Question

When I launch my game I want the screen to show a loading image while loading resources in the background. I do this by loading a simple UIImageView component and adding a “spinner” to it, to give the user feedback, that the device is loading something in the background.

While this image is showing I load all my images and textures and set up my OpenGL view and let it render.
When the 2nd frame gets rendered I want to hide the ImageView and only show the OpenGL view. I don’t want the OpenGL view to show on the first frame because it takes awfully long to render.

However, I have some problems with loading all my resources and setting up the DisplayLink for the OpenGL view to enter the render loop in a new thread and then showing the OpenGL view when loading is finished. The render loop doesn’t seem to start.

Here is the loadView method of my View Controller

- (void)loadView 
{
CGRect mainScreenFrame = [[UIScreen mainScreen] applicationFrame];

    // Set up the image view
    UIImage *img = [UIImage imageWithContentsOfFile: [[NSBundle mainBundle] pathForResource:@"Startscreen" ofType:@"png"]];
    _imageView = [[UIImageView alloc] initWithFrame:mainScreenFrame];
    _imageView.image = img;

    // Set up the spinner
    _spinner = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhiteLarge];
    [_spinner setCenter:CGPointMake(mainScreenFrame.size.height/3.0*1.85, mainScreenFrame.size.width/10.0*7.55)];
    [_imageView addSubview:_spinner];    
    [_spinner startAnimating];

    // Show the loading image
    self.view = _imageView;

    /* Load resources in a new thread -- this shows the spinner during loading */
    [NSThread detachNewThreadSelector:@selector(loadGLView) toTarget:self withObject:nil];
}

loadGLView only does the following and initializes the OpenGL View and starts the loading process.

_glView = [[JungleOpenGLView alloc] initWithFrame:mainScreenFrame];

This is how I set up the DisplayLink in the OpenGL View.

CADisplayLink* displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(setupRender:)];
[displayLink setFrameInterval:2];
[displayLink addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];

When the 2nd frame gets rendered I send a notification and the ViewController then sets

self.view = _glView;

Answer 1

I found my mistake.
Instead of creating a new thread for the loading method like this:

[NSThread detachNewThreadSelector:@selector(loadGLView) toTarget:self withObject:nil];

I used:

[self performSelectorInBackground:@selector(loadGLView) withObject:nil];

That does the trick. Good read on this subject (creating threads) can be found here: https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/Multithreading/CreatingThreads/CreatingThreads.html