text: define([
          '../Core/AssociativeArray',
          '../Core/Cartesian3',
          '../Core/Color',
          '../Core/defined',
          '../Core/destroyObject',
          '../Core/DeveloperError',
          '../Core/DistanceDisplayCondition',
          '../Core/NearFarScalar',
          '../Scene/createBillboardPointCallback',
          '../Scene/HeightReference',
          './BoundingSphereState',
          './Property'
      ], function(
          AssociativeArray,
          Cartesian3,
          Color,
          defined,
          destroyObject,
          DeveloperError,
          DistanceDisplayCondition,
          NearFarScalar,
          createBillboardPointCallback,
          HeightReference,
          BoundingSphereState,
          Property) {
      'use strict';
  
      var defaultColor = Color.WHITE;
      var defaultOutlineColor = Color.BLACK;
      var defaultOutlineWidth = 0.0;
      var defaultPixelSize = 1.0;
      var defaultDisableDepthTestDistance = 0.0;
  
      var colorScratch = new Color();
      var positionScratch = new Cartesian3();
      var outlineColorScratch = new Color();
      var scaleByDistanceScratch = new NearFarScalar();
      var translucencyByDistanceScratch = new NearFarScalar();
      var distanceDisplayConditionScratch = new DistanceDisplayCondition();
  
      function EntityData(entity) {
          this.entity = entity;
          this.pointPrimitive = undefined;
          this.billboard = undefined;
          this.color = undefined;
          this.outlineColor = undefined;
          this.pixelSize = undefined;
          this.outlineWidth = undefined;
      }
  
      /**
       * A {@link Visualizer} which maps {@link Entity#point} to a {@link PointPrimitive}.
       * @alias PointVisualizer
       * @constructor
       *
       * @param {EntityCluster} entityCluster The entity cluster to manage the collection of billboards and optionally cluster with other entities.
       * @param {EntityCollection} entityCollection The entityCollection to visualize.
       */
      function PointVisualizer(entityCluster, entityCollection) {
          //>>includeStart('debug', pragmas.debug);
          if (!defined(entityCluster)) {
              throw new DeveloperError('entityCluster is required.');
          }
          if (!defined(entityCollection)) {
              throw new DeveloperError('entityCollection is required.');
          }
          //>>includeEnd('debug');
  
          entityCollection.collectionChanged.addEventListener(PointVisualizer.prototype._onCollectionChanged, this);
  
          this._cluster = entityCluster;
          this._entityCollection = entityCollection;
          this._items = new AssociativeArray();
          this._onCollectionChanged(entityCollection, entityCollection.values, [], []);
      }
  
      /**
       * Updates the primitives created by this visualizer to match their
       * Entity counterpart at the given time.
       *
       * @param {JulianDate} time The time to update to.
       * @returns {Boolean} This function always returns true.
       */
      PointVisualizer.prototype.update = function(time) {
          //>>includeStart('debug', pragmas.debug);
          if (!defined(time)) {
              throw new DeveloperError('time is required.');
          }
          //>>includeEnd('debug');
  
          var items = this._items.values;
          var cluster = this._cluster;
          for (var i = 0, len = items.length; i < len; i++) {
              var item = items[i];
              var entity = item.entity;
              var pointGraphics = entity._point;
              var pointPrimitive = item.pointPrimitive;
              var billboard = item.billboard;
              var heightReference = Property.getValueOrDefault(pointGraphics._heightReference, time, HeightReference.NONE);
              var show = entity.isShowing && entity.isAvailable(time) && Property.getValueOrDefault(pointGraphics._show, time, true);
              var allowPicking = entity.allowPicking;
              var position;
              if (show) {
                  position = Property.getValueOrUndefined(entity._position, time, positionScratch);
                  show = defined(position);
              }
              if (!show) {
                  returnPrimitive(item, entity, cluster);
                  continue;
              }
  
              if (!Property.isConstant(entity._position)) {
                  cluster._clusterDirty = true;
              }
  
              var needsRedraw = false;
              var updateClamping = false;
              if ((heightReference !== HeightReference.NONE) && !defined(billboard)) {
                  if (defined(pointPrimitive)) {
                      returnPrimitive(item, entity, cluster);
                      pointPrimitive = undefined;
                  }
  
                  billboard = cluster.getBillboard(entity);
                  billboard.id = entity;
                  billboard.image = undefined;
                  item.billboard = billboard;
                  needsRedraw = true;
  
