# Primitive

#### new Cesium.Primitive(options)
Scene/Primitive.js 157

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.

Name | Type | Description
--- | --- | ---
`options` | Object | optional Object with the following properties:
Name | Type | Default | Description
--- | --- | --- | ---
`geometryInstances` | Array.<GeometryInstance> | GeometryInstance |  | optional The geometry instances - or a single geometry instance - to render.
`appearance` | Appearance |  | optional The appearance used to render the primitive.
`depthFailAppearance` | Appearance |  | optional The appearance used to shade this primitive when it fails the depth test.
`show` | Boolean | `true` | optional Determines if this primitive will be shown.
`modelMatrix` | Matrix4 | `Matrix4.IDENTITY` | optional The 4x4 transformation matrix that transforms the primitive (all geometry instances) from model to world coordinates.
`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.
`participatePicking` | Boolean | `true` | optional 是否参与场景pick。为true则代表可以被场景拾取到。为false组则代表不在场景拾取的图元中。
`cull` | Boolean | `true` | optional 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` | optional Determines if the primitive will be created asynchronously or block until ready.
`debugShowBoundingVolume` | Boolean | `false` | optional For debugging only. Determines if this primitive's commands' bounding spheres are shown.
`shadows` | ShadowMode | `ShadowMode.DISABLED` | optional Determines whether this primitive casts or receives shadows from light sources.

##### Examples:

    // 1. Draw a translucent ellipse on the surface with a checkerboard pattern
    var 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
    var 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)
      }
    });
    var 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
    }));

##### See:

- GeometryInstance
- Appearance
- ClassificationPrimitive
- GroundPrimitive

### Members

#### readonly allowPicking : Boolean
Scene/Primitive.js 415

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

Default Value: `true`

#### appearance : Appearance
Scene/Primitive.js 187

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`

#### readonly asynchronous : Boolean
Scene/Primitive.js 446

Determines if the geometry instances will be created and batched on a web worker.

Default Value: `true`

#### readonly compressVertices : Boolean
Scene/Primitive.js 462

When `true`, geometry vertices are compressed, which will save memory.

Default Value: `true`

#### cull : Boolean
Scene/Primitive.js 262

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.

Default Value: `true`

#### debugShowBoundingVolume : Boolean
Scene/Primitive.js 274

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`

#### depthFailAppearance : Appearance
Scene/Primitive.js 210

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.

Default Value: `undefined`

#### readonly geometryInstances : Array.<GeometryInstance>|GeometryInstance
Scene/Primitive.js 175

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`

#### readonly interleave : Boolean
Scene/Primitive.js 383

Determines if geometry vertex attributes are interleaved, which can slightly improve rendering performance.

Default Value: `false`

#### modelMatrix : Matrix4
Scene/Primitive.js 232

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.

Default Value: `Matrix4.IDENTITY`

##### Example:

    var origin = Cesium.Cartesian3.fromDegrees(-95.0, 40.0, 200000.0);
    p.modelMatrix = Cesium.Transforms.eastNorthUpToFixedFrame(origin);

#### readonly participatePicking : Boolean
Scene/Primitive.js 431

是否参与场景pick。为true则代表可以被场景拾取到。为false组则代表不在场景拾取的图元中。

Default Value: `true`

#### readonly ready : Boolean
Scene/Primitive.js 478

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.

#### readonly readyPromise : Promise.<Primitive>
Scene/Primitive.js 490

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

#### readonly releaseGeometryInstances : Boolean
Scene/Primitive.js 399

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

Default Value: `true`

#### shadows : ShadowMode
Scene/Primitive.js 294

Determines whether this primitive casts or receives shadows from light sources.

Default Value: `ShadowMode.DISABLED`

#### show : Boolean
Scene/Primitive.js 243

Determines if the primitive will be shown. This affects all geometry instances in the primitive.

Default Value: `true`

#### readonly vertexCacheOptimize : Boolean
Scene/Primitive.js 367

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

Default Value: `true`

### Methods

#### destroy()
Scene/Primitive.js 2260

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:

- Primitive#isDestroyed

#### getGeometryInstanceAttributes(id) → Object
Scene/Primitive.js 2173

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:

    var 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
Scene/Primitive.js 2239

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:

- Primitive#destroy

#### update()
Scene/Primitive.js 1946

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.