is commonly used
           * to align multiple labels and billboards at the same position, e.g., an image and text.  The
           * screen space origin is the top, left corner of the canvas; <code>x</code> increases from
           * left to right, and <code>y</code> increases from top to bottom.
           * <br /><br />
           * <div align='center'>
           * <table border='0' cellpadding='5'><tr>
           * <td align='center'><code>default</code><br/><img src='images/Label.setPixelOffset.default.png' width='250' height='188' /></td>
           * <td align='center'><code>l.pixeloffset = new Cartesian2(25, 75);</code><br/><img src='images/Label.setPixelOffset.x50y-25.png' width='250' height='188' /></td>
           * </tr></table>
           * The label's origin is indicated by the yellow point.
           * </div>
           * @memberof Label.prototype
           * @type {Cartesian2}
           */
          pixelOffset : {
              get : function() {
                  return this._pixelOffset;
              },
              set : function(value) {
                  //>>includeStart('debug', pragmas.debug);
                  if (!defined(value)) {
                      throw new DeveloperError('value is required.');
                  }
                  //>>includeEnd('debug');
  
                  var pixelOffset = this._pixelOffset;
                  if (!Cartesian2.equals(pixelOffset, value)) {
                      Cartesian2.clone(value, pixelOffset);
  
                      var glyphs = this._glyphs;
                      for (var i = 0, len = glyphs.length; i < len; i++) {
                          var glyph = glyphs[i];
                          if (defined(glyph.billboard)) {
                              glyph.billboard.pixelOffset = value;
                          }
                      }
                  }
              }
          },
  
          /**
           * Gets or sets near and far translucency properties of a Label based on the Label's distance from the camera.
           * A label's translucency will interpolate between the {@link NearFarScalar#nearValue} and
           * {@link NearFarScalar#farValue} while the camera distance falls within the upper and lower bounds
           * of the specified {@link NearFarScalar#near} and {@link NearFarScalar#far}.
           * Outside of these ranges the label's translucency remains clamped to the nearest bound.  If undefined,
           * translucencyByDistance will be disabled.
           * @memberof Label.prototype
           * @type {NearFarScalar}
           *
           * @example
           * // Example 1.
           * // Set a label's translucencyByDistance to 1.0 when the
           * // camera is 1500 meters from the label and disappear as
           * // the camera distance approaches 8.0e6 meters.
           * text.translucencyByDistance = new Cesium.NearFarScalar(1.5e2, 1.0, 8.0e6, 0.0);
           *
           * @example
           * // Example 2.
           * // disable translucency by distance
           * text.translucencyByDistance = undefined;
           */
          translucencyByDistance : {
              get : function() {
                  return this._translucencyByDistance;
              },
              set : function(value) {
                  //>>includeStart('debug', pragmas.debug);
                  if (defined(value) && value.far <= value.near) {
                      throw new DeveloperError('far distance must be greater than near distance.');
                  }
                  //>>includeEnd('debug');
  
                  var translucencyByDistance = this._translucencyByDistance;
                  if (!NearFarScalar.equals(translucencyByDistance, value)) {
                      this._translucencyByDistance = NearFarScalar.clone(value, translucencyByDistance);
  
                      var glyphs = this._glyphs;
                      for (var i = 0, len = glyphs.length; i < len; i++) {
                          var glyph = glyphs[i];
                          if (defined(glyph.billboard)) {
                              glyph.billboard.translucencyByDistance = value;
                          }
                      }
                  }
              }
          },
  
