如何将UIEdgeInsets应用于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)