UIBezierPath translation transform gives wrong answer - ios

Question

When I attempt to translate a path, to move it to an origin of {0, 0}, the resulting path bounds is in error. (Or, my assumptions are in error).
e.g. the path gives the following bounds info:
let bezier = UIBezierPath(cgPath: svgPath)
print(bezier.bounds)
// (0.0085, 0.7200, 68.5542, 41.1379)
print(bezier.cgPath.boundingBoxOfPath)
// (0.0085, 0.7200, 68.5542, 41.1379)
print(bezier.cgPath.boundingBox)
// (-1.25, -0.1070, 70.0360, 41.9650)
I (attempt to) move the path to the origin:
let origin = bezier.bounds.origin
bezier.apply(CGAffineTransform(translationX: -origin.x, y: -origin.y))
print(bezier.bounds)
// (0.0, -2.7755, 68.5542, 41.1379)
As you can see, the x origin component is correct at 0. But, the y component (-2.7755) has gone all kittywumpus. It should be 0, non?
The same thing happens when I perform the transform on the cgPath property.
Does anyone know what kind of circumstances could cause a UIBezierPath/CGPath to behave like this when translated? After reading the Apple docs, it seems that UIBezierPath/CGPath do not hold a transform state; the points are transformed immediately when the transform is called.
Thanks for any help.
Background:
The path data is from Font-Awesome SVGs, via PocketSVG. All files parse, and most draw OK. But a small subset exhibit the above translation issue. I'd like to know if I'm doing something fundamentally wrong or silly before I go ferreting through the SVG parsing, path-building code looking for defects.
BTW I am not drawing at this stage or otherwise dealing with a context; I am building paths prior to drawing.
[edit]
To check that PocketSVG was giving me properly formed data, I passed the same SVG to SwiftSVG, and got the same path data as PocketSVG, and the same result:
let svgURL = Bundle.main.url(forResource: "fa-mars-stroke-h", withExtension: "svg")!
var bezier = UIBezierPath.pathWithSVGURL(svgURL)!
print(bezier.bounds)
// (0.0085, 0.7200, 68.5542, 41.1379)
let origin = bezier.bounds.origin
let translation = CGAffineTransform(translationX: -origin.x, y: -origin.y)
bezier.apply(translation)
print(bezier.bounds)
// (0.0, -2.7755, 68.5542, 41.1379)
Once again, that y component should be 0, but is not. Very weird.
On a whim, I thought I'd try to apply a transformation again. And, it worked!
let translation2 = CGAffineTransform(translationX: -bezier.bounds.origin.x, y: -bezier.bounds.origin.y)
bezier.apply(translation2)
print(bezier.bounds)
// (0.0, 0.0, 68.5542491336633, 41.1379438254997)
Baffling! Am I overlooking something really basic here?

Answer 1

I have tried the same as you and is working for me in Xcode 8.3.2 / iOS 10

Answer 2

I struggled myself with the same problem, I managed to solve it by using the following snippet of code (Swift 5). I tested on an organic bezier shape and it works as expected:
extension CGRect {
var center: CGPoint { return CGPoint(x: midX, y: midY) }
}
extension UIBezierPath {
func center(inRect rect:CGRect) {
let rectCenter = rect.center
let bezierCenter = self.bounds.center
let translation = CGAffineTransform(translationX: rectCenter.x - bezierCenter.x, y: rectCenter.y - bezierCenter.y)
self.apply(translation)
}
}
Usage example:
override func viewDidLoad() {
super.viewDidLoad()
let bezier = UIBezierPath() // replace this with your bezier object
let shape = CAShapeLayer()
shape.strokeColor = UIColor.black.cgColor
shape.fillColor = UIColor.clear.cgColor
shape.bounds = self.view.bounds
shape.position = self.view.bounds.center
bezier.center(inRect: shape.bounds)
shape.path = bezier.cgPath
self.view.layer.addSublayer(shape)
}
It will display the shape in the center of the screen.