text: /*global define*/
  define([
          '../Core/BoundingSphere',
          '../Core/BoxOutlineGeometry',
          '../Core/Cartesian2',
          '../Core/Cartesian3',
          '../Core/Cartesian4',
          '../Core/Color',
          '../Core/ColorGeometryInstanceAttribute',
          '../Core/defaultValue',
          '../Core/defined',
          '../Core/defineProperties',
          '../Core/destroyObject',
          '../Core/DeveloperError',
          '../Core/Event',
          '../Core/FeatureDetection',
          '../Core/GeometryInstance',
          '../Core/GeometryPipeline',
          '../Core/IndexDatatype',
          '../Core/Intersect',
          '../Core/Math',
          '../Core/Matrix4',
          '../Core/OrientedBoundingBox',
          '../Core/PrimitiveType',
          '../Core/Rectangle',
          '../Core/SphereOutlineGeometry',
          '../Core/Visibility',
          '../Core/WebMercatorProjection',
          '../Renderer/Buffer',
          '../Renderer/BufferUsage',
          '../Renderer/ContextLimits',
          '../Renderer/DrawCommand',
          '../Renderer/RenderState',
          '../Renderer/VertexArray',
          '../Scene/BlendingState',
          '../Scene/DepthFunction',
          '../Scene/Pass',
          '../Scene/PerInstanceColorAppearance',
          '../Scene/Primitive',
          '../ThirdParty/when',
          './GlobeSurfaceTile',
          './ImageryLayer',
          './ImageryState',
          './QuadtreeTileLoadState',
          './SceneMode'
      ], function(
          BoundingSphere,
          BoxOutlineGeometry,
          Cartesian2,
          Cartesian3,
          Cartesian4,
          Color,
          ColorGeometryInstanceAttribute,
          defaultValue,
          defined,
          defineProperties,
          destroyObject,
          DeveloperError,
          Event,
          FeatureDetection,
          GeometryInstance,
          GeometryPipeline,
          IndexDatatype,
          Intersect,
          CesiumMath,
          Matrix4,
          OrientedBoundingBox,
          PrimitiveType,
          Rectangle,
          SphereOutlineGeometry,
          Visibility,
          WebMercatorProjection,
          Buffer,
          BufferUsage,
          ContextLimits,
          DrawCommand,
          RenderState,
          VertexArray,
          BlendingState,
          DepthFunction,
          Pass,
          PerInstanceColorAppearance,
          Primitive,
          when,
          GlobeSurfaceTile,
          ImageryLayer,
          ImageryState,
          QuadtreeTileLoadState,
          SceneMode) {
      "use strict";
  
      /**
       * Provides quadtree tiles representing the surface of the globe.  This type is intended to be used
       * with {@link QuadtreePrimitive}.
       *
       * @alias GlobeSurfaceTileProvider
       * @constructor
       *
       * @param {TerrainProvider} options.terrainProvider The terrain provider that describes the surface geometry.
       * @param {ImageryLayerCollection} option.imageryLayers The collection of imagery layers describing the shading of the surface.
       * @param {GlobeSurfaceShaderSet} options.surfaceShaderSet The set of shaders used to render the surface.
       *
       * @private
       */
      var GlobeSurfaceTileProvider = function GlobeSurfaceTileProvider(options) {
          //>>includeStart('debug', pragmas.debug);
          if (!defined(options)) {
              throw new DeveloperError('options is required.');
          }
          if (!defined(options.terrainProvider)) {
              throw new DeveloperError('options.terrainProvider is required.');
          } else if (!defined(options.imageryLayers)) {
              throw new DeveloperError('options.imageryLayers is required.');
          } else if (!defined(options.surfaceShaderSet)) {
              throw new DeveloperError('options.surfaceShaderSet is required.');
          }
          //>>includeEnd('debug');
  
          this.lightingFadeOutDistance = 6500000.0;
          this.lightingFadeInDistance = 9000000.0;
          this.hasWaterMask = false;
          this.oceanNormalMap = undefined;
          this.zoomedOutOceanSpecularIntensity = 0.5;
          this.enableLighting = false;
  
          this._quadtree = undefined;
          this._terrainProvider = options.terrainProvider;
          this._imageryLayers = options.imageryLayers;
          this._surfaceShaderSet = options.surfaceShaderSet;
  
          this._renderState = undefined;
          this._blendRenderState = undefined;
          this._pickRenderState = undefined;
  
          this._errorEvent = new Event();
  
          this._imageryLayers.layerAdded.addEventListener(GlobeSurfaceTileProvider.prototype._onLayerAdded, this);
          this._imageryLayers.layerRemoved.addEventListener(GlobeSurfaceTileProvider.prototype._onLayerRemoved, this);
          this._imageryLayers.layerMoved.addEventListener(GlobeSurfaceTileProvider.prototype._onLayerMoved, this);
          this._imageryLayers.layerShownOrHidden.addEventListener(GlobeSurfaceTileProvider.prototype._onLayerShownOrHidden, this);
  
          this._layerOrderChanged = false;
  
          this._tilesToRenderByTextureCount = [];
          this._drawCommands = [];
          this._uniformMaps = [];
          this._pickCommands = [];
          this._usedDrawCommands = 0;
          this._usedPickCommands = 0;
  
          this._debug = {
              wireframe : false,
              boundingSphereTile : undefined
          };
  
          this._baseColor = undefined;
          this._firstPassInitialColor = undefined;
          this.baseColor = new Color(0.0, 0.0, 0.5, 1.0);
      };
  
      defineProperties(GlobeSurfaceTileProvider.prototype, {
          /**
           * Gets or sets the color of the globe when no imagery is available.
           * @memberof GlobeSurfaceTileProvider.prototype
           * @type {Color}
           */
          baseColor : {
              get : function() {
                  return this._baseColor;
              },
              set : function(value) {
                  //>>includeStart('debug', pragmas.debug);
                  if (!defined(value)) {
                      throw new DeveloperError('value is required.');
                  }
                  //>>includeEnd('debug');
  
