text: define([
          '../Core/defaultValue',
          '../Core/defined',
          '../Core/defineProperties',
          '../Core/DeveloperError',
          '../Core/Event',
          './createPropertyDescriptor'
      ], function(
          defaultValue,
          defined,
          defineProperties,
          DeveloperError,
          Event,
          createPropertyDescriptor) {
      'use strict';
  
      /**
       * Describes a two dimensional icon located at the position of the containing {@link Entity}.
       * <p>
       * <div align='center'>
       * <img src='images/Billboard.png' width='400' height='300' /><br />
       * Example billboards
       * </div>
       * </p>
       *
       * @alias BillboardGraphics
       * @constructor
       *
       * @param {Object} [options] Object with the following properties:
       * @param {Property} [options.image] A Property specifying the Image, URI, or Canvas to use for the billboard.
       * @param {Property} [options.show=true] A boolean Property specifying the visibility of the billboard.
       * @param {Property} [options.scale=1.0] A numeric Property specifying the scale to apply to the image size.
       * @param {Property} [options.horizontalOrigin=HorizontalOrigin.CENTER] A Property specifying the {@link HorizontalOrigin}.
       * @param {Property} [options.verticalOrigin=VerticalOrigin.CENTER] A Property specifying the {@link VerticalOrigin}.
       * @param {Property} [options.eyeOffset=Cartesian3.ZERO] A {@link Cartesian3} Property specifying the eye offset.
       * @param {Property} [options.pixelOffset=Cartesian2.ZERO] A {@link Cartesian2} Property specifying the pixel offset.
       * @param {Property} [options.rotation=0] A numeric Property specifying the rotation about the alignedAxis.
       * @param {Property} [options.alignedAxis=Cartesian3.ZERO] A {@link Cartesian3} Property specifying the unit vector axis of rotation.
       * @param {Property} [options.width] A numeric Property specifying the width of the billboard in pixels, overriding the native size.
       * @param {Property} [options.height] A numeric Property specifying the height of the billboard in pixels, overriding the native size.
       * @param {Property} [options.color=Color.WHITE] A Property specifying the tint {@link Color} of the image.
       * @param {Property} [options.scaleByDistance] A {@link NearFarScalar} Property used to scale the point based on distance from the camera.
       * @param {Property} [options.translucencyByDistance] A {@link NearFarScalar} Property used to set translucency based on distance from the camera.
       * @param {Property} [options.pixelOffsetScaleByDistance] A {@link NearFarScalar} Property used to set pixelOffset based on distance from the camera.
       * @param {Property} [options.imageSubRegion] A Property specifying a {@link BoundingRectangle} that defines a sub-region of the image to use for the billboard, rather than the entire image, measured in pixels from the bottom-left.
       * @param {Property} [options.sizeInMeters] A boolean Property specifying whether this billboard's size should be measured in meters.
       * @param {Property} [options.heightReference=HeightReference.NONE] A Property specifying what the height is relative to.
       * @param {Property} [options.distanceDisplayCondition] A Property specifying at what distance from the camera that this billboard will be displayed.
       *
       * @demo {@link http://cesiumjs.org/Cesium/Apps/Sandcastle/index.html?src=Billboards.html|Cesium Sandcastle Billboard Demo}
       */
      function BillboardGraphics(options) {
          this._image = undefined;
          this._imageSubscription = undefined;
          this._imageSubRegion = undefined;
          this._imageSubRegionSubscription = undefined;
          this._width = undefined;
          this._widthSubscription = undefined;
          this._height = undefined;
          this._heightSubscription = undefined;
          this._scale = undefined;
          this._scaleSubscription = undefined;
          this._rotation = undefined;
          this._rotationSubscription = undefined;
          this._alignedAxis = undefined;
          this._alignedAxisSubscription = undefined;
          this._horizontalOrigin = undefined;
          this._horizontalOriginSubscription = undefined;
          this._verticalOrigin = undefined;
          this._verticalOriginSubscription = undefined;
          this._color = undefined;
          this._colorSubscription = undefined;
          this._eyeOffset = undefined;
          this._eyeOffsetSubscription = undefined;
          this._heightReference = undefined;
          this._heightReferenceSubscription = undefined;
          this._pixelOffset = undefined;
          this._pixelOffsetSubscription = undefined;
          this._show = undefined;
          this._showSubscription = undefined;
          this._scaleByDistance = undefined;
          this._scaleByDistanceSubscription = undefined;
          this._translucencyByDistance = undefined;
          this._translucencyByDistanceSubscription = undefined;
          this._pixelOffsetScaleByDistance = undefined;
          this._pixelOffsetScaleByDistanceSubscription = undefined;
          this._sizeInMeters = undefined;
          this._sizeInMetersSubscription = undefined;
          this._distanceDisplayCondition = undefined;
          this._distanceDisplayConditionSubscription = undefined;
          this._disableDepthTestDistance = undefined;
          this._disableDepthTestDistanceSubscription = undefined;
          this._definitionChanged = new Event();
  