                  // If this new billboard happens to have a position and height reference that match our new values,
                  // billboard._updateClamping will not be called automatically. That's a problem because the clamped
                  // height may be based on different terrain than is now loaded. So we'll manually call
                  // _updateClamping below.
                  updateClamping = Cartesian3.equals(billboard.position, position) && billboard.heightReference === heightReference;
              } else if ((heightReference === HeightReference.NONE) && !defined(pointPrimitive)) {
                  if (defined(billboard)) {
                      returnPrimitive(item, entity, cluster);
                      billboard = undefined;
                  }
  
                  pointPrimitive = cluster.getPoint(entity);
                  pointPrimitive.id = entity;
                  item.pointPrimitive = pointPrimitive;
              }
  
              if (defined(pointPrimitive)) {
                  pointPrimitive.show = true;
                  pointPrimitive.position = position;
                  pointPrimitive.scaleByDistance = Property.getValueOrUndefined(pointGraphics._scaleByDistance, time, scaleByDistanceScratch);
                  pointPrimitive.translucencyByDistance = Property.getValueOrUndefined(pointGraphics._translucencyByDistance, time, translucencyByDistanceScratch);
                  pointPrimitive.color = Property.getValueOrDefault(pointGraphics._color, time, defaultColor, colorScratch);
                  pointPrimitive.outlineColor = Property.getValueOrDefault(pointGraphics._outlineColor, time, defaultOutlineColor, outlineColorScratch);
                  pointPrimitive.outlineWidth = Property.getValueOrDefault(pointGraphics._outlineWidth, time, defaultOutlineWidth);
                  pointPrimitive.pixelSize = Property.getValueOrDefault(pointGraphics._pixelSize, time, defaultPixelSize);
                  pointPrimitive.distanceDisplayCondition = Property.getValueOrUndefined(pointGraphics._distanceDisplayCondition, time, distanceDisplayConditionScratch);
                  pointPrimitive.disableDepthTestDistance = Property.getValueOrDefault(pointGraphics._disableDepthTestDistance, time, defaultDisableDepthTestDistance);
                  pointPrimitive.allowPicking = allowPicking;
              } else if (defined(billboard)) {
                  billboard.show = true;
                  billboard.position = position;
                  billboard.scaleByDistance = Property.getValueOrUndefined(pointGraphics._scaleByDistance, time, scaleByDistanceScratch);
                  billboard.translucencyByDistance = Property.getValueOrUndefined(pointGraphics._translucencyByDistance, time, translucencyByDistanceScratch);
                  billboard.distanceDisplayCondition = Property.getValueOrUndefined(pointGraphics._distanceDisplayCondition, time, distanceDisplayConditionScratch);
                  billboard.disableDepthTestDistance = Property.getValueOrDefault(pointGraphics._disableDepthTestDistance, time, defaultDisableDepthTestDistance);
                  billboard.heightReference = heightReference;
                  billboard.allowPicking = allowPicking;
  
                  var newColor = Property.getValueOrDefault(pointGraphics._color, time, defaultColor, colorScratch);
                  var newOutlineColor = Property.getValueOrDefault(pointGraphics._outlineColor, time, defaultOutlineColor, outlineColorScratch);
                  var newOutlineWidth = Math.round(Property.getValueOrDefault(pointGraphics._outlineWidth, time, defaultOutlineWidth));
                  var newPixelSize = Math.max(1, Math.round(Property.getValueOrDefault(pointGraphics._pixelSize, time, defaultPixelSize)));
  
                  if (newOutlineWidth > 0) {
                      billboard.scale = 1.0;
                      needsRedraw = needsRedraw || //
                                   newOutlineWidth !== item.outlineWidth || //
                                   newPixelSize !== item.pixelSize || //
                                   !Color.equals(newColor, item.color) || //
                                   !Color.equals(newOutlineColor, item.outlineColor);
                  } else {
                      billboard.scale = newPixelSize / 50.0;
                      newPixelSize = 50.0;
                      needsRedraw = needsRedraw || //
                                   newOutlineWidth !== item.outlineWidth || //
                                   !Color.equals(newColor, item.color) || //
                                   !Color.equals(newOutlineColor, item.outlineColor);
                  }
  
                  if (needsRedraw) {
                      item.color = Color.clone(newColor, item.color);
                      item.outlineColor = Color.clone(newOutlineColor, item.outlineColor);
                      item.pixelSize = newPixelSize;
                      item.outlineWidth = newOutlineWidth;
  