                  this._baseColor = value;
                  this._firstPassInitialColor = Cartesian4.fromColor(value, this._firstPassInitialColor);
              }
          },
          /**
           * Gets or sets the {@link QuadtreePrimitive} for which this provider is
           * providing tiles.  This property may be undefined if the provider is not yet associated
           * with a {@link QuadtreePrimitive}.
           * @memberof GlobeSurfaceTileProvider.prototype
           * @type {QuadtreePrimitive}
           */
          quadtree : {
              get : function() {
                  return this._quadtree;
              },
              set : function(value) {
                  //>>includeStart('debug', pragmas.debug);
                  if (!defined(value)) {
                      throw new DeveloperError('value is required.');
                  }
                  //>>includeEnd('debug');
  
                  this._quadtree = value;
              }
          },
  
          /**
           * Gets a value indicating whether or not the provider is ready for use.
           * @memberof GlobeSurfaceTileProvider.prototype
           * @type {Boolean}
           */
          ready : {
              get : function() {
                  return this._terrainProvider.ready && (this._imageryLayers.length === 0 || this._imageryLayers.get(0).imageryProvider.ready);
              }
          },
  
          /**
           * Gets the tiling scheme used by the provider.  This property should
           * not be accessed before {@link GlobeSurfaceTileProvider#ready} returns true.
           * @memberof GlobeSurfaceTileProvider.prototype
           * @type {TilingScheme}
           */
          tilingScheme : {
              get : function() {
                  return this._terrainProvider.tilingScheme;
              }
          },
  
          /**
           * Gets an event that is raised when the geometry provider encounters an asynchronous error.  By subscribing
           * to the event, you will be notified of the error and can potentially recover from it.  Event listeners
           * are passed an instance of {@link TileProviderError}.
           * @memberof GlobeSurfaceTileProvider.prototype
           * @type {Event}
           */
          errorEvent : {
              get : function() {
                  return this._errorEvent;
              }
          },
  
          /**
           * Gets or sets the terrain provider that describes the surface geometry.
           * @memberof GlobeSurfaceTileProvider.prototype
           * @type {TerrainProvider}
           */
          terrainProvider : {
              get : function() {
                  return this._terrainProvider;
              },
              set : function(terrainProvider) {
                  if (this._terrainProvider === terrainProvider) {
                      return;
                  }
  
                  //>>includeStart('debug', pragmas.debug);
                  if (!defined(terrainProvider)) {
                      throw new DeveloperError('terrainProvider is required.');
                  }
                  //>>includeEnd('debug');
  
                  this._terrainProvider = terrainProvider;
  
                  if (defined(this._quadtree)) {
                      this._quadtree.invalidateAllTiles();
                  }
              }
          }
      });
  
      function sortTileImageryByLayerIndex(a, b) {
          var aImagery = a.loadingImagery;
          if (!defined(aImagery)) {
              aImagery = a.readyImagery;
          }
  
          var bImagery = b.loadingImagery;
          if (!defined(bImagery)) {
              bImagery = b.readyImagery;
          }
  
          return aImagery.imageryLayer._layerIndex - bImagery.imageryLayer._layerIndex;
      }
  
      /**
       * Called at the beginning of the update cycle for each render frame, before {@link QuadtreeTileProvider#showTileThisFrame}
       * or any other functions.
       *
       * @param {FrameState} frameState The frame state.
       */
      GlobeSurfaceTileProvider.prototype.beginUpdate = function(frameState) {
          this._imageryLayers._update();
  
          if (this._layerOrderChanged) {
              this._layerOrderChanged = false;
  
              // Sort the TileImagery instances in each tile by the layer index.
              this._quadtree.forEachLoadedTile(function(tile) {
                  tile.data.imagery.sort(sortTileImageryByLayerIndex);
              });
          }
  
          var i;
          var len;
  
          var tilesToRenderByTextureCount = this._tilesToRenderByTextureCount;
          for (i = 0, len = tilesToRenderByTextureCount.length; i < len; ++i) {
              var tiles = tilesToRenderByTextureCount[i];
              if (defined(tiles)) {
                  tiles.length = 0;
              }
          }
  
          this._usedDrawCommands = 0;
  
          // Add credits for terrain and imagery providers.
          var creditDisplay = frameState.creditDisplay;
  
          if (this._terrainProvider.ready && defined(this._terrainProvider.credit)) {
              creditDisplay.addCredit(this._terrainProvider.credit);
          }
  
          var imageryLayers = this._imageryLayers;
          for (i = 0, len = imageryLayers.length; i < len; ++i) {
              var imageryProvider = imageryLayers.get(i).imageryProvider;
              if (imageryProvider.ready && defined(imageryProvider.credit)) {
                  creditDisplay.addCredit(imageryProvider.credit);
              }
          }
      };
  
      /**
       * Called at the end of the update cycle for each render frame, after {@link QuadtreeTileProvider#showTileThisFrame}
       * and any other functions.
       *
       * @param {FrameState} frameState The frame state.
       */
      GlobeSurfaceTileProvider.prototype.endUpdate = function(frameState) {
          if (!defined(this._renderState)) {
              this._renderState = RenderState.fromCache({ // Write color and depth
                  cull : {
                      enabled : true
                  },
                  depthTest : {
                      enabled : true,
                      func : DepthFunction.LESS
                  }
              });
  
              this._blendRenderState = RenderState.fromCache({ // Write color and depth
                  cull : {
                      enabled : true
                  },
                  depthTest : {
                      enabled : true,
                      func : DepthFunction.LESS_OR_EQUAL
                  },
                  blending : BlendingState.ALPHA_BLEND
              });
          }
  
