title: showing progress indicator while scenekit is loading scene
body: <p>I am struggling to create a progress indicator which will show how much a an SCNScene is loading.
  I tried to use the SCNSceneScource class to get a status handler as described by apple's documentation. However, this only gets me so far as to tell me when the scene has loaded. Yet this is not the information I wanted - I would like to show the total progress including the loading time AND the time needed until the SCNNode is displayed ( I assume that is the time needed to push the loaded file into the graphic adapter's memory).</p>
  
  <p>My approach only shows the first of the two times. I did the following: I added an SCNView outlet (self.skView) a button who triggers loading the scene and a UIProgressBar to my View. The progress bar is reflecting the SCNSceneSource's totalProgress property.</p>
  
  <pre><code>- (void)viewDidLoad {
          [super viewDidLoad];
          // set up the SCNView
          if (_skView.scene==nil) _skView.scene = [SCNScene new];
  }
  
  -(void) loadScene {
          SCNSceneSource *s = [SCNSceneSource sceneSourceWithURL:[[NSBundle mainBundle] URLForResource:@"Muscles_V04" withExtension:@"dae"] options:nil];
          SCNScene *scene = [s sceneWithOptions:nil statusHandler:^(float totalProgress, SCNSceneSourceStatus status, NSError * _Nullable error, BOOL * _Nonnull stop) {
          self.proressBar.progress = totalProgress;
          NSLog(@"Total progress %.3f",totalProgress);
  
          // once finished remove the status indicator
          if (totalProgress&gt;=0.9999) {
                  [self.proressBar removeFromSuperview];
              }
          }];
  
          // add the nodes of the loaded scene to the existing scene
          for (SCNNode *n in scene.rootNode.childNodes) {
              NSLog(@"node: %@", n.name);
              [self.skView.scene.rootNode addChildNode:n];
          }
  }
  </code></pre>