primitive动态修改

以贴底线 GroundPolylinePrimitive 为例

我们知道，primitive的更新机制主要是通过update函数，所以通过源码我们可以很容易找到如何对针对性的更新属性。

可以看到，update 每次都会判断 _primitive 这个属性，如果他未定义，则重新构建geometry相关的属性，所以我们只需要将_primitive清空，然后让他自己重构即可。

注：记的设置 asynchronous 为 false，默认异步抖动严重。

primitive._primitive = undefined;
primitive.geometryInstances = [geometryInstances];

源码中update如下：

GroundPolylinePrimitive.prototype.update = function (frameState) {
  ...省略

  var that = this;
  var primitiveOptions = this._primitiveOptions;
  if (!defined(this._primitive)) {
    var geometryInstances = Array.isArray(this.geometryInstances)
      ? this.geometryInstances
      : [this.geometryInstances];
    var geometryInstancesLength = geometryInstances.length;
    var groundInstances = new Array(geometryInstancesLength);

    var attributes;

    // Check if each instance has a color attribute.
    for (i = 0; i < geometryInstancesLength; ++i) {
      attributes = geometryInstances[i].attributes;
      if (!defined(attributes) || !defined(attributes.color)) {
        this._hasPerInstanceColors = false;
        break;
      }
    }

    for (i = 0; i < geometryInstancesLength; ++i) {
      var geometryInstance = geometryInstances[i];
      attributes = {};
      var instanceAttributes = geometryInstance.attributes;
      for (var attributeKey in instanceAttributes) {
        if (instanceAttributes.hasOwnProperty(attributeKey)) {
          attributes[attributeKey] = instanceAttributes[attributeKey];
        }
      }

      // Automatically create line width attribute if not already given
      if (!defined(attributes.width)) {
        attributes.width = new GeometryInstanceAttribute({
          componentDatatype: ComponentDatatype.UNSIGNED_BYTE,
          componentsPerAttribute: 1.0,
          value: [geometryInstance.geometry.width],
        });
      }

      // Update each geometry for framestate.scene3DOnly = true and projection
      geometryInstance.geometry._scene3DOnly = frameState.scene3DOnly;
      GroundPolylineGeometry.setProjectionAndEllipsoid(
        geometryInstance.geometry,
        frameState.mapProjection
      );

      groundInstances[i] = new GeometryInstance({
        geometry: geometryInstance.geometry,
        attributes: attributes,
        id: geometryInstance.id,
        pickPrimitive: that,
      });
    }

    primitiveOptions.geometryInstances = groundInstances;
    primitiveOptions.appearance = this.appearance;

    primitiveOptions._createShaderProgramFunction = function (
      primitive,
      frameState,
      appearance
    ) {
      createShaderProgram(that, frameState, appearance);
    };
    primitiveOptions._createCommandsFunction = function (
      primitive,
      appearance,
      material,
      translucent,
      twoPasses,
      colorCommands,
      pickCommands
    ) {
      createCommands(
        that,
        appearance,
        material,
        translucent,
        colorCommands,
        pickCommands
      );
    };
    primitiveOptions._updateAndQueueCommandsFunction = function (
      primitive,
      frameState,
      colorCommands,
      pickCommands,
      modelMatrix,
      cull,
      debugShowBoundingVolume,
      twoPasses
    ) {
      updateAndQueueCommands(
        that,
        frameState,
        colorCommands,
        pickCommands,
        modelMatrix,
        cull,
        debugShowBoundingVolume
      );
    };

    this._primitive = new Primitive(primitiveOptions);
    this._primitive.readyPromise.then(function (primitive) {
      that._ready = true;

      if (that.releaseGeometryInstances) {
        that.geometryInstances = undefined;
      }

      var error = primitive._error;
      if (!defined(error)) {
        that._readyPromise.resolve(that);
      } else {
        that._readyPromise.reject(error);
      }
    });
  }

  if (
    this.appearance instanceof PolylineColorAppearance &&
    !this._hasPerInstanceColors
  ) {
    throw new DeveloperError(
      "All GeometryInstances must have color attributes to use PolylineColorAppearance with GroundPolylinePrimitive."
    );
  }

  this._primitive.appearance = this.appearance;
  this._primitive.show = this.show;
  this._primitive.debugShowBoundingVolume = this.debugShowBoundingVolume;
  this._primitive.update(frameState);
};