Putting a fade in fadeout Effect on objective C - objective-c

Question

I want this to be a background in my app for Ipad.
I'm building everything in objective C (native app)
I need a little help figuring out how to animate each of the triangles over the image (overlay) so it fades in and out independently of each other, the goal to make a constant shimmer like effect so the image doesn't feel sos tatic. Do i have to animate each triangle independently? Is there any algorithm that i should be looking at so it seems kinda random but isn't.
Here is the background image
I need some guidance on where to start and how to approach this problem, and feedback would be appreciated.

Answer 1

a) My advice is to use UIViewAnimationWithBlocks introduced in iOS 4. If you have a solid grasp on blocks, they can be very useful. Here's an example I created in as little as 5 minutes to illustrate:
typedef void(^FadeInOutBlock)(void);
#interface PMViewController ()
#property (nonatomic, copy) FadeInOutBlock fadeInOutBlock;
#end
Here we declare a typedef to save us from doing the block syntax all over again. We also create a property to hold the animation block.
#implementation PMViewController
#synthesize myView;
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
__block PMViewController *_self = self;
self.fadeInOutBlock = ^{
[UIView animateWithDuration:0.5f animations:^{
// fade out effect
_self.myView.alpha = 0.0f;
} completion:^(BOOL success){
[UIView animateWithDuration:0.5f animations:^{
// fade in effect
_self.myView.alpha = 1.0f;
} completion:^(BOOL success){
// recursively fire a new animation
if (_self.fadeInOutBlock)
_self.fadeInOutBlock();
}];
}];
};
}
We create the animation, within an animation. You start off with the fade out, where myView's alpha will be reduced to 0.0f in 0.5f seconds. After it's completed, a second animation will be fired, restoring the alpha for myView back to 1.0f and finally, firing out the first animation, again. (Animception)
- (void)viewDidAppear:(BOOL)animated
{
[super viewDidAppear:animated];
if (self.fadeInOutBlock)
self.fadeInOutBlock();
}
#end
And finally, in view did appear you fire it off for the first time.
b)
Now, for the shimmering animation that you mention, I suggest you separate each triangle into it's own UIView and use the technique above, using different durations and alphas.
If you have to many small UIViews, group them up into a bigger UIView (by using the addSubview method) and apply the animation to those 'container' UIViews.
For instance, you could have four separate UIView containers, that have a bunch of separate UIViews as their children. You could then create four block animations, one for each container, and then apply the animation to them. I bet experimenting with that, you would be able to create pretty good effects.

Answer 2

You can do this without any special librarys. So you need to create a black UIView with an alpha of 0. Then create an NSTimer that increases the alpha of the UIView.