                      var centerAlpha = newColor.alpha;
                      var cssColor = newColor.toCssColorString();
                      var cssOutlineColor = newOutlineColor.toCssColorString();
                      var textureId = JSON.stringify([cssColor, newPixelSize, cssOutlineColor, newOutlineWidth]);
  
                      billboard.setImage(textureId, createBillboardPointCallback(centerAlpha, cssColor, cssOutlineColor, newOutlineWidth, newPixelSize));
                  }
  
                  if (updateClamping) {
                      billboard._updateClamping();
                  }
              }
          }
          return true;
      };
  
      /**
       * Computes a bounding sphere which encloses the visualization produced for the specified entity.
       * The bounding sphere is in the fixed frame of the scene's globe.
       *
       * @param {Entity} entity The entity whose bounding sphere to compute.
       * @param {BoundingSphere} result The bounding sphere onto which to store the result.
       * @returns {BoundingSphereState} BoundingSphereState.DONE if the result contains the bounding sphere,
       *                       BoundingSphereState.PENDING if the result is still being computed, or
       *                       BoundingSphereState.FAILED if the entity has no visualization in the current scene.
       * @private
       */
      PointVisualizer.prototype.getBoundingSphere = function(entity, result) {
          //>>includeStart('debug', pragmas.debug);
          if (!defined(entity)) {
              throw new DeveloperError('entity is required.');
          }
          if (!defined(result)) {
              throw new DeveloperError('result is required.');
          }
          //>>includeEnd('debug');
  
          var item = this._items.get(entity.id);
          if (!defined(item) || !(defined(item.pointPrimitive) || defined(item.billboard))) {
              return BoundingSphereState.FAILED;
          }
  
          if (defined(item.pointPrimitive)) {
              result.center = Cartesian3.clone(item.pointPrimitive.position, result.center);
          } else {
              var billboard = item.billboard;
              if (!defined(billboard._clampedPosition)) {
                  return BoundingSphereState.PENDING;
              }
              result.center = Cartesian3.clone(billboard._clampedPosition, result.center);
          }
  
          result.radius = 0;
          return BoundingSphereState.DONE;
      };
  
      /**
       * Returns true if this object was destroyed; otherwise, false.
       *
       * @returns {Boolean} True if this object was destroyed; otherwise, false.
       */
      PointVisualizer.prototype.isDestroyed = function() {
          return false;
      };
  
      /**
       * Removes and destroys all primitives created by this instance.
       */
      PointVisualizer.prototype.destroy = function() {
          this._entityCollection.collectionChanged.removeEventListener(PointVisualizer.prototype._onCollectionChanged, this);
          var entities = this._entityCollection.values;
          for (var i = 0; i < entities.length; i++) {
              this._cluster.removePoint(entities[i]);
          }
          return destroyObject(this);
      };
  
      PointVisualizer.prototype._onCollectionChanged = function(entityCollection, added, removed, changed) {
          var i;
          var entity;
          var items = this._items;
          var cluster = this._cluster;
  
          for (i = added.length - 1; i > -1; i--) {
              entity = added[i];
              if (defined(entity._point) && defined(entity._position)) {
                  items.set(entity.id, new EntityData(entity));
              }
          }
  
          for (i = changed.length - 1; i > -1; i--) {
              entity = changed[i];
              if (defined(entity._point) && defined(entity._position)) {
                  if (!items.contains(entity.id)) {
                      items.set(entity.id, new EntityData(entity));
                  }
              } else {
                  returnPrimitive(items.get(entity.id), entity, cluster);
                  items.remove(entity.id);
              }
          }
  
          for (i = removed.length - 1; i > -1; i--) {
              entity = removed[i];
              returnPrimitive(items.get(entity.id), entity, cluster);
              items.remove(entity.id);
          }
      };
  
      function returnPrimitive(item, entity, cluster) {
          if (defined(item)) {
              var pointPrimitive = item.pointPrimitive;
              if (defined(pointPrimitive)) {
                  item.pointPrimitive = undefined;
                  cluster.removePoint(entity);
                  return;
              }
              var billboard = item.billboard;
              if (defined(billboard)) {
                  item.billboard = undefined;
                  cluster.removeBillboard(entity);
              }
          }
      }
  
      return PointVisualizer;
  });
  