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 beha

Answer 1

For completeness, here is how I animated my CALayer subclass — inspired by the other answers — using an explicit animation.

-(void)stopJiggle 
{
    [self removeAnimationForKey:@"jiggle"];
}

-(void)startJiggle 
{
    const float amplitude = 1.0f; // degrees
    float r = ( rand() / (float)RAND_MAX ) - 0.5f;
    float angleInDegrees = amplitude * (1.0f + r * 0.1f);
    float animationRotate = angleInDegrees / 180. * M_PI; // Convert to radians

    NSTimeInterval duration = 0.1;
    CABasicAnimation *animation = [CABasicAnimation animationWithKeyPath:@"transform.rotation"];
    animation.duration = duration;
    animation.additive = YES;
    animation.autoreverses = YES;
    animation.repeatCount = FLT_MAX;
    animation.fromValue = @(-animationRotate);
    animation.toValue = @(animationRotate);
    animation.timeOffset = ( rand() / (float)RAND_MAX ) * duration;
    [self addAnimation:animation forKey:@"jiggle"];
}