          // Add the tile render commands to the command list, sorted by texture count.
          var tilesToRenderByTextureCount = this._tilesToRenderByTextureCount;
          for (var textureCountIndex = 0, textureCountLength = tilesToRenderByTextureCount.length; textureCountIndex < textureCountLength; ++textureCountIndex) {
              var tilesToRender = tilesToRenderByTextureCount[textureCountIndex];
              if (!defined(tilesToRender)) {
                  continue;
              }
  
              for (var tileIndex = 0, tileLength = tilesToRender.length; tileIndex < tileLength; ++tileIndex) {
                  addDrawCommandsForTile(this, tilesToRender[tileIndex], frameState);
              }
          }
      };
  
      /**
       * Adds draw commands for tiles rendered in the previous frame for a pick pass.
       *
       * @param {FrameState} frameState The frame state.
       */
      GlobeSurfaceTileProvider.prototype.updateForPick = function(frameState) {
          if (!defined(this._pickRenderState)) {
              this._pickRenderState = RenderState.fromCache({
                  colorMask : {
                      red : false,
                      green : false,
                      blue : false,
                      alpha : false
                  },
                  depthTest : {
                      enabled : true
                  }
              });
          }
  
          this._usedPickCommands = 0;
          var drawCommands = this._drawCommands;
  
          // Add the tile pick commands from the tiles drawn last frame.
          for (var i = 0, length = this._usedDrawCommands; i < length; ++i) {
              addPickCommandsForTile(this, drawCommands[i], frameState);
          }
      };
  
      /**
       * Gets the maximum geometric error allowed in a tile at a given level, in meters.  This function should not be
       * called before {@link GlobeSurfaceTileProvider#ready} returns true.
       *
       * @param {Number} level The tile level for which to get the maximum geometric error.
       * @returns {Number} The maximum geometric error in meters.
       */
      GlobeSurfaceTileProvider.prototype.getLevelMaximumGeometricError = function(level) {
          return this._terrainProvider.getLevelMaximumGeometricError(level);
      };
  
      /**
       * Loads, or continues loading, a given tile.  This function will continue to be called
       * until {@link QuadtreeTile#state} is no longer {@link QuadtreeTileLoadState#LOADING}.  This function should
       * not be called before {@link GlobeSurfaceTileProvider#ready} returns true.
       *
       * @param {FrameState} frameState The frame state.
       * @param {QuadtreeTile} tile The tile to load.
       *
       * @exception {DeveloperError} <code>loadTile</code> must not be called before the tile provider is ready.
       */
      GlobeSurfaceTileProvider.prototype.loadTile = function(frameState, tile) {
          GlobeSurfaceTile.processStateMachine(tile, frameState, this._terrainProvider, this._imageryLayers);
      };
  
      var boundingSphereScratch = new BoundingSphere();
  
      /**
       * Determines the visibility of a given tile.  The tile may be fully visible, partially visible, or not
       * visible at all.  Tiles that are renderable and are at least partially visible will be shown by a call
       * to {@link GlobeSurfaceTileProvider#showTileThisFrame}.
       *
       * @param {QuadtreeTile} tile The tile instance.
       * @param {FrameState} frameState The state information about the current frame.
       * @param {QuadtreeOccluders} occluders The objects that may occlude this tile.
       *
       * @returns {Visibility} The visibility of the tile.
       */
      GlobeSurfaceTileProvider.prototype.computeTileVisibility = function(tile, frameState, occluders) {
          var distance = this.computeDistanceToTile(tile, frameState);
          tile._distance = distance;
  
          if (frameState.fog.enabled) {
              if (CesiumMath.fog(distance, frameState.fog.density) >= 1.0) {
                  // Tile is completely in fog so return that it is not visible.
                  return Visibility.NONE;
              }
          }
  
          var surfaceTile = tile.data;
          var cullingVolume = frameState.cullingVolume;
          var boundingVolume = defaultValue(surfaceTile.orientedBoundingBox, surfaceTile.boundingSphere3D);
  
          if (frameState.mode !== SceneMode.SCENE3D) {
              boundingVolume = boundingSphereScratch;
              BoundingSphere.fromRectangleWithHeights2D(tile.rectangle, frameState.mapProjection, surfaceTile.minimumHeight, surfaceTile.maximumHeight, boundingVolume);
              Cartesian3.fromElements(boundingVolume.center.z, boundingVolume.center.x, boundingVolume.center.y, boundingVolume.center);
  
              if (frameState.mode === SceneMode.MORPHING) {
                  boundingVolume = BoundingSphere.union(surfaceTile.boundingSphere3D, boundingVolume, boundingVolume);
              }
          }
  
          var intersection = cullingVolume.computeVisibility(boundingVolume);
          if (intersection === Intersect.OUTSIDE) {
              return Visibility.NONE;
          }
  
          if (frameState.mode === SceneMode.SCENE3D) {
              var occludeePointInScaledSpace = surfaceTile.occludeePointInScaledSpace;
              if (!defined(occludeePointInScaledSpace)) {
                  return intersection;
              }
  
              if (occluders.ellipsoid.isScaledSpacePointVisible(occludeePointInScaledSpace)) {
                  return intersection;
              }
  
              return Visibility.NONE;
          }
  
          return intersection;
      };
  
      var modifiedModelViewScratch = new Matrix4();
      var tileRectangleScratch = new Cartesian4();
      var rtcScratch = new Cartesian3();
      var centerEyeScratch = new Cartesian3();
      var southwestScratch = new Cartesian3();
      var northeastScratch = new Cartesian3();
  
