CAShapeLayer and animation position issue - iphone

Question

I am making an iPhone app that draws a circle on the screen. I use a timer (every 5 second), so that I can 'grow' the circle, then wait 5 seconds then grow again. Now I am having trouble when animating the increase in size of the circle (I use paths and a CAShapeLayer layer). The size (from and to) are fine with the animation, its just when it starts the circle moves to the upper left hand side and grows from there. Any help or suggestions would be great. Thanks
The class where this is implemented is a UIControl, which is added to a UIView.
//Called in init method
(void) initalPop {
//Circle
self.bubble = [CAShapeLayer layer];
self.bubble.bounds = self.bounds;
self.bubble.position = CGPointMake(CGRectGetMidX(self.bounds), CGRectGetMidY(self.bounds));
self.bubble.fillColor = [
[UIColor greenColor] CGColor
];
self.bubble.strokeColor = [
[UIColor greenColor] CGColor
];
self.bubble.lineWidth = 4.0;
CGMutablePathRef path = CGPathCreateMutable();
CGPathAddEllipseInRect(path, nil, self.bounds);
self.bubble.path = path;
[self.layer addSublayer: self.bubble];
}
//Called when timer goes off
- (void) StageGrow {
CGFloat growSize = 50.0;
//Change the size of us and center the circle (but dont want to animate this
[CATransaction begin];
[CATransaction setValue: (id) kCFBooleanTrue forKey: kCATransactionDisableActions];
self.bounds = CGRectMake(0, 0, self.bounds.size.width + growSize, self.bounds.size.height + growSize);
self.bubble.position = CGPointMake(CGRectGetMidX(self.bounds), CGRectGetMidY(self.bounds));
[CATransaction commit];
[self ActualGrowCircle];
} - (void) ActualGrowCircle {
CGMutablePathRef oldPath = CGPathCreateMutable();
CGPathAddEllipseInRect(oldPath, nil, self.bubble.bounds);
CGMutablePathRef path = CGPathCreateMutable();
CGPathAddEllipseInRect(path, nil, self.bounds);
CABasicAnimation * animation = [CABasicAnimation animationWithKeyPath: #"path"];
animation.duration = 2.0;
animation.timingFunction = [CAMediaTimingFunction functionWithName: kCAMediaTimingFunctionEaseInEaseOut];
animation.repeatCount = 1;
animation.delegate = self;
animation.autoreverses = NO;
animation.fromValue = (__bridge id) oldPath;
animation.toValue = (__bridge id) path;
self.bubble.bounds = self.bounds;
self.bubble.path = path;
[self.bubble addAnimation: animation forKey: #"animatePath"];
}

Answer 1

Let's say you're growing the bubble from size (100, 100) to size (150, 150).
You create oldPath as an ellipse in the rectangle (0, 0, 100, 100).
You create path as an ellipse in the rectangle (0, 0, 150, 150).
You set the bounds of the bubble layer to (0, 0, 150, 150), and you don't animate this change.
That means that oldPath will appear aligned to the top and left edges of the bubble layer.
One way to fix this is to create oldPath in a rectangle that is centered in the bubble's new bounds:
CGRect oldBubbleRect = CGRectInset(self.bounds, growSize / 2, growSize / 2);
CGPathRef oldPath = CGPathCreateWithEllipseInRect(oldBubbleRect, NULL);
By the way, you are leaking the paths you're creating. You need to call CGPathRelease on them after you're done with them.

Answer 2

Worked it out. In the long run I grouped the animations together and all became good (see code below). Thanks for your help Rob.
-(void)ActualGrowCircle {
CGMutablePathRef newPath = CGPathCreateMutable();
CGPathAddEllipseInRect(newPath, nil, self.bounds);
CABasicAnimation *animation = [CABasicAnimation animationWithKeyPath:#"path"];
animation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut];
animation.repeatCount = 1;
animation.autoreverses = NO;
animation.fromValue = (__bridge id)self.bubble.path;
animation.toValue = (__bridge id)newPath;
CABasicAnimation *animation2 = [CABasicAnimation animationWithKeyPath:#"bounds"];
animation2.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut];
animation2.repeatCount = 1;
animation2.autoreverses = NO;
animation2.fromValue = [NSValue valueWithCGRect:self.bubble.bounds];
animation2.toValue = [NSValue valueWithCGRect:self.bounds];
CAAnimationGroup *group = [CAAnimationGroup animation];
[group setAnimations:[NSArray arrayWithObjects: animation2, animation, nil]];
group.duration = 0.5;
group.delegate = self;
self.bubble.bounds = self.bounds;
self.bubble.path = newPath;
[self.bubble addAnimation:group forKey:#"animateGroup"];
CGPathRelease(newPath);
}