CGMutablePath.addArc not working in Swift 3? - ios

Question

In Xcode 8 beta 6, some of the functions to add a path changed, including those that add an arc:
func addArc(center: CGPoint, radius: CGFloat, startAngle: CGFloat, endAngle: CGFloat, clockwise: Bool, transform: CGAffineTransform = default)
Beyond a definition of the function, there is no documentation on Apple's site. I've been unable to get an actual arc from this function, and have been relying on a second version that uses tangents. Can anyone provide a working sample? Could it just be bugged?
Here is a function that is broken by the change:
public class func createHorizontalArcPath(_ startPoint:CGPoint, width:CGFloat, arcHeight:CGFloat, closed:Bool = false) -> CGMutablePath
{
// http://www.raywenderlich.com/33193/core-graphics-tutorial-arcs-and-paths
let arcRect = CGRect(x: startPoint.x, y: startPoint.y-arcHeight, width: width, height: arcHeight)
let arcRadius = (arcRect.size.height/2) + (pow(arcRect.size.width, 2) / (8*arcRect.size.height));
let arcCenter = CGPoint(x: arcRect.origin.x + arcRect.size.width/2, y: arcRect.origin.y + arcRadius);
let angle = acos(arcRect.size.width / (2*arcRadius));
let startAngle = CGFloat(M_PI)+angle // (180 degrees + angle)
let endAngle = CGFloat(M_PI*2)-angle // (360 degrees - angle)
let path = CGMutablePath();
path.addArc(center: arcCenter, radius: arcRadius, startAngle: startAngle, endAngle: endAngle, clockwise: true)
if(closed == true)
{path.addLine(to: startPoint)}
return path;
}

Answer 1

Your Swift code is based on the Objective-C code from http://www.raywenderlich.com/33193/core-graphics-tutorial-arcs-and-paths,
where the arc path is created as
CGPathAddArc(path, NULL, arcCenter.x, arcCenter.y, arcRadius,
startAngle, endAngle, 0);
In particular, 0 is passed as argument to the last parameter bool clockwise. That should be translated to false in Swift, not true:
path.addArc(center: arcCenter, radius: arcRadius,
startAngle: startAngle, endAngle: endAngle, clockwise: false)