      /**
       * Shows a specified tile in this frame.  The provider can cause the tile to be shown by adding
       * render commands to the commandList, or use any other method as appropriate.  The tile is not
       * expected to be visible next frame as well, unless this method is called next frame, too.
       *
       * @param {Object} tile The tile instance.
       * @param {FrameState} frameState The state information of the current rendering frame.
       */
      GlobeSurfaceTileProvider.prototype.showTileThisFrame = function(tile, frameState) {
          var readyTextureCount = 0;
          var tileImageryCollection = tile.data.imagery;
          for (var i = 0, len = tileImageryCollection.length; i < len; ++i) {
              var tileImagery = tileImageryCollection[i];
              if (defined(tileImagery.readyImagery) && tileImagery.readyImagery.imageryLayer.alpha !== 0.0) {
                  ++readyTextureCount;
              }
          }
  
          var tileSet = this._tilesToRenderByTextureCount[readyTextureCount];
          if (!defined(tileSet)) {
              tileSet = [];
              this._tilesToRenderByTextureCount[readyTextureCount] = tileSet;
          }
  
          tileSet.push(tile);
  
          var debug = this._debug;
          ++debug.tilesRendered;
          debug.texturesRendered += readyTextureCount;
      };
  
      var southwestCornerScratch = new Cartesian3();
      var northeastCornerScratch = new Cartesian3();
      var negativeUnitY = new Cartesian3(0.0, -1.0, 0.0);
      var negativeUnitZ = new Cartesian3(0.0, 0.0, -1.0);
      var vectorScratch = new Cartesian3();
  
      /**
       * Gets the distance from the camera to the closest point on the tile.  This is used for level-of-detail selection.
       *
       * @param {QuadtreeTile} tile The tile instance.
       * @param {FrameState} frameState The state information of the current rendering frame.
       * @param {Cartesian3} cameraCartesianPosition The position of the camera in world coordinates.
       * @param {Cartographic} cameraCartographicPosition The position of the camera in cartographic / geodetic coordinates.
       *
       * @returns {Number} The distance from the camera to the closest point on the tile, in meters.
       */
      GlobeSurfaceTileProvider.prototype.computeDistanceToTile = function(tile, frameState) {
          var surfaceTile = tile.data;
  
          var southwestCornerCartesian = surfaceTile.southwestCornerCartesian;
          var northeastCornerCartesian = surfaceTile.northeastCornerCartesian;
          var westNormal = surfaceTile.westNormal;
          var southNormal = surfaceTile.southNormal;
          var eastNormal = surfaceTile.eastNormal;
          var northNormal = surfaceTile.northNormal;
          var maximumHeight = surfaceTile.maximumHeight;
  
          if (frameState.mode !== SceneMode.SCENE3D) {
              southwestCornerCartesian = frameState.mapProjection.project(Rectangle.southwest(tile.rectangle), southwestCornerScratch);
              southwestCornerCartesian.z = southwestCornerCartesian.y;
              southwestCornerCartesian.y = southwestCornerCartesian.x;
              southwestCornerCartesian.x = 0.0;
              northeastCornerCartesian = frameState.mapProjection.project(Rectangle.northeast(tile.rectangle), northeastCornerScratch);
              northeastCornerCartesian.z = northeastCornerCartesian.y;
              northeastCornerCartesian.y = northeastCornerCartesian.x;
              northeastCornerCartesian.x = 0.0;
              westNormal = negativeUnitY;
              eastNormal = Cartesian3.UNIT_Y;
              southNormal = negativeUnitZ;
              northNormal = Cartesian3.UNIT_Z;
              maximumHeight = 0.0;
          }
  
          var cameraCartesianPosition = frameState.camera.positionWC;
          var cameraCartographicPosition = frameState.camera.positionCartographic;
  
          var vectorFromSouthwestCorner = Cartesian3.subtract(cameraCartesianPosition, southwestCornerCartesian, vectorScratch);
          var distanceToWestPlane = Cartesian3.dot(vectorFromSouthwestCorner, westNormal);
          var distanceToSouthPlane = Cartesian3.dot(vectorFromSouthwestCorner, southNormal);
  
          var vectorFromNortheastCorner = Cartesian3.subtract(cameraCartesianPosition, northeastCornerCartesian, vectorScratch);
          var distanceToEastPlane = Cartesian3.dot(vectorFromNortheastCorner, eastNormal);
          var distanceToNorthPlane = Cartesian3.dot(vectorFromNortheastCorner, northNormal);
  
          var cameraHeight;
          if (frameState.mode === SceneMode.SCENE3D) {
              cameraHeight = cameraCartographicPosition.height;
          } else {
              cameraHeight = cameraCartesianPosition.x;
          }
          var distanceFromTop = cameraHeight - maximumHeight;
  
          var result = 0.0;
  
          if (distanceToWestPlane > 0.0) {
              result += distanceToWestPlane * distanceToWestPlane;
          } else if (distanceToEastPlane > 0.0) {
              result += distanceToEastPlane * distanceToEastPlane;
          }
  
          if (distanceToSouthPlane > 0.0) {
              result += distanceToSouthPlane * distanceToSouthPlane;
          } else if (distanceToNorthPlane > 0.0) {
              result += distanceToNorthPlane * distanceToNorthPlane;
          }
  
          if (distanceFromTop > 0.0) {
              result += distanceFromTop * distanceFromTop;
          }
  
          return Math.sqrt(result);
      };
  
      /**
       * 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.
       *
       * @see GlobeSurfaceTileProvider#destroy
       */
      GlobeSurfaceTileProvider.prototype.isDestroyed = function() {
          return false;
      };
  
