Swift UIBezierPath() 和 DragGesture：连接点创建角而不是曲线

您将需要添加曲线到您的贝塞尔曲线，而不是线.为了使曲线看起来很好，您需要计算曲线上的连续点之间的适当控制点.

我正在改编来自this answer的代码.请注意，本例接受CGPoints数组，而不是您引用的类(Line).

像这样执行它

let path = quadCurvedPath(points) //points is [CGPoint]

并如下计算UIBezierPath

//adapted from https://stackoverflow.com/a/40203583/3680644
func quadCurvedPath(_ points: [CGPoint]) -> UIBezierPath {
    let path = UIBezierPath()

    var p1 = points[0]
    path.move(to: p1)

    if (points.count == 2) {
        path.addLine(to: points[1])
        return path
    }

    var oldControlP: CGPoint?

    for i in 1..<points.count {
        let p2 = points[i]
        var p3: CGPoint?
        if i < points.count - 1 {
            p3 = points[i+1]
        }

        let newControlP = controlPointForPoints(p1: p1, p2: p2, next: p3)

        path.addCurve(to: p2, controlPoint1: oldControlP ?? p1, controlPoint2: newControlP ?? p2)

        p1 = p2
        oldControlP = antipodalFor(point: newControlP, center: p2)
    }
    return path;
}

/// located on the opposite side from the center point
func antipodalFor(point: CGPoint?, center: CGPoint?) -> CGPoint? {
    guard let p1 = point, let center = center else {
        return nil
    }
    let newX = 2 * center.x - p1.x
    let diffY = abs(p1.y - center.y)
    let newY = center.y + diffY * (p1.y < center.y ? 1 : -1)

    return CGPoint(x: newX, y: newY)
}

/// halfway of two points
func midPointForPoints(p1: CGPoint, p2: CGPoint) -> CGPoint {
    return CGPoint(x: (p1.x + p2.x) / 2, y: (p1.y + p2.y) / 2);
}

/// Find controlPoint2 for addCurve
/// - Parameters:
///   - p1: first point of curve
///   - p2: second point of curve whose control point we are looking for
///   - next: predicted next point which will use antipodal control point for finded
func controlPointForPoints(p1: CGPoint, p2: CGPoint, next p3: CGPoint?) -> CGPoint? {
    guard let p3 = p3 else {
        return nil
    }

    let leftMidPoint  = midPointForPoints(p1: p1, p2: p2)
    let rightMidPoint = midPointForPoints(p1: p2, p2: p3)

    var controlPoint = midPointForPoints(p1: leftMidPoint, p2: antipodalFor(point: rightMidPoint, center: p2)!)

    if p1.y.between(a: p2.y, b: controlPoint.y) {
        controlPoint.y = p1.y
    } else if p2.y.between(a: p1.y, b: controlPoint.y) {
        controlPoint.y = p2.y
    }


    let imaginContol = antipodalFor(point: controlPoint, center: p2)!
    if p2.y.between(a: p3.y, b: imaginContol.y) {
        controlPoint.y = p2.y
    }
    if p3.y.between(a: p2.y, b: imaginContol.y) {
        let diffY = abs(p2.y - p3.y)
        controlPoint.y = p2.y + diffY * (p3.y < p2.y ? 1 : -1)
    }

    // make lines easier
    controlPoint.x += (p2.x - p1.x) * 0.1

    return controlPoint
}


extension CGFloat {
    func between(a: CGFloat, b: CGFloat) -> Bool {
        return self >= Swift.min(a, b) && self <= Swift.max(a, b)
    }
}