distance to point

distance to point

    func distanceToPoint(point p: CGPoint, fromLineSegmentBetween l1: CGPoint, and l2: CGPoint) -> Float {
        let a = p.x - l1.x
        let b = p.y - l1.y
        let c = l2.x - l1.x
        let d = l2.y - l1.y
        
        let dot = a * c + b * d
        let lenSq = c * c + d * d
        let param = dot / lenSq
        
        var xx:CGFloat!
        var yy:CGFloat!
        
        if param < 0 || (l1.x == l2.x && l1.y == l2.y) {
            xx = l1.x
            yy = l1.y
        } else if (param > 1) {
            xx = l2.x
            yy = l2.y
        } else {
            xx = l1.x + param * c
            yy = l1.y + param * d
        }
        
        let dx = Float(p.x - xx)
        let dy = Float(p.y - yy)
        
        return sqrtf(dx * dx + dy * dy)
    }