Swift中CGPathApply的等效或替代？

Question

在预发布文档中,似乎没有Swift版本的CGPathApply.有没有等价物或替代品？我正在尝试获取CGPath的所有子路径,以便我可以从不同的起点重绘它.

Answer 1

Swift 3.0

在Swift 3.0中,您可以这样使用CGPath.apply:

let path: CGPath = ...
// or let path: CGMutablePath

path.apply(info: nil) { (_, elementPointer) in
    let element = elementPointer.pointee
    let command: String
    let pointCount: Int
    switch element.type {
    case .moveToPoint: command = "moveTo"; pointCount = 1
    case .addLineToPoint: command = "lineTo"; pointCount = 1
    case .addQuadCurveToPoint: command = "quadCurveTo"; pointCount = 2
    case .addCurveToPoint: command = "curveTo"; pointCount = 3
    case .closeSubpath: command = "close"; pointCount = 0
    }
    let points = Array(UnsafeBufferPointer(start: element.points, count: pointCount))
    Swift.print("\(command) \(points)")
}

Swift 2.2

通过添加@convention(c),您现在可以CGPathApply直接从Swift 调用.这是一个做必要魔术的包装器:

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)
        }
        print(sizeofValue(body))
        let unsafeBody = unsafeBitCast(body, UnsafeMutablePointer<Void>.self)
        CGPathApply(self, unsafeBody, callback)
    }
}

(注意,@convention(c)我的代码中没有提到,但CGPathApply在Core Graphics模块的声明中使用.)

用法示例:

let path = UIBezierPath(roundedRect: CGRectMake(0, 0, 200, 100), cornerRadius: 15)
path.CGPath.forEach { element in
    switch (element.type) {
    case CGPathElementType.MoveToPoint:
        print("move(\(element.points[0]))")
    case .AddLineToPoint:
        print("line(\(element.points[0]))")
    case .AddQuadCurveToPoint:
        print("quadCurve(\(element.points[0]), \(element.points[1]))")
    case .AddCurveToPoint:
        print("curve(\(element.points[0]), \(element.points[1]), \(element.points[2]))")
    case .CloseSubpath:
        print("close()")
    }
}

Answer 2

（提示：如果您必须在 iOS 11 之前支持 iOS，请使用已接受的答案。如果您需要 iOS 11，则此答案要容易得多。）

从iOS 11 开始，Apple 就这个问题给出了官方答案：CGPath.applyWithBlock(_:).

这使得所有来自CGPath.apply(info:function:)C 函数问题的肮脏技巧都变得不必要了，该问题不允许信息以通常的快速方式传入和传出函数。

以下代码允许您执行以下操作：

let pathElements = path.pathElements()

为了能够做到这一点，复制和粘贴

import CoreGraphics

extension CGPath {
    func pathElements() -> [PathElement] {
        
        var result = [PathElement]()

        self.applyWithBlock { (elementPointer) in
            let element = elementPointer.pointee
            switch element.type {
            case .moveToPoint:
                let points = Array(UnsafeBufferPointer(start: element.points, count: 1))
                let el = PathElement.moveToPoint(points[0])
                result.append(el)
            case .addLineToPoint:
                let points = Array(UnsafeBufferPointer(start: element.points, count: 1))
                let el = PathElement.addLineToPoint(points[0])
                result.append(el)
            case .addQuadCurveToPoint:
                let points = Array(UnsafeBufferPointer(start: element.points, count: 2))
                let el = PathElement.addQuadCurveToPoint(points[0], points[1])
                result.append(el)
            case .addCurveToPoint:
                let points = Array(UnsafeBufferPointer(start: element.points, count: 3))
                let el = PathElement.addCurveToPoint(points[0], points[1], points[2])
                result.append(el)
            case .closeSubpath:
                result.append(.closeSubpath)
            @unknown default:
                fatalError()
            }
        }
        
        return result
    }

}

public enum PathElement {

    case moveToPoint(CGPoint)
    case addLineToPoint(CGPoint)
    case addQuadCurveToPoint(CGPoint, CGPoint)
    case addCurveToPoint(CGPoint, CGPoint, CGPoint)
    case closeSubpath

}

或者以这段代码为例来说明如何使用CGPath.applyWithBlock(_:)自己。

为完整起见，这是 Apple 的官方文档：https : //developer.apple.com/documentation/coregraphics/cgpath/2873218-applywithblock

自iOS 13以来，Apple 提供了更优雅的官方答案：使用SwiftUI（即使您的 UI 不在 中SwiftUI）

把你cgPath变成一个SwiftUI Path

let cgPath = CGPath(ellipseIn: rect, transform: nil)
let path =  Path(cgPath)
path.forEach { element in
    switch element {
    case .move(let to):
        break
    case .line(let to):
        break
    case .quadCurve(let to, let control):
        break
    case .curve(let to, let control1, let control2):
        break
    case .closeSubpath:
        break
    }
}

变量element是 Path.Element 类型，它是一个纯 Swift 枚举，因此甚至不需要从元素中获取值的技巧。

为了完整起见，这是苹果官方文档：https : //developer.apple.com/documentation/swiftui/path/3059547-foreach

Answer 3

这是Ole Begemann的精彩文章（感谢@Gouldsc！）的亮点，该文章适用于Swift 3，它允许访问组成UIBezierPath实例的各个元素：

extension UIBezierPath {

    var elements: [PathElement] {
        var pathElements = [PathElement]()
        withUnsafeMutablePointer(to: &pathElements) { elementsPointer in
            cgPath.apply(info: elementsPointer) { (userInfo, nextElementPointer) in
                let nextElement = PathElement(element: nextElementPointer.pointee)
                let elementsPointer = userInfo!.assumingMemoryBound(to: [PathElement].self)
                elementsPointer.pointee.append(nextElement)
            }
        }
        return pathElements
    }

}

public enum PathElement {

    case moveToPoint(CGPoint)
    case addLineToPoint(CGPoint)
    case addQuadCurveToPoint(CGPoint, CGPoint)
    case addCurveToPoint(CGPoint, CGPoint, CGPoint)
    case closeSubpath

    init(element: CGPathElement) {
        switch element.type {
        case .moveToPoint: self = .moveToPoint(element.points[0])
        case .addLineToPoint: self = .addLineToPoint(element.points[0])
        case .addQuadCurveToPoint: self = .addQuadCurveToPoint(element.points[0], element.points[1])
        case .addCurveToPoint: self = .addCurveToPoint(element.points[0], element.points[1], element.points[2])
        case .closeSubpath: self = .closeSubpath
        }
    }

}