获取UIBezierPath的起点

Question

我创建了一个UIBezierPath,但我不知道如何访问它的起点.我试过这样做:

let startPoint = path.currentPoint

该属性currentPoint给了我最后一点,而不是起点.我需要起点的原因是因为我想在路径的起点放置一个图像.

有任何想法吗？

Answer 1

您需要下拉CGPath并使用它CGPathApply来遍历元素.你只想要第一个,但你必须全部看看它们.

我假设你的道路格式正确,并以"移动"开始.对于一个人来说应该永远是对的UIBezierPath(我不知道有任何办法让它变得不真实.)

你需要一些来自rob mayoff的帮助CGPath.forEach,这非常棘手,但有了它,它非常简单:

// rob mayoff's CGPath.foreach
extension CGPath {
    func forEach(@noescape body: @convention(block) (CGPathElement) -> Void) {
        typealias Body = @convention(block) (CGPathElement) -> Void
        func callback(info: UnsafeMutablePointer<Void>, element: UnsafePointer<CGPathElement>) {
            let body = unsafeBitCast(info, Body.self)
            body(element.memory)
        }
        let unsafeBody = unsafeBitCast(body, UnsafeMutablePointer<Void>.self)
        CGPathApply(self, unsafeBody, callback)
    }
}

// Finds the first point in a path
extension UIBezierPath {
    func firstPoint() -> CGPoint? {
        var firstPoint: CGPoint? = nil

        self.CGPath.forEach { element in
            // Just want the first one, but we have to look at everything
            guard firstPoint == nil else { return }
            assert(element.type == .MoveToPoint, "Expected the first point to be a move")
            firstPoint = element.points.memory
        }
        return firstPoint
    }
}

在Swift 3中,它基本相同:

// rob mayoff's CGPath.foreach
extension CGPath {
    func forEach( body: @convention(block) (CGPathElement) -> Void) {
        typealias Body = @convention(block) (CGPathElement) -> Void
        func callback(info: UnsafeMutableRawPointer?, element: UnsafePointer<CGPathElement>) {
            let body = unsafeBitCast(info, to: Body.self)
            body(element.pointee)
        }
        let unsafeBody = unsafeBitCast(body, to: UnsafeMutableRawPointer.self)
        self.apply(info: unsafeBody, function: callback)
    }
}

// Finds the first point in a path
extension UIBezierPath {
    func firstPoint() -> CGPoint? {
        var firstPoint: CGPoint? = nil

        self.cgPath.forEach { element in
            // Just want the first one, but we have to look at everything
            guard firstPoint == nil else { return }
            assert(element.type == .moveToPoint, "Expected the first point to be a move")
            firstPoint = element.points.pointee
        }
        return firstPoint
    }
}