          /**
           * Gets or sets near and far pixel offset scaling properties of a Label based on the Label's distance from the camera.
           * A label's pixel offset will be scaled between the {@link NearFarScalar#nearValue} and
           * {@link NearFarScalar#farValue} while the camera distance falls within the upper and lower bounds
           * of the specified {@link NearFarScalar#near} and {@link NearFarScalar#far}.
           * Outside of these ranges the label's pixel offset scaling remains clamped to the nearest bound.  If undefined,
           * pixelOffsetScaleByDistance will be disabled.
           * @memberof Label.prototype
           * @type {NearFarScalar}
           *
           * @example
           * // Example 1.
           * // Set a label's pixel offset scale to 0.0 when the
           * // camera is 1500 meters from the label and scale pixel offset to 10.0 pixels
           * // in the y direction the camera distance approaches 8.0e6 meters.
           * text.pixelOffset = new Cesium.Cartesian2(0.0, 1.0);
           * text.pixelOffsetScaleByDistance = new Cesium.NearFarScalar(1.5e2, 0.0, 8.0e6, 10.0);
           *
           * @example
           * // Example 2.
           * // disable pixel offset by distance
           * text.pixelOffsetScaleByDistance = undefined;
           */
          pixelOffsetScaleByDistance : {
              get : function() {
                  return this._pixelOffsetScaleByDistance;
              },
              set : function(value) {
                  //>>includeStart('debug', pragmas.debug);
                  if (defined(value) && value.far <= value.near) {
                      throw new DeveloperError('far distance must be greater than near distance.');
                  }
                  //>>includeEnd('debug');
  
                  var pixelOffsetScaleByDistance = this._pixelOffsetScaleByDistance;
                  if (!NearFarScalar.equals(pixelOffsetScaleByDistance, value)) {
                      this._pixelOffsetScaleByDistance = NearFarScalar.clone(value, pixelOffsetScaleByDistance);
  
                      var glyphs = this._glyphs;
                      for (var i = 0, len = glyphs.length; i < len; i++) {
                          var glyph = glyphs[i];
                          if (defined(glyph.billboard)) {
                              glyph.billboard.pixelOffsetScaleByDistance = value;
                          }
                      }
                  }
              }
          },
  
          /**
           * Gets and sets the 3D Cartesian offset applied to this label in eye coordinates.  Eye coordinates is a left-handed
           * coordinate system, where <code>x</code> points towards the viewer's right, <code>y</code> points up, and
           * <code>z</code> points into the screen.  Eye coordinates use the same scale as world and model coordinates,
           * which is typically meters.
           * <br /><br />
           * An eye offset is commonly used to arrange multiple label or objects at the same position, e.g., to
           * arrange a label above its corresponding 3D model.
           * <br /><br />
           * Below, the label is positioned at the center of the Earth but an eye offset makes it always
           * appear on top of the Earth regardless of the viewer's or Earth's orientation.
           * <br /><br />
           * <div align='center'>
           * <table border='0' cellpadding='5'><tr>
           * <td align='center'><img src='images/Billboard.setEyeOffset.one.png' width='250' height='188' /></td>
           * <td align='center'><img src='images/Billboard.setEyeOffset.two.png' width='250' height='188' /></td>
           * </tr></table>
           * <code>l.eyeOffset = new Cartesian3(0.0, 8000000.0, 0.0);</code><br /><br />
           * </div>
           * @memberof Label.prototype
           * @type {Cartesian3}
           */
          eyeOffset : {
              get : function() {
                  return this._eyeOffset;
              },
              set : function(value) {
                  //>>includeStart('debug', pragmas.debug);
                  if (!defined(value)) {
                      throw new DeveloperError('value is required.');
                  }
                  //>>includeEnd('debug');
  
                  var eyeOffset = this._eyeOffset;
                  if (!Cartesian3.equals(eyeOffset, value)) {
                      Cartesian3.clone(value, eyeOffset);
  
                      var glyphs = this._glyphs;
                      for (var i = 0, len = glyphs.length; i < len; i++) {
                          var glyph = glyphs[i];
                          if (defined(glyph.billboard)) {
                              glyph.billboard.eyeOffset = value;
                          }
                      }
                  }
              }
          },
  
