Setting a rotation point for CGAffineTransformMakeRotation Swift

Question

I am using the code below to rotate UIImageViews to different angles.

self.imageOne.transform = CGAffineTransformMakeRotation(CGFloat(-rotation))
self.imageT         


        

Answer 1

Here's a Swift 3 extension based off of mttcrp's answer. It took me a while to figure out that the CGPoint isn't a coordinate in the view, but rather a proportion. For example, if you rotated the view around the point CGPoint(x: 0.5, y: 1) it would rotate around the bottom center of the view. Hope this helps!

extension UIView{
    func setAnchorPoint(anchorPoint: CGPoint) {

        var newPoint = CGPoint(x: self.bounds.size.width * anchorPoint.x, y: self.bounds.size.height * anchorPoint.y)
        var oldPoint = CGPoint(x: self.bounds.size.width * self.layer.anchorPoint.x, y: self.bounds.size.height * self.layer.anchorPoint.y)

        newPoint = newPoint.applying(self.transform)
        oldPoint = oldPoint.applying(self.transform)

        var position : CGPoint = self.layer.position

        position.x -= oldPoint.x
        position.x += newPoint.x;

        position.y -= oldPoint.y;
        position.y += newPoint.y;

        self.layer.position = position;
        self.layer.anchorPoint = anchorPoint;
    }
}

and you would use it like this:

let view = UIView() //This could be anything that inherits from UIView
view.setAnchorPoint(anchorPoint: CGPoint(x: 0.5, y: 1))