iphone - iOS icon jiggle algorithm

Question

I am writing an iPad app that presents user documents similar to the way Pages presents them (as large icons of the actual document). I also want to mimic the jiggling behavior when the user taps the edit button. This is the same jiggle pattern that icons make on the home screen when you tap and hold on them on both the iPhone and iPad.

I've searched the Internet and have found a few algorithms but they just cause the view to rock back and forth which is not at all like the Apple jiggle. It seems there is some randomness in there as each icon jiggles a little differently.

Does anyone have or know of some code that can re-create the same jiggle pattern (or something very close to it)? Thanks!!!

Answer 1

@Vic320's answer is good but personally I don't like the translation. I've edited his code to provide a solution that I personally feel looks more like the springboard wobble effect. Mostly, it's achieved by adding a little randomness and focusing on rotation, without translation:

#define degreesToRadians(x) (M_PI * (x) / 180.0)
#define kAnimationRotateDeg 1.0

- (void)startJiggling {
    NSInteger randomInt = arc4random_uniform(500);
    float r = (randomInt/500.0)+0.5;

    CGAffineTransform leftWobble = CGAffineTransformMakeRotation(degreesToRadians( (kAnimationRotateDeg * -1.0) - r ));
    CGAffineTransform rightWobble = CGAffineTransformMakeRotation(degreesToRadians( kAnimationRotateDeg + r ));

     self.transform = leftWobble;  // starting point

     [[self layer] setAnchorPoint:CGPointMake(0.5, 0.5)];

     [UIView animateWithDuration:0.1
                           delay:0
                         options:UIViewAnimationOptionAllowUserInteraction | UIViewAnimationOptionRepeat | UIViewAnimationOptionAutoreverse
                       animations:^{ 
                                 [UIView setAnimationRepeatCount:NSNotFound];
                                 self.transform = rightWobble; }
                      completion:nil];
}
- (void)stopJiggling {
    [self.layer removeAllAnimations];
    self.transform = CGAffineTransformIdentity;
}

Credit where credit's due though, @Vic320's answer provided the basis for this code so +1 for that.