          /**
           * Gets or sets the horizontal origin of this label, which determines if the label is drawn
           * to the left, center, or right of its position.
           * <br /><br />
           * <div align='center'>
           * <img src='images/Billboard.setHorizontalOrigin.png' width='400' height='300' /><br />
           * </div>
           * @memberof Label.prototype
           * @type {HorizontalOrigin}
           * @example
           * // Use a top, right origin
           * l.horizontalOrigin = Cesium.HorizontalOrigin.RIGHT;
           * l.verticalOrigin = Cesium.VerticalOrigin.TOP;
           */
          horizontalOrigin : {
              get : function() {
                  return this._horizontalOrigin;
              },
              set : function(value) {
                  //>>includeStart('debug', pragmas.debug);
                  if (!defined(value)) {
                      throw new DeveloperError('value is required.');
                  }
                  //>>includeEnd('debug');
  
                  if (this._horizontalOrigin !== value) {
                      this._horizontalOrigin = value;
                      repositionAllGlyphs(this);
                  }
              }
          },
  
          /**
           * Gets or sets the vertical origin of this label, which determines if the label is
           * to the above, below, or at the center of its position.
           * <br /><br />
           * <div align='center'>
           * <img src='images/Billboard.setVerticalOrigin.png' width='400' height='300' /><br />
           * </div>
           * @memberof Label.prototype
           * @type {VerticalOrigin}
           * @example
           * // Use a top, right origin
           * l.horizontalOrigin = Cesium.HorizontalOrigin.RIGHT;
           * l.verticalOrigin = Cesium.VerticalOrigin.TOP;
           */
          verticalOrigin : {
              get : function() {
                  return this._verticalOrigin;
              },
              set : function(value) {
                  //>>includeStart('debug', pragmas.debug);
                  if (!defined(value)) {
                      throw new DeveloperError('value is required.');
                  }
                  //>>includeEnd('debug');
  
                  if (this._verticalOrigin !== value) {
                      this._verticalOrigin = value;
  
                      var glyphs = this._glyphs;
                      for (var i = 0, len = glyphs.length; i < len; i++) {
                          var glyph = glyphs[i];
                          if (defined(glyph.billboard)) {
                              glyph.billboard.verticalOrigin = value;
                          }
                      }
  
                      repositionAllGlyphs(this);
                  }
              }
          },
  
          /**
           * Gets or sets the uniform scale that is multiplied with the label's size in pixels.
           * A scale of <code>1.0</code> does not change the size of the label; a scale greater than
           * <code>1.0</code> enlarges the label; a positive scale less than <code>1.0</code> shrinks
           * the label.
           * <br /><br />
           * Applying a large scale value may pixelate the label.  To make text larger without pixelation,
           * use a larger font size when calling {@link Label#font} instead.
           * <br /><br />
           * <div align='center'>
           * <img src='images/Label.setScale.png' width='400' height='300' /><br/>
           * From left to right in the above image, the scales are <code>0.5</code>, <code>1.0</code>,
           * and <code>2.0</code>.
           * </div>
           * @memberof Label.prototype
           * @type {Number}
           */
          scale : {
              get : function() {
                  return this._scale;
              },
              set : function(value) {
                  //>>includeStart('debug', pragmas.debug);
                  if (!defined(value)) {
                      throw new DeveloperError('value is required.');
                  }
                  //>>includeEnd('debug');
  
                  if (this._scale !== value) {
                      this._scale = value;
  
                      var glyphs = this._glyphs;
                      for (var i = 0, len = glyphs.length; i < len; i++) {
                          var glyph = glyphs[i];
                          if (defined(glyph.billboard)) {
                              glyph.billboard.scale = value;
                          }
                      }
  
                      repositionAllGlyphs(this);
                  }
              }
          },
  
          /**
           * Gets or sets the condition specifying at what distance from the camera that this label will be displayed.
           * @memberof Label.prototype
           * @type {DistanceDisplayCondition}
           * @default undefined
           */
          distanceDisplayCondition : {
              get : function() {
                  return this._distanceDisplayCondition;
              },
              set : function(value) {
                  //>>includeStart('debug', pragmas.debug);
                  if (defined(value) && value.far <= value.near) {
                      throw new DeveloperError('far must be greater than near');
                  }
                  //>>includeEnd('debug');
                  if (!DistanceDisplayCondition.equals(value, this._distanceDisplayCondition)) {
                      this._distanceDisplayCondition = DistanceDisplayCondition.clone(value, this._distanceDisplayCondition);
  
