How to get corner points of Rect rotated in Core Graphics?

Question

I have a CGRect which I have rotated using translation and rotation function as below:-

        let ctx: CGContext = UIGraphicsGetCurrentContext()!
        ctx.saveGState()
        let halfWidth = (selectedCropRect?.size.width)! / 2.0
        let halfHeight = (selectedCropRect?.size.height)! / 2.0
        let center = CGPoint(x: (selectedCropRect?.origin.x)! + halfWidth, y: (selectedCropRect?.origin.y)! + halfHeight)

        // Move to the center of the rectangle:
        ctx.translateBy(x: center.x, y: center.y)
        // Rotate:
        ctx.rotate(by: rotationAngle!);
        // Draw the rectangle centered about the center:
        let rect = CGRect(x: -halfWidth, y: -halfHeight, width: (selectedCropRect?.size.width)!, height: (selectedCropRect?.size.height)!)
        let path = UIBezierPath(rect: rect).cgPath
        ctx.addPath(path)
        ctx.restoreGState()

Now the problem is i need to get all the corner points of the rotated rect and place circular views on the corner points so that the user can drag the corner points and increase/decrease size of rect. Any idea how i can place the circular views on the 4 corner points of rotated rect?

Answer 1

Untested but this should help point you in the right direction

guard let rect = selectedCropRect else {
    return
}

let rectCenter = CGPoint(x: rect.width/2, y: rect.height/2)

// Or whatever angle you supply
let rotAngle = CGFloat.pi/4.0

// Rotate around center of rect
/*
  Instead of creating a new transform you should store a transform 
  inside of the object you are transforming like UIView does 
*/
var transform = CGAffineTransform(translationX: rectCenter.x, y: rectCenter.y)
transform = transform.rotated(by: rotAngle)
transform = transform.translatedBy(x: -rectCenter.x, y: -rectCenter.y)

// Get transformed center
let originalCenter = rectCenter.applying(transform)

var topLeft = originalCenter
topLeft.x -= rectCenter.x
topLeft.y -= rectCenter.y
topLeft = topLeft.applying(transform)

var topRight = originalCenter
topRight.x += rectCenter.x
topRight.y -= rectCenter.y
topRight = topRight.applying(transform)

var botLeft = originalCenter
botLeft.x -= rectCenter.x
botLeft.y += rectCenter.y
botLeft = botLeft.applying(transform)

var botRight = originalCenter
botRight.x += rectCenter.x
botRight.y += rectCenter.y
botRight = botRight.applying(transform)

// Create new path using the orignal supplied rect and transform
let path = CGPath(rect: rect, transform: &transform)
let bez = UIBezierPath(cgPath: path)

// Do whatever you need with the context