          this.merge(defaultValue(options, defaultValue.EMPTY_OBJECT));
      }
  
      defineProperties(BillboardGraphics.prototype, {
          /**
           * Gets the event that is raised whenever a property or sub-property is changed or modified.
           * @memberof BillboardGraphics.prototype
           *
           * @type {Event}
           * @readonly
           */
          definitionChanged : {
              get : function() {
                  return this._definitionChanged;
              }
          },
  
          /**
           * Gets or sets the Property specifying the Image, URI, or Canvas to use for the billboard.
           * @memberof BillboardGraphics.prototype
           * @type {Property}
           */
          image : createPropertyDescriptor('image'),
  
          /**
           * Gets or sets the Property specifying a {@link BoundingRectangle} that defines a
           * sub-region of the <code>image</code> to use for the billboard, rather than the entire image,
           * measured in pixels from the bottom-left.
           * @memberof BillboardGraphics.prototype
           * @type {Property}
           */
          imageSubRegion : createPropertyDescriptor('imageSubRegion'),
  
          /**
           * Gets or sets the numeric Property specifying the uniform scale to apply to the image.
           * A scale greater than <code>1.0</code> enlarges the billboard while a scale less than <code>1.0</code> shrinks it.
           * <p>
           * <div align='center'>
           * <img src='images/Billboard.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>
           * </p>
           * @memberof BillboardGraphics.prototype
           * @type {Property}
           * @default 1.0
           */
          scale : createPropertyDescriptor('scale'),
  
          /**
           * Gets or sets the numeric Property specifying the rotation of the image
           * counter clockwise from the <code>alignedAxis</code>.
           * @memberof BillboardGraphics.prototype
           * @type {Property}
           * @default 0
           */
          rotation : createPropertyDescriptor('rotation'),
  
          /**
           * Gets or sets the {@link Cartesian3} Property specifying the unit vector axis of rotation
           * in the fixed frame. When set to Cartesian3.ZERO the rotation is from the top of the screen.
           * @memberof BillboardGraphics.prototype
           * @type {Property}
           * @default Cartesian3.ZERO
           */
          alignedAxis : createPropertyDescriptor('alignedAxis'),
  
          /**
           * Gets or sets the Property specifying the {@link HorizontalOrigin}.
           * @memberof BillboardGraphics.prototype
           * @type {Property}
           * @default HorizontalOrigin.CENTER
           */
          horizontalOrigin : createPropertyDescriptor('horizontalOrigin'),
  
          /**
           * Gets or sets the Property specifying the {@link VerticalOrigin}.
           * @memberof BillboardGraphics.prototype
           * @type {Property}
           * @default VerticalOrigin.CENTER
           */
          verticalOrigin : createPropertyDescriptor('verticalOrigin'),
  
          /**
           * Gets or sets the Property specifying the {@link Color} that is multiplied with the <code>image</code>.
           * This has two common use cases.  First, the same white texture may be used by many different billboards,
           * each with a different color, to create colored billboards. Second, the color's alpha component can be
           * used to make the billboard translucent as shown below. An alpha of <code>0.0</code> makes the billboard
           * transparent, and <code>1.0</code> makes the billboard opaque.
           * <p>
           * <div align='center'>
           * <table border='0' cellpadding='5'><tr>
           * <td align='center'><code>default</code><br/><img src='images/Billboard.setColor.Alpha255.png' width='250' height='188' /></td>
           * <td align='center'><code>alpha : 0.5</code><br/><img src='images/Billboard.setColor.Alpha127.png' width='250' height='188' /></td>
           * </tr></table>
           * </div>
           * </p>
           * @memberof BillboardGraphics.prototype
           * @type {Property}
           * @default Color.WHITE
           */
          color : createPropertyDescriptor('color'),
  
