core-graphics - Core-Graphics (iPhone) - 我们能知道 CGPath 是否关闭吗？

Question

是否有任何解决方法可以知道 a CGpath（使用坐标数组创建）在哪里关闭。

我无法在标题中找到任何合适的方法CGPath。

我希望跟踪用户跟踪的路径。如果它是一个闭环，那么我希望从上下文中提取该部分。诸如屏蔽或剪辑上下文之类的东西，但它应该是用户跟踪的剪辑。

谢谢！

Answer 1

实际上，一条路径可以由多个子路径组成。当您移动路径的当前点而不连接两个点时，将创建一个新的子路径。对于要关闭的路径，它的所有子路径实际上必须是关闭的。

extension CGPath {

    /// Note that adding a line or curve to the start point of the current
    /// subpath does not close it. This can be visualized by stroking such a
    /// path with a line cap of `.butt`.
    public var isClosed: Bool {
        var completedSubpathsWereClosed = true
        var currentSubpathIsClosed = true

        self.applyWithBlock({ pointer in
            let element = pointer.pointee

            switch element.type {
            case .moveToPoint:
                if !currentSubpathIsClosed {
                    completedSubpathsWereClosed = false
                }

                currentSubpathIsClosed = true
            case .addLineToPoint, .addQuadCurveToPoint, .addCurveToPoint:
                currentSubpathIsClosed = false
            case .closeSubpath:
                currentSubpathIsClosed = true
            }
        })

        return completedSubpathsWereClosed && currentSubpathIsClosed
    }
}

Answer 2

以防你在过去的 4 1/2 年一直坚持这一点，这里是如何在 Swift 3 中做到这一点。我从这个答案中大量借鉴。我真的只是添加了这个功能。isClosed()

extension CGPath {

func isClosed() -> Bool {
    var isClosed = false
    forEach { element in
        if element.type == .closeSubpath { isClosed = true }
    }
    return isClosed
}

func forEach( body: @convention(block) (CGPathElement) -> Void) {
    typealias Body = @convention(block) (CGPathElement) -> Void
    let callback: @convention(c) (UnsafeMutableRawPointer, UnsafePointer<CGPathElement>) -> Void = { (info, element) in
        let body = unsafeBitCast(info, to: Body.self)
        body(element.pointee)
    }
    print(MemoryLayout.size(ofValue: body))
    let unsafeBody = unsafeBitCast(body, to: UnsafeMutableRawPointer.self)
    self.apply(info: unsafeBody, function: unsafeBitCast(callback, to: CGPathApplierFunction.self))
}
}

并假设path是CGPathor CGMutablePath，这是你如何使用它：

path.isClosed()