      /**
       * Destroys the WebGL resources held by this object.  Destroying an object allows for deterministic
       * release of WebGL resources, instead of relying on the garbage collector to destroy this object.
       * <br /><br />
       * Once an object is destroyed, it should not be used; calling any function other than
       * <code>isDestroyed</code> will result in a {@link DeveloperError} exception.  Therefore,
       * assign the return value (<code>undefined</code>) to the object as done in the example.
       *
       * @returns {undefined}
       *
       * @exception {DeveloperError} This object was destroyed, i.e., destroy() was called.
       *
       * @see GlobeSurfaceTileProvider#isDestroyed
       *
       * @example
       * provider = provider && provider();
       */
      GlobeSurfaceTileProvider.prototype.destroy = function() {
          this._tileProvider = this._tileProvider && this._tileProvider.destroy();
          return destroyObject(this);
      };
  
      GlobeSurfaceTileProvider.prototype._onLayerAdded = function(layer, index) {
          if (layer.show) {
              var terrainProvider = this._terrainProvider;
  
              // create TileImagerys for this layer for all previously loaded tiles
              this._quadtree.forEachLoadedTile(function(tile) {
                  if (layer._createTileImagerySkeletons(tile, terrainProvider)) {
                      tile.state = QuadtreeTileLoadState.LOADING;
                  }
              });
  
              this._layerOrderChanged = true;
          }
      };
  
      GlobeSurfaceTileProvider.prototype._onLayerRemoved = function(layer, index) {
          // destroy TileImagerys for this layer for all previously loaded tiles
          this._quadtree.forEachLoadedTile(function(tile) {
              var tileImageryCollection = tile.data.imagery;
  
              var startIndex = -1;
              var numDestroyed = 0;
              for (var i = 0, len = tileImageryCollection.length; i < len; ++i) {
                  var tileImagery = tileImageryCollection[i];
                  var imagery = tileImagery.loadingImagery;
                  if (!defined(imagery)) {
                      imagery = tileImagery.readyImagery;
                  }
                  if (imagery.imageryLayer === layer) {
                      if (startIndex === -1) {
                          startIndex = i;
                      }
  
                      tileImagery.freeResources();
                      ++numDestroyed;
                  } else if (startIndex !== -1) {
                      // iterated past the section of TileImagerys belonging to this layer, no need to continue.
                      break;
                  }
              }
  
              if (startIndex !== -1) {
                  tileImageryCollection.splice(startIndex, numDestroyed);
              }
          });
      };
  
      GlobeSurfaceTileProvider.prototype._onLayerMoved = function(layer, newIndex, oldIndex) {
          this._layerOrderChanged = true;
      };
  
      GlobeSurfaceTileProvider.prototype._onLayerShownOrHidden = function(layer, index, show) {
          if (show) {
              this._onLayerAdded(layer, index);
          } else {
              this._onLayerRemoved(layer, index);
          }
      };
  
      function createTileUniformMap() {
          var uniformMap = {
              u_initialColor : function() {
                  return this.initialColor;
              },
              u_zoomedOutOceanSpecularIntensity : function() {
                  return this.zoomedOutOceanSpecularIntensity;
              },
              u_oceanNormalMap : function() {
                  return this.oceanNormalMap;
              },
              u_lightingFadeDistance : function() {
                  return this.lightingFadeDistance;
              },
              u_center3D : function() {
                  return this.center3D;
              },
              u_tileRectangle : function() {
                  return this.tileRectangle;
              },
              u_modifiedModelView : function() {
                  return this.modifiedModelView;
              },
              u_dayTextures : function() {
                  return this.dayTextures;
              },
              u_dayTextureTranslationAndScale : function() {
                  return this.dayTextureTranslationAndScale;
              },
              u_dayTextureTexCoordsRectangle : function() {
                  return this.dayTextureTexCoordsRectangle;
              },
              u_dayTextureAlpha : function() {
                  return this.dayTextureAlpha;
              },
              u_dayTextureBrightness : function() {
                  return this.dayTextureBrightness;
              },
              u_dayTextureContrast : function() {
                  return this.dayTextureContrast;
              },
              u_dayTextureHue : function() {
                  return this.dayTextureHue;
              },
              u_dayTextureSaturation : function() {
                  return this.dayTextureSaturation;
              },
              u_dayTextureOneOverGamma : function() {
                  return this.dayTextureOneOverGamma;
              },
              u_dayIntensity : function() {
                  return this.dayIntensity;
              },
              u_southAndNorthLatitude : function() {
                  return this.southAndNorthLatitude;
              },
              u_southMercatorYAndOneOverHeight : function() {
                  return this.southMercatorYAndOneOverHeight;
              },
              u_waterMask : function() {
                  return this.waterMask;
              },
              u_waterMaskTranslationAndScale : function() {
                  return this.waterMaskTranslationAndScale;
              },
  
              initialColor : new Cartesian4(0.0, 0.0, 0.5, 1.0),
              zoomedOutOceanSpecularIntensity : 0.5,
              oceanNormalMap : undefined,
              lightingFadeDistance : new Cartesian2(6500000.0, 9000000.0),
  
              center3D : undefined,
              modifiedModelView : new Matrix4(),
              tileRectangle : new Cartesian4(),
  
              dayTextures : [],
              dayTextureTranslationAndScale : [],
              dayTextureTexCoordsRectangle : [],
              dayTextureAlpha : [],
              dayTextureBrightness : [],
              dayTextureContrast : [],
              dayTextureHue : [],
              dayTextureSaturation : [],
              dayTextureOneOverGamma : [],
              dayIntensity : 0.0,
  
              southAndNorthLatitude : new Cartesian2(),
              southMercatorYAndOneOverHeight : new Cartesian2(),
  
              waterMask : undefined,
              waterMaskTranslationAndScale : new Cartesian4()
          };
  
          return uniformMap;
      }
  
      function createWireframeVertexArrayIfNecessary(context, provider, tile) {
          var surfaceTile = tile.data;
  
          if (defined(surfaceTile.wireframeVertexArray)) {
              return;
          }
  
          if (defined(surfaceTile.meshForWireframePromise)) {
              return;
          }
  
          surfaceTile.meshForWireframePromise = surfaceTile.terrainData.createMesh(provider._terrainProvider.tilingScheme, tile.x, tile.y, tile.level);
          if (!defined(surfaceTile.meshForWireframePromise)) {
              // deferrred
              return;
          }
  
          var vertexArray = surfaceTile.vertexArray;
  
          when(surfaceTile.meshForWireframePromise, function(mesh) {
              if (surfaceTile.vertexArray === vertexArray) {
                  surfaceTile.wireframeVertexArray = createWireframeVertexArray(context, surfaceTile.vertexArray, mesh);
              }
              surfaceTile.meshForWireframePromise = undefined;
          });
      }
  
