On-demand OpenGL ES rendering using GLKit

Question

I am looking into converting my OpenGL rendering code to take advantage of a few features of GLKit (namely the asynchronous texture loading and the automation provided by GLKView/Controller). However, it appears that the classes are designed mainly to accommodate people rendering using an animation loop, whereas I'm working with on-demand rendering. Additionally, some of the rendering is to a texture rather than the GLKView's framebuffer, so should I be looking to just subclass the GLKView and add additional FBOs?

Is there a recommended approach for this type of setup? I would expect something along the lines of:

• Set the view controller's preferredFramesPerSecond to 0, or just pause the frame updates?
• Ignore the glkViewControllerUpdate or glkView:drawInRect: methods and just draw what I need, when I need it.
• Use the view's setNeedsDisplay as with a normal UIView in order to display the frame (do I need to call bindDrawable given that I will be rendering to a texture as well?).

Perhaps it's not worth the effort if this is not what the new API is designed for? I wish the documentation was a little more thorough than it is. Perhaps more samples will be provided when the API has 'matured' a little...

Thanks

Answer 1

The approach I ended up using was to not bother with the GLKViewController, but just use GLKView directly under a UIViewController subclass.

Clearly, the GLKViewController is intended for use by people who need a consistent rendering loop for apps such as games. Without it, drawing to the GLKView is as simple as calling [glkView setNeedsDisplay]. Be sure to set enableSetNeedsDisplay to YES in order to enable this behaviour.

If you did still want to make use of a GLKViewController, you can disable the animation rendering loop in viewWillAppear like so:

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];    // setPaused automatically set to NO in super's implementation

    [self setPaused:YES];
}

Also, set resumeOnDidBecomeActive to NO to prevent the view controller from resuming again automatically.

Using a plain UIViewController with a GLKView is perfectly acceptable however, and I have seen it recommended by an Apple engineer as an appropriate way to perform on-demand drawing.