Primitive
查阅Mars3D API

new Cesium.Primitive(options)
engine/Source/Scene/Primitive.js 154

A primitive represents geometry in the Scene. The geometry can be from a single GeometryInstance as shown in example 1 below, or from an array of instances, even if the geometry is from different geometry types, e.g., an RectangleGeometry and an EllipsoidGeometry as shown in Code Example 2.

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.

Combining multiple instances into one primitive is called batching, and significantly improves performance for static data. Instances can be individually picked; Scene#pick returns their GeometryInstance#id. Using per-instance appearances like PerInstanceColorAppearance, each instance can also have a unique color.

Geometry can either be created and batched on a web worker or the main thread. The first two examples show geometry that will be created on a web worker by using the descriptions of the geometry. The third example shows how to create the geometry on the main thread by explicitly calling the createGeometry method.

参数名称 类型 描述信息
options object 可选 Object with the following properties:
参数名称 类型 默认值 描述信息
geometryInstances Array.<GeometryInstance> | GeometryInstance 可选 The geometry instances - or a single geometry instance - to render.
appearance Appearance 可选 The appearance used to render the primitive.
depthFailAppearance Appearance 可选 The appearance used to shade this primitive when it fails the depth test.
show boolean true 可选 Determines if this primitive will be shown.
modelMatrix Matrix4 Matrix4.IDENTITY 可选 The 4x4 transformation matrix that transforms the primitive (all geometry instances) from model to world coordinates.
vertexCacheOptimize boolean false 可选 When true, geometry vertices are optimized for the pre and post-vertex-shader caches.
interleave boolean false 可选 When true, geometry vertex attributes are interleaved, which can slightly improve rendering performance but increases load time.
compressVertices boolean true 可选 When true, the geometry vertices are compressed, which will save memory.
releaseGeometryInstances boolean true 可选 When true, the primitive does not keep a reference to the input geometryInstances to save memory.
allowPicking boolean true 可选 When true, each geometry instance will only be pickable with Scene#pick. When false, GPU memory is saved.
cull boolean true 可选 When true, the renderer frustum culls and horizon culls the primitive's commands based on their bounding volume. Set this to false for a small performance gain if you are manually culling the primitive.
asynchronous boolean true 可选 Determines if the primitive will be created asynchronously or block until ready.
debugShowBoundingVolume boolean false 可选 For debugging only. Determines if this primitive's commands' bounding spheres are shown.
shadows ShadowMode ShadowMode.DISABLED 可选 Determines whether this primitive casts or receives shadows from light sources.
使用示例s:
// 1. Draw a translucent ellipse on the surface with a checkerboard pattern
const instance = new Cesium.GeometryInstance({
  geometry : new Cesium.EllipseGeometry({
      center : Cesium.Cartesian3.fromDegrees(-100.0, 20.0),
      semiMinorAxis : 500000.0,
      semiMajorAxis : 1000000.0,
      rotation : Cesium.Math.PI_OVER_FOUR,
      vertexFormat : Cesium.VertexFormat.POSITION_AND_ST
  }),
  id : 'object returned when this instance is picked and to get/set per-instance attributes'
});
scene.primitives.add(new Cesium.Primitive({
  geometryInstances : instance,
  appearance : new Cesium.EllipsoidSurfaceAppearance({
    material : Cesium.Material.fromType('Checkerboard')
  })
}));
// 2. Draw different instances each with a unique color
const rectangleInstance = new Cesium.GeometryInstance({
  geometry : new Cesium.RectangleGeometry({
    rectangle : Cesium.Rectangle.fromDegrees(-140.0, 30.0, -100.0, 40.0),
    vertexFormat : Cesium.PerInstanceColorAppearance.VERTEX_FORMAT
  }),
  id : 'rectangle',
  attributes : {
    color : new Cesium.ColorGeometryInstanceAttribute(0.0, 1.0, 1.0, 0.5)
  }
});
const ellipsoidInstance = new Cesium.GeometryInstance({
  geometry : new Cesium.EllipsoidGeometry({
    radii : new Cesium.Cartesian3(500000.0, 500000.0, 1000000.0),
    vertexFormat : Cesium.VertexFormat.POSITION_AND_NORMAL
  }),
  modelMatrix : Cesium.Matrix4.multiplyByTranslation(Cesium.Transforms.eastNorthUpToFixedFrame(
    Cesium.Cartesian3.fromDegrees(-95.59777, 40.03883)), new Cesium.Cartesian3(0.0, 0.0, 500000.0), new Cesium.Matrix4()),
  id : 'ellipsoid',
  attributes : {
    color : Cesium.ColorGeometryInstanceAttribute.fromColor(Cesium.Color.AQUA)
  }
});
scene.primitives.add(new Cesium.Primitive({
  geometryInstances : [rectangleInstance, ellipsoidInstance],
  appearance : new Cesium.PerInstanceColorAppearance()
}));
// 3. Create the geometry on the main thread.
scene.primitives.add(new Cesium.Primitive({
  geometryInstances : new Cesium.GeometryInstance({
    geometry : Cesium.EllipsoidGeometry.createGeometry(new Cesium.EllipsoidGeometry({
      radii : new Cesium.Cartesian3(500000.0, 500000.0, 1000000.0),
      vertexFormat : Cesium.VertexFormat.POSITION_AND_NORMAL
    })),
    modelMatrix : Cesium.Matrix4.multiplyByTranslation(Cesium.Transforms.eastNorthUpToFixedFrame(
      Cesium.Cartesian3.fromDegrees(-95.59777, 40.03883)), new Cesium.Cartesian3(0.0, 0.0, 500000.0), new Cesium.Matrix4()),
    id : 'ellipsoid',
    attributes : {
      color : Cesium.ColorGeometryInstanceAttribute.fromColor(Cesium.Color.AQUA)
    }
  }),
  appearance : new Cesium.PerInstanceColorAppearance(),
  asynchronous : false
}));
参考:

