A ground primitive represents geometry draped over terrain or 3D Tiles in the
Scene.
A primitive combines geometry instances 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.
Support for the WEBGL_depth_texture extension is required to use GeometryInstances with different PerInstanceColors or materials besides PerInstanceColorAppearance.
Textured GroundPrimitives were designed for notional patterns and are not meant for precisely mapping
textures to terrain - for that use case, use SingleTileImageryProvider.
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:
|
Example:
// Example 1: Create primitive with a single instance
const 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
const color = new Cesium.ColorGeometryInstanceAttribute(0.0, 1.0, 1.0, 0.5); // Both instances must have the same color.
const 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
}
});
const 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
When
true, each geometry instance will only be pickable with Scene#pick. When false, GPU memory is saved.
-
Default Value:
true
appearance : Appearance
The
Appearance used to shade this primitive. Each geometry
instance is shaded with the same appearance. Some appearances, like
PerInstanceColorAppearance allow giving each instance unique
properties.
-
Default Value:
undefined
Determines if the geometry instances will be created and batched on a web worker.
-
Default Value:
true
classificationType : ClassificationType
Determines whether terrain, 3D Tiles or both will be classified.
-
Default Value:
ClassificationType.BOTH
When
true, geometry vertices are compressed, which will save memory.
-
Default Value:
true
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
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
readonly geometryInstances : Array|GeometryInstance
The geometry instances 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.
-
Default Value:
undefined
Determines if geometry vertex attributes are interleaved, which can slightly improve rendering performance.
-
Default Value:
false
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.
readonly readyPromise : Promise.<GroundPrimitive>
Gets a promise that resolves when the primitive is ready to render.
When
true, the primitive does not keep a reference to the input geometryInstances to save memory.
-
Default Value:
true
Determines if the primitive will be shown. This affects all geometry
instances in the primitive.
-
Default Value:
true
When
true, geometry vertices are optimized for the pre and post-vertex-shader caches.
-
Default Value:
true
Methods
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.
Determines if GroundPrimitive rendering is supported.
| Name | Type | Description |
|---|---|---|
scene |
Scene | The scene. |
Returns:
true if GroundPrimitives are supported; otherwise, returns false
Checks if the given Scene supports materials on GroundPrimitives.
Materials on GroundPrimitives require support for the WEBGL_depth_texture extension.
| Name | Type | Description |
|---|---|---|
scene |
Scene | The current scene. |
Returns:
Whether or not the current scene supports materials on GroundPrimitives.
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.
Throws:
-
DeveloperError : This object was destroyed, i.e., destroy() was called.
Example:
e = e && e.destroy();See:
Returns the modifiable per-instance attributes for a
GeometryInstance.
| Name | Type | Description |
|---|---|---|
id |
* |
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:
const attributes = primitive.getGeometryInstanceAttributes('an id');
attributes.color = Cesium.ColorGeometryInstanceAttribute.toValue(Cesium.Color.AQUA);
attributes.show = Cesium.ShowGeometryInstanceAttribute.toValue(true);
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.
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 : For synchronous GroundPrimitive, you must call GroundPrimitive.initializeTerrainHeights() and wait for the returned promise to resolve.
-
DeveloperError : All instance geometries must have the same primitiveType.
-
DeveloperError : Appearance and material have a uniform with the same name.