如何围绕其自身边界的中心旋转 UIBezierPath？

Question

假设我们有一个 UIBezierPath...它的边界是完全正方形的...像这样：

func getExponentPath(rotate180: Bool) -> UIBezierPath {

    // establish unit of measure (grid) based on this containing view's bounds... (not to be confused with this bezierpath's bounds)

    let G = bounds.width / 5

    let exponentPath = UIBezierPath()

    let sstartPoint = CGPoint(x:(3.8)*G,y:(1.2)*G)
    exponentPath.move(to: sstartPoint)
    exponentPath.addLine(to: CGPoint(x:(5)*G,y:(1.2)*G))
    exponentPath.addLine(to: CGPoint(x:(4.4)*G,y:(0.2)*G))
    exponentPath.addLine(to: CGPoint(x:(5)*G,y:(0.2)*G))
    exponentPath.addLine(to: CGPoint(x:(5)*G,y:(0)*G))
    exponentPath.addLine(to: CGPoint(x:(3.8)*G,y:(0)*G))
    exponentPath.addLine(to: CGPoint(x:(3.8)*G,y:(0.2)*G))
    exponentPath.addLine(to: CGPoint(x:(4.4)*G,y:(0.2)*G))
    exponentPath.addLine(to: sstartPoint)

    exponentPath.close()

    // this does not work:
    // if rotate180 { exponentPath.apply(CGAffineTransform(rotationAngle: CGFloat.pi)) }

    return exponentPath

}

如果旋转，此 bezierpath 仍需要在其包含视图中占据完全相同的区域。

我只能假设这是行不通的，因为旋转中心存在一些问题，不是我想要的...尽管即使说 "rotate by 0."[=11 我也会得到相同（错误）的结果=]

那么路径如何围绕它自己的中心点旋转？

似乎应该有一个简单的线性代数矩阵乘法类型可以应用于点集。 =T

Answer 1

我认为您不需要轮换。要绘制相同的倒置形状，只需将其翻转即可：

        exponentPath.apply(CGAffineTransform(scaleX: 1, y: -1))
        exponentPath.apply(CGAffineTransform(translationX: 0, y: G))

Answer 2

所以如果其他人试图在它自己的边界矩形的中心旋转 UIBezierPath...这是在之前 answers/comments:

的帮助下得出的实际工作解决方案

func getExponentPath(rotationAngle: CGFloat) -> UIBezierPath {

    // ...

    let x_translation = -( (bounds.width) - ( exponentPath.bounds.width/2) )
    let y_translation = -exponentPath.bounds.height/2

    exponentPath.apply(CGAffineTransform(translationX: x_translation, y: y_translation))
    exponentPath.apply(CGAffineTransform(rotationAngle: rotationAngle))
    exponentPath.apply(CGAffineTransform(translationX: -x_translation, y: -y_translation))

    // ...

}

Answer 3

extension UIBezierPath
{
    func rotateAroundCenter(angle: CGFloat)
    {
        let center = self.bounds.getCenter()
        var transform = CGAffineTransform.identity
        transform = transform.translatedBy(x: center.x, y: center.y)
        transform = transform.rotated(by: angle)
        transform = transform.translatedBy(x: -center.x, y: -center.y)
        self.apply(transform)
    }
}

如何围绕其自身边界的中心旋转 UIBezierPath？

How to rotate UIBezierPath around center of its own bounds?

core-graphics

rotation

cgaffinetransform

uibezierpath