Shadow on UIView layer

Question

I've make a path in order to mask my view:

let path = // create magic path (uiview bounds + 2 arcs)
let mask = CAShapeLayer()
mask.path = path.cgPath
view.layer.masksToBounds = false
view.layer.mask = mask

Up to here all ok.

Now I would like to add a shadow that follows path, is it possibile?

I try in several way, the last one is:

mask.shadowPath = path.cgPath
mask.shadowColor = UIColor.red.cgColor
mask.shadowOffset = CGSize(width: 10, height: 2.0)       
mask.shadowOpacity = 0.5

But this produce a partial shadow and with color of the original view..

With debug view hierarchy:

Any advice?

Final result should be similar to this, but with shadow that "follows" arcs on path.

Answer 1

When you add a mask to a layer, it clips anything outside that mask - including the shadow. To achieve this you'll need to add a "shadow" view below your masked view, that has the same path as the mask.

Or add a shadow layer to the masked view's superview.

let view = UIView(frame: CGRect(x: 50, y: 70, width: 100, height: 60))
view.backgroundColor = .cyan

let mask = CAShapeLayer()
mask.path = UIBezierPath(roundedRect: view.bounds, cornerRadius: 10).cgPath
view.layer.mask = mask

let shadowLayer = CAShapeLayer()
shadowLayer.frame = view.frame
shadowLayer.path = UIBezierPath(roundedRect: view.bounds, cornerRadius: 10).cgPath
shadowLayer.shadowOpacity = 0.5
shadowLayer.shadowRadius = 5
shadowLayer.masksToBounds = false
shadowLayer.shadowOffset = .zero    

let container = UIView(frame: CGRect(x: 0, y: 0, width: 200, height: 200))
container.backgroundColor = .white
container.layer.addSublayer(shadowLayer)
container.addSubview(view)

If you're going to be using this elsewhere, you could create a ShadowMaskedView that contains the shadow layer, and the masked view - maybe with a path property.