                      var glyphs = this._glyphs;
                      for (var i = 0, len = glyphs.length; i < len; i++) {
                          var glyph = glyphs[i];
                          if (defined(glyph.billboard)) {
                              glyph.billboard.distanceDisplayCondition = value;
                          }
                      }
                  }
              }
          },
  
          /**
           * Gets or sets the user-defined object returned when the label is picked.
           * @memberof Label.prototype
           * @type {Object}
           */
          id : {
              get : function() {
                  return this._id;
              },
              set : function(value) {
                  if (this._id !== value) {
                      this._id = value;
  
                      var glyphs = this._glyphs;
                      for (var i = 0, len = glyphs.length; i < len; i++) {
                          var glyph = glyphs[i];
                          if (defined(glyph.billboard)) {
                              glyph.billboard.id = value;
                          }
                      }
                  }
              }
          },
  
          /**
           * Keeps track of the position of the label based on the height reference.
           * @memberof Label.prototype
           * @type {Cartesian3}
           * @private
           */
          _clampedPosition : {
              get : function() {
                  return this._actualClampedPosition;
              },
              set : function(value) {
                  this._actualClampedPosition = Cartesian3.clone(value, this._actualClampedPosition);
  
                  var glyphs = this._glyphs;
                  for (var i = 0, len = glyphs.length; i < len; i++) {
                      var glyph = glyphs[i];
                      if (defined(glyph.billboard)) {
                          // Set all the private values here, because we already clamped to ground
                          //  so we don't want to do it again for every glyph
  
                          glyph.billboard._clampedPosition = value;
  
                          value = defaultValue(value, this._position);
                          Cartesian3.clone(value, glyph.billboard._position);
                          Cartesian3.clone(value, glyph.billboard._actualPosition);
                      }
                  }
              }
          },
  
          /**
           * Determines whether or not this label will be shown or hidden because it was clustered.
           * @memberof Label.prototype
           * @type {Boolean}
           * @private
           */
          clusterShow : {
              get : function() {
                  return this._clusterShow;
              },
              set : function(value) {
                  if (this._clusterShow !== value) {
                      this._clusterShow = value;
  
                      var glyphs = this._glyphs;
                      for (var i = 0, len = glyphs.length; i < len; i++) {
                          var glyph = glyphs[i];
                          if (defined(glyph.billboard)) {
                              // Set all the private values here, because we already clamped to ground
                              //  so we don't want to do it again for every glyph
                              glyph.billboard.clusterShow = value;
                          }
                      }
                  }
              }
          }
      });
  
      Label.prototype._updateClamping = function() {
          Billboard._updateClamping(this._labelCollection, this);
      };
  
      /**
       * Computes the screen-space position of the label's origin, taking into account eye and pixel offsets.
       * The screen space origin is the top, left corner of the canvas; <code>x</code> increases from
       * left to right, and <code>y</code> increases from top to bottom.
       *
       * @param {Scene} scene The scene the label is in.
       * @param {Cartesian2} [result] The object onto which to store the result.
       * @returns {Cartesian2} The screen-space position of the label.
       *
       *
       * @example
       * console.log(l.computeScreenSpacePosition(scene).toString());
       *
       * @see Label#eyeOffset
       * @see Label#pixelOffset
       */
      Label.prototype.computeScreenSpacePosition = function(scene, result) {
          //>>includeStart('debug', pragmas.debug);
          if (!defined(scene)) {
              throw new DeveloperError('scene is required.');
          }
          //>>includeEnd('debug');
  
          if (!defined(result)) {
              result = new Cartesian2();
          }
  
          var labelCollection = this._labelCollection;
          var modelMatrix = labelCollection.modelMatrix;
          var actualPosition = defined(this._actualClampedPosition) ? this._actualClampedPosition : this._position;
  
          var windowCoordinates = Billboard._computeScreenSpacePosition(modelMatrix, actualPosition,
                  this._eyeOffset, this._pixelOffset, scene, result);
          return windowCoordinates;
      };
  
