如何获取 CGPath 的 CGPoint(s)

Question

如何获取包含在给定CGPath ( CGMutablePathRef ) 中的所有CGPoint (s) 的数组？

Answer 1

使用Swift 2.x （对于Swift 3.x 、 Swift 4.x和Swift 5.x，请在下面阅读..），我发现了这篇关于Swift 中的 C 回调的精彩文章。

正如Lily Ballard所解释的那样，试图获得“所有CGPoint (s)”可能是一个坏主意。

所以，我认为也许最好的方法是获取用于创建特定CGPath的路径元素点：

//MARK: - CGPath extensions
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)
    }

    func getPathElementsPoints() -> [CGPoint] {
        var arrayPoints : [CGPoint]! = [CGPoint]()
        self.forEach { element in
            switch (element.type) {
            case CGPathElementType.MoveToPoint:
                arrayPoints.append(element.points[0])
            case .AddLineToPoint:
                arrayPoints.append(element.points[0])
            case .AddQuadCurveToPoint:
                arrayPoints.append(element.points[0])
                arrayPoints.append(element.points[1])
            case .AddCurveToPoint:
                arrayPoints.append(element.points[0])
                arrayPoints.append(element.points[1])
                arrayPoints.append(element.points[2])
            default: break
            }
        }
        return arrayPoints
    }
}

使用此扩展程序，您可以执行以下操作，例如：

var bezier = UIBezierPath(ovalInRect: CGRectMake(0, 0, 400, 300))
let myOval = bezier.CGPath
let junctionPoints = myOval.getPathElementsPoints()
print("junction points are: \(junctionPoints)")

Swift 3.x 和 Swift 4.1（查看下面的 Swift 4.2 或主要版本..）

（由于@convention(c)语法重新引入，有一些更正）：

extension CGPath {

    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))
    }


    func getPathElementsPoints() -> [CGPoint] {
        var arrayPoints : [CGPoint]! = [CGPoint]()
        self.forEach { element in
            switch (element.type) {
            case CGPathElementType.moveToPoint:
                arrayPoints.append(element.points[0])
            case .addLineToPoint:
                arrayPoints.append(element.points[0])
            case .addQuadCurveToPoint:
                arrayPoints.append(element.points[0])
                arrayPoints.append(element.points[1])
            case .addCurveToPoint:
                arrayPoints.append(element.points[0])
                arrayPoints.append(element.points[1])
                arrayPoints.append(element.points[2])
            default: break
            }
        }
        return arrayPoints
    }

    func getPathElementsPointsAndTypes() -> ([CGPoint],[CGPathElementType]) {
        var arrayPoints : [CGPoint]! = [CGPoint]()
        var arrayTypes : [CGPathElementType]! = [CGPathElementType]()
        self.forEach { element in
            switch (element.type) {
            case CGPathElementType.moveToPoint:
                arrayPoints.append(element.points[0])
                arrayTypes.append(element.type)
            case .addLineToPoint:
                arrayPoints.append(element.points[0])
                arrayTypes.append(element.type)
            case .addQuadCurveToPoint:
                arrayPoints.append(element.points[0])
                arrayPoints.append(element.points[1])
                arrayTypes.append(element.type)
                arrayTypes.append(element.type)
            case .addCurveToPoint:
                arrayPoints.append(element.points[0])
                arrayPoints.append(element.points[1])
                arrayPoints.append(element.points[2])
                arrayTypes.append(element.type)
                arrayTypes.append(element.type)
                arrayTypes.append(element.type)
            default: break
            }
        }
        return (arrayPoints,arrayTypes)
    }
}

