Any quick and dirty anti-aliasing techniques for a rotated UIImageView?

Question

I've got a UIImageView (full frame and rectangular) that i'm rotating with a CGAffineTransform. The UIImage of the UIImageView fills the entire frame. When the image is rotated and drawn the edges appear noticeably jagged. Is there anything I can do to make it look better? It's clearly not being anti-aliased with the background.

Answer 1

The edges of CoreAnimation layers aren't antialiased by default on iOS. However, there is a key that you can set in Info.plist that enables antialiasing of the edges: UIViewEdgeAntialiasing.

https://developer.apple.com/library/content/documentation/General/Reference/InfoPlistKeyReference/Articles/iPhoneOSKeys.html

If you don't want the performance overhead of enabling this option, a work-around is to add a 1px transparent border around the edge of the image. This means that the 'edges' of the image are no longer on the edge, so don't need special treatment!