Changed Anchor Point of CALayer in Layer-backed NSView - macos

Question

I am trying to have a zoom animation run on a layer-backed NSView by animating the transform of the backing layer. The issue I am having with this, is that the animation zooms into the bottom left corner instead of the center of the view. I figured out that this is because NSView sets its backing layer's anchor point to (0, 0), even after I change it to some other value. This post talks about a similar issue.
I know that to get around this, I could make the view a layer-hosting view. However, I would like to use auto layout, which is why that is not really an option.
Does anyone know another way to get around this behavior and keep the anchor point of the view's backing layer at (0.5, 0.5)? The excerpt from apple's documentation in the post I linked above talks about NSView cover methods. What could such cover method be for the anchor point?
Thanks a lot!

Answer 1

The trick is to override the backing layer and pass an anchor point of choice (to be able to zoom from top left, for instance). Here's what I use:
extension CGPoint {
static let topLeftAnchor: Self = .init(x: 0.0, y: 1.0)
static let bottomLeftAnchor: Self = .init(x: 0.0, y: 0.0)
static let topRightAnchor: Self = .init(x: 1.0, y: 1.0)
static let bottomRightAnchor: Self = .init(x: 1.0, y: 0.0)
static let centerAnchor: Self = .init(x: 0.5, y: 0.5)
}
class AnchoredLayer: CALayer {
public var customAnchorPoint = CGPoint.topLeftAnchor
override var anchorPoint: CGPoint {
get { customAnchorPoint }
set { super.anchorPoint = customAnchorPoint }
}
}
class AnchoredView: NSView {
required convenience init(anchoredTo point: CGPoint) {
self.init(frame: .zero)
self.wantsLayer = true
self.anchorPoint = point
}
public override func makeBackingLayer() -> CALayer {
let roundedLayer = AnchoredLayer()
return roundedLayer
}
public var anchorPoint: CGPoint {
get { (layer as! AnchoredLayer).customAnchorPoint }
set { (layer as! AnchoredLayer).customAnchorPoint = newValue }
}
}
Then use AnchoredView as normal:
let myView = AnchoredView(anchoredTo: .topLeftAnchor)
// Create the scale animation
let transformScaleXyAnimation = CASpringAnimation()
transformScaleXyAnimation.fillMode = .forwards
transformScaleXyAnimation.keyPath = "transform.scale.xy"
transformScaleXyAnimation.toValue = 1
transformScaleXyAnimation.fromValue = 0.8
transformScaleXyAnimation.stiffness = 300
transformScaleXyAnimation.damping = 55
transformScaleXyAnimation.mass = 0.8
transformScaleXyAnimation.initialVelocity = 4
transformScaleXyAnimation.duration = transformScaleXyAnimation.settlingDuration
myView.layer?.add(transformScaleXyAnimation, forKey: "transformScaleXyAnimation")
...