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# fewlinesofcode/UIBezierPath+RoundedCorners.swift

Last active Jul 20, 2020
 import UIKit public extension CGPoint { func distance(to point: CGPoint) -> CGFloat { let xDist = x - point.x let yDist = y - point.y return (xDist * xDist + yDist * yDist).squareRoot() } } public func radiusOfCircle(inscribedInto triangle: (pa: CGPoint, pb: CGPoint, pc: CGPoint)) -> CGFloat { let (pa, pb, pc) = triangle let a = pa.distance(to: pb) let b = pb.distance(to: pc) let c = pc.distance(to: pa) let halfP = (a + b + c) / 2 return ((halfP - a) * (halfP - b) * (halfP - c) / halfP).squareRoot() } extension UIBezierPath { private static func addCorner( _ path: UIBezierPath, p1: CGPoint, p: CGPoint, p2: CGPoint, radius: CGFloat, isStart: Bool = false ) { // Override `radius` with maximum available radius // which is the radius of the circle inscribed into triangle defined by our points var radius = min( radiusOfCircle(inscribedInto: (p1, p, p2)), radius ) // Find the angle defined by our points let angle = CGFloat(atan2(p.y - p1.y, p.x - p1.x) - atan2(p.y - p2.y, p.x - p2.x)).positiveAngle // Get the length of segment between angular point and the points of intersection with the circle. var tangentLength = radius / abs(tan(angle / 2)) // Check the length of segment and the minimal length from let p_p1 = p.distance(to: p1) let p_p2 = p.distance(to: p2) // Update `tangentLenghth` according to the smaller triangle side tangentLength = min(tangentLength, min(p_p1, p_p2)) // Update `radius` according to the smaller triangle side radius = tangentLength * abs(tan(angle / 2)) // Find distance from angle vertex to circle origin let p_o = sqrt(radius.sqr + tangentLength.sqr) // Segment intersected by parallel lines is divided keeping proportion // Project angle sides onto axis and calculate circle origin from the proportion let c1 = CGPoint( x: (p.x - (p.x - p1.x) * tangentLength / p_p1), y: (p.y - (p.y - p1.y) * tangentLength / p_p1) ) let c2 = CGPoint( x: (p.x - (p.x - p2.x) * tangentLength / p_p2), y: (p.y - (p.y - p2.y) * tangentLength / p_p2) ) let dx = p.x * 2 - c1.x - c2.x let dy = p.y * 2 - c1.y - c2.y let p_c = (dx.sqr + dy.sqr).squareRoot() // Find Circle origin let o = CGPoint( x: p.x - dx * p_o / p_c, y: p.y - dy * p_o / p_c ) // Find start and end angle (required for Arc drawing) let startAngle = (atan2((c1.y - o.y), (c1.x - o.x))).positiveAngle let endAngle = (atan2((c2.y - o.y), (c2.x - o.x))).positiveAngle if isStart { path.move(to: c1) } else { path.addLine(to: c1) } path.addArc(withCenter: o, radius: radius, startAngle: startAngle, endAngle: endAngle, clockwise: angle < .pi) } public static func roundedCornersPath(_ pts: [CGPoint], _ r: CGFloat) -> UIBezierPath? { guard pts.isEmpty == false else { return nil } let path = UIBezierPath() for i in 1...pts.count { let prev = pts[i-1] let curr = pts[i % pts.count] let next = pts[(i + 1) % pts.count] addCorner(path, p1: prev, p: curr, p2: next, radius: r, isStart: i == 1) } path.close() return path } } public extension CGFloat { var sqr: CGFloat { self * self } var positiveAngle: CGFloat { self < 0 ? self + 2 * .pi : self } }

### miku1958 commented May 7, 2020 • edited

 where is implement of CGFolat.positiveAngle?

### fewlinesofcode commented May 7, 2020

 @miku1958, sorry. Here it is: ``````public extension CGFloat { var positiveAngle: CGFloat { self < 0 ? self + 2 * .pi : self } } ``````

### fewlinesofcode commented May 7, 2020

 @miku1958, implementation also edited.

### miku1958 commented May 7, 2020

 thanks!