GroundPrimitive

new Cesium.GroundPrimitive(options)

A ground primitive represents geometry draped over the terrain in the Scene. The geometry must be from a single GeometryInstance. Batching multiple geometries is not yet supported.

A primitive combines the geometry instance with an Appearance that describes the full shading, including Material and RenderState. Roughly, the geometry instance defines the structure and placement, and the appearance defines the visual characteristics. Decoupling geometry and appearance allows us to mix and match most of them and add a new geometry or appearance independently of each other. Only the PerInstanceColorAppearance is supported at this time.

For correct rendering, this feature requires the EXT_frag_depth WebGL extension. For hardware that do not support this extension, there will be rendering artifacts for some viewing angles.

Valid geometries are CircleGeometry, CorridorGeometry, EllipseGeometry, PolygonGeometry, and RectangleGeometry.

Name Type Description
options Object optional Object with the following properties:
Name Type Default Description
geometryInstances Array | GeometryInstance optional The geometry instances to render.
show Boolean true optional Determines if this primitive will be shown.
vertexCacheOptimize Boolean false optional When true, geometry vertices are optimized for the pre and post-vertex-shader caches.
interleave Boolean false optional When true, geometry vertex attributes are interleaved, which can slightly improve rendering performance but increases load time.
compressVertices Boolean true optional When true, the geometry vertices are compressed, which will save memory.
releaseGeometryInstances Boolean true optional When true, the primitive does not keep a reference to the input geometryInstances to save memory.
allowPicking Boolean true optional When true, each geometry instance will only be pickable with Scene#pick. When false, GPU memory is saved.
asynchronous Boolean true optional Determines if the primitive will be created asynchronously or block until ready. If false initializeTerrainHeights() must be called first.
debugShowBoundingVolume Boolean false optional For debugging only. Determines if this primitive's commands' bounding spheres are shown.
debugShowShadowVolume Boolean false optional For debugging only. Determines if the shadow volume for each geometry in the primitive is drawn. Must be true on creation for the volumes to be created before the geometry is released or options.releaseGeometryInstance must be false.
Example:
// Example 1: Create primitive with a single instance
var rectangleInstance = new Cesium.GeometryInstance({
  geometry : new Cesium.RectangleGeometry({
    rectangle : Cesium.Rectangle.fromDegrees(-140.0, 30.0, -100.0, 40.0)
  }),
  id : 'rectangle',
  attributes : {
    color : new Cesium.ColorGeometryInstanceAttribute(0.0, 1.0, 1.0, 0.5)
  }
});
scene.primitives.add(new Cesium.GroundPrimitive({
  geometryInstances : rectangleInstance
}));

// Example 2: Batch instances
var color = new Cesium.ColorGeometryInstanceAttribute(0.0, 1.0, 1.0, 0.5); // Both instances must have the same color.
var rectangleInstance = new Cesium.GeometryInstance({
  geometry : new Cesium.RectangleGeometry({
    rectangle : Cesium.Rectangle.fromDegrees(-140.0, 30.0, -100.0, 40.0)
  }),
  id : 'rectangle',
  attributes : {
    color : color
  }
});
var ellipseInstance = new Cesium.GeometryInstance({
    geometry : new Cesium.EllipseGeometry({
        center : Cesium.Cartesian3.fromDegrees(-105.0, 40.0),
        semiMinorAxis : 300000.0,
        semiMajorAxis : 400000.0
    }),
    id : 'ellipse',
    attributes : {
        color : color
    }
});
scene.primitives.add(new Cesium.GroundPrimitive({
  geometryInstances : [rectangleInstance, ellipseInstance]
}));
See:

Members

readonlyallowPicking : Boolean

When true, each geometry instance will only be pickable with Scene#pick. When false, GPU memory is saved.
Default Value: true

readonlyasynchronous : Boolean

Determines if the geometry instances will be created and batched on a web worker.
Default Value: true

readonlycompressVertices : Boolean

When true, geometry vertices are compressed, which will save memory.
Default Value: true

debugShowBoundingVolume : Boolean

This property is for debugging only; it is not for production use nor is it optimized.

Draws the bounding sphere for each draw command in the primitive.

Default Value: false

debugShowShadowVolume : Boolean

This property is for debugging only; it is not for production use nor is it optimized.

Draws the shadow volume for each geometry in the primitive.

Default Value: false

geometryInstances : Array|GeometryInstance

The geometry instance rendered with this primitive. This may be undefined if options.releaseGeometryInstances is true when the primitive is constructed.

Changing this property after the primitive is rendered has no effect.

Because of the rendering technique used, all geometry instances must be the same color. If there is an instance with a differing color, a DeveloperError will be thrown on the first attempt to render.

Default Value: undefined

readonlyinterleave : Boolean

Determines if geometry vertex attributes are interleaved, which can slightly improve rendering performance.
Default Value: false

readonlyready : Boolean

Determines if the primitive is complete and ready to render. If this property is true, the primitive will be rendered the next time that GroundPrimitive#update is called.

readonlyreadyPromise : Promise.<GroundPrimitive>

Gets a promise that resolves when the primitive is ready to render.

readonlyreleaseGeometryInstances : Boolean

When true, the primitive does not keep a reference to the input geometryInstances to save memory.
Default Value: true

show : Boolean

Determines if the primitive will be shown. This affects all geometry instances in the primitive.
Default Value: true

readonlyvertexCacheOptimize : Boolean

When true, geometry vertices are optimized for the pre and post-vertex-shader caches.
Default Value: true

Methods

staticCesium.GroundPrimitive.initializeTerrainHeights() → Promise

Initializes the minimum and maximum terrain heights. This only needs to be called if you are creating the GroundPrimitive synchronously.
Returns:
A promise that will resolve once the terrain heights have been loaded.

staticCesium.GroundPrimitive.isSupported(scene) → Boolean

Determines if GroundPrimitive rendering is supported.
Name Type Description
scene Scene The scene.
Returns:
true if GroundPrimitives are supported; otherwise, returns false

destroy() → undefined

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.

Once an object is destroyed, it should not be used; calling any function other than isDestroyed will result in a DeveloperError exception. Therefore, assign the return value (undefined) to the object as done in the example.

Returns:
Throws:
  • DeveloperError : This object was destroyed, i.e., destroy() was called.
Example:
e = e && e.destroy();
See:

getGeometryInstanceAttributes(id) → Object

Returns the modifiable per-instance attributes for a GeometryInstance.
Name Type Description
id Object The id of the GeometryInstance.
Returns:
The typed array in the attribute's format or undefined if the is no instance with id.
Throws:
  • DeveloperError : must call update before calling getGeometryInstanceAttributes.
Example:
var attributes = primitive.getGeometryInstanceAttributes('an id');
attributes.color = Cesium.ColorGeometryInstanceAttribute.toValue(Cesium.Color.AQUA);
attributes.show = Cesium.ShowGeometryInstanceAttribute.toValue(true);

isDestroyed() → Boolean

Returns true if this object was destroyed; otherwise, false.

If this object was destroyed, it should not be used; calling any function other than isDestroyed will result in a DeveloperError exception.

Returns:
true if this object was destroyed; otherwise, false.
See:

update()

Called when Viewer or CesiumWidget render the scene to get the draw commands needed to render this primitive.

Do not call this function directly. This is documented just to list the exceptions that may be propagated when the scene is rendered:

Throws:
  • DeveloperError : All instance geometries must have the same primitiveType.
  • DeveloperError : Appearance and material have a uniform with the same name.
  • DeveloperError : Not all of the geometry instances have the same color attribute.