Cesium中的Globe.js

Globe顾名思义就是地球的意思吧。

先看构造函数：

function Globe(ellipsoid) {
  ellipsoid = defaultValue(ellipsoid, Ellipsoid.WGS84);
  var terrainProvider = new EllipsoidTerrainProvider({
    ellipsoid: ellipsoid,
  });
  var imageryLayerCollection = new ImageryLayerCollection();

  this._ellipsoid = ellipsoid;
  this._imageryLayerCollection = imageryLayerCollection;

  this._surfaceShaderSet = new GlobeSurfaceShaderSet();
  this._material = undefined;

  this._surface = new QuadtreePrimitive({
    tileProvider: new GlobeSurfaceTileProvider({
      terrainProvider: terrainProvider,
      imageryLayers: imageryLayerCollection,
      surfaceShaderSet: this._surfaceShaderSet,
    }),
  });

  this._terrainProvider = terrainProvider;
  this._terrainProviderChanged = new Event();

  this._undergroundColor = Color.clone(Color.BLACK);
  this._undergroundColorAlphaByDistance = new NearFarScalar(
    ellipsoid.maximumRadius / 1000.0,
    0.0,
    ellipsoid.maximumRadius / 5.0,
    1.0
  );

  this._translucency = new GlobeTranslucency();

  makeShadersDirty(this);

  /**
   * Determines if the globe will be shown.
   *
   * @type {Boolean}
   * @default true
   */
  this.show = true;

  this._oceanNormalMapResourceDirty = true;
  this._oceanNormalMapResource = new Resource({
    url: buildModuleUrl("Assets/Textures/waterNormalsSmall.jpg"),
  });

  /**
   * The maximum screen-space error used to drive level-of-detail refinement.  Higher
   * values will provide better performance but lower visual quality.
   *
   * @type {Number}
   * @default 2
   */
  this.maximumScreenSpaceError = 2;

  /**
   * The size of the terrain tile cache, expressed as a number of tiles.  Any additional
   * tiles beyond this number will be freed, as long as they aren't needed for rendering
   * this frame.  A larger number will consume more memory but will show detail faster
   * when, for example, zooming out and then back in.
   *
   * @type {Number}
   * @default 100
   */
  this.tileCacheSize = 100;

  /**
   * Gets or sets the number of loading descendant tiles that is considered "too many".
   * If a tile has too many loading descendants, that tile will be loaded and rendered before any of
   * its descendants are loaded and rendered. This means more feedback for the user that something
   * is happening at the cost of a longer overall load time. Setting this to 0 will cause each
   * tile level to be loaded successively, significantly increasing load time. Setting it to a large
   * number (e.g. 1000) will minimize the number of tiles that are loaded but tend to make
   * detail appear all at once after a long wait.
   * @type {Number}
   * @default 20
   */
  this.loadingDescendantLimit = 20;

  /**
   * Gets or sets a value indicating whether the ancestors of rendered tiles should be preloaded.
   * Setting this to true optimizes the zoom-out experience and provides more detail in
   * newly-exposed areas when panning. The down side is that it requires loading more tiles.
   * @type {Boolean}
   * @default true
   */
  this.preloadAncestors = true;

  /**
   * Gets or sets a value indicating whether the siblings of rendered tiles should be preloaded.
   * Setting this to true causes tiles with the same parent as a rendered tile to be loaded, even
   * if they are culled. Setting this to true may provide a better panning experience at the
   * cost of loading more tiles.
   * @type {Boolean}
   * @default false
   */
  this.preloadSiblings = false;

  /**
   * The color to use to highlight terrain fill tiles. If undefined, fill tiles are not
   * highlighted at all. The alpha value is used to alpha blend with the tile's
   * actual color. Because terrain fill tiles do not represent the actual terrain surface,
   * it may be useful in some applications to indicate visually that they are not to be trusted.
   * @type {Color}
   * @default undefined
   */
  this.fillHighlightColor = undefined;

  /**
   * Enable lighting the globe with the scene's light source.
   *
   * @type {Boolean}
   * @default false
   */
  this.enableLighting = false;

  /**
   * Enable dynamic lighting effects on atmosphere and fog. This only takes effect
   * when <code>enableLighting</code> is <code>true</code>.
   *
   * @type {Boolean}
   * @default true
   */
  this.dynamicAtmosphereLighting = true;

  /**
   * Whether dynamic atmosphere lighting uses the sun direction instead of the scene's
   * light direction. This only takes effect when <code>enableLighting</code> and
   * <code>dynamicAtmosphereLighting</code> are <code>true</code>.
   *
   * @type {Boolean}
   * @default false
   */
  this.dynamicAtmosphereLightingFromSun = false;

