如何修复 convenience init w/closure NSBezierPath 扩展以使用在 Swift 5.0 中失败的 CGPath？

Question

下面的内联是我在某处获得的一种方法，用于使用以 CGPath 作为参数的便利初始值设定项来扩展 NSBezierPath，因此它的行为更像 UIBezierPath on [=28] =].

它以前工作过，但是当我尝试在 Swift 5 上编译它（多年后）时，我得到以下编译时错误：

C函数指针不能由捕获上下文的闭包构成

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;
        }
    })
}

Answer 1

我建议使用 path.applyWithBlock。我也会丢失所有那些笨拙的 break 语句并直接访问 element.points。

可能是这样的：

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
        }
    }
}

作为概念证明，我创建了一个包含所有不同元素类型的 CGPath，并使用上面的内容创建了一个 NSBezierPath。然后我用它们各自的 API 抚摸它们（深蓝色笔划中的 NSBezierPath，白色笔划中的 CGPath，在它上面）。这是转换逻辑产生等效路径的快速经验验证：

Answer 2

这是问题的补充 'answer'...它是@Rob 修复的问题中便捷方法的补充功能，它将 NSBezierPath 转换为 CGPath.两者一起使得在 macOS 和 iOS 之间移植变得很方便，并且可以更轻松地与其他 CoreGraphics 代码一起使用 NSBezierPath。

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
}

如何修复 convenience init w/closure NSBezierPath 扩展以使用在 Swift 5.0 中失败的 CGPath？

How to fix convenience init w/closure Extension of NSBezierPath to use CGPath that fails in Swift 5.0?

macos

cgpath

nsbezierpath

swift

swift5