What is the best way to rotate a CGPoint on a grid?

Question

I want to rotate a CGPoint on the screen depending on the angle and the rotation is anchored on another point. Was wondering what is the most efficient way of doing this?

Answer 1

Using Vladimir’s answer, below is the Swift 3 answer:

    let initialPoint = CGPoint(x: 100, y: 100) // the point you want to rotate
    let translateTransform = CGAffineTransform(translationX: initialPoint.x, y: initialPoint.y)
    let rotationTransform = CGAffineTransform(rotationAngle: angle)
    let customRotation = (rotationTransform.concatenating(translateTransform.inverted())).concatenating(translateTransform)
    rotatedPoint = initialPoint.applying(customRotation)