      /**
       * Gets a label's screen space bounding box centered around screenSpacePosition.
       * @param {Label} label The label to get the screen space bounding box for.
       * @param {Cartesian2} screenSpacePosition The screen space center of the label.
       * @param {BoundingRectangle} [result] The object onto which to store the result.
       * @returns {BoundingRectangle} The screen space bounding box.
       *
       * @private
       */
      Label.getScreenSpaceBoundingBox = function(label, screenSpacePosition, result) {
          var width = 0;
          var height = 0;
  
          var glyphs = label._glyphs;
          var length = glyphs.length;
          for (var i = 0; i < length; ++i) {
              var glyph = glyphs[i];
              var billboard = glyph.billboard;
              if (!defined(billboard)) {
                  continue;
              }
  
              width += billboard.width;
              height = Math.max(height, billboard.height);
          }
  
          var scale = label.scale;
          width *= scale;
          height *= scale;
  
          var x = screenSpacePosition.x;
          if (label.horizontalOrigin === HorizontalOrigin.RIGHT) {
              x -= width;
          } else if (label.horizontalOrigin === HorizontalOrigin.CENTER) {
              x -= width * 0.5;
          }
  
          var y = screenSpacePosition.y;
          if (label.verticalOrigin === VerticalOrigin.TOP) {
              y -= height;
          } else if (label.verticalOrigin === VerticalOrigin.CENTER) {
              y -= height * 0.5;
          }
  
          if (!defined(result)) {
              result = new BoundingRectangle();
          }
  
          result.x = x;
          result.y = y;
          result.width = width;
          result.height = height;
  
          return result;
      };
  
      /**
       * Determines if this label equals another label.  Labels are equal if all their properties
       * are equal.  Labels in different collections can be equal.
       *
       * @param {Label} other The label to compare for equality.
       * @returns {Boolean} <code>true</code> if the labels are equal; otherwise, <code>false</code>.
       */
      Label.prototype.equals = function(other) {
          return this === other ||
                 defined(other) &&
                 this._show === other._show &&
                 this._scale === other._scale &&
                 this._style === other._style &&
                 this._verticalOrigin === other._verticalOrigin &&
                 this._horizontalOrigin === other._horizontalOrigin &&
                 this._heightReference === other._heightReference &&
                 this._text === other._text &&
                 this._font === other._font &&
                 Cartesian3.equals(this._position, other._position) &&
                 Color.equals(this._fillColor, other._fillColor) &&
                 Color.equals(this._outlineColor, other._outlineColor) &&
                 Cartesian2.equals(this._pixelOffset, other._pixelOffset) &&
                 Cartesian3.equals(this._eyeOffset, other._eyeOffset) &&
                 NearFarScalar.equals(this._translucencyByDistance, other._translucencyByDistance) &&
                 NearFarScalar.equals(this._pixelOffsetScaleByDistance, other._pixelOffsetScaleByDistance) &&
                 DistanceDisplayCondition.equals(this._distanceDisplayCondition, other._distanceDisplayCondition) &&
                 this._id === other._id;
      };
  
      /**
       * Returns true if this object was destroyed; otherwise, false.
       * <br /><br />
       * If this object was destroyed, it should not be used; calling any function other than
       * <code>isDestroyed</code> will result in a {@link DeveloperError} exception.
       *
       * @returns {Boolean} True if this object was destroyed; otherwise, false.
       */
      Label.prototype.isDestroyed = function() {
          return false;
      };
  
      return Label;
  });
  