CAKeyframeAnimation.rotationMode

viewController.m

- (void)viewDidLoad
{
    [super viewDidLoad];    
    self.view.backgroundColor = [UIColor blackColor];    
    [self action];
}

- (void)action
{
    //Create Content Layer
    CALayer* layer = [CALayer layer];
    layer.frame = CGRectMake(0, 0, 150, 150);
    UIImage* image = [UIImage imageNamed:@"Sgt600.jpg"];
    layer.contents = (id)image.CGImage;    
    [self.view.layer addSublayer:layer];
    
    CAKeyframeAnimation* animation;
    animation = [CAKeyframeAnimation animationWithKeyPath:@"position"];
    animation.duration = 3.0;
    animation.repeatCount = FLT_MAX;
    
    //Create circle path
    CGMutablePathRef path = CGPathCreateMutable();
    CGPathAddArc(path,
                 NULL,
                 self.view.center.x, 
                 self.view.center.y,
                 100,
                 0, 
                 M_PI * 2, false);
    animation.path = path;
    animation.rotationMode = kCAAnimationRotateAuto;
    [layer addAnimation:animation forKey:nil];
    CFRelease(path);
}

kCAAnimationRotateAutoReverseにすると、アニメーションするLayerの上下が逆になる。

CGPathCreateWithEllipseInRectで簡単にやりたいところだけど、これでPath作ると、終点が長くなるみたいで、そこでアニメーションがかなりの時間止まってしまう。