      /**
       * Creates a vertex array for wireframe rendering of a terrain tile.
       *
       * @private
       *
       * @param {Context} context The context in which to create the vertex array.
       * @param {VertexArray} vertexArray The existing, non-wireframe vertex array.  The new vertex array
       *                      will share vertex buffers with this existing one.
       * @param {TerrainMesh} terrainMesh The terrain mesh containing non-wireframe indices.
       * @returns {VertexArray} The vertex array for wireframe rendering.
       */
      function createWireframeVertexArray(context, vertexArray, terrainMesh) {
          var geometry = {
              indices : terrainMesh.indices,
              primitiveType : PrimitiveType.TRIANGLES
          };
  
          GeometryPipeline.toWireframe(geometry);
  
          var wireframeIndices = geometry.indices;
          var wireframeIndexBuffer = Buffer.createIndexBuffer({
              context : context,
              typedArray : wireframeIndices,
              usage : BufferUsage.STATIC_DRAW,
              indexDatatype : IndexDatatype.UNSIGNED_SHORT
          });
          return new VertexArray({
              context : context,
              attributes : vertexArray._attributes,
              indexBuffer : wireframeIndexBuffer
          });
      }
  
      var getDebugOrientedBoundingBox;
      var getDebugBoundingSphere;
      var debugDestroyPrimitive;
  
      (function() {
          var instanceOBB = new GeometryInstance({
              geometry: BoxOutlineGeometry.fromDimensions({ dimensions: new Cartesian3(2.0, 2.0, 2.0) })
          });
          var instanceSphere = new GeometryInstance({
              geometry: new SphereOutlineGeometry({ radius: 1.0 })
          });
          var modelMatrix = new Matrix4();
          var previousVolume;
          var primitive;
  
          function createDebugPrimitive(instance) {
              return new Primitive({
                  geometryInstances : instance,
                  appearance : new PerInstanceColorAppearance({
                      translucent : false,
                      flat : true
                  }),
                  asynchronous : false
              });
          }
  
          getDebugOrientedBoundingBox = function(obb, color) {
              if (obb === previousVolume) {
                  return primitive;
              }
              debugDestroyPrimitive();
  
              previousVolume = obb;
              modelMatrix = Matrix4.fromRotationTranslation(obb.halfAxes, obb.center, modelMatrix);
  
              instanceOBB.modelMatrix = modelMatrix;
              instanceOBB.attributes.color = ColorGeometryInstanceAttribute.fromColor(color);
  
              primitive = createDebugPrimitive(instanceOBB);
              return primitive;
          };
  
          getDebugBoundingSphere = function(sphere, color) {
              if (sphere === previousVolume) {
                  return primitive;
              }
              debugDestroyPrimitive();
  
              previousVolume = sphere;
              modelMatrix = Matrix4.fromTranslation(sphere.center, modelMatrix);
              modelMatrix = Matrix4.multiplyByUniformScale(modelMatrix, sphere.radius, modelMatrix);
  
              instanceSphere.modelMatrix = modelMatrix;
              instanceSphere.attributes.color = ColorGeometryInstanceAttribute.fromColor(color);
  
              primitive = createDebugPrimitive(instanceSphere);
              return primitive;
          };
  
          debugDestroyPrimitive = function() {
              if (defined(primitive)) {
                  primitive.destroy();
                  primitive = undefined;
                  previousVolume = undefined;
              }
          };
      })();
  
      var otherPassesInitialColor = new Cartesian4(0.0, 0.0, 0.0, 0.0);
  
      function addDrawCommandsForTile(tileProvider, tile, frameState) {
          var surfaceTile = tile.data;
  
          var viewMatrix = frameState.camera.viewMatrix;
  
          var maxTextures = ContextLimits.maximumTextureImageUnits;
  
          var waterMaskTexture = surfaceTile.waterMaskTexture;
          var showReflectiveOcean = tileProvider.hasWaterMask && defined(waterMaskTexture);
          var oceanNormalMap = tileProvider.oceanNormalMap;
          var showOceanWaves = showReflectiveOcean && defined(oceanNormalMap);
          var hasVertexNormals = tileProvider.terrainProvider.ready && tileProvider.terrainProvider.hasVertexNormals;
          var enableFog = frameState.fog.enabled;
  
          if (showReflectiveOcean) {
              --maxTextures;
          }
          if (showOceanWaves) {
              --maxTextures;
          }
  
          var rtc = surfaceTile.center;
  
          // Not used in 3D.
          var tileRectangle = tileRectangleScratch;
  
          // Only used for Mercator projections.
          var southLatitude = 0.0;
          var northLatitude = 0.0;
          var southMercatorY = 0.0;
          var oneOverMercatorHeight = 0.0;
  
          var useWebMercatorProjection = false;
  
          if (frameState.mode !== SceneMode.SCENE3D) {
              var projection = frameState.mapProjection;
              var southwest = projection.project(Rectangle.southwest(tile.rectangle), southwestScratch);
              var northeast = projection.project(Rectangle.northeast(tile.rectangle), northeastScratch);
  
              tileRectangle.x = southwest.x;
              tileRectangle.y = southwest.y;
              tileRectangle.z = northeast.x;
              tileRectangle.w = northeast.y;
  
