How to find the scale from a CGAffineTransform

Written by Paul Hudson    @twostraws

If you have a CGAffineTransform and want to know what its scale component is – regardless of whether it has been rotated or translated – use this code:

func scale(from transform: CGAffineTransform) -> Double {
    return sqrt(Double(transform.a * transform.a + transform.c * transform.c))
}

Available from iOS 2.0

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This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.