  /**
   * Enable the ground atmosphere, which is drawn over the globe when viewed from a distance between <code>lightingFadeInDistance</code> and <code>lightingFadeOutDistance</code>.
   *
   * @demo {@link https://sandcastle.cesium.com/index.html?src=Ground%20Atmosphere.html|Ground atmosphere demo in Sandcastle}
   *
   * @type {Boolean}
   * @default true
   */
  this.showGroundAtmosphere = true;

  /**
   * The distance where everything becomes lit. This only takes effect
   * when <code>enableLighting</code> or <code>showGroundAtmosphere</code> is <code>true</code>.
   *
   * @type {Number}
   * @default 10000000.0
   */
  this.lightingFadeOutDistance = 1.0e7;

  /**
   * The distance where lighting resumes. This only takes effect
   * when <code>enableLighting</code> or <code>showGroundAtmosphere</code> is <code>true</code>.
   *
   * @type {Number}
   * @default 20000000.0
   */
  this.lightingFadeInDistance = 2.0e7;

  /**
   * The distance where the darkness of night from the ground atmosphere fades out to a lit ground atmosphere.
   * This only takes effect when <code>showGroundAtmosphere</code>, <code>enableLighting</code>, and
   * <code>dynamicAtmosphereLighting</code> are <code>true</code>.
   *
   * @type {Number}
   * @default 10000000.0
   */
  this.nightFadeOutDistance = 1.0e7;

  /**
   * The distance where the darkness of night from the ground atmosphere fades in to an unlit ground atmosphere.
   * This only takes effect when <code>showGroundAtmosphere</code>, <code>enableLighting</code>, and
   * <code>dynamicAtmosphereLighting</code> are <code>true</code>.
   *
   * @type {Number}
   * @default 50000000.0
   */
  this.nightFadeInDistance = 5.0e7;

  /**
   * True if an animated wave effect should be shown in areas of the globe
   * covered by water; otherwise, false.  This property is ignored if the
   * <code>terrainProvider</code> does not provide a water mask.
   *
   * @type {Boolean}
   * @default true
   */
  this.showWaterEffect = true;

  /**
   * True if primitives such as billboards, polylines, labels, etc. should be depth-tested
   * against the terrain surface, or false if such primitives should always be drawn on top
   * of terrain unless they're on the opposite side of the globe.  The disadvantage of depth
   * testing primitives against terrain is that slight numerical noise or terrain level-of-detail
   * switched can sometimes make a primitive that should be on the surface disappear underneath it.
   *
   * @type {Boolean}
   * @default false
   *
   */
  this.depthTestAgainstTerrain = false;

  /**
   * Determines whether the globe casts or receives shadows from light sources. Setting the globe
   * to cast shadows may impact performance since the terrain is rendered again from the light's perspective.
   * Currently only terrain that is in view casts shadows. By default the globe does not cast shadows.
   *
   * @type {ShadowMode}
   * @default ShadowMode.RECEIVE_ONLY
   */
  this.shadows = ShadowMode.RECEIVE_ONLY;

  /**
   * The hue shift to apply to the atmosphere. Defaults to 0.0 (no shift).
   * A hue shift of 1.0 indicates a complete rotation of the hues available.
   * @type {Number}
   * @default 0.0
   */
  this.atmosphereHueShift = 0.0;

  /**
   * The saturation shift to apply to the atmosphere. Defaults to 0.0 (no shift).
   * A saturation shift of -1.0 is monochrome.
   * @type {Number}
   * @default 0.0
   */
  this.atmosphereSaturationShift = 0.0;

  /**
   * The brightness shift to apply to the atmosphere. Defaults to 0.0 (no shift).
   * A brightness shift of -1.0 is complete darkness, which will let space show through.
   * @type {Number}
   * @default 0.0
   */
  this.atmosphereBrightnessShift = 0.0;

  /**
   * Whether to show terrain skirts. Terrain skirts are geometry extending downwards from a tile's edges used to hide seams between neighboring tiles.
   * Skirts are always hidden when the camera is underground or translucency is enabled.
   *
   * @type {Boolean}
   * @default true
   */
  this.showSkirts = true;

  /**
   * Whether to cull back-facing terrain. Back faces are not culled when the camera is underground or translucency is enabled.
   *
   * @type {Boolean}
   * @default true
   */
  this.backFaceCulling = true;

  this._oceanNormalMap = undefined;
  this._zoomedOutOceanSpecularIntensity = undefined;
}