Question

I am trying to animate the width of a rounded rectangle, the problem is when going from bigger width to thinner width, the animation does an “aberration ease jump”.

Here’s the code:

shapeLayer = [CAShapeLayer layer];
shapeRect = CGRectMake(0.0f, 0.0f, 150.0f, 200.0f);
[shapeLayer setBounds:shapeRect];
[shapeLayer setPosition:CGPointMake(iniPosX, 80.0f)];
[shapeLayer setFillColor:[[UIColor blackColor] CGColor]];
[shapeLayer setStrokeColor:[[UIColor clearColor] CGColor]];
[shapeLayer setLineWidth:1.0f];
[shapeLayer setLineJoin:kCALineJoinRound];
[shapeLayer setOpacity:0.2];
path = [UIBezierPath bezierPathWithRoundedRect:shapeRect cornerRadius:15.0];
[shapeLayer setPath:path.CGPath];
[self.layer addSublayer:shapeLayer];

And when I start the animation:

- (void)adjustSelectorToPosAndSize:(float)posX andWidth:(float)width
{
    shapeRect = CGRectMake(0.0f, 0.0f, width, 200.0f);
    [shapeLayer setBounds:shapeRect];
    [shapeLayer setPosition:CGPointMake(posX, 80.0f)];
    path = [UIBezierPath bezierPathWithRoundedRect:shapeRect cornerRadius:15.0];
    [shapeLayer setPath:path.CGPath];
}

What am I doing wrong?

Answer 1

Doing this with a CAShapeLayer seems overly complicated to me if you are only using it for a rounded rectangle. Why not simply use a CALayer with the cornerRadius properly set?

Animating the frame with cornerRadius set will work fine.

myLayer = [CALayer layer];
shapeRect = CGRectMake(0.0f, 0.0f, 150.0f, 200.0f);
[myLayer setBounds:shapeRect];
[myLayer setPosition:CGPointMake(iniPosX, 80.0f)];
[myLayer setBackgroundColor:[[UIColor blackColor] CGColor]];
[myLayer setBorderColor:[[UIColor clearColor] CGColor]];
[myLayer setBorderWidth:1.0f];
[myLayer setOpacity:0.2];
[myLayer setCornerRadius:15.0];
[self.layer addSublayer:myLayer];

Animating it is done by simply chaining the frame (not the path)

- (void)adjustSelectorToPosAndSize:(float)posX andWidth:(float)width
{
    shapeRect = CGRectMake(0.0f, 0.0f, width, 200.0f);
    [myLayer setBounds:shapeRect];
    [myLayer setPosition:CGPointMake(posX, 80.0f)];
}

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Important:

Some of the properties changed name like fillColor became backgroundColor and the strokeColor and lineWidth became borderColor and borderWidth etc.