          /**
           * Gets or sets the {@link Cartesian3} Property specifying the billboard's offset 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.
           * <p>
           * An eye offset is commonly used to arrange multiple billboards or objects at the same position, e.g., to
           * arrange a billboard above its corresponding 3D model.
           * </p>
           * Below, the billboard 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.
           * <p>
           * <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>b.eyeOffset = new Cartesian3(0.0, 8000000.0, 0.0);</code>
           * </div>
           * </p>
           * @memberof BillboardGraphics.prototype
           * @type {Property}
           * @default Cartesian3.ZERO
           */
          eyeOffset : createPropertyDescriptor('eyeOffset'),
  
          /**
           * Gets or sets the Property specifying the {@link HeightReference}.
           * @memberof BillboardGraphics.prototype
           * @type {Property}
           * @default HeightReference.NONE
           */
          heightReference : createPropertyDescriptor('heightReference'),
  
          /**
           * Gets or sets the {@link Cartesian2} Property specifying the billboard's pixel offset in screen space
           * from the origin of this billboard.  This is commonly used to align multiple billboards and labels 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.
           * <p>
           * <div align='center'>
           * <table border='0' cellpadding='5'><tr>
           * <td align='center'><code>default</code><br/><img src='images/Billboard.setPixelOffset.default.png' width='250' height='188' /></td>
           * <td align='center'><code>b.pixeloffset = new Cartesian2(50, 25);</code><br/><img src='images/Billboard.setPixelOffset.x50y-25.png' width='250' height='188' /></td>
           * </tr></table>
           * The billboard's origin is indicated by the yellow point.
           * </div>
           * </p>
           * @memberof BillboardGraphics.prototype
           * @type {Property}
           * @default Cartesian2.ZERO
           */
          pixelOffset : createPropertyDescriptor('pixelOffset'),
  
          /**
           * Gets or sets the boolean Property specifying the visibility of the billboard.
           * @memberof BillboardGraphics.prototype
           * @type {Property}
           * @default true
           */
          show : createPropertyDescriptor('show'),
  
          /**
           * Gets or sets the numeric Property specifying the billboard's width in pixels.
           * When undefined, the native width is used.
           * @memberof BillboardGraphics.prototype
           * @type {Property}
           */
          width : createPropertyDescriptor('width'),
  
          /**
           * Gets or sets the numeric Property specifying the height of the billboard in pixels.
           * When undefined, the native height is used.
           * @memberof BillboardGraphics.prototype
           * @type {Property}
           */
          height : createPropertyDescriptor('height'),
  
          /**
           * Gets or sets {@link NearFarScalar} Property specifying the scale of the billboard based on the distance from the camera.
           * A billboard's scale 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 billboard's scale remains clamped to the nearest bound.
           * @memberof BillboardGraphics.prototype
           * @type {Property}
           */
          scaleByDistance : createPropertyDescriptor('scaleByDistance'),
  
          /**
           * Gets or sets {@link NearFarScalar} Property specifying the translucency of the billboard based on the distance from the camera.
           * A billboard'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 billboard's translucency remains clamped to the nearest bound.
           * @memberof BillboardGraphics.prototype
           * @type {Property}
           */
          translucencyByDistance : createPropertyDescriptor('translucencyByDistance'),
  
          /**
           * Gets or sets {@link NearFarScalar} Property specifying the pixel offset of the billboard based on the distance from the camera.
           * A billboard's pixel offset 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 billboard's pixel offset remains clamped to the nearest bound.
           * @memberof BillboardGraphics.prototype
           * @type {Property}
           */
          pixelOffsetScaleByDistance : createPropertyDescriptor('pixelOffsetScaleByDistance'),
  
          /**
           * Gets or sets the boolean Property specifying if this billboard's size will be measured in meters.
           * @memberof BillboardGraphics.prototype
           * @type {Property}
           * @default false
           */
          sizeInMeters : createPropertyDescriptor('sizeInMeters'),
  
