How to apply UIEdgeInsets to CGImage?

Question

How does one apply UIEdgeInsets (or some variation thereof) to a CGImage? This is what I'm ultimately trying to achieve but the CGImage is not recognizing the bottom inset applied to the UIImage before it is converted to a CGImage.

var image = someUIImage
image = image.withAlignmentRectInsets(UIEdgeInsets(top: 0, left: 0, bottom: (image.size.height / 2), right: 0))
let imageCG: CGImage = image.cgImage!
layer.contents = imageCG

And I can't apply an inset to the CGImage directly (as seen here).

let image = someUIImage.cgImage!
image. // can't apply any inset here
layer.contents = image

Workaround?

Answer 1

You cannot “apply UIEdgeInsets” to a CGImage because a CGImage doesn't have an alignmentRectInsets property. A UIImage stores several properties that a CGImage does not, including alignmentRectInsets.

Note that the alignmentRectInsets property exists to influence how auto layout poses a UIImageView containing the image. A UIImageView sets its own alignmentRectInsets from the alignmentRectInsets of its UIImage. Auto layout then uses the alignment rect when computing the frame of the UIImageView.

Auto layout doesn't work with layers, so a CALayer has no need for a alignmentRectInsets property.

In other words, what you're asking for doesn't really make sense.

If you revise your question to explain what visual effect you want, I might be able to offer advice on how to get it.

Answer 2

Try this way :

let resizable = img.resizableImage(withCapInsets: UIEdgeInsets(top: 8, left: 8, bottom: 8, right: 8), resizingMode: .stretch)