Swift > 4.1（还有 Swift 5.x）和 iOS 9.x 和 > 兼容

extension CGPath {
    func forEach( body: @escaping @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))
    }
    func getPathElementsPoints() -> [CGPoint] {
        var arrayPoints : [CGPoint]! = [CGPoint]()
        self.forEach { element in
            switch (element.type) {
            case CGPathElementType.moveToPoint:
                arrayPoints.append(element.points[0])
            case .addLineToPoint:
                arrayPoints.append(element.points[0])
            case .addQuadCurveToPoint:
                arrayPoints.append(element.points[0])
                arrayPoints.append(element.points[1])
            case .addCurveToPoint:
                arrayPoints.append(element.points[0])
                arrayPoints.append(element.points[1])
                arrayPoints.append(element.points[2])
            default: break
            }
        }
        return arrayPoints
    }
    func getPathElementsPointsAndTypes() -> ([CGPoint],[CGPathElementType]) {
        var arrayPoints : [CGPoint]! = [CGPoint]()
        var arrayTypes : [CGPathElementType]! = [CGPathElementType]()
        self.forEach { element in
            switch (element.type) {
            case CGPathElementType.moveToPoint:
                arrayPoints.append(element.points[0])
                arrayTypes.append(element.type)
            case .addLineToPoint:
                arrayPoints.append(element.points[0])
                arrayTypes.append(element.type)
            case .addQuadCurveToPoint:
                arrayPoints.append(element.points[0])
                arrayPoints.append(element.points[1])
                arrayTypes.append(element.type)
                arrayTypes.append(element.type)
            case .addCurveToPoint:
                arrayPoints.append(element.points[0])
                arrayPoints.append(element.points[1])
                arrayPoints.append(element.points[2])
                arrayTypes.append(element.type)
                arrayTypes.append(element.type)
                arrayTypes.append(element.type)
            default: break
            }
        }
        return (arrayPoints,arrayTypes)
    }
}

Answer 2

苹果添加实例方法CGPath.applyWithBlock ，适用于iOS11.0+ 和 macOS10.13+

您仍然可以使用 CGPath.apply 检查路径的每个元素，如先前答案中所述。 但是如果你想避免使用 C 风格的指针和 unsafeBitCast ，你应该使用更方便的实例方法applyWithBlock 。 例如，如果您想获取 CGPath 的 CGPoints 数组，您可以向 CGPath添加扩展，在本例中，计算属性（点）收集 CGPath 的 CGPoints ：

/// Extension to collect CGPath points
extension CGPath {

  /// this is a computed property, it will hold the points we want to extract
  var points: [CGPoint] {

     /// this is a local transient container where we will store our CGPoints
     var arrPoints: [CGPoint] = []

     // applyWithBlock lets us examine each element of the CGPath, and decide what to do
     self.applyWithBlock { element in

        switch element.pointee.type
        {
        case .moveToPoint, .addLineToPoint:
          arrPoints.append(element.pointee.points.pointee)

        case .addQuadCurveToPoint:
          arrPoints.append(element.pointee.points.pointee)
          arrPoints.append(element.pointee.points.advanced(by: 1).pointee)

        case .addCurveToPoint:
          arrPoints.append(element.pointee.points.pointee)
          arrPoints.append(element.pointee.points.advanced(by: 1).pointee)
          arrPoints.append(element.pointee.points.advanced(by: 2).pointee)

        default:
          break
        }
     }

    // We are now done collecting our CGPoints and so we can return the result
    return arrPoints

  }
}

Answer 3

您可以使用CGPathApply()迭代路径中的每个段并使用该段运行自定义函数。 这将为您提供路径的所有信息。

但是，如果通过“所有 CGPoint(s)”，您的意思是每个点都有一个像素渲染到它，那是一个无限大小的集合。 尽管您当然可以使用 apply 函数来获取每个段，然后对于每个非移动段，请使用段的控制点评估您自己的数学运算，以获得您想要的任何密度的点列表。

Answer 4

CGPath是一种不透明的数据类型，不一定存储所有使用的点。 除此之外，路径实际上可能不会绘制所有用作输入的点（例如，考虑 Bézier 控制点）。

从路径中获取信息的唯一两种记录方法是使用CGPathGetBoundingBox获取边界框，或者使用CGPathApply调用回调函数的更复杂的方法，如果CGPathElement类型，它将为您提供序列。