如何解决使用NSBezierPath的便捷扩展/封闭扩展以使用在Swift 5.0中失败的CGPath？

Question

_{UPDATE：由于@Rob很好地回答了问题，并且解决了问题，因此我更新了答案，以包含将NSBezier路径转换为CGPath的反函数。可能对某人有用。例如，在iOS和macOS应用程序之间移植时提供帮助。}

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下面的内联是我在某处获取的用于使用方便初始化程序扩展NSBezierPath的方法，该初始化程序以CGPath作为参数，因此其行为更像iOS上的UIBezierPath。

它以前可以工作，但是当我尝试在Swift 5上编译它（几年后）时，出现以下编译时错误：

C函数指针不能由捕获上下文的闭包形成

我该如何解决？

convenience init(path : CGPath) {
    path.apply(info: nil, function: { (_, elementPointer) in
        let element = elementPointer.pointee
        switch element.type {
        case .moveToPoint:
            let points = Array(UnsafeBufferPointer(start: element.points, count: 1))
            self.move(to: points[0])
            break
        case .addLineToPoint:
            let points = Array(UnsafeBufferPointer(start: element.points, count: 1))
            self.line(to: points[0])
            break
        case .addQuadCurveToPoint:
            let points = Array(UnsafeBufferPointer(start: element.points, count: 2))
            let qp0 = self.currentPoint
            let qp1 = points[0]
            let qp2 = points[1]
            let m = CGFloat(2.0 / 3.0)
            var cp1 = NSPoint()
            var cp2 = NSPoint()
            cp1.x = (qp0.x + ((qp1.x - qp0.x) * m))
            cp1.y = (qp0.y + ((qp1.y - qp0.y) * m))
            cp2.x = (qp2.x + ((qp1.x - qp2.x) * m))
            cp2.y = (qp2.y + ((qp1.y - qp2.y) * m))
            self.curve(to: qp2, controlPoint1:cp1, controlPoint2:cp2)
        case .addCurveToPoint:
            let points = Array(UnsafeBufferPointer(start: element.points, count: 3))
            self.curve(to:points[2], controlPoint1:points[0], controlPoint2:points[1])
            break
        case .closeSubpath:
            self.close()
        @unknown default:
            break;
        }
    })
}

private func transformToCGPath() -> CGPath {

    let path = CGMutablePath()
    let points = UnsafeMutablePointer<NSPoint>.allocate(capacity: 3)
    let numElements = self.elementCount

    if numElements > 0 {

        var didClosePath = true

        for index in 0..<numElements {

            let pathType = self.element(at: index, associatedPoints: points)

            switch pathType {
            case .moveTo:
                path.move(to: CGPoint(x: points[0].x, y: points[0].y))
            case .lineTo:
                path.addLine(to: CGPoint(x: points[0].x, y: points[0].y))
                didClosePath = false
            case .curveTo:
                path.addCurve(to: CGPoint(x: points[0].x, y: points[0].y), control1: CGPoint(x: points[1].x, y: points[1].y), control2: CGPoint(x: points[2].x, y: points[2].y))
                didClosePath = false
            case .closePath:
                path.closeSubpath()
                didClosePath = true
            @unknown default:
                print("Warning! New NSBezierPath.ElementTypes() added, may affect transformToCGPath!")
            }
        }

        if !didClosePath { path.closeSubpath() }
    }
    points.deallocate()
    return path
}

Answer 1

我建议使用path.applyWithBlock。我也将丢失所有那些简单的break语句，而直接访问element.points。

也许类似：

convenience init(path: CGPath) {
    self.init()

    path.applyWithBlock { elementPointer in
        let element = elementPointer.pointee
        switch element.type {
        case .moveToPoint:
            move(to: element.points[0])

        case .addLineToPoint:
            line(to: element.points[0])

        case .addQuadCurveToPoint:
            let qp0 = self.currentPoint
            let qp1 = element.points[0]
            let qp2 = element.points[1]
            let m = CGFloat(2.0 / 3.0)
            let cp1 = NSPoint(x: qp0.x + ((qp1.x - qp0.x) * m),
                              y: qp0.y + ((qp1.y - qp0.y) * m))
            let cp2 = NSPoint(x: qp2.x + ((qp1.x - qp2.x) * m),
                              y: qp2.y + ((qp1.y - qp2.y) * m))
            curve(to: qp2, controlPoint1: cp1, controlPoint2: cp2)

        case .addCurveToPoint:
            curve(to: element.points[2], controlPoint1: element.points[0], controlPoint2: element.points[1])

        case .closeSubpath:
            close()

        @unknown default:
            break
        }
    }
}

[仅作为概念证明，我创建了具有所有不同元素类型的CGPath，并使用上述内容创建了一个NSBezierPath。然后，我使用适当的API（仅比另一个厚）对它们两个进行了描边，这是对转换逻辑的快速验证，产生了两个等效的路径：