成员(属性)

readonly allowPicking : boolean
engine/Source/Scene/Primitive.js 424

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

appearance : Appearance
engine/Source/Scene/Primitive.js 182

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.
默认值: undefined

readonly asynchronous : boolean
engine/Source/Scene/Primitive.js 440

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

readonly compressVertices : boolean
engine/Source/Scene/Primitive.js 456

When true, geometry vertices are compressed, which will save memory.
默认值: true

cull : boolean
engine/Source/Scene/Primitive.js 261

When true, the renderer frustum culls and horizon culls the primitive's commands based on their bounding volume. Set this to false for a small performance gain if you are manually culling the primitive.
默认值: true

debugShowBoundingVolume : boolean
engine/Source/Scene/Primitive.js 273

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.

默认值: false

depthFailAppearance : Appearance
engine/Source/Scene/Primitive.js 205

The Appearance used to shade this primitive when it fails the depth test. Each geometry instance is shaded with the same appearance. Some appearances, like PerInstanceColorAppearance allow giving each instance unique properties.

When using an appearance that requires a color attribute, like PerInstanceColorAppearance, add a depthFailColor per-instance attribute instead.

Requires the EXT_frag_depth WebGL extension to render properly. If the extension is not supported, there may be artifacts.

默认值: undefined

readonly geometryInstances : Array.<GeometryInstance>|GeometryInstance
engine/Source/Scene/Primitive.js 170

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.

默认值: undefined

readonly interleave : boolean
engine/Source/Scene/Primitive.js 392

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

modelMatrix : Matrix4
engine/Source/Scene/Primitive.js 227

The 4x4 transformation matrix that transforms the primitive (all geometry instances) from model to world coordinates. When this is the identity matrix, the primitive is drawn in world coordinates, i.e., Earth's WGS84 coordinates. Local reference frames can be used by providing a different transformation matrix, like that returned by Transforms.eastNorthUpToFixedFrame.

This property is only supported in 3D mode.

默认值: Matrix4.IDENTITY
使用示例:
const origin = Cesium.Cartesian3.fromDegrees(-95.0, 40.0, 200000.0);
p.modelMatrix = Cesium.Transforms.eastNorthUpToFixedFrame(origin);

readonly ready : boolean
engine/Source/Scene/Primitive.js 485

Determines if the primitive is complete and ready to render. If this property is true, the primitive will be rendered the next time that Primitive#update is called.
使用示例:
// Wait for a primitive to become ready before accessing attributes
const removeListener = scene.postRender.addEventListener(() => {
  if (!frustumPrimitive.ready) {
    return;
  }

  const attributes = primitive.getGeometryInstanceAttributes('an id');
  attributes.color = Cesium.ColorGeometryInstanceAttribute.toValue(Cesium.Color.AQUA);

  removeListener();
});

readonly releaseGeometryInstances : boolean
engine/Source/Scene/Primitive.js 408

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

shadows : ShadowMode
engine/Source/Scene/Primitive.js 303

Determines whether this primitive casts or receives shadows from light sources.
默认值: ShadowMode.DISABLED

show : boolean
engine/Source/Scene/Primitive.js 240

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

readonly vertexCacheOptimize : boolean
engine/Source/Scene/Primitive.js 376

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

方法

destroy()
engine/Source/Scene/Primitive.js 2479

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.
使用示例:
e = e && e.destroy();
参考:

getGeometryInstanceAttributes(id) → object
engine/Source/Scene/Primitive.js 2390

Returns the modifiable per-instance attributes for a GeometryInstance.
参数名称 类型 描述信息
id * The id of the GeometryInstance.
返回值:
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.
使用示例:
const attributes = primitive.getGeometryInstanceAttributes('an id');
attributes.color = Cesium.ColorGeometryInstanceAttribute.toValue(Cesium.Color.AQUA);
attributes.show = Cesium.ShowGeometryInstanceAttribute.toValue(true);
attributes.distanceDisplayCondition = Cesium.DistanceDisplayConditionGeometryInstanceAttribute.toValue(100.0, 10000.0);
attributes.offset = Cesium.OffsetGeometryInstanceAttribute.toValue(Cartesian3.IDENTITY);

isDestroyed() → boolean
engine/Source/Scene/Primitive.js 2458

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.

返回值:
true if this object was destroyed; otherwise, false.
参考:

update()
engine/Source/Scene/Primitive.js 2091

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 : Primitive.modelMatrix is only supported in 3D mode.
  • RuntimeError : Vertex texture fetch support is required to render primitives with per-instance attributes. The maximum number of vertex texture image units must be greater than zero.
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