              // In 2D and Columbus View, use the center of the tile for RTC rendering.
              if (frameState.mode !== SceneMode.MORPHING) {
                  rtc = rtcScratch;
                  rtc.x = 0.0;
                  rtc.y = (tileRectangle.z + tileRectangle.x) * 0.5;
                  rtc.z = (tileRectangle.w + tileRectangle.y) * 0.5;
                  tileRectangle.x -= rtc.y;
                  tileRectangle.y -= rtc.z;
                  tileRectangle.z -= rtc.y;
                  tileRectangle.w -= rtc.z;
              }
  
              if (projection instanceof WebMercatorProjection) {
                  southLatitude = tile.rectangle.south;
                  northLatitude = tile.rectangle.north;
  
                  southMercatorY = WebMercatorProjection.geodeticLatitudeToMercatorAngle(southLatitude);
  
                  oneOverMercatorHeight = 1.0 / (WebMercatorProjection.geodeticLatitudeToMercatorAngle(northLatitude) - southMercatorY);
  
                  useWebMercatorProjection = true;
              }
          }
  
          var centerEye = Matrix4.multiplyByPoint(viewMatrix, rtc, centerEyeScratch);
          Matrix4.setTranslation(viewMatrix, centerEye, modifiedModelViewScratch);
  
          var tileImageryCollection = surfaceTile.imagery;
          var imageryIndex = 0;
          var imageryLen = tileImageryCollection.length;
  
          var firstPassRenderState = tileProvider._renderState;
          var otherPassesRenderState = tileProvider._blendRenderState;
          var renderState = firstPassRenderState;
  
          var initialColor = tileProvider._firstPassInitialColor;
  
          var context = frameState.context;
  
          if (!defined(tileProvider._debug.boundingSphereTile)) {
              debugDestroyPrimitive();
          }
  
          do {
              var numberOfDayTextures = 0;
  
              var command;
              var uniformMap;
  
              if (tileProvider._drawCommands.length <= tileProvider._usedDrawCommands) {
                  command = new DrawCommand();
                  command.owner = tile;
                  command.cull = false;
                  command.boundingVolume = new BoundingSphere();
                  command.orientedBoundingBox = undefined;
  
                  uniformMap = createTileUniformMap();
  
                  tileProvider._drawCommands.push(command);
                  tileProvider._uniformMaps.push(uniformMap);
              } else {
                  command = tileProvider._drawCommands[tileProvider._usedDrawCommands];
                  uniformMap = tileProvider._uniformMaps[tileProvider._usedDrawCommands];
              }
  
              command.owner = tile;
  
              ++tileProvider._usedDrawCommands;
  
              if (tile === tileProvider._debug.boundingSphereTile) {
                  // If a debug primitive already exists for this tile, it will not be
                  // re-created, to avoid allocation every frame. If it were possible
                  // to have more than one selected tile, this would have to change.
                  if (defined(surfaceTile.orientedBoundingBox)) {
                      getDebugOrientedBoundingBox(surfaceTile.orientedBoundingBox, Color.RED).update(frameState);
                  } else if (defined(surfaceTile.boundingSphere3D)) {
                      getDebugBoundingSphere(surfaceTile.boundingSphere3D, Color.RED).update(frameState);
                  }
              }
  
              Cartesian4.clone(initialColor, uniformMap.initialColor);
              uniformMap.oceanNormalMap = oceanNormalMap;
              uniformMap.lightingFadeDistance.x = tileProvider.lightingFadeOutDistance;
              uniformMap.lightingFadeDistance.y = tileProvider.lightingFadeInDistance;
              uniformMap.zoomedOutOceanSpecularIntensity = tileProvider.zoomedOutOceanSpecularIntensity;
  
              uniformMap.center3D = surfaceTile.center;
  
              Cartesian4.clone(tileRectangle, uniformMap.tileRectangle);
              uniformMap.southAndNorthLatitude.x = southLatitude;
              uniformMap.southAndNorthLatitude.y = northLatitude;
              uniformMap.southMercatorYAndOneOverHeight.x = southMercatorY;
              uniformMap.southMercatorYAndOneOverHeight.y = oneOverMercatorHeight;
              Matrix4.clone(modifiedModelViewScratch, uniformMap.modifiedModelView);
  
              // For performance, use fog in the shader only when the tile is in fog.
              var applyFog = enableFog && CesiumMath.fog(tile._distance, frameState.fog.density) > CesiumMath.EPSILON3;
  
              var applyBrightness = false;
              var applyContrast = false;
              var applyHue = false;
              var applySaturation = false;
              var applyGamma = false;
              var applyAlpha = false;
  
              while (numberOfDayTextures < maxTextures && imageryIndex < imageryLen) {
                  var tileImagery = tileImageryCollection[imageryIndex];
                  var imagery = tileImagery.readyImagery;
                  ++imageryIndex;
  
                  if (!defined(imagery) || imagery.state !== ImageryState.READY || imagery.imageryLayer.alpha === 0.0) {
                      continue;
                  }
  
                  var imageryLayer = imagery.imageryLayer;
  
                  if (!defined(tileImagery.textureTranslationAndScale)) {
                      tileImagery.textureTranslationAndScale = imageryLayer._calculateTextureTranslationAndScale(tile, tileImagery);
                  }
  
                  uniformMap.dayTextures[numberOfDayTextures] = imagery.texture;
                  uniformMap.dayTextureTranslationAndScale[numberOfDayTextures] = tileImagery.textureTranslationAndScale;
                  uniformMap.dayTextureTexCoordsRectangle[numberOfDayTextures] = tileImagery.textureCoordinateRectangle;
  
