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How to calculate the distance between two CGPoints

Paul Hudson       @twostraws

You can calculate the distance between two CGPoints by using Pythagoras's theorem, but be warned: calculating square roots is not fast, so if possible you want to avoid it. More on that in a moment, but first here's the code you need:

func CGPointDistanceSquared(from: CGPoint, to: CGPoint) -> CGFloat {
    return (from.x - to.x) * (from.x - to.x) + (from.y - to.y) * (from.y - to.y)
}

func CGPointDistance(from: CGPoint, to: CGPoint) -> CGFloat {
    return sqrt(CGPointDistanceSquared(from: from, to: to))
}

Note that there are two functions: one for returning the distance between two points, and one for returning the distance squared between two points. The latter one doesn't use a square root, which makes it substantially faster. This means if you want to check "did the user tap within a 10-point radius of this position?" it's faster to square that 10 (to make 100) then use CGPointDistanceSquared() instead.

Available from iOS 2.0

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