Sceneform ---Node ,Renderable关系

Node与Renderable到底啥关系？
Node和Renderable没有直接关系，是通过RenderableInstance关联的。而RenderableInstance是由renderable创建的，Node一直持有RenderableInstance 的引用，故而设置renderable的时候，会根据新renderable来更新RenderableInstance。
renderable构造时先生成renderable对象，然后把LoadRenderableFromFilamentGltfTask加载后的
RenderableInternalFilamentAssetData 赋值给renderable。这样renderable就有了数据

LoadRenderableFromFilamentGltfTask(T renderable, Context context, Uri sourceUri, @Nullable Function<String, Uri> urlResolver) {
  this.renderable = renderable;
  IRenderableInternalData data = renderable.getRenderableData();
  if (data instanceof RenderableInternalFilamentAssetData) {
    this.renderableData =
        (com.google.ar.sceneform.rendering.RenderableInternalFilamentAssetData) data;
  } else {
    throw new IllegalStateException("Expected task type " + TAG);
  }
  this.renderableData.resourceLoader =
      new ResourceLoader(EngineInstance.getEngine().getFilamentEngine());
  this.renderableData.urlResolver =
      missingPath -> getUriFromMissingResource(sourceUri, missingPath, urlResolver);
  this.renderableData.context = context.getApplicationContext();
  this.renderable.getId().update();
}

请君听我细细说来。
Node有个方法setRenderable(@Nullable Renderable renderable)

/**
   * Sets the {@link Renderable} to display for this node. If {@link
   * Node#setCollisionShape(CollisionShape)} is not set, then {@link Renderable#getCollisionShape()}
   * is used to detect collisions for this {@link Node}.
   *
   * @see ModelRenderable
   * @see com.google.ar.sceneform.rendering.ViewRenderable
   * @param renderable Usually a 3D model. If null, this node's current renderable will be removed.
   */
  public void setRenderable(@Nullable Renderable renderable) {
    AndroidPreconditions.checkUiThread();

    // Renderable hasn't changed, return early.
    if (renderableInstance != null && renderableInstance.getRenderable() == renderable) {
      return;
    }

    //设置新的Renderable时，先把RenderableInstance从render里移除，然后置空，如果Renderable不为空，再创建一个
    if (renderableInstance != null) {
      if (active) {
//        Log.d("steven","renderableInstance.detachFromRenderer() ....");
        renderableInstance.detachFromRenderer();
      }
      renderableInstance = null;
    }

    if (renderable != null) {
      RenderableInstance instance = renderable.createInstance(this);
      if (active && (scene != null && !scene.isUnderTesting())) {
        instance.attachToRenderer(getRendererOrDie());
      }
      renderableInstance = instance;
      renderableId = renderable.getId().get();
    } else {
      renderableId = ChangeId.EMPTY_ID;
    }

    refreshCollider();
  }

从上面代码我们可知，如果设置一个Renderable，会先判断这个Renderable和现在的是否同一个，是就返回。否则会先通过renderableInstance.detachFromRenderer(); 把renderableInstance从renderder里移除掉。我们顺便看看移除都做了什么

 /**
     * @hide
     */
    public void detachFromRenderer() {
        Renderer rendererToDetach = attachedRenderer;
        if (rendererToDetach != null) {
            detachFilamentAssetFromRenderer();
            // this method was not called before
            destroyAsset();
            rendererToDetach.removeInstance(this);
            renderable.detatchFromRenderer();
        }
    }

我们分别跟下上面方法的实现。

1. 第一步 RenderableInstance:  detachFilamentAssetFromRenderer()
void detachFilamentAssetFromRenderer() {
    FilamentAsset currentFilamentAsset = filamentAsset;
    if (currentFilamentAsset != null) {
        int[] entities = currentFilamentAsset.getEntities();
        for (int entity : entities) {
            Preconditions.checkNotNull(attachedRenderer).getFilamentScene().removeEntity(entity);
        }
        int root = currentFilamentAsset.getRoot();
        Preconditions.checkNotNull(attachedRenderer).getFilamentScene().removeEntity(root);
    }
}

从代码中看到从这里开始调用filament的类Scene去移除entity了。

2. 第二步 RenderableInstance: destroyAsset() 这里调用了filament的类AssetLoader去销毁asset

public void destroyAsset() {

    if (filamentAsset != null) {
        loader.destroyAsset(filamentAsset);
        filamentAsset = null;
    }
}

3. 第三步 Renderer: rendererToDetach.removeInstance()
   第一行代码 removeModelInstanceInternal()其实是个空实现，啥也没处理。
   第二行代码 则是调用了filament的Scene去移除entity 。
   第三行代码很简单就是把instance从集合里移除掉，这个集合会在RenderableInstance.attachToRenderer()时把instance添加到集合里。

/** @hide */
void removeInstance(RenderableInstance instance) {
  removeModelInstanceInternal(instance);
  scene.remove(instance.getRenderedEntity());
  renderableInstances.remove(instance);
}

private void removeModelInstanceInternal(RenderableInstance instance) {return ;}

4. 第四步 Renderable：detatchFromRenderer()-这个是个抽象方法，具体实现我们需要看子类的实现。
   Renderable有两个子类分别是ModelRenderable和ViewRenderable。很奇怪的是ModelRenderable没有实现（这里会不会内存泄漏？），只有ViewRenderable实现了，如下所示

 @Override
  void detatchFromRenderer() {
//    Log.d("steven","detatchFromRenderer");
    Preconditions.checkNotNull(viewRenderableData).getRenderView().detachView();
    this.renderer = null;
  }

这里仅仅把view从frameLayout移除

void detachView() {
  if (viewAttachmentManager != null) {
    viewAttachmentManager.removeView(this);
    viewAttachmentManager = null;
  }
}

void removeView(View view) {
  if (view.getParent() != frameLayout) {
    return;
  }

  frameLayout.removeView(view);
}