                  uniformMap.dayTextureAlpha[numberOfDayTextures] = imageryLayer.alpha;
                  applyAlpha = applyAlpha || uniformMap.dayTextureAlpha[numberOfDayTextures] !== 1.0;
  
                  uniformMap.dayTextureBrightness[numberOfDayTextures] = imageryLayer.brightness;
                  applyBrightness = applyBrightness || uniformMap.dayTextureBrightness[numberOfDayTextures] !== ImageryLayer.DEFAULT_BRIGHTNESS;
  
                  uniformMap.dayTextureContrast[numberOfDayTextures] = imageryLayer.contrast;
                  applyContrast = applyContrast || uniformMap.dayTextureContrast[numberOfDayTextures] !== ImageryLayer.DEFAULT_CONTRAST;
  
                  uniformMap.dayTextureHue[numberOfDayTextures] = imageryLayer.hue;
                  applyHue = applyHue || uniformMap.dayTextureHue[numberOfDayTextures] !== ImageryLayer.DEFAULT_HUE;
  
                  uniformMap.dayTextureSaturation[numberOfDayTextures] = imageryLayer.saturation;
                  applySaturation = applySaturation || uniformMap.dayTextureSaturation[numberOfDayTextures] !== ImageryLayer.DEFAULT_SATURATION;
  
                  uniformMap.dayTextureOneOverGamma[numberOfDayTextures] = 1.0 / imageryLayer.gamma;
                  applyGamma = applyGamma || uniformMap.dayTextureOneOverGamma[numberOfDayTextures] !== 1.0 / ImageryLayer.DEFAULT_GAMMA;
  
                  if (defined(imagery.credits)) {
                      var creditDisplay = frameState.creditDisplay;
                      var credits = imagery.credits;
                      for (var creditIndex = 0, creditLength = credits.length; creditIndex < creditLength; ++creditIndex) {
                          creditDisplay.addCredit(credits[creditIndex]);
                      }
                  }
  
                  ++numberOfDayTextures;
              }
  
              // trim texture array to the used length so we don't end up using old textures
              // which might get destroyed eventually
              uniformMap.dayTextures.length = numberOfDayTextures;
              uniformMap.waterMask = waterMaskTexture;
              Cartesian4.clone(surfaceTile.waterMaskTranslationAndScale, uniformMap.waterMaskTranslationAndScale);
  
              command.shaderProgram = tileProvider._surfaceShaderSet.getShaderProgram(context, frameState.mode, surfaceTile, numberOfDayTextures, applyBrightness, applyContrast, applyHue, applySaturation, applyGamma, applyAlpha, showReflectiveOcean, showOceanWaves, tileProvider.enableLighting, hasVertexNormals, useWebMercatorProjection, applyFog);
              command.renderState = renderState;
              command.primitiveType = PrimitiveType.TRIANGLES;
              command.vertexArray = surfaceTile.vertexArray;
              command.uniformMap = uniformMap;
              command.pass = Pass.GLOBE;
  
              if (tileProvider._debug.wireframe) {
                  createWireframeVertexArrayIfNecessary(context, tileProvider, tile);
                  if (defined(surfaceTile.wireframeVertexArray)) {
                      command.vertexArray = surfaceTile.wireframeVertexArray;
                      command.primitiveType = PrimitiveType.LINES;
                  }
              }
  
              var boundingVolume = command.boundingVolume;
              var orientedBoundingBox = command.orientedBoundingBox;
  
              if (frameState.mode !== SceneMode.SCENE3D) {
                  BoundingSphere.fromRectangleWithHeights2D(tile.rectangle, frameState.mapProjection, surfaceTile.minimumHeight, surfaceTile.maximumHeight, boundingVolume);
                  Cartesian3.fromElements(boundingVolume.center.z, boundingVolume.center.x, boundingVolume.center.y, boundingVolume.center);
  
                  if (frameState.mode === SceneMode.MORPHING) {
                      boundingVolume = BoundingSphere.union(surfaceTile.boundingSphere3D, boundingVolume, boundingVolume);
                  }
              } else {
                  command.boundingVolume = BoundingSphere.clone(surfaceTile.boundingSphere3D, boundingVolume);
                  command.orientedBoundingBox = OrientedBoundingBox.clone(surfaceTile.orientedBoundingBox, orientedBoundingBox);
              }
  
              frameState.commandList.push(command);
  
              renderState = otherPassesRenderState;
              initialColor = otherPassesInitialColor;
          } while (imageryIndex < imageryLen);
      }
  
      function addPickCommandsForTile(tileProvider, drawCommand, frameState) {
          var pickCommand;
          if (tileProvider._pickCommands.length <= tileProvider._usedPickCommands) {
              pickCommand = new DrawCommand();
              pickCommand.cull = false;
  
              tileProvider._pickCommands.push(pickCommand);
          } else {
              pickCommand = tileProvider._pickCommands[tileProvider._usedPickCommands];
          }
  
          ++tileProvider._usedPickCommands;
  
          var useWebMercatorProjection = frameState.projection instanceof WebMercatorProjection;
  
          pickCommand.shaderProgram = tileProvider._surfaceShaderSet.getPickShaderProgram(frameState.context, frameState.mode, useWebMercatorProjection);
          pickCommand.renderState = tileProvider._pickRenderState;
  
          pickCommand.owner = drawCommand.owner;
          pickCommand.primitiveType = drawCommand.primitiveType;
          pickCommand.vertexArray = drawCommand.vertexArray;
          pickCommand.uniformMap = drawCommand.uniformMap;
          pickCommand.boundingVolume = drawCommand.boundingVolume;
          pickCommand.orientedBoundingBox = pickCommand.orientedBoundingBox;
          pickCommand.pass = drawCommand.pass;
  
          frameState.commandList.push(pickCommand);
      }
  
      return GlobeSurfaceTileProvider;
  });