          /**
           * Gets or sets the {@link DistanceDisplayCondition} Property specifying at what distance from the camera that this billboard will be displayed.
           * @memberof BillboardGraphics.prototype
           * @type {Property}
           */
          distanceDisplayCondition : createPropertyDescriptor('distanceDisplayCondition'),
  
          /**
           * Gets or sets the distance from the camera at which to disable the depth test to, for example, prevent clipping against terrain.
           * When set to zero, the depth test is always applied. When set to Number.POSITIVE_INFINITY, the depth test is never applied.
           * @memberof BillboardGraphics.prototype
           * @type {Property}
           */
          disableDepthTestDistance : createPropertyDescriptor('disableDepthTestDistance')
      });
  
      /**
       * Duplicates this instance.
       *
       * @param {BillboardGraphics} [result] The object onto which to store the result.
       * @returns {BillboardGraphics} The modified result parameter or a new instance if one was not provided.
       */
      BillboardGraphics.prototype.clone = function(result) {
          if (!defined(result)) {
              return new BillboardGraphics(this);
          }
          result.color = this._color;
          result.eyeOffset = this._eyeOffset;
          result.heightReference = this._heightReference;
          result.horizontalOrigin = this._horizontalOrigin;
          result.image = this._image;
          result.imageSubRegion = this._imageSubRegion;
          result.pixelOffset = this._pixelOffset;
          result.scale = this._scale;
          result.rotation = this._rotation;
          result.alignedAxis = this._alignedAxis;
          result.show = this._show;
          result.verticalOrigin = this._verticalOrigin;
          result.width = this._width;
          result.height = this._height;
          result.scaleByDistance = this._scaleByDistance;
          result.translucencyByDistance = this._translucencyByDistance;
          result.pixelOffsetScaleByDistance = this._pixelOffsetScaleByDistance;
          result.sizeInMeters = this._sizeInMeters;
          result.distanceDisplayCondition = this._distanceDisplayCondition;
          result.disableDepthTestDistance = this._disableDepthTestDistance;
          return result;
      };
  
      /**
       * Assigns each unassigned property on this object to the value
       * of the same property on the provided source object.
       *
       * @param {BillboardGraphics} source The object to be merged into this object.
       */
      BillboardGraphics.prototype.merge = function(source) {
          //>>includeStart('debug', pragmas.debug);
          if (!defined(source)) {
              throw new DeveloperError('source is required.');
          }
          //>>includeEnd('debug');
  
          this.color = defaultValue(this._color, source.color);
          this.eyeOffset = defaultValue(this._eyeOffset, source.eyeOffset);
          this.heightReference = defaultValue(this._heightReference, source.heightReference);
          this.horizontalOrigin = defaultValue(this._horizontalOrigin, source.horizontalOrigin);
          this.image = defaultValue(this._image, source.image);
          this.imageSubRegion = defaultValue(this._imageSubRegion, source.imageSubRegion);
          this.pixelOffset = defaultValue(this._pixelOffset, source.pixelOffset);
          this.scale = defaultValue(this._scale, source.scale);
          this.rotation = defaultValue(this._rotation, source.rotation);
          this.alignedAxis = defaultValue(this._alignedAxis, source.alignedAxis);
          this.show = defaultValue(this._show, source.show);
          this.verticalOrigin = defaultValue(this._verticalOrigin, source.verticalOrigin);
          this.width = defaultValue(this._width, source.width);
          this.height = defaultValue(this._height, source.height);
          this.scaleByDistance = defaultValue(this._scaleByDistance, source.scaleByDistance);
          this.translucencyByDistance = defaultValue(this._translucencyByDistance, source.translucencyByDistance);
          this.pixelOffsetScaleByDistance = defaultValue(this._pixelOffsetScaleByDistance, source.pixelOffsetScaleByDistance);
          this.sizeInMeters = defaultValue(this._sizeInMeters, source.sizeInMeters);
          this.distanceDisplayCondition = defaultValue(this._distanceDisplayCondition, source.distanceDisplayCondition);
          this.disableDepthTestDistance = defaultValue(this._disableDepthTestDistance, source.disableDepthTestDistance);
      };
  
      return BillboardGraphics;
  });
  